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Item H13BOARD OF COUNTY COMMISSIONERS AGENDA ITEM SUMMARY Meeting Date: September 16, 2015 Department: Building Bulk Item: Yes X No _ Staff Contact Person/Phone #: Christine Hurley, 289-2517 Ed Koconis, 453-8727 AGENDA ITEM WORDING: Approval of a resolution of the Monroe County Board of County Commissioners adopting FEMA P-55, Volumes I and II "Coastal Construction. Manual" dated August 2011 as required pursuant to Monroe County Code Section 122-2(c). ITEM BACKGROUND: Chapter 122 of the Monroe County Code "Floodplain Management" includes rules for interpreting flood hazard issues. The building official shall be guided by the current edition of FEMA's 44 CFR, and FEMA's interpretive letters, policy statements and technical bulletins as adopted from time to time by the board of county commissioners. FEMA's Technical Bulletins ("bulletins") provide guidance concerning the building performance standards of the National Flood Insurance Program (NFIP), which are contained in Title 44 of the U.S. Code of Federal Regulations. The bulletins are intended for use primarily by State and local officials responsible for interpreting and enforcing NFIP regulations and by members of the development community, such as design professionals and builders. New bulletins, as well as updates to existing bulletins, are issued periodically as needed. The bulletins do not create regulations; rather they provide specific guidance for complying with the minimum requirements of existing NFIP regulations. Adopting these documents as well as internal County policies would serve to allow the County to not only remain in the NFIP as stated in Section 122-1(b), but also to move forward with the intent of becoming eligible to enter FEMA's Community Rating System (CRS). The proposed resolution would adopt FEMA P- 55, Volumes I and II "Coastal Construction Manual" dated August 2011 as required pursuant to Monroe County Code Section 122-2(c). PREVIOUS RELEVANT BOCC ACTION: January 18, 1994 — BOCC approved Ordinance No. 002-1994 adding the language "as adopted by resolution from time to time by the Board of County Commissioners" to the rules for interpreting flood hazard issues. July 15, 2015 — BOCC rejected proposed ordinance amending Section 122-2(c) and directed staff to continue proposing resolutions for adoption of both new and amended documents to be used by the building official for guidance on floodplain management. CONTRACT/AGREEMENT CHANGES: NIA STAFF RECOMMENDATION: Approval TOTAL COST: NIA INDIRECT COST: NIA BUDGETED: Yes No NIA DIFFERENTIAL OF LOCAL PREFERENCE: NIA COST TO COUNTY: NIA SOURCE OF FUNDS: NIA REVENUE PRODUCING: Yes _ No NIA AMOUNT PER MONTH NIA Year _ APPROVED BY: County Atty X % OMB/Purchasing Risk Management DOCUMENTATION: Included X Not Required_ DISPOSITION: AGENDA ITEM # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 MONROE COUNTY, FLORIDA MONROE COUNTY BOARD OF COUNTY COMMISSIONERS RESOLUTION NO. - 2015 A RESOLUTION OF THE MONROE COUNTY BOARD OF COUNTY COMMISSIONERS ADOPTING FEMA P-55, VOLUMES I AND II "COASTAL CONSTRUCTION MANUAL" DATED AUGUST 2011 AS REQUIRED PURSUANT TO MONROE COUNTY CODE SECTION 122-2(C) WHEREAS, Monroe County is currently a participating community in the National Flood Insurance Program (NFIP) and is working on internal County policies to improve upon its interpretation of NFIP regulations; and WHEREAS, Monroe County desires to become eligible to enter FEMA's Community Rating System (CRS); and WHEREAS, Monroe County Code Section 122-2(c), in part, requires that in interpreting other provisions of this chapter, the building official shall be guided by the current edition of FEMA's 44 CFR, and FEMA's interpretive letters, policy statements and technical bulletins as adopted by resolution from time to time by the board of county commissioners; NOW, THEREFORE, BE IT RESOLVED BY THE BOARD OF COUNTY COMMISSIONERS OF MONROE COUNTY, FLORIDA: Section 1. Pursuant to Monroe County Code Section 122-2(c), the Board hereby adopts FEMA P-55, Volumes I and II "Coastal Construction Manual" dated August 2011, a copy of which is attached hereto. Section 2. The Clerk of the Board is hereby directed to forward one (1) certified copy of this Resolution to the Building Department. 1 2 3 4 5 6 7 8 9 la 11 12 13 14 15 16 17 18 19 20 21 22 23 PASSED AND ADOPTED by the Board of County Commissioners of Monroe County, Florida, at a regular meeting held on the 16'h of September, 2015. Mayor Danny L. Kolhage Mayor pro tem Heather Carruthers Commissioner Sylvia Murphy Commissioner George Neugent Commissioner David Rice BOARD OF COUNTY COMMISSIONERS OF MONROE COUNTY, FLORIDA e (SEAL) ATTEST: AMY HEAVILIN, CLERK Deputy Clerk Mayor Danny L. Kolhage MONROE COUNTY ATTORNEY LAIPPROVEDIUT9 FORM: Date te'TAN" COUNTY A" TORNEY a`ll1 o •l.� — fit.. AT Via' i � f I II Coastal Construction Manual Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas (Fourth Edition) FEMA P-55 / Volume I / August 2011 �w�ax1 yr: FEMA All illustrations in this document were created by FEMA or a FEMA contractor unless otherwise noted. All photographs in this document are public domain or taken by FEMA or a FEMA contractor, unless otherwise noted. I I � � Ali ��!� �► - � � � . � - .�� Preface Y.., The 2011 Coastal Construction Manual, Fourth Edition (FEMA P-55), is a two -volume publication that provides a comprehensive approach to planning, siting, designing, constructing, and maintaining homes in the coastal environment. Volume I provides information about hazard identification, siting decisions, regulatory requirements, economic implications, and risk management. The primary audience for Volume I is design professionals, officials, and those involved in the decision -making process. Volume II contains in-depth descriptions of design, construction, and maintenance practices that, when followed, will increase the durability of residential buildings in the harsh coastal environment and reduce economic losses associated with coastal natural disasters. The primary audience for Volume II is the design professional who is familiar with building codes and standards and has a basic understanding of engineering principles. For additional information on residential coastal construction, see the FEMA Residential Coastal Construction Web site at http://www.fema.gov/rebuild/mat/fema55.shtm. COASTAL CONSTRUCTION MANUAL Fourth Edition Authors and Key Contributors William Coulbourne, Applied Technology Council Christopher P. Jones, Durham, NC Omar Kapur, URS Group, Inc. Vasso Koumoudis, URS Group, Inc. Philip Line, URS Group, Inc. David K. Low, DK Low and Associates Acknowledgments Glenn Overcash, URS Group, Inc. Samantha Passman, URS Group, Inc. Adam Reeder, Atkins Laura Seitz, URS Group, Inc. Thomas Smith, TLSmith Consulting Scott Tezak, URS Group, Inc. — Consultant Project Manager Fourth Edition Volume I Reviewers and Contributors Marcus Barnes, FEMA Headquarters Mark Crowell, FEMA Headquarters Lois Forster, FEMA Headquarters John Ingargiola, FEMA Headquarters — Technical Assistance and Research Contracts Program Manager Tucker Mahoney, FEMA Headquarters Alan Springett, FEMA Region II Paul Tertell, FEMA Headquarters — Project Manager Mark Vieira, FEMA Region IV Jonathan Westcott, FEMA Headquarters David Zaika, FEMA Headquarters Dana Bres, U.S. Department of Housing and Urban Development Stuart Davis, U.S. Army Corps of Engineers Roy Domangue, Wooden Creations, Inc. Brad Douglas, American Forest and Paper Association Russell J. Coco, Jr., Engensus Carol Friedland, Louisiana State University Trudie Johnson, Town of Hilton Head Island Ernie Katzwinkel, Dewberry Vladimir Kochkin, National Association of Home Builders Stephen Leatherman, Florida International University Amit Mahadevia, URS Group, Inc. Peter Mazikins, American Forest and Paper Association Deborah Mills, Dewberry Manuel Perotin, Atkins Rebecca Quinn, RCQuinn Consulting, Inc. Billy Ward, Champion Builders, LLC Fourth Edition Technical Editing, Layout, and Illustration Diana Burke, URS Group, Inc. Lee -Ann Lyons, URS Group, Inc. Susan Ide Patton, URS Group, Inc. Billy Ruppert, URS Group, Inc. COASTAL CONSTRUCTION MANUAL iii Contents Chapter1. Introduction......................................................................................................................1-1 1.1 Background................................................................................................................................1-1 1.2 Purpose..................................................................................................................................... 1-2 1.3 Objectives...................................................................................................................................1-3 1.3.1 Planning for Construction............................................................................................. 1-3 1.3.2 Successful Buildings....................................................................................................... 1-3 1.3.2.1 Premise and Framework for Achieving Successful Designs ............................. 1-4 1.3.2.2 Best Practices Approach...................................................................................1-5 1.4 Organization and Use of This Manual........................................................................................1-6 1.4.1 Organization...................................................................................................................1-7 Resources and Supporting Material................................................................................ 1-8 1.4.2 Using the Manual.......................................................................................................... 1-9 1.4.3 Hazard Icons.................................................................................................................. 1-9 1.4.4. Contact Information.....................................................................................................1-10 1.5 References..................................................................................................................................1-11 Chapter 2. Historical Perspective.......................................................................................................2-1 2.1 Introduction............................................................................................................................... 2-1 2.2 Coastal Flood and Wind Events................................................................................................. 2-2 2.2.1 North Atlantic Coast..................................................................................................... 2-4 2.2.2 Mid -Atlantic Coast........................................................................................................ 2-7 2.2.3 South Atlantic Coast...................................................................................................... 2-8 2.2.4 Gulf of Mexico Coast..................................................................................................... 2-9 2.2.5 U.S. Caribbean Territories.............................................................................................2-11 2.2.6 Great Lakes Coast........................................................................................................ 2-12 COASTAL CONSTRUCTION MANUAL v CONTENTS Volume I 2.2.7 Pacific Coast.................................................................................................................2-13 2.2.8 Hawaii and U.S. Pacific Territories................................................................................2-15 2.3 Breaking the Disaster -Rebuild -Disaster Cycle........................................................................... 2-16 2.3.1 Hazard Identification....................................................................................................2-16 2.3.2 Siting............................................................................................................................2-18 2.3.3 Design..........................................................................................................................2-20 2.3.4 Construction................................................................................................................2-24 2.3.5 Enclosures.................................................................................................................... 2-26 2.3.6 Maintenance................................................................................................................ 2-30 2.4 References.................................................................................................................................2-30 Chapter 3. Identifying Hazards.......................................................................................................... 3-1 3.1 Coastline Characteristics............................................................................................................3-2 3.1.1 Coastal Environment..................................................................................................... 3-2 3.1.2 United States Coastline..................................................................................................3-4 3.2 Coastal Storm Events..................................................................................................................3-7 3.2.1.1 Tropical Cyclones........................................................................................... 3-8 3.2.1.2 Other Coastal Storms....................................................................................3-10 3.3 Coastal Hazards....................................................................................................................... 3-12 3.3.1 High Winds................................................................................................................. 3-12 3.3.1.1 Speedup of Winds Due to Topographic Effects.............................................3-15 3.3.1.2 Wind -Borne Debris and Rainfall Penetration................................................3-15 3.3.1.3 Tornadoes......................................................................................................3-16 3.3.2 Earthquakes..................................................................................................................3-17 3.3.3 Tsunamis......................................................................................................................3-19 3.3.4 Other Hazards and Environmental Effects................................................................... 3-20 3.3.4.1 Sea and Lake Level Rise............................................................................... 3-21 3.3.4.2 Subsidence and Uplift................................................................................... 3-24 3.3.4.3 Salt Spray and Moisture................................................................................ 3-25 3.3.4.4 Rain............................................................................................................. 3-26 3.3.4.5 Hail..............................................................................................................3-26 3.3.4.6 Termites....................................................................................................... 3-26 3.3.4.7 Wildfire........................................................................................................3-27 3.3.4.8 Floating Ice.................................................................................................. 3-27 3.3.4.9 Snow............................................................................................................ 3-27 vi COASTAL CONSTRUCTION MANUAL Volume I CONTENTS 3.3.4.10 Atmospheric Ice............................................................................................ 3-27 3.4 Coastal Flood Effects................................................................................................................3-28 3.4.1 Hydrostatic Forces...................................................................................................... 3-28 3.4.2 Hydrodynamic Forces.................................................................................................. 3-28 3.4.3 Waves...........................................................................................................................3-31 3.4.4 Flood -Borne Debris...................................................................................................... 3-33 3.5 Erosion..................................................................................................................................... 3-35 3.5.1 Describing and Measuring Erosion.............................................................................. 3-40 3.5.2 Causes of Erosion.........................................................................................................3-42 3.5.2.1 Erosion During Storms.................................................................................3-42 3.5.2.2 Erosion Near Tidal Inlets, Harbor, Bay, and River Entrances .......................3-44 3.5.2.3 Erosion Due to Manmade Structures and Human Activities ........................ 3-47 3.5.2.4 Long -Term Erosion....................................................................................... 3-49 3.5.2.5 Localized Scour.............................................................................................3-51 3.5.3 Overwash and Sediment Burial.................................................................................... 3-52 3.5.4 Landslides and Ground Failures................................................................................... 3-52 3.6 NFIP Flood Hazard Zones....................................................................................................... 3-53 3.6.1 Base Flood Elevations................................................................................................... 3-54 3.6.2 Flood Insurance Zones................................................................................................. 3-55 3.6.3 FIRMS, DFIRMs, and FISs......................................................................................... 3-56 3.6.4 Wave Heights and Wave Crest Elevations..................................................................... 3-59 3.6.5 Wave Runup................................................................................................................ 3-61 3.6.6 Primary Frontal Dune.................................................................................................. 3-61 3.6.7 Erosion Considerations and Flood Hazard Mapping .................................................... 3-62 3.6.8 Dune Erosion Procedures.............................................................................................3-62 3.6.9 Levees and Levee Protection.........................................................................................3-64 3.7 Flood Hazard Assessments for Design Purposes.......................................................................3-64 3.7.1 Determine If Updated or More Detailed Flood Hazard Assessment is Needed ............. 3-65 3.7.1.1 Does the FIRM Accurately Depict Present Flood Hazards? .......................... 3-65 3.7.1.2 Will Long -Term Erosion Render a FIRM Obsolete? ..................................... 3-66 3.7.1.3 Will Sea Level Rise Render a FIRM Obsolete? ............................................. 3-66 3.7.2 Updating or Revising Flood Hazard Assessments......................................................... 3-67 3.8 Milestones of FEMA Coastal Flood Hazard Mapping Procedures and FIRMS .........................3-67 3.9 References.................................................................................................................................3-69 COASTAL CONSTRUCTION MANUAL vii CONTENTS Volume I Chapter4. Siting............................................................................................................................... 4-1 4.1 Identifying Suitable Property for Coastal Residential Structures.................................................4-4 4.2 Compiling Information on Coastal Property..............................................................................4-6 4.3 Evaluating Hazards and Potential Vulnerability..........................................................................4-9 4.3.1 Define Coastal Hazards Affecting the Property.............................................................. 4-9 4.3.2 Evaluate Hazard Effects on the Property.......................................................................4-10 4.4 General Siting Considerations.................................................................................................. 4-11 4.5 Raw Land Development Guidelines.......................................................................................... 4-13 4.5.1 Road Placement near Shoreline.....................................................................................4-15 4.5.2 Lot Configurations along Shoreline...............................................................................4-17 4.5.3 Lot Configurations near Tidal Inlets, Bay Entrances, and River Mouths ..................... 4-22 4.6 Development Guidelines for Existing Lots................................................................................ 4-23 4.6.1 Building on Lots Close to Shoreline............................................................................. 4-25 4.6.2 Siting near Erosion Control Structures......................................................................... 4-26 4.6.3 Siting Adjacent to Large Trees...................................................................................... 4-27 4.6.4 Siting of Pedestrian Access........................................................................................... 4-27 4.7 Influence of Beach Nourishment and Dune Restoration on Siting Decisions............................4-28 4.8 Decision Time..........................................................................................................................4-30 4.9 References................................................................................................................................4-30 Chapter 5. Investigating Regulatory Requirements............................................................................. 5-1 5.1 Land Use Regulations................................................................................................................. 5-2 5.1.1 Coastal Barrier Resource Areas and Other Protected Areas ............................................ 5-3 5.1.2 Coastal Zone Management Regulations......................................................................... 5-4 5.2 National Flood Insurance Program............................................................................................. 5-5 5.2.1 History of the NFIP....................................................................................................... 5-6 5.2.2 FEMA Flood Hazard Studies.........................................................................................5-6 5.2.3 Minimum Regulatory Requirements.............................................................................. 5-7 5.2.3.1 Minimum Requirements in All SFHAs.......................................................... 5-7 5.2.3.2 Additional Minimum Requirements for Buildings in Zone A ......................... 5-9 5.2.3.3 Additional Minimum Requirements for Buildings in Zone V .......................5-10 5.2.4 Community Rating System...........................................................................................5-14 viii COASTAL CONSTRUCTION MANUAL Volume I CONTENTS 5.3 Building Codes and Standards................................................................................................. 5-15 5.4 Best Practices for Exceeding Minimum NFIP Regulatory Requirements .................................. 5-18 5.4.1 Zone A..........................................................................................................................5-18 5.4.2 Coastal A Zone and Zone V.........................................................................................5-18 5.4.3 Summary......................................................................................................................5-19 5.5 References.................................................................................................................................5-20 Chapter 6. Fundamentals of Risk Analysis and Risk Reduction........................................................... 6-1 6.1 Assessing Risk.............................................................................................................................6-2 6.1.1 Identifying Hazards for Design Criteria......................................................................... 6-2 6.1.2 Probability of Hazard Occurrence and Potential Consequences ..................................... 6-3 6.2 Reducing Risk...........................................................................................................................6-5 6.2.1 Reducing Risk through Design and Construction..........................................................6-6 6.2.1.1 Factors of Safety and Designing for Events that Exceed Design Minimums ... 6-7 6.2.1.2 Designing above Minimum Requirements and Preparing for Events That Exceed Design Events............................................................................. 6-9 6.2.1.3 Role of Freeboard in Coastal Construction..................................................... 6-9 6.2.2 Managing Residual Risk through Insurance................................................................ 6-10 6.2.2.1 Types of Hazard Insurance............................................................................6-11 6.2.2.2 Savings, Premium, and Penalties................................................................... 6-12 6.3 Communicating Risk to Clients............................................................................................... 6-13 6.3.1 Misconceptions about the 100 Year Flood Event...........................................................6-14 6.3.2 Misconceptions about Levee Protection.........................................................................6-14 6.4 References.................................................................................................................................6-17 Acronyms........................................................................................................................................ A-1 Glossary.......................................................................................................................................... G-1 Index.................................................................................................................................................I-1 COASTAL CONSTRUCTION MANUAL ix CONTENTS Volume I List of Figures Chapter 1 Figure 1-1. Design framework to achieve successful buildings Chapter 2 1-4 Figure 2-1. Map and timeline of significant coastal flood and wind events, and milestones for regulations, building codes, and building practices .......................................... 2-2-2-5 Figure 2-2. Schell Beach before and after the Long Island Express Hurricane in 1938......................2-6 Figure 2-3. Although this house seems to have lost only several decks and a porch during the March 1989 nor'easter, the loss of supporting soil due to long-term erosion left its structural integrity in question following successive storms ............................................ 2-7 Figure 2-4. Roof structure failure due to inadequate bracing and inadequate fastening of the roofdeck........................................................................................................................2-8 Figure 2-5. This elevated house atop a masonry pier foundation was lost, probably due to waves and storm surge reaching above the top of the foundation...................................2-11 Figure 2-6. This house lost most of its metal roof covering due to high winds during Hurricane Marilyn in 1995.......................................................................................... 2-12 Figure 2-7. Erosion along the Lake Michigan shoreline at Holland, MI resulting from high lake levels and storm activity.........................................................................................2-13 Figure 2-8. This building experienced structural damage due to a landslide in La Conchita, CA, after a January 2005 storm event...........................................................................2-14 Figure 2-9. Tsunami damage at Poloa, American Samoa.................................................................2-15 Figure 2-10. School located approximately 1.3 miles from the Gulf shoreline damaged by storm surge and small waves..........................................................................................2-17 Figure 2-11. Galveston Island beach house with wind damage to roof in high pressure zones at roof edge and roof corners.........................................................................................2-18 Figure 2-12. Structures built close to the downdrift side of groins and jetties can experience increased erosion rates.................................................................................................. 2-20 Figure 2-13. Extreme case of localized scour undermining a Zone A slab -on -grade house located several hundred feet from the shoreline.............................................................2-21 Figure 2-14. Successful example of well -elevated and embedded pile foundation tested by HurricaneKatrina........................................................................................................ 2-22 x COASTAL CONSTRUCTION MANUAL Volume I CONTENTS Figure 2-15. The pre -FIRM house experienced damage due to surge and waves while the newer, elevated, post -FIRM house experienced minimal damage ................................. 2-22 Figure 2-16. The unprotected building sustained roof damage due to pressurization while the other sustained only minor damage because it was protected by shutters ...................... 2-23 Figure 2-17. Wind damage to roof structure and gable end wall ...................................................... 2-24 Figure 2-18. Failed masonry column connection.............................................................................. 2-25 Figure 2-19. Breakaway walls below the first floor of this house broke as intended under the flood forces of Hurricane Ike........................................................................................ 2-27 Figure 2-20. Flood opening in an enclosure with breakaway walls .................................................... 2-27 Figure 2-21. Louvers installed beneath an elevated house are a good alternative to breakawaywalls............................................................................................................ 2-28 Figure 2-22. An enclosure formed by open lattice............................................................................. 2-28 Figure 2-23. Above -grade enclosure.................................................................................................. 2-29 Figure 2-24. Two-story enclosure..................................................................................................... 2-30 Chapter 3 Figure 3-1. Coastal region terminology............................................................................................ 3-2 Figure 3-2. Generalized depiction of erosion process along a rocky coastline....................................3-4 Figure 3-3. United States coastline................................................................................................... 3-5 Figure 3-4. Storm surge flooded this home in Ascension Parish, LA ................................................. 3-7 Figure 3-5. Classification (by Saffir-Simpson Hurricane scale) of landfalling tropical cyclones along the U.S. Atlantic and Gulf of Mexico coasts, 1851-2009...................................... 3-9 Figure 3-6. Flooding, erosion, and overwash at Fenwick Island, DE, following March 1962 nor'easter..............................................................................................................3-11 Figure 3-7. ASCE 7-10 wind speed map for Risk Category II buildings ......................................... 3-13 Figure 3-8. End -wall failure of typical first -floor masonry/second-floor wood -frame building in DadeCounty, FL..........................................................................................................3-14 Figure 3-9. Loss of roof sheathing due to improper nailing design and schedule in Kauai County, HI...................................................................................................................3-14 Figure 3-10. Beach house with roof structure removed by Hurricane Ike..........................................3-14 COASTAL CONSTRUCTION MANUAL xi CONTENTS Volume I Figure 3-11. Apartment building with gable end wind damage from Hurricane Ike as a result of poor connection between brick veneer and wall structure.........................................3-15 Figure 3-12. Damage from the 2009 tsunami...................................................................................3-19 Figure 3-13. Observations of rates of change in mean sea level in the United States in feet percentury................................................................................................................... 3-21 Figure 3-14. Mean sea level rise data for a station in Atlantic City, NJ ............................................. 3-22 Figure 3-15. Figure 3-16. Figure 3-17. Figure 3-18. Figure 3-19. Figure 3-20, Monthly bulletin of lake levels for Lakes Michigan and Huron .................................... 3-23 Land subsidence in the Houston -Galveston area, 1906-2000...................................... 3-24 Example of corrosion, and resulting failure, of metal connectors Intact houses floated off their foundations and carried inland Storm surge at Horseshoe Beach, FL Flow channeled between large buildings during Hurricane Opal in 1995 scoured a deep channel and damaged infrastructure and houses ....................................... Figure 3-21. Pile -supported house in the area of channeled flow shown in Figure 3-20. . Figure 3-22. This house, located in an area of channeled flow near that shown in Figure 3-20, was undermined, washed into the bay behind the barrier island, and became a threatto navigation............................................................................................. 3-25 3-29 3-29 3-30 3-30 gil :u1] Figure 3-23. Storm waves breaking against a seawall in front of a coastal residence .......................... 3-31 Figure 3-24. Wave runup beneath elevated buildings at Scituate, MA .............................................. 3-31 Figure 3-25. The sand underneath this Pensacola Beach, FL, building was eroded due to wave runupand storm surge................................................................................................. 3-32 Figure 3-26. Concrete slab -on -grade flipped up by wave action came to rest against two foundation members, generating large unanticipated loads on the building foundation................................................................................................................... 3-32 Figure 3-27. A pile -supported house at Dauphin Island, AL, was toppled and washed into another house, which suffered extensive damage.......................................................... 3-33 Figure 3-28. Pier pilings were carried over 2 miles by storm surge and waves before they came to rest against this elevated house................................................................................. 3-34 Figure 3-29. Debris generated by destroyed buildings at Pass Christian, MS .................................... 3-34 Figure 3-30. Drift logs driven into coastal houses at Sandy Point, WA ............................................. 3-35 Figure 3-31. Dune erosion in Ocean City, NJ, caused by the remnants of Hurricane Ida and aprevious nor'easter..................................................................................................... 3-36 xii COASTAL CONSTRUCTION MANUAL Volume I CONTENTS Figure 3-32. Erosion and seawall damage in New Smyrna Beach, FL ............................................... 3-37 Figure 3-33. Erosion undermining a coastal residence in Oak Island, NC ........................................ 3-37 Figure 3-34. Overwash on Topsail Island, NC, after Hurricane Bonnie in 1998 .............................. 3-38 Figure 3-35. A January 1987 nor'easter cut a breach across Nauset Spit on Cape Cod, MA .............. 3-38 Figure 3-36. Undermined house at Chatham, MA, in 1988............................................................. 3-39 Figure 3-37. Bluff failure by a combination of marine, terrestrial, and seismic processes led to progressive undercutting of blufftop apartments........................................................... 3-39 Figure 3-38. Shoreline changes through time at a location approximately 1.5 miles south of Indian River Inlet, DE.................................................................................................3-41 Figure 3-39. Breach through barrier island at Pine Beach, AL, before Hurricane Ivan (2001) andafter (2004)........................................................................................................... 3-43 Figure 3-40. Cape San Blas, Gulf County, FL in November 1984, before and after storm - inducederosion............................................................................................................3-43 Figure 3-41. Ocean City Inlet, MD, was opened by a hurricane in 1933 and stabilized by jetties in 1934-35 that have resulted in extreme shoreline offset and downdrift erosion .........3-44 Figure 3-42. Buildings threatened by erosion at Ocean Shores, WA, in 1998................................... 3-45 Figure 3-43. July 1989 photograph of vacant lot owned by Lucas, Isle of Palms, SC and photograph taken in December 1997 of lot with new home ......................................... 3-46 Figure 3-44. Example of littoral sediments being trapped behind offshore breakwaters ................... 3-47 Figure 3-45. Failure of seawall in Bay County, FL, led to undermining and collapse of the building behind the wall............................................................................................. 3-48 Figure 3-46. Long-term erosion of the bluff along the Lake Michigan shoreline in Ozaukee County, WI, increases the threat to residential buildings outside the floodplain .......... 3-49 Figure 3-47. Long-term erosion at South Bethany Beach, DE, has lowered ground elevations beneath buildings and left them more vulnerable to storm damage .............................. 3-50 Figure 3-48. Determination of localized scour from changes in sand color, texture, and bedding .....3-51 Figure 3-49. Residential foundation that suffered severe scour on Bolivar Peninsula, TX ................. 3-52 Figure 3-50. Overwash from Hurricane Opal (1995) at Pensacola Beach, FL ................................... 3-53 Figure 3-51. Unstable coastal bluff at Beacon's Beach, San Diego, CA ............................................. 3-53 Figure 3-52. Portion of a paper FIRM showing coastal flood insurance rate zones ........................... 3-57 COASTAL CONSTRUCTION MANUAL xiii CONTENTS Volume I Figure 3-53. Typical shoreline -perpendicular transect showing stillwater and wave crest elevations and associated flood zones............................................................................ 3-57 Figure 3-54. Example DFIRM for a coastal area that shows the LiMWA......................................... 3-58 Figure 3-55. BFE determination for coastal flood hazard areas where wave crest elevations exceed wave runup elevations.......................................................................................3-60 Figure 3-56. Where wave runup elevations exceed wave crest elevations, the BFE is equal to therunup elevation...................................................................................................... 3-61 Figure 3-57. Portions of pre- and post -Hurricane Fran FIRMS for Surf City, NC ............................ 3-63 Figure 3-58. Current FEMA treatment of dune removal and dune retreat ........................................ 3-63 Chapter 4 Figure 4-1. Evaluation of coastal property........................................................................................ 4-2 Figure 4-2. Redevelopment on a previously developed lot as part of the rebuilding process after Hurricane Katrina.................................................................................................. 4-3 Figure 4-3. Long-term erosion left this well-built Kitty Hawk, NC, house standing in the ocean ..... 4-4 Figure 4-4. Although sited away from the shore, winds from Hurricane Floyd tore off the large overhanging roof of this house in Wrightstville Beach, NC ............................. 4-4 Figure 4-5. Groins were installed in an attempt to stop erosion........................................................ 4-6 Figure 4-6. Cumulative effects of storms occurring within a short period at one housing development in Jacksonville, NC, July —September 1996...............................................4-11 Figure 4-7. When siting a foundation in two different flood zones, requirements for the most restrictive zone apply to the whole building.................................................................. 4-12 Figure 4-8. Flood and debris damage to new construction in Zone A ............................................. 4-12 Figure 4-9. Example of parcels well -suited to coastal development in Louisiana..............................4-14 Figure 4-10. Example of parcels difficult to develop..........................................................................4-14 Figure 4-11. Roads placed near shorelines can wash out, causing access problems for homes such as these located at Garcon Point, FL......................................................................4-16 Figure 4-12. Recommended lot layout for road setback near the shoreline.........................................4-16 Figure 4-13. Comparison of Nags Head, NC, oceanfront lot layouts permitted before and after1987......................................................................................................................4-17 Figure 4-14. Problematic versus recommended layouts for shore -parallel roadways and associatedutilities..........................................................................................................4-18 xiv COASTAL CONSTRUCTION MANUAL Volume I CONTENTS Figure 4-15. Problematic versus recommended layouts for shoreline lots...........................................4-19 Figure 4-16. Narrow, low-lying areas and barrier islands are routinely subjected to coastal stormeffects..................................................................................................................4-19 Figure 4-17. Lots created in line with natural or manmade features can concentrate floodwaters ..... 4-20 Figure 4-18. Coastal lot development scenarios................................................................................ 4-21 Figure 4-19. As buildings in this Humbolt County, CA, community are threatened by bluff erosion along the Pacific Ocean, they are moved to other sites on the jointlyowned parcel..................................................................................................... 4-22 Figure 4-20. Three 2-year-old South Carolina houses left standing on the beach as a result of rapid erosion associated with a nearby tidal inlet ...................................................... 4-23 Figure 4-21. Condominiums built along the shoreline at the mouth of the Susquehanna River on the Chesapeake Bay were subjected to flood -borne debris after Hurricane Isabel..... 4-23 Figure 4-22. Coastal building site in Aptos, CA, provides an example of a coastal building site subject to multiple hazards........................................................................................... 4-25 Figure 4-23. Damage to buildings sited behind a rock revetment close to an eroding shoreline atGarden City Beach, SC............................................................................................ 4-26 Figure 4-24. Beach erosion and damage due to a destroyed bulkhead at Bonita Beach, FL, froma subtropical storm.............................................................................................. 4-27 Figure 4-25. Notching the building and roofline around a tree can lead to roof and envelope damage during a high -wind event................................................................................ 4-28 Chapter 5 Figure 5-1. Recommended elevation for buildings in Zone A compared to minimum requirements.................................................................................................................5-19 Figure 5-2. Recommended elevation for buildings in Coastal A Zone and Zone V compared to minimum requirements........................................................................... 5-20 Chapter 6 Figure 6-1. Initial risk is reduced to residual risk through physical and financial risk reduction elements......................................................................................................................... 6-6 COASTAL CONSTRUCTION MANUAL xv CONTENTS Volume I List of Tables Chapter 3 Table 3-1. Table 3-2. Table 3-3. Table 3-4. Table 3-5. Chapter 4 Table 4-1. Table 4-2. Table 4-3. Chapter 5 Table 5-1. Table 5-2. Chapter 6 Table 6-1. Saffir-Simpson Hurricane Wind Scale............................................................................ 3-9 Direct Hurricane Hits to U.S. Coastline Between 1851 and 2009 from Texas toMaine.......................................................................................................................3-10 Enhanced Fujito Scale in Use Since 2007......................................................................3-16 EarthquakeMMI Scale.................................................................................................3-18 Areas of Observed Tsunami Events in the United States and Territories ....................... 3-20 General Information Needed to Evaluate Coastal Property Planning and Site Development Guidelines for Raw Land. Guidelines for Siting Buildings on Existing Lots ................ . 4-7 4-15 4-24 Minimum NFIP Requirements for Building in All SHFAs............................................ 5-8 Summary of NFIP Regulatory Requirements and Recommendations for Exceeding the Requirements.........................................................................................5-21 Probability of Natural Hazard Event Occurrence for Various Periods of Time ............... 6-5 xvi COASTAL CONSTRUCTION MANUAL production 1.1 Background The Federal Emergency Management Agency (FEMA) first published theCoastal Construction Manual (FEMA 55) in 1981. The Manual was updated in 1986 and provided guidance to public officials, designers, architects, engineers, and contractors for over a decade. In that time, however, construction practices and materials changed, and more information on hazards and building performance was developed and used to update the Manual again in 2000. Over the past several decades, the coastal population in the United States has increased significantly. The increased coastal population led to increased coastal development, which led in turn to greater numbers of structures at risk from coastal hazards. Additionally, many of the residential buildings constructed today are larger and more valuable than those of the past, resulting in the potential for larger economic losses when disasters strike. A FEMA study estimates that the combination of population growth and sea level rise may increase the portion of the U.S. population residing in a coastal floodplain from 3 percent in 2010 to as much as 4 percent in 2100 (FEMA CROSS REFERENCE 2010a [draft]). Regulatory requirements, including the I -Codes, CZMA, In response to increased hazards and lessons learned from and the NFIP, are addressed in past storms, regulatory requirements for construction in Chapter 5. coastal areas have increased over the past decade. In 2000, the The Coastal High Hazard International Code Council (ICC) created the International Area (or Zone V) is explained in Code Series (I -Codes) based on the three regional model Section 3.6.2 of this Manual. building codes: the Building Officials Code Administrators COASTAL CONSTRUCTION MANUAL 1-1 INTRODUCTION International (BOCA) National Building Code (NBC), the Southern Building Code Congress International (SBCCI) Southern Building Code (SBC), and the International Conference of Building Officials (ICBO) Uniform Building Code (UBC). Based on data included in the Insurance Services Office (ISO) Building Code Effectiveness Grading Schedule (BCEGS) database, 86.5 percent of jurisdictions in the hurricane - prone region have adopted wind -resistant building codes, and 47.25 percent of flood -prone jurisdictions have adopted flood -resistant building codes (ISO 2011). As of the publication of this Manual, 33 of the 35 coastal States and U.S. territories, in implementing the Coastal Zone Management Act (CZMA) of 1972, have instituted construction setbacks and coastal resource protection programs. Many jurisdictions now require geotechnical studies and certifications from design professionals for construction along the coastline. Finally, as of May 2011, over 21,450 communities participate in the National Flood Insurance Program (NFIP), which requires, among other things, that plans for new buildings constructed in Coastal High Hazard Areas be certified by a design professional. Investigations conducted by FEMA and other organizations after major coastal disasters have consistently shown that properly sited, well -designed, and well -constructed coastal residential buildings generally perform well (refer to Chapter 2 for a discussion of the FEMA investigations). This updated Coastal Construction Manual —prepared by FEMA with assistance from other agencies, organizations, and professionals involved in coastal construction and regulation —is intended to help designers and contractors identify and evaluate practices that will improve the quality of construction in coastal areas and reduce the economic losses associated with coastal disasters. The design and construction techniques included in this Manual are based on a comprehensive evaluation of. Coastal residential buildings, both existing and under construction Siting, design, and construction practices employed along the U.S. coastlines Building codes, floodplain management ordinances, and standards applicable to coastal construction Performance of coastal buildings based on post -disaster field investigations 1.2 Purpose This Manual provides guidance for designing and constructing residential buildings in coastal areas that will be more resistant to the damaging effects of natural hazards. The focus is on new residential construction and substantial improvement or repairs of substantial damage to existing residential buildings —principally detached single-family homes, attached single-family homes (townhouses), and low-rise (three-story or less) multi -family buildings. Some of the recommendations of the Manual may also apply to non -substantial improvements or repairs. Discussions, examples, and example problems are provided for buildings in or near coastal flood hazard areas in a variety of coastal environments subject to high winds, flooding, seismic activity, erosion, and other hazards. This Manual is intended to be used by contractors, designers, architects, and engineers who are familiar with the design and construction of one- to three-story residential buildings in coastal areas of the United States and its territories. Readers less familiar with design and construction practices, as well as State and community officials, should also refer to FEMA P-762, Local Officials Guide for Coastal Construction (FEMA 2009), 1-2 COASTAL CONSTRUCTION MANUAL INTRODUCTION for guidance on planning and design considerations for improving the performance of coastal residential buildings before using this Manual. 1.3 Objectives The goal of this Manual is to provide professionals guidance to assist them in pre -design, planning tasks and decisions as well as design and construction practices that will lead to building successful, disaster -resistant homes. For any project, it is critical that the project be well planned in order to minimize potential issues later on during the design and construction process and when the building is impacted by an event. These items are summarized in the following sections and elaborated on in detail throughout this Manual. 1.3.1 Planning for Construction One objective of this Manual is to highlight the many tasks and decisions that must be made before actual construction begins. These tasks include, but may not be limited to: Evaluating the suitability of coastal lands for residential construction Planning for development of raw land and for infill or redevelopment of previously developed land Identifying regulatory, environmental, and other constraints on construction or development Evaluating site -specific hazards and loads at a building site Evaluating techniques to mitigate hazards and reduce loads Identifying risk, insurance, and financial implications of siting, design, and construction decisions 1.3.2 Successful Buildings A second objective of this Manual is to identify the best design and construction practices for building successful disaster - resistant structures. In coastal areas, a building can be considered successful only if it is capable of resisting damage from coastal hazards and processes over a period of decades. This does not mean that a coastal residential building will remain undamaged over its intended lifetime, but that undermining from erosion and the effects of a design -level flood or wind event (or series of lesser events with combined impacts equivalent to a design event) will be limited. NOTE The designer should be familiar with the recommendations in this Manual, along with the building codes and engineering standards cited, as these may establish an expected level of professional care. A successful building is considered a building for which the following are true after a design -level event: The building foundation is intact and functional The envelope (lowest floor, walls, openings, and roof) is structurally sound and capable of minimizing penetration of wind, rain, and debris COASTAL CONSTRUCTION MANUAL 1-3 I INTRODUCTION The lowest floor elevation is high enough to prevent floodwaters from entering the building envelope The utility connections (e.g., electricity, water, sewer, natural gas) remain intact or can be easily restored The building is accessible and habitable Any damage to enclosures below the lowest floor does not result in damage to the foundation, utility connections, or elevated portions of the building or nearby structures For buildings affected by a design level seismic event, the building protects life and provides safety, even if the structure itself sustains significant damage 1.3.2.1 Premise and Framework for Achieving Successful Designs The underlying goal of a successful design is expressed through its basic premise: Anticipated loads must be transferred through the building in a continuous path to the supporting soils. Any weakness in that continuous path is a potential point of failure. To fulfill this design premise, designers must address a variety of issues and constraints. These are illustrated in Figure 1-1 and summarized as follows: Funding. Any project is constrained by available funding, and designers must balance building size and expense against the 1-4 COASTAL CONSTRUCTION MANUAL INTRODUCTION desire for building success. Initial and long-term costs should be factored into the design. Higher initial construction costs may result in increased closing costs or higher mortgage rates, but may minimize potential building damage, reduce insurance rates, and reduce future maintenance costs. Risk tolerance. Some owners are willing and able to assume a high degree of financial and other risks, while other owners are more conservative and seek to minimize potential building damage and future costs. Building use. The intended use of the building will affect its layout, form, and function. Location. The location of the building will determine the nature and intensity of hazards to which the building will be exposed; loads and conditions that the building must withstand; and building codes, standards, and regulations that must be satisfied. Materials. A variety of building materials are available, and some are better suited to coastal environments than others. Owners and designers must select appropriate materials that address both aesthetic and durability issues. If an owner is prepared for frequent maintenance and replacement, the range of available materials will be wider; however, most owners are not prepared to do so, and the most durable materials should be used. Continuous load paths. Continuous load paths must be constructed and maintained over the intended life of the building. Resist or avoid hazards. The magnitudes of design forces acting on structures, coupled with project funding, building location, and other factors, will determine which forces can be resisted and which must be avoided. Structures are typically designed to resist wind loads and avoid flood loads (through elevation on strong foundations). Conditions greater than design conditions. Design loads and conditions are based on some probability of exceedance, and it is always possible that design loads and conditions can be exceeded. Designers can anticipate this and modify their initial design to better accommodate higher forces and more extreme conditions. The benefits of doing so often exceed the costs of building higher and stronger. Constructability. Ultimately, designs will only be successful if they can be implemented by contractors. Complex designs with many custom details may be difficult to construct and could lead to a variety of problems, both during construction and once the building is occupied. 1.3.2.2 Best Practices Approach To promote best practices, portions of the Manual recommend and advocate techniques that exceed the minimum requirements of model building codes; design and construction standards; or Federal, State, and local regulations. The authors of the Manual are aware of the implications of such recommendations on the design, construction, and cost of coastal buildings, and make them only after careful review of building practices and subsequent building performance during design level events. Some of the recommended best practices and technical solutions presented in the previous version of FEMA 55 (2000, third edition) have been incorporated into the model building codes. For example: The 2009 and 2012 editions of the International Residential Code (IRC)—see sections R322.2.1(2) and R322.3.2(1)require 1 foot of freeboard in the Coastal A Zone and in certain Zone V situations. Past minimum code provisions did not require any freeboard. Note that more than 1 foot of freeboard may COASTAL CONSTRUCTION MANUAL 1-5 I INTRODUCTION be indicated once the design framework steps Ij outlined in Figure 1-1 are accomplished. TERMINOLOGY: FREEBOARD The 2006, 2009, and 2012 editions of the International Building Code (IBC) require Freeboard is an additional height that conformance with American Society of Civil buildings are elevated above the base flood Engineers (ASCE) Standard 24-05, Flood elevation (BFE). Freeboard acts as a factor Resistant Design and Construction. ASCE 24-05 of safety to compensate for uncertainties in the determination of flood elevations, requires new buildings situated in the Coastal and provides an increased level of flood A Zone to be designed and constructed protection. Freeboard will result in reduced to Zone V requirements. Thus, the 2000 flood insurance premiums. version of the Coastal Construction Manual recommendation to treat Coastal A Zone buildings like Zone V buildings is now being implemented for IBC -governed buildings through the building code. Sustainable building design concepts are increasingly being incorporated into residential building design and construction through green building rating systems. While the environmental benefits associated with adopting green building practices can be significant, these practices must be implemented in a manner that does not compromise the building's resistance to natural hazards. FEMA P-798, Natural Hazards and Sustainability for Residential Buildings (FEMA 2010b), examines current green building rating systems in a broader context. It identifies green building practices —the tools of today's green building rating systems —that are different from historical residential building practices and that, unless implemented with an understanding of their interactions with the rest of the structure, have the potential to compromise a building's resistance to natural hazards. FEMA P-798 discusses how to retain or improve natural hazard resistance while incorporating green building practices. 1.4 Organization and Use of This Manual This Manual first provides a history of coastal disasters in the United States, an overview of the U.S. coastal environment, and fundamental considerations for constructing a building in a coastal region. The Manual covers every step in the process of constructing a home in a coastal area: evaluating potential sites; selecting a site; locating, designing, and constructing the building; and insuring and maintaining the building. Flowcharts, checklists, maps, equations, and details are provided throughout the Manual to help the reader understand the entire process. In addition, example problems are presented to demonstrate decisions and calculations designers must make to reduce the potential for damage to the building from natural hazard events. The Manual also includes numerous examples of siting, design, and construction practices —both good and bad —to illustrate the results and ramifications of those practices. The intent is twofold: (1) to highlight the benefits of practices that have been employed successfully by communities, designers, and contractors, and (2) to warn against practices that have resulted in otherwise avoidable damage or loss of coastal residential buildings. 1-6 COASTAL CONSTRUCTION MANUAL INTRODUCTION 1.4.1 Organization Because of its size, the Manual is divided into two volumes, with a total of 15 chapters. Additional supporting materials and resources are available at the FEMA Residential Coastal Construction Web site. Volume I Chapter 1 — Introduction. This chapter describes the purpose of the Manual, outlines the content and organization, and explains how icons are used throughout the Manual to guide and advise the reader. Chapter 2 — Historical Perspective. This chapter summarizes selected past coastal flood and wind events and post -event evaluations, and other major milestones. It documents the causes and types of damage associated with storms and tsunamis ranging from the 1900 hurricane that struck Galveston, TX, to the Samoan tsunami that struck American Samoa following an earthquake in September 2009. Chapter 3 — Identifying Hazards. This chapter describes coastal processes, coastal geomorphology, and coastal hazards. Regional variations for the Great Lakes, North Atlantic, Middle Atlantic, South Atlantic, Gulf of Mexico, Pacific, Alaska, Hawaii, and U.S. territories are discussed. This chapter also discusses hazards that influence the design and construction of a coastal building (coastal storms, erosion, tsunamis, and earthquakes) and their effects. Chapter 4 — Siting. This chapter describes the factors that should be considered when selecting building sites, including small parcels in areas already developed, large parcels of undeveloped land, and redevelopment sites. Guidance is also provided to help designers and contractors determine how a building should be placed on a site. Detailed discussions of the coastal construction process begin in this chapter. Chapter 5 — Investigating Regulatory Requirements. This chapter presents an overview of building codes and Federal, State, and local regulations that may affect construction on a coastal building site. Additionally, the NFIP, Coastal Barrier Resources Act (CBRA), and Coastal Zone Management (CZM) programs are described. Chapter 6 — Fundamentals of Risk Analysis and Risk Reduction. This chapter summarizes acceptable levels of risk; tradeoffs in decisions concerning siting, design, construction, and maintenance; and cost and insurance implications that should be considered in coastal construction. Volume II Chapter 7 — Pre -Design Considerations. This chapter introduces the design process, minimum design requirements, inspections, and sustainable design considerations. It discusses the cost and insurance implications of decisions made during design and construction. It also outlines the contents of Volume II. Chapter 8 — Determining Site -Specific Loads. This chapter explains how to calculate site -specific loads, including loads from high winds, flooding, seismic events, and tsunamis, as well as combinations of more than one load. Example problems are provided to illustrate the application of design load provisions of ASCE 7-10, Minimum Design Loads for Buildings and Other Structures (ASCE 2010). Chapter 9 — Designing the Building. This chapter contains information on designing each part of a building to withstand expected loads. Topics covered include structural failure modes, load paths, building COASTAL CONSTRUCTION MANUAL 1-7 INTRODUCTION systems, application of loads, structural connections, building material considerations, requirements for breakaway walls, and considerations for designing appurtenances. Chapter 10 — Designing the Foundation. This chapter presents recommendations for the selection and design of foundations. Design of foundation elements including pile capacity in soil, installation methods, and material durability considerations are discussed. Chapter 11 — Designing the Building Envelope. This chapter describes how to design roof coverings, exterior wall coverings, exterior doors and windows, shutters, and soffits to resist natural hazards. Chapter 12 — Mechanical Equipment and Utilities. This chapter provides guidance on design considerations of mechanical equipment and utilities, as well as techniques that can improve the capability of equipment to survive a natural disaster. Chapter 13 — Constructing the Building. This chapter describes how to properly construct a building in a coastal area and how to avoid common construction mistakes that may lessen the ability of a building to withstand a natural disaster. It includes guidance on material choices and durability, and construction techniques for improved resistance to decay and corrosion. Chapter 14 — Maintaining the Building. This chapter explains special maintenance concerns for new and existing buildings in coastal areas. Methods to reduce damage from corrosion, moisture, weathering, and termites are discussed, along with building elements that require frequent maintenance. Chapter 15 —Retrofitting Existing Buildings. This chapter includes broad guidance for evaluating existing residential structures to assess the need and feasibility for wildfire, seismic, flood, and wind retrofitting. It also includes a discussion of wind retrofit packages that encourage homeowners to take advantage of opportunities to strengthen their homes while performing routine maintenance (e.g., roof shingle replacement). Resources and Supporting Material The FEMA Residential Coastal Construction Web site (http://www.FEMA.gov/rebuild/mat/fema55.shtm) provides guidance and other information to augment the content of this Manual. The material provided on the Web site includes a glossary for this Manual as well as: Resource documents. Examples include Dune Walkover Guidance, Material Durability in Coastal Environments, and NOTE Swimming Pool Design Guidance. Links and contact information. Government agencies, professional and trade organizations, code and standard organizations, and natural hazard and coastal science organizations. Links to additional Web sites and coastal construction resources published by FEMA. Examples include the Wind Retrofit Guide for Residential Buildings (FEMA P-804), Home Builder's Guide to Coastal Construction (FEMA P-499), and the FEMA Safe Room and Building Science Web sites. In previous editions of the Coastal Construction Manual, Volume III contained appendices and information that expanded on content provided in Volumes I and II. The FEMA Residential Coastal Construction Web site now serves as the location for additional content. 1-8 COASTAL CONSTRUCTION MANUAL INTRODUCTION 1.4.2 Using the Manual This Manual uses icons as visual guides to help readers quickly find information. These icons call out notes, warnings, definitions, cross references, cost considerations, equations, example problems, and specific hazards. Notes. Notes contain supplemental information that readers may find helpful, including things to consider when undertaking a coastal construction project, suggestions that can expedite the project, and the titles and sources of other publications related to coastal construction. Full references for publications are presented at the end of each chapter of the Manual. COASTAL CONSTRUCTION MANUAL 1-9 INTRODUCTION Zone V. Portion of the Special Flood HazardArea (SFHA) that extends from offshore to the inland limit of a primary frontal dune along an open coast, and any other area subject to high -velocity wave action from storms or tsunamis. COASTAL Coastal A Zone. A subset of Zone A. Specifically, that portion of the SFHA landward of Zone V (or landward of a coastline without a mapped Zone V) in which the principal source of flooding is coastal storms, and where the potential base flood wave height is between 1.5 and 3.0 feet. Zone A. Portion of the SFHA in which the principal source of flooding is runoff from rainfall, snowmelt, or coastal storms where the potential base flood wave height is between 0.0 and 3.0 feet. 140 TERMINOLOGY: SPECIAL FLOOD HAZARD AREA The SFHA is the land area covered by the floodwaters of the base flood on NFIP maps. It is the area where the NFIP's floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies. The SFHA includes Zones A, AO, AH, Al-30, AE, A99, AR, AR/Al-30, AR/AE, AR/AO, AR/AH, AR/A, VO, V1-30, VIE, and V. x Zone X. Includes shaded and unshaded Zone X. The flood hazard is less severe here than in the SFHA. 1.4.4. Contact Information Every effort has been made to make this Manual as comprehensive as possible. However, no single manual can anticipate every situation or need that may arise in a coastal construction project. Readers who have questions not addressed herein should consult local officials. Information is also available from the FEMA Building Science Helpline (Web: http://www.fema.gov/rebuild/buildingscience/, e-mail: FEMA-Buildingsciencehelp@ dhs.gov, telephone: 866-927-2104), and the Mitigation Division of the appropriate FEMA Regional Office. Contact information for FEMA personnel, the State NFIP Coordinating Agencies, and the State Coastal Zone Management Agencies are provided on the FEMA Residential Coastal Construction Web page. 1-10 COASTAL CONSTRUCTION MANUAL INTRODUCTION J 1.5 References ASCE (American Society of Civil Engineers). 2005. Flood Resistant Design and Construction. ASCE Standard ASCE 24-05. ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. FEMA (Federal Emergency Management Agency). 2000. FEMA 55 (3rd Edition). Coastal Construction Manual.• Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in CoastalAreas. May. FEMA. 2009. P-762, Local Officials Guide for Coastal Construction: Design Considerations, Regulatory Guidance, and Best Practices for Coastal Communities. February. FEMA. 2010a (draft). The Impact of Climate Change on the National Flood Insurance Program. August 2010 draft; still draft as of July 2011). FEMA. 2010b. P-798, Natural Hazards and Sustainability for Residential Buildings. September. ISO (Insurance Service Office, Inc.). 2011. Building Code Effective Grading Schedule. http://www. isomitigation.com/bcegs/0000/bcegs0001.html. Accessed June 28, 2011. COASTAL CONSTRUCTION MANUAL 1-11 i r"I A torical Perspective 2.1 Introduction Through the years, FEMA, other Federal agencies, State and local agencies, and other private groups have documented and evaluated the effects of coastal flood and wind events and the performance of buildings located in coastal areas during those events. These evaluations provide a historical perspective on the siting, design, and construction of buildings along the Atlantic, Pacific, Gulf of Mexico, and Great Lakes coasts. These studies provide a baseline against which the effects of later coastal flood events can be measured. Within this context, certain hurricanes, coastal storms, and other coastal flood events stand out as being especially important, either because of the nature and extent of the damage they caused or because of particular flaws they exposed in hazard identification, siting, design, construction, or maintenance practices. Many of these events —particularly those occurring since 1979—have been documented by FEMA in Flood Damage Assessment Reports, Building Performance Assessment Team (BPAT) reports, and Mitigation Assessment Team (MAT) reports. These reports summarize investigations that FEMA conducts shortly after major disasters. Drawing on the combined resources of a Federal, State, local, and private sector partnership, a team of investigators CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http:// www.fema.gov/rebuild/mat/ fema55.shtm). �J NOTE Hurricane categories reported in this Manual should be interpreted cautiously. Storm categorization based on wind speed may differ from that based on barometric pressure or storm surge. Also, storm effects vary geographically — only the area near the point of landfall will experience effects associated with the reported storm category. COASTAL CONSTRUCTION MANUAL 2-1 HISTORICAL PERSPECTIVE is tasked with evaluating the performance of buildings and related infrastructure in response to the effects of natural and man-made hazards. The teams conduct field investigations at disaster sites; work closely with local and State officials to develop recommendations for improvements in building design and construction; and prepare recommendations concerning code development, code enforcement, and mitigation activities that will lead to greater resistance to hazard events. This chapter summarizes coastal flood and wind events that have affected the United States and its territories since the beginning of the twentieth century. The lessons learned regarding factors that contribute to flood and wind damage are discussed. 2.2 Coastal Flood and Wind Events This section summarizes major coastal flood and wind events in the United States from 1900 to 2010. Many of these events have led to changes in building codes, regulations, mapping, and mitigation practices. The map and timeline in Figure 2-1 provide a chronological list of the major coastal flood and wind events in combination with the major milestones resulting from the events. They show the evolution of coastal hazard 4 r ALASKA RTH ANTIC MANTIC U.S. VIRGIN PUERTO AMERICAN ISLANDS RICO'' HAWAII SAMOA GUAM CARIBBEAN HAWAII & U.S. PACIFIC TERRITORIES Figure 2-1. Map and timeline of significant coastal flood and wind events, and milestones for regulations, building codes, and building practices 2-2 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE I COASTAL CONSTRUCTION MANUAL 2-3 HISTORICAL PERSPECTIVE CARIBBEAN HAWAII & U.S. PACIFIC TERRITORIES RTH ANTIC 'LANTIC 2-4 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE Figure 2-1 (concluded). Map and timeline of significant coastal flood and wind events, and milestones for regulations, building codes, and building practices COASTAL CONSTRUCTION MANUAL 2-5 HISTORICAL PERSPECTIVE In 1938, the "Long Island Express" hurricane moved rapidly up the east coast from New York through New England. The storm caused widespread surge and wind damage to buildings, and is still used as a benchmark for predicting worst -case scenario damage in the region (Figure 2-2). Although not shown in the photograph, this hurricane also destroyed many elevated homes along this stretch of coastline. In September 1985, Hurricane Gloria hit Long Island, NY, and New Jersey, causing minor storm surge and erosion damage and significant wind damage. In 1991, New England was hit by two major storms Hurricane Bob in August and a nor'easter in October. A FEMA Flood Damage Assessment Report noted that flood damage to buildings constructed before the local adoption of the Flood Insurance Rate Map (FIRM), known as pre -FIRM construction, that had not been elevated or that had not been elevated sufficiently suffered major damage, while properly elevated buildings constructed after the adoption of the FIRM (post -FIRM) performed well (URS 1991c). These storms provided insight into successful foundation design practices. Figure 2-2. Schell Beach before and after the Long Island Express Hurricane in 1938; houses near the shoreline were destroyed and more distant houses were damaged (Guilford, CT) SOURCE: WORKS PROGRESS ADMINISTRATION PHOTOGRAPH FROM MINSINGER 1988 2-6 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE 2.2.2 Mid -Atlantic Coast The Mid -Atlantic Coast is generally considered the coastal area from New Jersey to Virginia. This coastal area is susceptible to both nor'easters and hurricanes with flood and wind damage similar to the damage that occur in New England. In March 1962, a significant nor'easter, known as the GreatAtlantic Storm of 1962 or the Ash Wednesday Storm, affected almost the entire eastern seaboard and caused extreme damage in the Mid -Atlantic region. The combination of sustained high winds with spring tides resulted in severe beachfront erosion and flooding, sweeping many buildings out to sea. In June 1972, Tropical Storm Agnes produced rains up to 19 inches, resulting in severe riverine flooding from New York to Virginia and billions of dollars in flood damage. The catastrophic damage from this storm led to the "Mandatory Flood Insurance Purchase Requirement" in the Flood Disaster Protection Act of 1973 (see Section 5.2 for more on the history of the NFIP). A March 1984 nor'easter caused significant erosion problems. As a result of damage observed after this storm and Hurricane Gloria (see Section 2.2.1), New Jersey implemented several changes to its coastal development practices in 1985. An April 1988 nor'easter caused foundation damage to elevated homes in Virginia and North Carolina. Long-term shoreline erosion, coupled with the effects of three previous coastal storms, had left the area vulnerable. Inspections following the 1988 nor'easter revealed that repairs to previous foundation damage were only partially effective. In some cases, ineffective repairs implemented after storms resulted in subsequent storm damage that may not have occurred if the original repair had been properly made (URS 1989). AMarch 1989 nor easter in the same area caused even further foundation damage. The damage from the 1988 and 1989 storms showed that long- term erosion makes buildings increasingly vulnerable (Figure 2-3) to the effects of even minor storms (URS 1990). A few years later, an intense January 1992 nor'easter hit Delaware and Maryland. Observations made by the FEMA BPAT after this storm noted damage due to storm surge, wave action, and erosion, as well as many load path failures in coastal buildings (FEMA 1992). Figure 2-3. Although this house seems to have lost only several decks and a porch during the March 1989 nor'easter, the loss of supporting soil due to long-term erosion left its structural integrity in question following successive storms COASTAL CONSTRUCTION MANUAL 2-7 HISTORICAL PERSPECTIVE In September 2003, Hurricane Isabel made landfall near Cape Lookout, NC, as a Category 2 hurricane, breaching the barrier island. Storm surge and heavy rainfall caused extensive flooding across the Mid -Atlantic region, especially in areas adjacent to the Chesapeake Bay. Maximum observed water levels at stations along the Chesapeake Bay exceeded historical observations (NOAA 2004). 2.2.3 South Atlantic Coast The South Atlantic Coast is generally considered the coastal area from North Carolina up to and including the Florida Keys. This region, especially the North Carolina Outer Banks and south Florida, is often subjected to hurricanes. States in the northern part of this region, such as North Carolina, are also susceptible to nor'easters. Damage is typically caused by flooding, waves, erosion, water -borne debris, wind, and wind- borne debris. The degree of damage ranges from slight to severe, depending on the characteristics of the storm. After a September 1926 hurricane hit Miami, FL, a south Florida engineer, Theodore Eefting, wrote an article on the damage pointing out many weaknesses in buildings and construction that continue to be discussed today. Most notably, he stressed the consequences of poor quality construction, and the importance of strengthening building codes (Eefting 1927). In late September 1989, Hurricane Hugo struck South Carolina. Observations following this hurricane revealed notable differences between the performance of pre- and post -FIRM buildings. Additionally, the BPAT deployed after Hurricane Hugo noted that some of the most severely damaged buildings were several rows back from the shoreline, and as a result recommended that design standards for Coastal A Zones (defined in Chapter 1) be more stringent. The wind damage from Hurricane Hugo also exposed deficiencies in residential roofing practices (URS 1991a, URS 1991b, and Texas Tech 1990). In August 1992, Hurricane Andrew struck the southeast Atlantic coast. This hurricane remains one of the most memorable hurricanes to hit this region and one of the costliest to date. The majority of the damage from this hurricane was due to wind; many of the failures were traced to inadequate connections between building elements (Figure 2-4). As such, buildings could not resist wind forces because of the lack Figure 2-4. Roof structure failure due to inadequate bracing and inadequate fastening of the roof deck, Hurricane Andrew (Dade County, FL, 1992) 2-8 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE of continuous load transfer paths from the roofs to the foundations (FEMA 1993). Hurricane Andrew was a major catalyst for building code changes involving wind design that improved wind pressure calculation procedures and emphasized the need for a continuous load transfer path in buildings for uplift and lateral loads, not just for the traditional downward -acting gravity loads. Hurricane Andrew destroyed 97 percent of the manufactured homes in its path, leading the Department of Housing and Urban Development (HUD) to adopt more stringent wind design criteria for manufactured homes (FEMA 2009a). In 1996, Hurricane Fran hit North Carolina. The resulting wave damage reinforced the idea that buildings in Coastal A Zones should be more hazard -resistant. The FEMA BPAT report noted that more stringent design codes and standards were needed to achieve improved performance (FEMA 1997). In September 1999, Hurricane Floyd briefly touched Florida before making landfall in North Carolina and moving north along the east coast as a tropical storm all the way to Maine. Although inland flood damage was severe in eastern North Carolina, high winds, storm surge and torrential rains caused moderate damage to coastal and inland communities along much of the east coast. 2.2.4 Gulf of Mexico Coast The Gulf of Mexico coast includes the coastal area from the Florida Keys northward and westward to Texas. This coastal area has long been susceptible to strong hurricanes, and in recent years the northern Gulf Coast (Florida panhandle to east Texas) has experienced a number of them. Low-lying areas are especially vulnerable to damage from erosion, waves, and storm surge. The September 1900 hurricane that hit Galveston, TX, is still the deadliest natural disaster to affect the United States. Shortly after, as a result of destruction due to poor siting practices, Galveston Island completed the first large-scale retrofit project in the United States: roads and hundreds of buildings were elevated, ground levels in the city were raised several feet, and the Galveston seawall was built (Walden 1990). In 1961, the extensive damage caused by erosion from Hurricane Carla again highlighted the need for proper siting and construction in coastal areas (Hayes 1967). Hurricane Camille, a Category 5 hurricane, made landfall in Mississippi in August 1969 and caused "near total destruction" in some areas near the beach as a result of waves and storm surge (Thom and Marshall 1971). High winds also caused damage farther inland. The studies performed by Thom and Marshall after the hurricane led to building design criteria that resulted in the construction of new homes with improved resistance to higher wind forces. In September 1979, Hurricane Frederic hit Alabama and caused widespread damage, including the destruction of many houses elevated to the BFE. After Hurricane Frederic, FEMA began to include wave heights in its determination of BFEs in coastal flood hazard areas (FEMA 1980). 1i TERMINOLOGY BASE FLOOD ELEVATION (BFE): The BFE is the water surface elevation resulting from a flood that has a 1 percent chance of equaling or exceeding that level in any given year. Section 3.6.1 has more information on how the BFE is established. DESIGN FLOOD ELEVATION (DFE): The DFE is the locally adopted regulatory flood elevation. If a community regulates to minimum NFIP requirements, the DFE is identical to the BFE. If a community chooses to exceed minimum NFIP requirements, the DFE exceeds the BFE. COASTAL CONSTRUCTION MANUAL 2-9 HISTORICAL PERSPECTIVE Hurricane Alicia made landfall in August 1983 in the Houston -Galveston area, causing extensive wind and flood damage. Wood frame houses were the hardest hit, and most of the damage was traced to poor roof construction and inadequate roof -to -wall connections (National Academy of Sciences 1984). Homes near the water were washed off their foundations, leading to the recommendation that grade -level enclosures be constructed with breakaway walls. NOTE The NFIP regulates structures to the BFE while building codes regulate to the DFE. The DFE is either equivalent to or greater than the BFE, depending on the governing codes of the jurisdiction in which the structure is located. In October 1995, Hurricane Opal hit the Florida panhandle, exacerbating erosion and structural damage from a weaker hurricane (Hurricane Erin) that hit the area I month earlier. A FEMA BPAT revealed that post - FIRM Zone A and pre -FIRM buildings failed most often, especially those with insufficient pile embedment. In addition, damage observations confirmed that State regulations that exceeded NFIP requirements helped reduce storm damage (FEMA 1996). Hurricane Georges made landfall in Mississippi in September 1998 and moved north and east through Alabama and Florida, causing both flood and wind damage. The FEMA BPAT found that buildings constructed in accordance with building codes and regulations, and buildings using specialized materials such as siding and roof shingles designed for higher wind speeds, performed well. The FEMA BPAT also confirmed that manufactured homes built after 1994 (when HUD wind design criteria were adopted following Hurricane Andrew) performed well. Most of the observed flood damage was attributed to inadequately elevated and improperly designed foundations, as well as poor siting practices (FEMA 1999a). In June 2001, Tropical Storm Allison made landfall in Galveston, TX. It took a unique path, stalling and then making a loop around Houston, resulting in heavy rainfall of more than 30 inches over a 4-day period. Severe flooding destroyed over 2,700 homes in Houston (RMS 2001). Flood damage to commercial and government buildings in the greater Houston area was severe. Tropical Storm Allison made it clear that some of the most destructive tropical systems are not hurricanes, but slow -moving tropical storms dropping large amounts of rainfall. Hurricane Charley made landfall in Florida in August 2004. After observing extensive wind damage, the FEMA MAT concluded that buildings built to the 2001 Florida Building Code (FBC) generally performed well structurally (FEMA 2005a), but older buildings experienced damage because design wind loads underestimated wind pressures on some building components, buildings lacked a continuous load path, and building elements were poorly constructed and poorly maintained. In September 2004, Hurricane Ivan made landfall in Alabama and Florida. Although not a design wind event, Ivan caused extensive envelope damage that allowed heavy rains to infiltrate buildings and damage interiors. This damage highlighted weaknesses in older building stock and the need for improved guidance and design criteria for better building performance at these "below code" events. Flood -borne debris and wave damage extended into Coastal A Zones (FEMA 2005b). In August 2005, Hurricane Katrina caused extensive storm surge damage and flooding well beyond the SFHA in Louisiana and Mississippi. Flooding in New Orleans was worsened by levee failures, and floodwaters rose well above the first floor of elevated buildings (Figure 2-5). The long duration of the flooding added to the destruction (FEMA 2006). After Katrina, FEMA issued new flood maps for the area that built on the 2-10 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE it i T� ~'gar` • r ' ', �.+'-}'ii a >"�. _ M , � .. 1. T �.. Figure 2-5. This elevated house atop a masonry pier foundation was lost, probably due to waves and storm surge reaching above the top of the foundation, Hurricane Katrina (Long Beach, MS, 2005) hazard knowledge gained in the 25+ years since the original FIRMs for that area were published. These flood maps continue to aid in rebuilding stronger and safer Gulf Coast communities. In September 2008, Hurricane Ike made landfall over Galveston, TX, and although wind speeds were below design levels, storm surge was more characteristic of a Category 4 hurricane. High waves and storm surge destroyed or substantially damaged over two-thirds of the buildings on Bolivar Peninsula. The FEMA MAT recommended enforcement of the Coastal A Zone building requirements that were recommended in earlier editions of the Coastal Construction Manual and discussed in Chapter 5 of this Manual, as well as designing critical facilities to standards that exceed current codes (FEMA 2009b). 2.2.5 U.S. Caribbean Territories The U.S. Caribbean Territories of the U.S. Virgin Islands and Puerto Rico are frequently hit by tropical storms and hurricanes. Damage in the Caribbean Territories is generally made worse by poor construction practices and less stringent building codes. In 1989, Hurricane Hugo destroyed many buildings in the U.S. Virgin Islands and Puerto Rico (York 1989). In 1995, the U.S. Virgin Islands and Puerto Rico were again struck by a hurricane. High winds from Hurricane Marilyn damaged roofs (Figure 2-6), allowing water to penetrate and damage building interiors (National Roofing Contractors Association [NRCA] 1996). This storm highlighted the need for more stringent building codes, and the U.S. Virgin Islands adopted the 1994 UBC. In 1998, the high winds and flooding from Hurricane Georges caused extensive structural damage in Puerto Rico. While not all of the damage could have been prevented, a significant amount could have been avoided if more buildings had been constructed to meet the requirements of the Puerto Rico building code and floodplain management regulations in effect at the time (FEMA 1999b). In 1999, as a result of FEMA BPAT recommendations, Puerto Rico adopted the 1997 UBC. COASTAL CONSTRUCTION MANUAL 2-11 HISTORICAL PERSPECTIVE Figure 2-6. This house lost most of its metal roof covering due to high winds during Hurricane Marilyn in 1995 (location unknown) SOURCE: NRCA 1996 2.2.6 Great Lakes Coast The Great Lakes Coast extends westward from New York to Minnesota. The biggest threat to coastal properties in the Great Lakes region is wave damage and erosion brought on by high winds associated with storms passing across the region during periods of high lake levels. Sometimes, stalled storm systems bring extremely heavy precipitation to local coastal areas, resulting in massive property damage from flooding, bluff and ravine slope erosion from storm runoff, and bluff destabilization from elevated groundwater. NOTE Lake levels in the Great Lakes fluctuate seasonally by 1 to 2 feet. High lake levels can intensify flood damage. In November 1940, the Armistice Day Storm brought high winds and heavy rain to the eastern shoreline of Lake Michigan, tearing roofs off buildings and blowing out windows. The wind damage also uprooted trees and downed telephone and power lines. A November 1951 storm hit Lake Michigan exacerbating already near -record high lake levels and causing extensive erosion and flooding that broke through seawalls. Damage observed as a result of this storm was consistent with the concept of Great Lakes shoreline erosion as a slow, cumulative process, driven by lakebed erosion, high water levels, and storms. An April 1973 storm caused storm surge resulting in erosion damage around Lake Michigan. The storm caused flooding 4 feet deep in downtown Green Bay, WI. The floodwaters here reached the elevation of the 0.2-percent-annual-chance flood due to strong winds blowing along the length of the bay piling up a storm surge on already high lake levels. ANovember 1975storm hit the western Great Lakes, undermining harbors, destroying jetties, and sinking an ore carrier with its crew onboard. The storm severely undermined the harbor breakwater at Bayfield, WI, requiring its replacement the following year. 2-12 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE High winds from a March 1985 storm caused storm surge flooding in upstate New York and Lake Erie, where lake levels rose to record levels. That month, Wisconsin's Lake Michigan lakeshore suffered rapid shoreline recession in successive storms, and some homes had to be relocated. The southeastern Wisconsin coast of Lake Michigan experienced rainfall in excess of the 0.2-percent-annual- chance precipitation event as a result of a 1986 storm, causing massive property damage from flooding, erosion, and bluff destabilization (U.S. Army Corp of Engineers [USACE] 1997, 1998). A February 1987 storm hit Chicago, IL, during a period of record high lake levels on Lake Michigan (Figure 2-7 shows damage from a similar storm). High waves destroyed a seawall and caused severe erosion to Chicago's lakeshore. Waves slammed high-rise condominiums, smashing first floor windows, and flooding basements. The southeastern Wisconsin coast of Lake Michigan experienced two rainfall events, in 1996and 1997, each of which resulted in precipitation in excess of the 0.2-percent-annual-chance event. These events, similar to the 1986 storm, caused massive property damage from flooding, erosion, and bluff destabilization (USACE 1997, 1998). I � •e,r tr ¢��- .z -y —a:r�: •• �a�'t'Y,I�S. ti'1+�-'iJC6. _.�:.+.5 R-F yY: .2.7 Pacific Coast Figure 2-7. Erosion along the Lake Michigan shoreline at Holland, MI, resulting from high lake levels and storm activity (August 1988) SOURCE: MARK CROWELL, FEMA The Pacific Coast extends from Alaska to southern California. The Pacific Coast is mostly affected by high waves and erosion during winter storms, though tsunamis occasionally affect the area. Hurricanes can affect the southern Pacific Coast, but this is rare. Damage to homes from El Nino -driven storms over the past several decades reinforces the importance of improving siting practices near coastal bluffs and cliffs on the Pacific Coast. A March 1964 earthquake with an epicenter in Prince William Sound, Alaska, generated a tsunami that affected parts of Washington, Oregon, California, and Hawaii. The tsunami flooded entire towns and triggered landslides. A post -disaster report provided several recommendations on foundation design, such COASTAL CONSTRUCTION MANUAL 2-13 HISTORICAL PERSPECTIVE as deep foundations to resist scour and undermining, and placement of wood frame buildings (Wilson and Torum 1968). In the winter of 1982-83, a series of El Nino -driven coastal storms caused widespread and significant damage to beaches, cliffs, and buildings along the coast between Baja California and Washington. These storms prompted a conference on coastal erosion, which concluded that siting standards were needed for homes built in areas subject to erosion, especially those atop coastal bluffs (McGrath 1985). The California Coastal Commission now uses the 1982-83 storms as its design event for new development (California Coastal Commission, 1997). In January 1988, a rapidly developing coastal storm struck southern California. The waves from the storm were the highest on record at the time and severely damaged shore protection structures and oceanfront buildings. This storm demonstrated the severity of damage that could be caused by a winter storm. In the winter of 1997-98, another notable series of severe El Nino -driven coastal storms battered the coasts of California and Oregon. Heavy rainfall caused widespread soil saturation, resulting in debris flow, landslides, and bluff collapse. California experienced severe storms in the winter of 2004-05, where heavy rain, debris flow, and landslides damaged buildings. A single landslide in Conchita, CA, destroyed 13 houses and severely damaged 23 houses in 2005 (Figure 2-8) (Jibson 2005). Figure 2-8. This building experienced structural damage due to a landslide in La Conchita, CA, after a January 2005 storm event SOURCE: JOHN SHEA, FEMA 2-14 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE 2.2.8 Hawaii and U.S. Pacific Territories Hawaii and the U.S. Pacific Territories of Guam, the Northern Marianas Islands, and American Samoa are subject to tropical cyclones (called hurricanes in Hawaii and American Samoa, and typhoons in Guam and the Northern Marianas Islands) and tsunamis. Tropical cyclones can cause damage in these areas from high winds, large waves, erosion, and rapid flow of rainfall runoff down steep terrain. Tsunamis can cause damage from rapidly moving water and debris across the shoreline area. In 1992, Hurricane Iniki, the strongest hurricane to affect the Hawaiian Islands in recent memory, caused significant flood and wave damage to buildings near the shoreline. Following the hurricane, FEMA recalculated BFEs to include hurricane flood effects, instead of just tsunami effects. This revision made flood maps more accurate and aided in the rebuilding process. A FEMA BPAT after the hurricane revealed problems with foundation construction that resulted in some buildings being washed off their foundations. It also concluded that inadequately designed roofs and generally poor quality of construction resulted in wind damage that could have been avoided. In December 1997, Typhoon Paka hit Guam causing substantial damage to wood -frame buildings, but minimal damage to concrete and masonry buildings. After the typhoon, Guam adopted ASCE 7-98 design wind speeds, which incorporated topographic influences in wind speeds for the first time. In September 2009, an 8.0 magnitude earthquake occurred approximately 160 miles southwest of American Samoa. Within 20 minutes, a series of tsunami waves struck the island. Due to high waves and runup, at least 275 residences were destroyed and several hundred others were damaged (Figure 2-9). Damage to commercial buildings, churches, schools and other buildings was also widespread. Elevated buildings and buildings farther inland generally performed better because they were able to avoid dynamic flood loads. 7-0-5 II� �J iOW _ <N Figure 2-9. Tsunami damage at Poloa, American Samoa SOURCE: ASCE, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 2-15 HISTORICAL PERSPECTIVE 2.3 Breaking the Disaster -Rebuild - Disaster Cycle Although the physiographic features vary throughout the coastal areas of the United States, post -event damage assessments and reports show that the nature and extent of damage caused by coastal flood events are remarkably similar. Similar findings have been noted for coastal storms in which high winds damage the built environment. In the case of wind, the evolution of building for "wind resistance" is characterized by improved performance of some building components (e.g., structural systems), but continued poor performance of other elements (e.g., building envelope components). == CROSS REFERENCE Although many aspects of coastal design and construction have improved over the years, the harsh coastal environment Chapter 3 discusses coastal hazards in more detail and their continues to highlight deficiencies in the design and effects on coastal buildings. construction process. The design and construction communityshould incorporate the lessons learned from past Sections 1. ai and 3.3 of this p p Manual explain the concept of the events in order to avoid repeating past mistakes, and to break Coastal A Zone. the disaster -rebuild -disaster cycle. The conclusions of post -event assessments can be classified according to those factors that contribute to both building damage and successful building performance: hazard WARNING identification, siting, design, construction, and maintenance. Special attention must also be paid when designing and FIRMs do not account for future constructing enclosures in coastal buildings. Reduction effects of sea level rise and long- of building damage in coastal areas requires attention to term erosion. All mapped flood hazard zones (V, A, and X) in areas these factors and coordination between owners, designers, subject to sea level rise and/or long - builders, and local officials. term erosion likely underestimate the extent and magnitude of actual flood hazards that a coastal building 2e e1 Hazard Identification will experience over its lifetime. FIRMs also do not account for Understanding and identifying the hazards that affect coastal storm -induced erosion that has areas is a key factor in successful mitigation. Historical and occurred after the FIRM effective recent hurricanes have provided insight into coastal hazards date. and their effects on coastal buildings. An all -hazards Refer to Section 3.5 for more approach to design is needed to address all possible impacts detailed information on erosion. of coastal storms and other coastal hazards. The minimum Zone A foundation and elevation requirements should not be assumed to provide buildings with resistance to coastal flood forces. The Coastal A Zone recommendations in this Manual should be considered as a part of the best practices approach to designing a successful building. Flood hazards in areas mapped as Zone A on coastal FIRMs can be much greater than flood hazards in riverine Zone A for two reasons: 2-16 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE 1. Waves 1.5 to 3 feet high (i.e., too small for an area to be classified as Zone V, but still capable of causing structural damage and erosion) occur during base flood conditions in many areas. 2. Older FIRMs may fail to reflect changing site conditions (e.g., as a result of long-term erosion, loss of dunes during previous storms) and improved flood hazard mapping procedures. Addressing all potential flood hazards will help reduce the likelihood of building damage or loss. The building in Figure 2-10 was approximately 1.3 miles from the Gulf of Mexico shoreline, but was damaged by storm surge and small waves during Hurricane Ike. Flood damage can result from the effects of short- and long-term increases in water levels (storm surge, tsunami, riverine flooding, poor drainage, seiche, and sea - level rise), wave action, high -velocity flows, erosion, and debris. Failure to consider long-term hazards, such as long-term erosion and the effects of multiple storms, can increase coastal flood hazards over time. Long-term erosion and accumulation of short-term erosion impacts over time can cause loss of protective beaches, dunes, and bluffs, and soils supporting building foundations. Failure to account for long-term erosion is one of the more common errors made by those siting and designing coastal residential buildings. Similarly, failure to consider the effects of multiple storms or flood events may lead to underestimating flood hazards in coastal areas. Coastal buildings left intact by one storm may be vulnerable to damage or destruction by successive storms. In coastal bluff areas, consideration of the potential effects of surface and subsurface drainage, removal of vegetation, and site development activities can help reduce the likelihood of slope stability hazards and landslides. Drainage from septic systems on coastal land can destabilize coastal bluffs and banks, accelerate erosion, and increase the risk of damage and loss to coastal buildings. Vertical cracks in the soils of some cohesive bluffs can cause a rapid rise of groundwater levels in the bluffs during extremely heavy and prolonged precipitation events. The presence of these cracks can rapidly reduce the stability of such bluffs. High winds can cause both structural and building envelope damage. Exposure and topography can increase wind pressures and wind damage. Homes on barrier islands and facing large bays or bodies of water Figure 2-10. School located approximately 1.3 miles from the Gulf shoreline damaged by storm surge and small waves, Hurricane Ike (Cameron Parish, LA, 2008) COASTAL CONSTRUCTION MANUAL 2-17 HISTORICAL PERSPECTIVE may be exposed to wind pressures higher than in areas of flat terrain, especially at high pressure zones of the roof. The house in Figure 2-11 sustained damage at the roof edge and roof corners, even though the hurricane was below the design event and wind damage should not have occurred. Recent studies have influenced wind design standards to increase design wind pressures on these exposed structures. Failure to consider the effects of topography (and changes in topography such as bluff erosion) on wind speeds can lead to an underestimation of design wind speeds. Siting buildings on bluffs or near high -relief topography requires special attention by the designer. CROSS REFERENCE Section 8.7.1 explains the increased wind pressures on certain zones of a roof (Figure 8-17). Some coastal areas are also susceptible to seismic hazards. Although the likelihood of simultaneous flood and seismic hazards is small, each hazard should be identified carefully and factored into siting, design, and construction practices. Figure 2-11. Galveston Island beach house with wind damage to roof in high pressure zones at roof edge and roof corners, Hurricane Ike, 2008 2.3.2 Siting There is inherent risk in building near a coast, but this risk can be reduced through proper siting practices. The effects of coastal storms CROSS and hurricanes on buildings provide regular lessons on the effects of REFERENCE siting in coastal environments. Chapter 4 discusses siting Building close to the shoreline is a common, and often poor, siting considerations, siting practices to avoid, and practice. It generally renders a building more vulnerable to wave, recommended alternatives. flood, and erosion effects and reduces any margin of safety against multiple storms or erosion events. If flood hazards increase over time, the building may require removal, protection, or demolition. In coastal areas subject to long-term or episodic erosion, poor siting often leads to otherwise well-built elevated buildings standing on the active beach. While considered a structural success, such buildings are generally uninhabitable because of the loss of utilities and 2-18 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE access. The presence of homes on active beaches can also lead to conflicts over beach use and increase pressure to armor or re -nourish beaches (both controversial and expensive measures). Buildings sited on naturally occurring rocky shorelines are better protected from erosion and direct wave impacts, but may still be subject to wave overtopping. Buildings subject to storm -induced erosion, including those in low-lying areas and buildings sited on the tops of erodible dunes CROSS and bluffs are vulnerable to damage caused by the undermining of REFERENCE foundations and the loss of supporting soil around vertical foundation Figures 3-37 and 3-46 members. Building on dunes and bluffs is discouraged. If buildings show the consequences of are constructed on dunes or bluffs they must be sited far from erodible siting buildings on the tops slopes and must have a deep, well -designed, and well -constructed pile of erodible bluffs. or column foundation. The additional hazards associated with building near naturally occurring geographic features should be considered. Siting along shorelines protected against wave attack by barrier islands or other land masses does not guarantee protection from flooding. In fact, storm surge elevations along low-lying shorelines in embayments are often higher than storm surge elevations on open coast shorelines. Buildings sited near unstabilized tidal inlets or in areas subject to large-scale shoreline fluctuations may be vulnerable to even minor storms or erosion events. Building close to other structures may increase the potential for damage from flood, wind, debris, and erosion hazards. Siting homes or other small buildings adjacent to large, engineered high-rise structures is a particular concern. The larger structures can redirect and concentrate flood, wave, and wind forces, and have been observed to increase flood and wind forces, as well as scour and erosion, to adjacent structures. Siting near erosion control or flood protection structures has contributed to building damage or destruction because these structures may not afford the required protection during a design event. Seawalls, revetments, berms, and other structures may themselves be vulnerable as a result of erosion and scour or other prior storm impacts. Siting too close to protective structures may preclude or make difficult any maintenance of the protective structure. Buildings sited on the downdrift shoreline of a groin or stabilized tidal inlet (an inlet whose location has been fixed by jetties) may be subject to increased erosion. Figure 2-12 shows how increased erosion rates on the downdrift side of groins can threaten structures. Building in a levee -impacted area has special risks that should be understood. Levees are common flood protection structures in some coastal areas. The purpose of a levee is to reduce risk from temporary flooding to the people and property behind it (known as levee -impacted areas). Levees are designed to provide a specific level of risk reduction (e.g., protection from the 1-percent-annual-chance flood). It must be remembered that levees can be overtopped or breached during floods that are larger than they were designed to withstand. Levees can also fail during floods that are less than the design level due to inadequacies in design, construction, operation, or maintenance. TERMINOLOGY: LEVEE A levee is a man-made structure, usually an earthen embankment, built parallel to a waterway to contain, control, or divert the flow of water. A levee system may also include concrete or steel floodwalls, fixed or operable floodgates and other closure structures, pump stations for rainwater drainage, and/or other elements, all of which must perform as designed to prevent failure. COASTAL CONSTRUCTION MANUAL 2-19 HISTORICAL PERSPECTIVE Figure 2-12. Structures built close to the downdrift side of groins and jetties can experience increased erosion rates SOURCE: ADAPTED FROM MAINE GEOLOGICAL SURVEY 2005 2-20 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE Foundation design is an important factor in the success of a coastal building. Use of shallow spreadfootingandslab foundations in CROSS REFERENCE areas subject to wave impact and/or erosion can result in building collapse, even during minor flood or erosion events. Because of Chapter 10 provides ti detailed discussion of foundation the potential for undermining by erosion and scour, this type of design. foundation may not be appropriate for coastal bluff areas outside the mapped floodplain and some Coastal A Zones. Figure 2-13 shows an extreme case of localized scour undermining a slab -on -grade house after Hurricane Fran. The lot was mapped as Zone A and located several hundred feet from the shoreline. This case illustrates the need for open foundations in Coastal A Zones. Use of continuous perimeter wall foundations, such as crawlspace foundations (especially unreinforced masonry) in areas subject to wave impact and/or erosion may result in building damage, collapse, or total loss. For open foundations, inadequate depth of foundation members is a common cause of failure in pile -elevated one- to four -family residential buildings. Figure 2-14 shows a building that survived Hurricane Katrina with a deeply embedded pile foundation that is sufficiently PIevated _ In addition, insufficient elevation of a building exposes the superstructure to damaging wave forces. Designs should incorporate freeboard above the required elevation of the lowest floor or bottom of the lowest horizontal member. Figure 2-15 shows two neighboring homes. The pre -FIRM house on the left experienced significant structural damage due to surge and waves. The newer, post -FIRM house on the right sustained minor damage because it was elevated above grade, and grade had been raised a few feet by fill. In addition to foundation design, there are other commonly observed points of failure in the design of coastal buildings. Failure to provide a continuous load path from the roof to the foundation using adequate connections may lead to structural c :� � ,, � .-•+:fir TERMINOLOGY: LOWEST FLOOR Under the NFIR the "lowest floor" of a building includes the floor of a basement. The NFIP regulations define a basement as "... any area of a building having its floor subgrade (below ground level) on all sides." For insurance rating purposes, this definition applies even when the subgrade floor is not enclosed by full -height walls. Figure 2-13. Extreme case of localized scour undermining a Zone A continuous perimeter wall foundation located several hundred feet from the shoreline, Hurricane Fran (Topsail Island, NC, 1996) COASTAL CONSTRUCTION MANUAL 2-21 HISTORICAL PERSPECTIVE Figure 2-14. Successful example of well -elevated and embedded pile foundation tested by Hurricane Katrina. Note adjacent building failures (Dauphin Island, AL, 2005) Figure 2-15. The pre -FIRM house (left) experienced damage due to surge and waves while the newer, elevated, post -FIRM house (right) experienced minimal damage, Hurricane Ivan (Santa Marina, Pensacola, FL, 2005) �rm�ruril . T �+cif' failure. Failure to use corrosion -resistant structural CROSS REFERENCE connectors can compromise structural integrity and may lead to building failures under less than design conditions. Chapter 9 includes discussion Examples of corrosion -resistant connectors include wooden designing a continuous load path . connectors, heavy gauge galvanized connectors, and stainless Section 9.2.3 discusses steel connectors. Salt spray and breaking waves accelerate connectors. 2-22 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE corrosion of metal building components. Nails, screws, sheet -metal connector straps, and truss plates made of ferrous metals are the most likely to corrode. Decks and roofs supported by inadequately embedded vertical members, especially those that are multiple stories, can lead to major structural damage even during minor flood and erosion events. Failure to adequately connect porch roofs and to limit the size of roof overhangs can lead to extensive damage to the building envelope during minor wind events. Roof overhangs should be designed to remain intact without vertical supports. Alternatively, supports should be designed to the same standards as the main foundation. Decks must be designed to withstand all design loads or should be designed so that they do not damage the main building when they fail. Building envelopes are susceptible to wind damage, wind debris, and water penetration. Protection of the entire building envelope is necessary in high -wind areas. It is recommended that glazing CROSS REFERENCE in hurricane -prone areas be protected; however, in wind-borne Chapter 11 provides a detailed debris regions as defined by the governing building code and discussion of building envelope ASCE-7, glazing is required to be protected by temporary or design, including exterior walls, permanent storm shutters or impact -resistant glass. In addition to windows, doors, and roofs. preventing pressurization, opening protection will reduce damage caused by wind, wind-borne debris, and rainfall penetration. However, proper specification of windows, doors, and their attachment to the structural frame is essential for full protection. Figure 2-16 shows two similar buildings in the same neighborhood that survived Hurricane Charley. The building on the left lost its roof structure due to internal pressurization resulting from unprotected windows and doors. The building on the right was protected with shutters and the roof sustained relatively minor damage. Many commonly used residential roofing designs, techniques, systems, and materials are susceptible to damage from wind and wind-borne debris. Designers should carefully consider the selection and attachment of roof sheathing and roof coverings in coastal areas. Low -slope roofs may experience higher wind loads and must effectively drain the heavy rains accompanying coastal storms. As with all houses, the designer should l k I .i toil, Figure 2-16. The unprotected building sustained roof damage due to pressurization (left) while the other sustained only minor damage because it was protected by shutters (right), Hurricane Charley (Captiva Island, FL, 2004) COASTAL CONSTRUCTION MANUAL 2-23 HISTORICAL PERSPECTIVE ensure that all loads, drainage, and potential water infiltration problems are addressed. Roof designs that incorporate gable ends (especially those that are unbraced) and wide overhangs are susceptible to failure (Figure 2-17) unless adequately designed and constructed for the expected loads. Alternative designs that are more resistant to wind effects should be used in coastal areas. The design and placement of swimming pools can affect the performance of adjacent buildings. In -ground and above -ground (but below the DFE) pools should not be structurally attached to buildings. An attached pool can transfer flood loads to the building. Building foundation designs should also account for the effects of non-attached but adjacent pools: increased flow velocities, wave runup, wave reflection, and scour that can result from the redirection of flow by the pool. In addition, swimming pools should not be installed in enclosures below elevated buildings. Figure 2-17. Wind damage to roof structure and gable end wall, Hurricane Katrina (Pass Christian, MS, 2005) 2.3.4 Construction Post -disaster observations often indicate that damage could have been reduced if buildings had been constructed according to CROSS REFERENCE approved designs and using best practices. Careful preparation of design documents and attention to construction details can Chapter provides details on construction of coastal reduce damage to coastal homes. FEMA P-499, Home Builder's buildings. Guide to Coastal Construction (FEMA 2010) and the NFIP Technical Bulletin Series Numbers 1 through 11 (FEMA 1993- 2011, available at provide detailed technical guidance and recommendations concerning the construction of coastal residential buildings. 2-24 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE Failure to achieve the pile or foundation embedment specified by building plans or local and State requirements will render an otherwise properly constructed building vulnerable to flood, erosion, and scour damage. Improperly constructed breakaway walls (e.g., improperly fastened wall panels or panels constructed immediately seaward of foundation cross -bracing) can cause preventable damage to the main structure during a flood event. Poorly made structural connections, particularly in wood frame and masonry structures, (e.g., pile/pier/ column -to -beam, joist -to -beam) have caused the failure of residential structures throughout the coastal areas of the United States. Proper embedment and lap splicing of reinforcing in concrete piers and footings is critical. Figure 2-18 shows an example of a masonry column connection that failed during Hurricane Katrina. Post -event investigations have revealed many instances of inadequate connections (e.g., improper or inadequately sized fasteners) that either failed during the event or could have failed if the design loads had been realized at the connection. Connections must be made with the appropriate fastener for the design structural capacity. Nail guns, frequently used to speed construction, can easily over drive nails, or drive them at an angle, leading to connections with reduced capacity. In addition, the nail gun operator may not be able to determine whether the nail has penetrated an unexposed wood member as intended, such as for a rafter or truss below the roof sheathing. Staples are not appropriate for connecting wood members in coastal areas. Bracing and fastening roofs and walls can help prevent building envelope failures in high -wind events. While bracing and fastening is adequately addressed in most current codes, older buildings built to older codes may be constructed with inadequate bracing and fastening. Lack of, or inadequate, connections between shingles and roofsheathing and between sheathing and roof framing (e.g., nails that fail to penetrate roof truss members or rafters) can cause roof failures and subsequent building failures. Figure 2-18. Failed masonry column connection, Hurricane Katrina (Jackson County, MS, 2005) COASTAL CONSTRUCTION MANUAL 2-25 HISTORICAL PERSPECTIVE 2.3.5 Enclosures Enclosures present a unique situation to coastal construction. NFIP regulations state that the area below an elevated building can be used only for parking, building access, and storage. These areas must not be finished or used for recreational or habitable purposes. No mechanical, electrical, or plumbing equipment is to be installed below the BFE. However, post - construction conversion of enclosures to habitable space remains a common violation of floodplain management requirements and is difficult for communities and States to control. Designers and owners should realize that: (1) enclosures and items in them are likely to be damaged or destroyed even during minor flood events; (2) enclosures, and most items in them, are not covered by flood insurance and, if damaged, the owner may incur significant costs to repair or replace them; and (3) even if enclosures are properly constructed with breakaway walls, the presence of enclosures increases flood insurance premiums for the entire building (the premium rate increases with the size of the enclosed area). Therefore, enclosed areas below elevated buildings, even if compliant with NFIP design and construction requirements, can have significant future cost implications for homeowners. Enclosures can have two types of walls: Enclosures with breakaway walls are designed to collapse under flood loads and act independently from the elevated building, leaving the foundation intact (Figure 2-19). All enclosures below elevated buildings in Zone V must have breakaway walls. Enclosures in Zone A and Coastal A Zones may have breakaway walls, but the walls must have flood openings to comply with Zone A requirements. Ij TERMINOLOGY: ENCLOSURE An enclosure is formed when any space below the lowest floor is enclosed on all sides by walls or partitions. v CROSS REFERENCE Section 9.3 discusses the proper design of breakaway walls. NOTE A change beginning with the May 2009 FEMA Flood Insurance Manual rates Zone V enclosures as "free of obstructions" if they are constructed with louvers or lattice on all walls except one (for garage door or solid breakaway wall). Previous rating practice called this "with obstruction." Enclosures and closed foundations that do not have breakaway walls can be constructed below elevated buildings in Zone A but are not recommended in Coastal A Zones. The walls of enclosures and foundation walls below elevated buildings in Zone A must have flood openings to allow the free entry and exit of floodwaters (Figure 2-20). Taller breakaway walls appear to produce larger pieces of flood -borne debris. Post -disaster investigations have observed some breakaway walls in excess of 11 feet high (FEMA 2009b). These investigations have also observed that louvered panels (Figure 2-21) remained intact longer than solid breakaway walls under the same flood conditions. As a result, houses with louvered panels had less flood -related damage (and repair cost) and generated less flood -borne debris. The use of louver panels can also result in lower flood insurance 2-26 COASTAL CONSTRUCTION MANUAL fig it i M HISTORICAL PERSPECTIVE Figure 2-19. Breakaway walls below the first floor of this house broke as intended under the flood forces of Hurricane Ike (Bolivar Peninsula, TX, 2008) Figure 2-20. Flood opening in an enclosure with breakaway walls, Hurricane Ike (Galveston Bay shoreline, San Leon, TX) premiums. Flood insurance premiums for a building located in Zone V are much less when a below-BFE enclosure is formed by louvers than by breakaway walls. A building with an enclosure formed by louvers is classified the same as if it had insect screening or open lattice (Figure 2-22), i.e., as "free of obstructions," while a solid breakaway wall enclosure results in a "with obstruction" rating for the building. COASTAL CONSTRUCTION MANUAL 2-27 HISTORICAL PERSPECTIVE Figure 2-21. Louvers installed beneath an elevated house are a good alternative to breakaway walls SOURCE: FEMA P-499 2010 Figure 2-22. An enclosure formed by open lattice (Isle of Palms, SC) 2-28 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE Two other enclosure scenarios have design and flood insurance implications. Designers should be cautious when an owner asks for either type of enclosure, and should consult with the community and a knowledgeable flood insurance agent: Enclosures that do not extend all the way to the ground (sometimes called "above -grade," "hanging," or "elevated" enclosures). These enclosures have a floor system that is not in contact with the ground, but that may be connected to the building foundation or supported on the primary pile system or short posts (Figure 2-23). Having the floor of the enclosure above grade means frequent flooding passes underneath, which may reduce the frequency and severity of damage. These enclosures were not contemplated when flood insurance premium rate tables were prepared, and thus can result in significantly higher flood insurance premiums. As of early 2011, the NFIP was working to address this type of construction, but until such time as it is resolved, owners will pay a substantial premium penalty for this type of enclosure. Two-story enclosures. In flood hazard areas with very high BFEs, some owners have constructed two- story, solid walls to enclose areas below elevated buildings, typically with a floor system approximately midway between the ground and the elevated building (Figure 2-24). These enclosures present unique problems. In Zone A, the walls at both levels of the enclosure must have flood openings; there must be some means to relieve water pressure against the floor system between the upper and lower enclosures; and special ingress and egress code requirements may apply. These enclosures may also result in substantially higher flood insurance premiums. Figure 2-23. Above -grade enclosure (Perry, FL) COASTAL CONSTRUCTION MANUAL 2-29 HISTORICAL PERSPECTIVE Figure 2-24. Two-story enclosure SOURCE: FEMA P-499 2010 2.3.6 Maintenance Repairing and replacing structural elements, connectors, and building envelope components that have deteriorated because of decay or corrosion CROSS helps to maintain a building's resistance to natural hazards. Maintenance REFERENCE of building components in coastal areas should be an ongoing process. The Chapter 14 provides ultimate costs of deferred maintenance in coastal areas can be high when details on the natural disasters strike. Failure to inspect and repair damage caused maintenance of by wind, flood, erosion, or other hazard makes a building even more coastal buildings. vulnerable during the next event. Failure to maintain erosion control or coastal flood protection structures leads to increased vulnerability of those structures and the buildings behind them. 2.4 References ASCE (American Society of Civil Engineers). 1998. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-98. ASCE. 2010a. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. ASCE. 2010b. So, You Live Behind a Levee! California Coastal Commission. 1997. Questions and Answers on El Nino. http://www.coastal.ca.gov/elnino/ enqa.html. Accessed 03/02/11. Eefting, T. 1927. "Structural Lessons of the South Florida Hurricane." Florida Engineer and Contractor. September. pp. 162-170. 2-30 COASTAL CONSTRUCTION MANUAL HISTORICAL PERSPECTIVE FEMA (Federal Emergency Management Agency). 1980. Elevating to the Wave Crest Level A Benefit- CostAnalysis. FIA-6. FEMA. 1992. Building Performance Assessment Team, Field Trip and Assessment within the States of Maryland and Delaware in Response to a Nor'easter Coastal Storm on January 4, 1992. Final Report. March 4. FEMA. 1993. Building Performance: Hurricane Andrew in Florida, Observations, Recommendations and Technical Guidance. FIA-22. FEMA.1996. Hurricane Opal in Florida, A Building Performance Assessment. FEMA-281. FEMA. 1997. Building Performance Assessment: Hurricane Fran in North Carolina, Observations, Recommendations and Technical Guidance. FEMA-290. FEMA. 1999a. Hurricane Georges in the Gulf Coast - Observations, Recommendations, and Technical Guidance. FEMA 338. FEMA. 1999b. Hurricane Georges in Puerto Rico - Observations, Recommendations, and Technical Guidance. FEMA 339. FEMA. 2005a. Hurricane Charley in Florida - Observations, Recommendations, and Technical Guidance. FEMA 488. FEMA. 2005b. Hurricane Ivan in Alabama and Florida - Observations, Recommendations, and Technical Guidance. FEMA 489. FEMA. 2006. Hurricane Katrina in the Gulf Coast- Building Performance Observations, Recommendations, and Technical Guidance. FEMA 549. FEMA. 2009a. Protecting Manufactured Homes from Floods and Other Hazards - A Multi -Hazard Foundation and Installation Guide. FEMA P-85, Second Edition. FEMA. 2009b. Hurricane Ike in Texas and Louisiana - Building Performance Observations, Recommendations, and Technical Guidance. FEMA P-757. FEMA. 2010. Home Builder's Guide to Coastal Construction Technical Fact Sheet Series. FEMA P-499. FEMA. 2011. National Flood Insurance Program, Flood Insurance Manual. Hayes, M. O. 1967. "Hurricanes as Geological Agents: Case Studies of Hurricanes Carla, 1961, and Cindy, 1963." Bureau ofEconomic Geology Report oflnvestigation No. 61. Austin, TX: University of Texas. Jibson, R. 2005. Landslide Hazards at La Conchita, California. Prepared for the United States Geological Survey. Open -File Report 2005-1067. Maine Geological Survey. 2005. Coastal Marine Geology: Frequently Asked Questions. http://www.maine. gov/doc/nrimc/mgs/explore/marine/faq/groins.htm. Accessed 11/24/2010. McGrath, J., ed. 1985. "California's Battered Coast." Proceedings from a February 6-8, 1985, Conference on Coastal Erosion. California Coastal Commission. COASTAL CONSTRUCTION MANUAL 2-31 HISTORICAL PERSPECTIVE Minsinger, W.E. 1988. The 1938 Hurricane, An Historical and Pictorial Summary. Blue Hill Meteorological Observatory, East Milton, MA. Greenhills Books, Randolph Center, VT. National Academy of Sciences, National Research Council, Commission on Engineering and Technical Systems. 1984. Hurricane Alicia, Galveston and Houston, Texas, August 17-18, 1983. NOAA (National Oceanic and Atmospheric Administration). 2004. Effects of Hurricane Isabel on Water Levels: Data Report. NOS CO-OPS O40. National Roofing Contractors Association. 1996. Hurricane Marilyn, Photo Report of Roof Performance. Prepared for the Federal Emergency Management Agency. March. RMS (Risk Management Solutions). 2001. Tropical Storm Allison, June 2001: RMS Event Report. Thom, H. C. S.; R. D. Marshall. 1971. "Wind and Surge Damage due to Hurricane Camille." ASCE Journal of Waterways, Harbors and Coastal Engineering Division. May. pp. 355-363. TTU (Texas Tech University). 1990. Performance of roofing systems in Hurricane Hugo. August. URS Group, Inc. (URS). 1989. Flood Damage Assessment Report: Sandbridge Beach, Virginia, and Nags Head, North Carolina, April 13, 1988, Northeaster. Prepared for the Federal Emergency Management Agency. March. URS. 1990. Flood Damage Assessment Report: Nags Head, North Carolina, Kill Devil Hills, North Carolina, and Sandbridge Beach, Virginia, March 6-10, 1989, Northeaster. Prepared for the Federal Emergency Management Agency. April. URS. 1991a. Flood Damage Assessment Report: Surfside Beach to Folly Island, South Carolina, Hurricane Hugo, September 21-22, 1989. Volume I. Prepared for the Federal Emergency Management Agency. August. URS. 1991b. Follow -Up Investigation Report: Repair Efforts 9 Months After Hurricane Hugo, Surfside Beach to Folly Island, South Carolina. Volume I. Prepared for the Federal Emergency Management Agency. August. URS. 1991c. Flood Damage Assessment Report: Buzzard s Bay Area, Massachusetts, Hurricane Bob, August 19, 1991. October. USACE (U.S. Army Corps of Engineers). 1997. "Annual Summary." Great Lakes Update. Vol. No. 126. Detroit, MI: Detroit District. January 3. USACE. 1998. "Annual Summary." Great Lakes Update. Detroit, MI: Detroit District. Waldon, D. 1990. "Raising Galveston." American Heritage oflnvention and Technology. Vol. 5, No. 3, pp. 8-18. Wilson, B. W. and A. Torum. 1968. The Tsunami of the Alaskan Earthquake, 1964: Engineering Evaluation. Technical Memorandum No. 25. U.S. Army Corps of Engineers, Coastal Engineering Research Center. York, Michael. "Deadly Hugo Slams Puerto Rico, Virgin Islands." Washington Post. September 19, 1989. 2-32 COASTAL CONSTRUCTION MANUAL i ntifying Hazards r"I Buildings constructed in coastal areas are subject to natural hazards. The most significant natural hazards that affect the coastlines of the United States and territories can be divided into four general categories: Coastal flooding (including waves) Erosion High winds Earthquakes This chapter addresses each of these categories, as well as other hazards and environmental effects, but focuses on flooding and erosion (Sections 3.4 and 3.5). These two hazards are among the least understood and the least discussed in design and construction documents. Designers have numerous resources available that discuss wind and seismic hazards in detail, so they will be dealt with in less detail here. In order to construct buildings to resist these natural hazards and reduce existing buildings' vulnerability to such hazards, proper planning, siting, design, and construction are critical and require an understanding of the coastal environment, including coastal geology, coastal processes, regional variations in coastline characteristics, and coastal sediment budgets. Proper siting and design also require accurately assessing the CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/ mat/fema55.shtm). WARNING Natural hazards can act individually, but often act in combination (e.g., high winds and coastal flooding, coastal flooding and erosion, etc.). Long-term changes in underlying conditions —such as sea level rise —can magnify the adverse effects of some of these hazards. For more information on load combinations, see Chapter 8. COASTAL CONSTRUCTION MANUAL 3-1 IDENTIFYING HAZARDS vulnerability of any proposed structure, including the nature and extent of its exposure to coastal hazards. Failure to properly identify and design to resist coastal hazards expected over the life of a building can lead to severe consequences, most often building damage or destruction. This chapter provides an overview of coastline characteristics (Section 3.1); tropical cyclones and coastal storms (Section 3.2); coastal hazards (Section 3.3); coastal flood effects, including erosion (Sections 3.4 and 3.5); and flood hazard zones and assessments, including hazard mapping procedures used by the NFIP (Sections 3.6 and 3.7). Although general guidance on identifying hazards that may affect a coastal building site is provided, this chapter does not provide specific hazard information for a particular site. Designers should consult the sources of information listed in Chapter 4 of this Manual and in the resource titled "Information about Storms, Big Waves, and Water Levels" on the FEMA Residential Coastal Construction Web page. Siting considerations are discussed in more detail in Chapter 4. 3.1 Coastline Characteristics This section contains general information on the coastal environment and the characteristics of the United States coastline. 3.1.1 Coastal Environment Coastal geology and geomorphology refer to the origin, structure, and characteristics of the rocks and sediments that make up the coastal region. The coastal region is considered the area from the uplands to the nearshore as shown in Figure 3-1. Coastal sediments can vary from small particles of silt or sand (a Figure 3-1. Coastal region terminology SOURCE: ADAPTED FROM USACE 2008 3-2 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS few thousandths or hundredths of an inch across), to larger particles of gravel and cobble (up to several inches across), to formations of consolidated sediments and rock. The sediments can be easily erodible and transportable by water and wind, as in the case of silts and sands, or can be highly resistant to erosion. The sediments and rock units that compose a coastline are the product of physical and chemical processes that take place over thousands of years. Coastal processes refer to physical processes that act upon and shape the coastline. These processes, which influence the configuration, orientation, and movement of the coast, include the following: Tides and fluctuating water levels Waves Currents (usually generated by tides or waves) Winds Coastal processes interact with the local coastal geology to form and modify the physical features that are referred to frequently in this Manual: beaches, dunes, bluffs, and upland areas. Water levels, waves, currents, and winds vary with time at a given location (according to short-term, seasonal, or longer -term patterns) and vary geographically at any point in time. A good analogy is weather; weather conditions at a given location undergo significant variability over time, but tend to follow NOTE seasonal and other patterns. Further, weather conditions can differ substantially from one location to another at the same Although calculating coastal point in time. Regional variations in coastlines are the product of variations in coastal processes and coastal geology. These variations can be quite substantial, as described in the following sections of this chapter. Thus, shoreline siting and design practices appropriate to one area of the coastline may not be suitable for another. The coastal sediment budget is based on the identification of sediment sources and sinks, and refers to the quantification of the amounts and rates of sediment transport, erosion, and deposition within a defined region. Sediment budgets are used by coastal engineers and geologists to analyze and explain shoreline changes and to project future shoreline behavior. Typical sediment sources include longshore transport of sediment into an area, beach nourishment, and dune or bluff erosion (which supply sediment to the beach). Typical sediment sinks include longshore sediment transport out of an area, storm overwash (sediment carried inland from the beach), and loss of sediment into tidal inlets or submarine canyons. While calculating sediment budgets is beyond the scope of typical planning and design studies for coastal residential structures, sediment budgets may have been calculated by others for the shoreline segment containing a proposed building sediment budgets can be complicated, the premise behind it is simple: if more sediment is transported by coastal processes or human actions into a given area than is transported out, shore accretion results; if more sediment is transported out of an area than is transported in, shore erosion results. TERMINOLOGY LONGSHORE SAND TRANSPORT is wave- and/or tide -generated movement of shallow -water coastal sediments parallel to the shoreline. CROSS -SHORE SAND TRANSPORT is wave- and/or tide -generated movement of shallow -water coastal sediments toward or away from the shoreline. COASTAL CONSTRUCTION MANUAL 3-3 IDENTIFYING HAZARDS site. Designers should contact State coastal management agencies and universities to determine if sediment budget and shoreline change information for their site is available, since this information will be useful in site selection, planning, and design. The concept of sediment budgets does not apply to all coastlines, particularly rocky coastlines that are resistant to erosion and whose existence does not depend on littoral sediments transported by coastal processes. Rocky coastlines typical of many Pacific, Great Lakes, New England, and Caribbean areas are better represented by Figure 3-2. The figure illustrates the slow process by which rocky coasts erode in response to elevated water levels, waves, and storms. 3.1.2 United States Coastline The estimated total shoreline length of the continental United States, Alaska, and Hawaii is 84,240 miles, including 34,520 miles of exposed shoreline and 49,720 miles of sheltered shoreline (USACE 1971). The shoreline length of the continental United States alone is estimated as 36,010 miles (13,370 miles exposed, 22,640 miles sheltered). Several sources (National Research Council 1990, Shepard and Wanless 1971, USACE 1971) were used to characterize and divide the coastline of the United States into six major segments and several smaller subsegments (see Figure 3-3). Each of the subsegments includes coastlines of similar origin, characteristics, and hazards. Figure 3-2. Generalized depiction of erosion process along a rocky coastline SOURCE: ADAPTED FROM HORNING GEOSCIENCES 1998 3-4 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Great Lakes coast Northern ....:...:.:.:. Pacific A North coast Atlantic Alaska l coast Mid -Atlantic a R coast .. R 0 0 o _ Southern South R a California - Atlantic coast _ coast a Coast of Hawaii t s s and U.S. Pacific ao Territories s �o%�,�:�� Coast of U.S. Florida Keys Caribbean Hawaii, Northern �s� O °- Territories Islandsa _ Puerto Rico o� �� American U.S. Samoa Guam Virgin Islands Gulf of Mexico coast Figure 3-3. United States coastline Atlantic Coast The Atlantic coast extends from Maine to the Florida Keys and includes the North Atlantic coast, the Mid - Atlantic coast, the South Atlantic coast, and the Florida Keys. The North Atlantic coast, extending from Maine to Long Island, NY, is glacial in origin. It is highly irregular, with erosion -resistant rocky headlands and pocket beaches in northern New England, and erodible bluffs and sandy barrier islands in southern New England and along Long Island, NY. The Mid -Atlantic coast extends from New Jersey to Virginia, and includes two of the largest estuaries in the United States; Delaware Bay and Chesapeake Bay. The open coast shoreline is generally composed of long barrier islands separated by tidal inlets and bay entrances. The South Atlantic coast extends from North Carolina to South Florida and consists of three regions: (1) the North Carolina and northern South Carolina shoreline, composed of long barrier and mainland beaches (including the Outer Banks and the South Carolina Grand Strand region); (2) the region extending from Charleston, SC, to the St. Johns River entrance at Jacksonville, FL (a tide -dominated coast composed of numerous short barrier islands, separated by large tidal inlets and backed by wide expanses of tidal marsh); and (3) the east coast of Florida (composed of barrier and mainland beaches backed by narrow bays and rivers). COASTAL CONSTRUCTION MANUAL 3-5 IDENTIFYING HAZARDS The Florida Keys are a series of low -relief islands formed by limestone and reef rock, with narrow, intermittent carbonate beaches. The entire Atlantic coast is subject to waves and high storm surges from hurricanes and/or nor'easters. Wave runup on steeply sloping beaches and shorelines in New England is also a common source of coastal flooding. Gulf of Mexico Coast The Gulf of Mexico coast extends from the Florida Keys to Texas. It can be divided into three regions: (1) the eastern Gulf Coast from southwest Florida to Mississippi, which is composed of low-lying sandy barrier islands south of Tarpon Springs, FL, and west of St. Marks, FL, with a marsh -dominated coast in between in the Big Bend area of Florida; (2) the Mississippi Delta Coast of southeast Louisiana, characterized by wide, marshy areas and a low-lying coastal plain; and (3) the western Gulf Coast, including the cheniers of southwest Louisiana, and the long, sandy barrier islands of Texas. The entire Gulf of Mexico coast is vulnerable to high storm surges and waves from hurricanes. Some areas (e.g., the Big Bend area of Florida) are especially vulnerable because of the presence of a wide, shallow continental shelf and low-lying upland areas. Coast of U.S. Caribbean Territories The islands of Puerto Rico and the U.S. Virgin Islands are the products of ancient volcanic activity. The coastal lowlands of Puerto Rico, which occupy nearly one-third of the island's area, contain sediment eroded and transported from the steep, inland mountains by rivers and streams. Ocean currents and wave activity rework the sediments on pocket beaches around each island. Coastal flooding is usually due to hurricanes, although tsunami events are not unknown in the Caribbean. Great Lakes Coast The shorelines of the Great Lakes coast extend from Minnesota to New York. They are highly variable and include wetlands, low and high cohesive bluffs, low sandy banks, and lofty sand dunes perched on bluffs (200 feet or more above lake level). Storm surges along the Great Lakes are generally less than 2 feet except in small bays (2 to 4 feet) and on Lake Erie (up to 8 feet). Large waves can accompany storm surges. Periods of active erosion are triggered by heavy precipitation events, storm waves, rising lake levels, and changes in groundwater outflow along the coast. The Pacific coast extends from California to Washington, and includes Alaska. It can be divided into three regions: (1) the southern California coast, which extends from San Diego County to Point Conception (Santa Barbara County), CA, and is characterized by long, sandy beaches and coastal bluffs; (2) the northern Pacific coast, which extends from Point Conception, CA, to Washington and is characterized by rocky Cliffs, pocket beaches, and occasional long sandy barriers near river mouths; and (3) the coast ofAlaska. Open coast storm surges along the Pacific shoreline are generally small (less than 2 feet) because of the narrow continental shelf and deep water close to shore. However, storm wave conditions along the Pacific 3-6 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS shoreline are severe, and the resulting wave runup can be very destructive. In some areas of the Pacific coast, tsunami flood elevations can be much higher than flood elevations associated with coastal storms. The coast of Alaska can further be divided into two areas: (1) the southern coast, dominated by steep mountainous islands indented by deep fjords, and (2) the Bering Sea and Arctic coasts, backed by a coastal plain dotted with lakes and drained by numerous streams and rivers. The climate of Alaska and the action of ice along the shorelines set it apart from most other coastal areas of the United States. Coast of Hawaii and U.S. Pacific Territories The islands that make up Hawaii are submerged volcanoes; thus, the coast of Hawaii is formed by rocky cliffs and intermittent sandy beaches. Coastlines along the Pacific Territories are similar to those of Hawaii. Coastal flooding can be due to two sources: storm surges and waves from hurricanes or cyclones, and wave runup from tsunamis. 3.2 Coastal Storm Events Tropical cyclones and coastal storms occur in varying strengths and intensities in all coastal regions of the United States and its territories. These storms are the primary source of the flood and wind damage that the recommendations of this Manual aim to reduce. Tropical cyclones and coastal storms include all storms associated with circulation around an area of atmospheric low pressure. When the storm origin is tropical and the circulation is closed, tropical storms, hurricanes, or typhoons result. Tropical cyclones and coastal storms are capable of generating high winds, coastal flooding, high -velocity flows, damaging waves, significant erosion, and intense rainfall (see Figure 3-4). Like all flood events, they are also capable of generating and moving large quantities of water -borne sediments and floating debris. Consequently, the risk to improperly sited, designed, or constructed coastal buildings can be great. Figure 3-4. Storm surge flooded this home in Ascension Parish, LA (Tropical Storm Allison, 2001) COASTAL CONSTRUCTION MANUAL 3-7 IDENTIFYING HAZARDS One parameter not mentioned in the storm classifications described in `r the following sections —storm coincidence with spring tides or higher CROSS than normal water levels —also plays a major role in determining storm REFERENCE impacts and property damage. If a tropical cyclone or other coastal storm See Section 3.5.5 for coincides with abnormally high water levels or with the highest monthly, a discussion of high seasonal, or annual tides, the flooding and erosion impacts of the storm are water levels and sea magnified by the higher water levels, to which the storm surge and wave level rise. effects are added. 3.2.1.1 Tropical Cyclones Tropical storms have 1-minute sustained winds averaging 39 to 74 miles #J per hour (mph). When sustained winds intensify to greater than 74 mph, NOTE the resulting storms are called hurricanes (in the North Atlantic basin or in the Central or South Pacific basins east of the International Date Line) NOAA has detailed or typhoons (in the western North Pacific basin). tropical storm and hurricane track Hurricanes are divided into five classes according to the Saffir-Simpson information from 1848 to the present Hurricane Wind Scale (SSHWS), which uses 1-minute sustained wind (http://csc.noaa.gov/ speed at a height of 33 feet over open water as the sole parameter to hurricanes). categorize storm damage potential (see Table 3-1). The SSHWS, which replaces the Saffir-Simpson Hurricane Scale, was introduced for the 2010 hurricane season to reduce confusion about the impacts associated with the hurricane categories and to provide a more scientifically defensible scale CROSS (there is not a strict correlation between wind speed and storm surge, as the REFERENCE original scale implied, as demonstrated by recent storms [e.g., Hurricanes Katrina and Ike] which produced devastating surge damage even though See Chapter 2 for wind speeds at landfall were associated with lower hurricane categories). a summary of the The storm surge ranges, flooding impact, and central pressure statements g g g p p storms listed in Table 3-1. More were removed from the original scale, and only peak wind speeds are details can be found included in the SSHWS (NOAA 2010). The categories and associated in the "Coastal peak wind speeds in the SSHWS are the same as they were in the Saffir- Flood and Wind Simpson Hurricane Scale. Event Summaries" resource on the FEMA Typhoons are divided into two categories; those with sustained winds Residential Coastal Construction Web less than 150 mph are referred to as typhoons, while those with sustained page. winds equal to or greater than 150 mph are known as super typhoons. Tropical cyclone records for the period 1851 to 2009 show that approximately one in five named storms (tropical storms and hurricanes) in the North Atlantic basin make landfall as hurricanes along the Atlantic or Gulf of Mexico coast of the United States. Figure 3-5 shows the average percentages of landfalling hurricanes in the United States. Tropical cyclone landfalls are not evenly distributed on a geographic basis. In fact, the incidence of landfalls varies greatly. Approximately 40 percent of all U.S. landfalling hurricanes directly hit Florida, and 83 percent of Category 4 and 5 hurricane strikes have directly hit either Florida or Texas. Table 3-2 shows direct hurricane hits to the mainland U.S. from 1851 to 2009 categorized using the Saffir-Simpson Hurricane Scale. 3-8 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Table 3-1. Saffir-Simpson Hurricane Wind Scale Agnes (1972 - Florida) 1 74-95 Minimal Earl (1998 - Florida) (89-116) Dolly (2008 - Texas) 3 111-130 Extensive Alicia (1983 - Texas) (135-159) Ivan (2004 - Alabama) 5 >155 Catastrophic Florida Keys (1935) (>189) p Camille (1969 - Louisiana, Mississippi) DATA SOURCE: NOAA HISTORICAL HURRICANE TRACKS (http://csc.noaa.gov/hurricanes) (a) Hurricanes are listed according to their respective category at landfall based on wind speed. Figure 3-5. Classification (by Saffir- Simpson Hurricane scale) of landfalling tropical cyclones along the U.S. Atlantic and Gulf of Mexico coasts, 1851-2009 DATA SOURCES: BLAKE ET AL. 2005, JARRELL ET AL. 2001. NOAA 2011a COASTAL CONSTRUCTION MANUAL 3-9 IDENTIFYING HAZARDS Table 3-2. Direct Hurricane Hits to U.S. Coastline Between 1851 and 2009 from Texas to Maine Texas 25 19 12 7 0 63 Louisiana 18 15 15 4 1' 53 Mississippi 2 5 8 0 1 16 Alabama 12' 5' 6' 0' 0 23 Florida 44 33 29 6 2 114 Georgia 12' 5' 2' 1' 0' 20 South Carolina 19 6 4 2 0 31 North Carolina' 22' 13' 11' 1' 0 46 Virginia 9 2 1 0 0 12 Maryland 1' 1' 0' 0' 0 2 Delaware 2 0 0 0 0 2 New Jersey 2' 0' 0' 0' 0 2 Pennsylvania 1 0 0 0 0 1 New York 6' 1 5 0' 0 12 Connecticut 4 3 3 0 0 10 Rhode Island 3' 2' 4' 0' 0 9 Massachusetts 5 2 3 0 0 10 New Hampshire 1' 1' 0 0 0 2 Maine 5 1 0 0 0 6 DATA SOURCES: BLAKE ET AL. 2005, JARRELL ET AL. 2001, NOAA 2011a Note: A direct hurricane hit means experiencing the core of strong winds and/or storm surge of a hurricane. State totals will not add up to U.S. totals because some storms are counted for more than one State Another method of analyzing tropical cyclone incidence data is to compute the mean return period, or the average time (in years) between landfall or nearby passage of a tropical storm or hurricane. Note that over short periods of time, the actual number and timing of tropical cyclone passage/landfall may deviate substantially from the long-term statistics. Some years see little tropical cyclone activity with no landfalling storms; other years see many storms with several landfalls. A given area may not experience the effects of a tropical cyclone for years or decades, and then be affected by several storms in a single year. 3.2.1.2 Other Coastal Storms Other coastal storms include storms lacking closed circulation, but capable of producing strong winds. These storms usually occur during winter months and can affect the Atlantic coast, Pacific coast, the Great Lakes coast, and, rarely, the Gulf of Mexico coast. Along the Atlantic coast, these storms are known as extratropical storms or nor'easters. Two of the most powerful and damaging nor 'easters on record are the March 5-7, 1962 storm (see Figure 3-6) and the October 28—November 3, 1991 storm. 3-10 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Coastal storms along the Pacific coast of the United States are usually associated with the passage of weather fronts during the winter months. These storms produce little or no storm surge (generally 2 feet or less) along the ocean shoreline, but they are capable of generating hurricane -force winds and large, damaging waves. Storm characteristics and patterns along the Pacific coast are strongly influenced by the occurrence of the El Nino Southern Oscillation (ENSO)a climatic anomaly resulting in above -normal ocean temperatures and elevated sea levels along the U.S. Pacific coast. During El Nino years, sea levels along the Pacific shoreline tend to rise as much as 12 to 18 inches above normal, the incidence of coastal storms increases, and the typical storm track shifts from the Pacific Northwest to southern and central California. The net result of these effects is increased storm -induced erosion, changes in longshore sediment transport (due to changes in the direction of wave approach, which changes erosion/deposition patterns along the shoreline), and increases the incidence of rainfall and landslides in coastal regions. Storms on the Great Lakes are usually associated with the passage of low-pressure systems or cold fronts. Storm effects (high winds, storm surge, and wave runup) may last a few hours or a few days. Storm surges and damaging wave conditions on the Great Lakes are a function of wind speed, direction, duration, and fetch; if high winds occur over a long fetch for more than an hour or so, the potential for flooding and erosion exists. However, because of the sizes and depths of the Great Lakes, storm surges are usually limited to less than 2 feet, except in embayments (2 to 4 feet) and on Lake Erie (up to 8 feet). Periods of active erosion are triggered by heavy precipitation events, storm waves, rising lake levels, and changes in groundwater outflow along the coast. Ocean . Figure 3-6. Flooding, erosion, and overwash at Fenwick Island, DE, following March 1962 nor'easter COASTAL CONSTRUCTION MANUAL 3-11 IDENTIFYING HAZARDS 3.3 Coastal Hazards #j NOTE This section addresses coastal hazards of high wind, earthquakes, tsunamis, and other hazards and environmental effects. Coastal Basic wind speeds given by flooding and erosion hazards are discussed separately, in Sections ASCE 7-10, shown in Figure 3-7 3.4 and 3.5, respectively. of this Manual, correspond to a wind with a recurrence interval of 700 years for Risk Category 3.3.1 High Winds II buildings. The 2012 IRC contains a High winds can originate from a number of events. Tropical simplified table based on storms, hurricanes, typhoons, other coastal storms, and tornadoes ASCE 7-10, which can be used generate the most significant coastal wind hazards. to obtain an effective basic wind speed for sites where topographic wind effects are a The most current design wind speeds are given by the national concern. load standard, ASCE 7-10, Minimum Design Loads for Buildings and Other Structures (ASCE 2010). Figure 3-7, taken from ASCE 7-10, shows the geographic distribution of design wind speeds for the continental United States and Alaska, and lists design wind speeds for Hawaii, Puerto Rico, Guam, American Samoa, and the Virgin Islands. The Hawaii State Building Code includes detailed design wind speed maps for all four counties in Hawaii. They are available online at http://hawaii.gov/dags/bcc/comments/wind-maps-for-state-building-code. High winds are capable of imposing large lateral (horizontal) and uplift (vertical) forces on buildings. Residential buildings can suffer extensive wind damage when they are improperly designed and constructed and when wind speeds exceed design levels (see Figures 3-8 and 3-9). The effects of high winds on a building depend on many factors, including: Wind speed (sustained and gusts) and duration of high winds Height of building above ground Exposure or shielding of the building (by topography, vegetation, or other buildings) relative to wind direction Strength of the structural frame, connections, and envelope (walls and roof) Shape of building and building components n\ NOTE It is generally beyond the scope of most building designs to account for a direct strike by a tornado (the ASCE 7-10 wind map in Figure 3-7 excludes tornado effects). However, use of wind -resistant design techniques will reduce damage caused by a tornado passing nearby. Section 3.3.1.3 discusses tornado effects. Number, size, location, and strength of openings (e.g., windows, doors, vents) Presence and strength of shutters or opening protection Type, quantity, and velocity of wind-borne debris Even when wind speeds do not exceed design levels, such as during Hurricane Ike, residential buildings can suffer extensive wind damage when they are improperly designed and constructed. The beach house shown in Figure 3-10 experienced damage to its roof structure. The apartment building in Figure 3-11 experienced 3-12 COASTAL CONSTRUCTION MANUAL r cP W y O = cmo_ en(D a oOC U N W � C y U) - I� CDy Q75 M 75 i i� W W 0 w Ua O U = < E_5 OUP C rco IDENTIFYING HAZARDS r- . N" co Lo L7 O O O D cD r N m N lG d d ti u 9+ � :71 tt R y C o� �w � oy W c o 3a 3 lC N lG O � ❑ W to L V 7 V �O 4! O � C d Y 0 d N ell ❑ C N C ❑ _ a1 UX f4 L] 10 N R ❑ 0. N y 17 y � ❑ � e c ❑ I� p C ld 3 CL , n, N y N N " M D 4; ❑ of R C C7 ❑ 'C y V +y D 0. l9 C Vl � d O fir❑+ t31 3 � o C y i-W i MO e4 ❑ � � �7 C � � +W+ L❑1 c a a 0 to L W ❑ ❑ W ut s N +R+ N a ❑ ❑ C ZrC4 c 4 W3 COASTAL CONSTRUCTION MANUAL 3-13 IDENTIFYING HAZARDS Figure 3-8. End -wall failure of typical first -floor masonry/ second -floor wood -frame building in Dade County, FL (Hurricane Andrew, 1992) �s3� rw Yr Figure 3-9. Loss of roof sheathing due to improper nailing design and schedule in Kauai County, HI (Hurricane Iniki, 1992) Figure 3-10. Beach house with roof structure removed by Hurricane Ike (Galveston, TX, 2008) 3-14 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Figure 3-11. Apartment building with gable end wind damage from Hurricane Ike as a result of poor connection between brick veneer and wall structure (Galveston, TX, 2008) gable end wall damage when the wall sheathing failed as a result of a poor connection between the brick veneer and the stud walls. Proper design and construction of residential structures, particularly those close to open water or near the coast, demand that every factor mentioned above be investigated and addressed carefully. Failure to do so may ultimately result in building damage or destruction by wind. Three wind -related topics that deserve special attention from design professionals are speedup of wind due to topographic effects, wind-borne debris and rainfall penetration into buildings, and tornadoes. 3.3.1.1 Speedup of Winds Due to Topographic Effects Speedup of winds due to topographic effects can occur wherever mountainous areas, gorges, and ocean promontories exist. Thus, the potential for increased wind speeds should be investigated for any construction on or near the crests of high coastal bluffs, cliffs, or dunes, or in gorges and canyons. ASCE 7-10 provides guidance on calculating increased wind speeds in such situations. Designers should also consider the effects of long-term erosion on the wind speeds a building may experience over its lifetime. For example, a building sited atop a tall bluff, but away from the bluff edge, is not prone to wind speedup initially, but long-term erosion may move the bluff edge closer to the building and expose the building to increased wind speeds due to topographic changes. 3.3.1.2 Wind -Borne Debris and Rainfall Penetration Wind loads and wind-borne debris are both capable of causing damage to a building envelope. Even small failures in the building envelope, at best, lead to interior damage by rainfall penetration and winds and, at worst, lead to internal pressurization of the building, roof loss, and complete structural disintegration. COASTAL CONSTRUCTION MANUAL 3-15 IDENTIFYING HAZARDS Sparks et al. (1994) investigated the dollar value of insured wind losses following Hurricanes Hugo and Andrew and found the following: Most wind damage to houses is restricted to the building envelope COST CONSIDERATION Even minor damage to the building envelope can lead to large economic losses, as the building interior and contents get wet. Rainfall entering a building through envelope failures causes the dollar value of direct building damage to be magnified by a factor of two (at lower wind speeds) to nine (at higher wind speeds) Lower levels of damage magnification are associated with water seeping through exposed roof sheathing (e.g., following loss of shingles or roof tiles) Higher levels of damage magnification are associated with rain pouring through areas of lost roof sheathing and through broken windows and doors 3.3.1.3 Tornadoes A tornado is a rapidly rotating vortex or funnel of air extending groundward from a cumulonimbus cloud. Tornadoes are spawned by severe thunderstorms and by hurricanes. Tornadoes often form in the right forward quadrant of a hurricane, far from the hurricane eye. The strength and number of tornadoes are not related to the strength of the hurricane that generates them. In fact, the weakest hurricanes often produce the most tornadoes. Tornadoes can lift CROSS REFERENCE The FEMA MAT program has published several MAT reports and recovery advisories following tornado disasters in the United States. These publications offer both insight into the performance of buildings during tornadoes and solutions. To obtain copies of these publications, see the FEMA MAT Web page (http://www.fema.gov/rebuild/mat). and move huge objects, move or destroy houses, and siphon large volumes from bodies of water. Tornadoes also generate large amounts of debris, which then become wind-borne and cause additional damage. Tornadoes are rated using the Enhanced Fujita (EF) Scale, which correlates tornado wind speeds to categories EFO through EF5 based on damage indicators and degrees of damage. Table 3-3 shows the EF Scale. For more information on how to assess tornado damage based on the EF Scale, refer to A Recommendation for an Enhanced Fujita Scale by the Texas Tech Wind Science and Engineering Center at http://www.spc.noaa.gov/ faq/tornado/ef-ttu.pdf (TTU 2004). Table 3-3. Enhanced Fujita Scale in Use Since 2007 3-16 COASTAL CONSTRUCTION MANUAL Hardened buildings and newer structures designed and constructed to modern, hazard -resistant codes can generally resist the wind loads from weak tornadoes. When stronger tornadoes strike, not all damage is from the rotating vortex of the tornado. Much of the damage is caused by straight-line winds being pulled into and rushing toward the tornado itself Homes built to modern codes may survive some tornadoes without structural failure, but often experience damage to the cladding, roof covering, roof deck, exterior walls, and windows. For most building uses, it is economically impractical to design the entire building to resist tornadoes. Portions of buildings can be designed as safe rooms to protect occupants from tornadoes. 3.3.2 Earthquakes IDENTIFYING HAZARDS CROSS REFERENCE FEMA 320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business (FEMA 2008a) provides guidance and designs for residential safe rooms that provide near -absolute protection against the forces of extreme winds. For more information, see the FEMA safe room Web page (http://www. fema.gov/plan/prevent/saferoom/ index.shtm). Earthquakes can affect coastal areas just as they can affect inland areas through ground shaking, liquefaction, surface fault ruptures, and other ground failures. Therefore, coastal construction in seismic hazard areas must take potential earthquake hazards into account. Since basic principles of earthquake -resistant design can contradict flood -resistant design principles, proper design in coastal seismic hazard areas must strike a balance between: The need to elevate buildings above flood hazards and minimize obstructions to flow and waves beneath a structure The need to stabilize or brace the building against potentially violent accelerations and shaking due to earthquakes Earthquakes are classified according to magnitude and intensity. Magnitude refers to the total energy released by the event. Intensity refers to the effects at a particular site. Thus, an earthquake has a single magnitude, but the intensity varies with location. The Richter Scale is used to report earthquake magnitude, while the Modified Mercalli Intensity (MMI) Scale is used to report felt intensity. The MMI Scale (see Table 3-4) ranges from I (imperceptible) to XII (catastrophic). Ni CROSS REFERENCE Seismic load provisions and earthquake ground motion maps can be found in the following codes and standards: ® IBC Section 1613 a IRC R301.2.2 a ASCE 7 Chapters 11 through 23 For best practices guidance, see FEMA 232, Homebuilders' Guide to Earthquake Resistant Design and Construction (FEMA 2006a). The ground motion produced by earthquakes can shake buildings (laterally and vertically) and cause structural failure by excessive deflection. Earthquakes can cause building failures by rapid uplift, subsidence, ground rupture, soil liquefaction, or consolidation. In coastal areas, the structural effects of ground shaking can be magnified when buildings are elevated above the natural ground elevation to mitigate flooding. One of the site parameters controlling seismic -resistant design of buildings is the maximum considered earthquake ground motion, which is defined in the IBC as the most severe earthquake effects considered in the IBC, and has been mapped based on the 0.2-second spectral response acceleration and the 1.0-second spectral response acceleration as a percent of the gravitational constant ("g"). COASTAL CONSTRUCTION MANUAL 3-17 IDENTIFYING HAZARDS Table 3-4. Earthquake MMI Scale Not felt except by very few people under special conditions. Detected mostly by instruments. III Felt noticeably indoors. Standing automobiles may rock slightly. V Felt by nearly everyone. Many people are awakened. Some dishes and windows are broken. Unstable objects are overturned. VII Most people are alarmed and run outside. Damage is negligible in buildings of good construction, considerable in buildings of poor construction. IX Damage is considerable in specially designed buildings. Buildings shift from their foundations and partly collapse. Underground pipes are broken. A Few, if any, masonry structures remain standing. Rails are bent. Broad fissures appear in the ground. SOURCE: FEMA 1997 The structural effects of earthquakes are a function of many factors (e.g., soil characteristics; local geology; and building weight, shape, height, structural system, and foundation type). Design of earthquake -resistant buildings requires careful consideration of both site and structure. In many cases, elevating a building 8 to 10 feet above grade on a pile or column foundationa common practice in low-lying Zone V and Coastal A Zone areas —can result in what earthquake engineers term an "inverted pendulum" as well as a discontinuity in the floor diaphragm and vertical lateral force -resisting system. Both conditions require the building be designed for a larger earthquake force. Thus, designs for pile- or column -supported residential buildings should be verified for necessary strength and rigidity below the first -floor level (see Chapter 10) to account for increased stresses in the foundation members during an earthquake. For buildings elevated on fill, earthquake ground motions can be exacerbated if the fill and underlying soils are not properly compacted and stabilized. Liquefaction of the supporting soil can be another damaging consequence of ground shaking. In granular soils with high water tables (like those found in many coastal areas), the ground motion can create a semi- liquid soil state. The soil then can temporarily lose its bearing capacity, and settlement and differential movement of buildings can result. Seismic effects on buildings vary with structural configuration, stiffness, ductility, and strength. Properly designed and built wood -frame buildings are quite ductile, meaning that they can withstand large deformations without losing strength. Failures, when they occur in wood -frame buildings, are usually at connections. Properly designed and built steel construction is also inherently ductile, but can fail at 3-18 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS non -ductile connections, especially at welded connections. Bolted connections have performed better than welded connections under seismic loads. Modern concrete construction can be dimensioned and reinforced to provide sufficient strength and ductility to resist earthquakes; older concrete structures are typically more vulnerable. Elements of existing concrete structures can be retrofitted with a variety of carbon -fiber, glass - fiber, glass -fiber -reinforced or fiber -reinforced polymer wraps and strips to increase the building's resistance to seismic effects, although this is typically a costly option. Failures in concrete masonry structures are likely to occur if reinforcing and cell grouting do not meet seismic -resistant requirements. 3.3.3 Tsunamis Tsunamis are long -period water waves generated by undersea shallow -focus earthquakes, undersea crustal displacements (subduction of tectonic plates), landslides, or volcanic activity. Tsunamis can travel great distances, undetected in deep water, but shoaling rapidly in coastal waters and producing a series of large waves capable of destroying harbor facilities, shore protection structures, and upland buildings (see Figure 3-12). Tsunamis have been known to damage some structures thousands of feet inland and over 50 feet above sea level. Coastal construction in tsunami hazard zones must consider the effects of tsunami runup, flooding, erosion, and debris loads. Designers should also #j be aware that the "rundown" or return of water to the sea can also damage NOTE the landward sides of structures that withstood the initial runup. Information about tsunamis and their Tsunami effects at a site are determined by four basic factors: effects is available Magnitude of the earthquake or triggering event from the National Tsunami Hazard Location of the triggering event Mitigation Program Web site: http:// Configuration of the continental shelf and shoreline Web sinthmp.te: http:.gov. Upland topography � a bM1 - i r Figure 3-12. Damage from the 2009 tsunami (Amanave, American Samoa) SOURCE: ASCE, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 3-19 IDENTIFYING HAZARDS The magnitude of the triggering event determines the period of the resulting waves, and generally (but not always) the tsunami magnitude and damage potential. Unlike typical wind -generated water waves with periods between 5 and 20 seconds, tsunamis can have wave periods ranging from a few minutes to over 1 hour (Camfield 1980). As wave periods increase, the potential for coastal inundation and damage also increases. Wave period is also important because of the potential for resonance and wave amplification within bays, harbors, estuaries, and other semi -enclosed bodies of coastal water. The location of the triggering event has two important consequences. First, the distance between the point of tsunami generation and the shoreline determines the maximum available warning time. Tsunamis generated at a remote source take longer to reach a given shoreline than locally generated tsunamis. Second, the point of generation determines the direction from which a tsunami approaches a given site. Direction of approach can affect tsunami characteristics at the shoreline because of the sheltering or amplification effects of other land masses and offshore bathymetry. The configuration of the continental shelfandshoreline affect tsunami impacts at the shoreline through wave reflection, refraction, and shoaling. Variations in offshore bathymetry and shoreline irregularities can focus or disperse tsunami wave energy along certain shoreline reaches, increasing or decreasing tsunami impacts. Upland elevations and topography also determine tsunami impacts at a site. Low-lying tsunami -prone coastal sites are more susceptible to inundation, tsunami runup, and damage than sites at higher elevations. Table 3-5 lists areas where tsunami events have been observed in the United States and its territories, and the sources of those events. Note that other areas may be subject to rare tsunami events. Table 3-5. Areas of Observed Tsunami Events in the United States and Territories North Pacific coast Locally generated events (landslides, subduction, submarine landslides, volcanic activity) Alaska: Aleutian Islands Locally generated events and remote source earthquakes Gulf of Alaska coast Locally generated events and remote source earthquakes American Samoa Locally generated events and remote source earthquakes Washington Locally generated events and remote source earthquakes Puerto Rico Locally generated events 3.3.4 Other Hazards and Environmental Effects Other hazards to which coastal construction may be exposed include a wide variety of hazards whose incidence and severity may be highly variable and localized. Examples include subsidence and uplift, landslides and ground failures, salt spray and moisture, rain, hail, wood decay and termites, wildfires, floating ice, snow, and atmospheric ice. These hazards do not always come to mind when coastal hazards are mentioned, but like 3-20 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS the other hazards described in this chapter, they can affect coastal construction and should be considered in siting, design, and construction decisions. 3.3.4.1 Sea and Lake Level Rise Coastal flood effects, described in detail in Section 3.4, typically occur over a period of hours or days. However, longer -term water level changes also occur. Sea level tends to rise or fall over centuries or thousands of years, in response to long-term global climate changes. Great Lakes water levels fluctuate both seasonally and over decades in response to regional climate changes. In either case, medium- and long-term increases in water levels increase the damage -causing potential of coastal flood and storm events and often cause a permanent horizontal recession of the shoreline. Global mean sea level has been rising at long-term rates averaging 1.7 (+/-OS) millimeters annually for the twentieth century (over 6 inches total during the twentieth century) (Intergovernmental Panel on Climate Change [IPCC] 2007). Rates of mean sea level rise along the Louisiana and Texas coasts, as well as portions of the Atlantic coast, are significantly higher than the global average (as high as 3.03 feet per century in Grand Isle, LA). Records for U.S. Pacific coast stations show that some areas have experienced rises in relative sea levels of over 1 foot per century. Other areas have experienced a fall in relative sea levels; Alaska's relative sea level fall rate is as high as 3.42 feet per century (see Figure 3-13). Neah Bay, WA Garibaldi, OR Charleston, OR North Spit, CA Rincon Island, CA Seattle, WA San Diego, CA r Granc Cordova, AK Honolulu, HI Kodiak Island, AK Unalaska, AK A Hilo, HI . Bar Harbor, ME Nantucket Island, MA l New London, CT )eake City, MD .: The Battery, NY Annapolis, MD Sandy Hook, NJ / Atlantic City, NJ nial Beach, VA 1/ Say Bridge, VA I Lewes, DE rtle Beach SCE Ocean City, MD Savannahs GA\ Nags Head, NC Mayport, FIL ......° : \ Wilmington, NC :., Charleston, SC A ---------Apalachicola, \ Pensacola, FL �Apalachicola, FL ., Dapuhln St. Petersburg, FIL Island, AL \ Miami Beach FL \ Naples, FL Key West, FL ...::: Eugene Island, LA Sabine Pass, TX San Juan, PR Galveston, TX Rockport, TX =_........ Port Isabel, TX NOTE Rates of change in mean sea level are given in feet/century. Negative values indicate falling mean sea level. Figure 3-13. Observations of rates of change in mean sea level in the United States in feet per century DATA SOURCE: NOAA CENTER FOR OPERATIONAL OCEANOGRAPHIC PRODUCTS AND SERVICES (http://tidesandcurrents.noaa.gov/sltrends/sltrends.htm1) COASTAL CONSTRUCTION MANUAL 3-21 IDENTIFYING HAZARDS Detailed historical and recent sea level data for U.S. coastal stations are available from NOAA Center for Operational Oceanographic Products and Services at http://tidesandcurrents.noaa.gov/sltrends/sltrends.html (see Figure 3-14 for an example of mean sea level trend for a station in Atlantic City, NJ). The EPA provides links to recent reports (including those of the IPCC) and data at http://www.epa.gov/ climatechange/science/recentslc.html. CROSS REFERENCE For more information on measured and projected Great Lakes water levels, see the USACE Detroit District Monthly Bulletin of Great Lakes Water Levels Web page at http://www.Ire.usace.army.mil/ g reatlakes/h h/great lakeswaterlevels/ wate r I eve I fo recast s/ month lybuI let nofgreatlakeswaterlevels. Great Lakes water -level records dating from 1860 are maintained by the USACE Detroit District. The records show seasonal water levels typically fluctuate between 1 and 2 feet. The records also show that long-term (approximately 100 years) water levels in Lakes Michigan, Huron, Erie, and Ontario have fluctuated approximately 6 feet, and water levels in Lake Superior have fluctuated approximately 4 feet. Figure 3-15 shows a typical plot of actual and projected lake levels for Lakes Michigan and Huron. Mean Sea Level Trend 8534720 Atlantic City, New Jersey Atlantic City, NJ 3.99 +1- 0.18 mmtyr Data -A!) the average seasonal SOUKe.110AA cycle iemo• ed Higher 95%ronfiden[eirber:al LIr)e3r wean sea reoeIIreno Loner 9_%confldelxe nnel.al i I ifi i I � N N L i -i_I 17 i f fi 1 i00 0 1 u f 0 0 1 y-"0 0 1 +�0 0 9S0 0 1 y;0 0 19i0 0 1970 0 1 i30 ] 5'a90 0 :000 0 _010 0 The mean sea level trend is 3.99 millimetersiyear with a 95 ,•:. confidence Interval of +,- 0.18 mm!yr based on monthly mean sea level data from 1911 to 2006 vihich is equivalent to a change of 1.31 feet in 100 years. Figure 3-14. Mean sea level rise data for a station in Atlantic City, NJ SOURCE: NOAA2011b 3-22 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS LAKES MICHIGAN-HURGN WATER LEVELS - DECEMBER 2010 1aEE: _-_—._�.}�}i; . 13c . ]3 E - 195n —.- •. -.— • 133e • — •—�' -: - 1, o —•..— • a�^�— -- k� . 197i — - — I�AF �' --- — -- -- ..};gig: — risl! - 74N6 - - - - - - ! • 1911E 1 - - - - - t?[ri. - 1356 - ' I LH0T 6aT11H 3 • - i '.^ EET , 1,. -C WTI - - s - - - - d a' ---- - _- --- - LEGEND 4iE IEM FRIAR 1!1'A110® ._ _ _ — •• mm1 " I?8: 193: 1c7i i9 i3 193-0 •• s. rage, MJ6 Wd wini. m fN ps iod 1=19 2CH Figure 3-15. Monthly bulletin of lake levels for Lakes Michigan and Huron SOURCE: USACE DETROIT DISTRICT. ACCESSED DECEMBER 2010 Keillor (1998) discusses the implications of both high and low lake levels on Great Lakes shorelines. In general, beach and bluff erosion rates tend to increase as water levels rise over a period of several years, such as occurred in the mid-1980s. As water levels fall, erosion rates diminish. Low lake levels lead to generally stable shorelines and bluffs, but make navigation through harbor entrances difficult (see Section 3.5 for more information on coastal bluff erosion). �J NOTE Because coastal land masses can move up (uplift) or down (subsidence) independent of water levels, discussions related to water level change must be expressed in terms of relative sea level or relative lake level. Designers, community officials, and owners should note that FIRMS do not account for sea level rise or Great Lakes water level trends. Relying on FIRMs for estimates of elevations for future water and wave effects is not advised for any medium- to long-term planning horizon (10 to 20 years or longer). Instead, forecasts of future water levels should be incorporated into project planning. This has been done at the Federal level in the USACE publication titled Water Resource Policies and Authorities Incorporating Sea -Level Change Considerations in Civil Works Program (USACE 2009a), which includes guidance on where to obtain water level change information and how to interpret and use such information. The USACE publication contains a flow chart COASTAL CONSTRUCTION MANUAL 3-23 IDENTIFYING HAZARDS and a step-by-step process to follow. Although the publication was written with USACE projects in mind, the guidance will be helpful to those planning and designing coastal residential buildings. 3.3.4.2 Subsidence and Uplift Subsidence is a hazard that typically affects areas where (1) withdrawal of groundwater or petroleum has occurred on a large scale, (2) organic soils are drained and settlement results, (3) younger sediments deposit over older sediments and cause those older sediments to compact (e.g., river delta areas), or (4) surface sediments collapse into underground voids. The last of these four is most commonly associated with mining and rarely affects coastal areas (coastal limestone substrates would be an exception because these areas could be affected by collapse). The remaining three causes (groundwater or petroleum withdrawal, organic soil drainage, and sediment compaction) have all affected coastal areas in the past (FEMA 1997). One consequence of coastal subsidence, even when small in magnitude, is an increase in coastal flood hazards due to an increase in flood depth. For example, Figure 3-16 shows land subsidence in the Houston -Galveston area. In portions of Texas, subsidence has been measured for over 100 years, and subsidence of several feet has been recorded over a wide area; some land areas in Texas have dropped 10 feet in elevation since 1906. Subsidence also complicates flood hazard mapping and can render some flood hazard maps obsolete before they would otherwise need to be updated. Figure 3-16. Land subsidence in the Houston -Galveston area, 1906-2000 SOURCE: HARR IS -GALVESTON SUBSIDENCE DISTRICT 2010 3-24 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Land uplift is the result of the ground rising due to various geological processes. Although few people regard land uplift as a coastal hazard, Larsen (1994) has shown that differential uplift in the vicinity of the Great Lakes can lead to increased water levels and flooding. As the ground rises in response to the removal of the great ice sheet, it does so in a non -uniform fashion. On Lake Superior, the outlet at the eastern end of the lake is rising at a rate of nearly 10 inches per century, relative to the city of Duluth -Superior at the western end of the lake. This causes a corresponding water level rise at Duluth -Superior. Similarly, the northern ends of Lakes Michigan and Huron are rising relative to their southern portions. On Lake Michigan, the northern outlet at the Straits of Mackinac is rising at a rate of 9 inches per century, relative to Chicago, at the southern end of the lake. The outlet of Lakes Michigan and Huron is rising only about 3 inches per century relative to the land at Chicago. 3.3.4.3 Salt Spray and Moisture Salt spray and moisture effects frequently lead to corrosion and decay of building materials in the coastal environment. These hazards are commonly overlooked or underestimated by designers. Any careful inspection of coastal buildings (even new or recent buildings) near a large body of water will reveal deterioration of improperly selected or installed materials. For example, metal connectors, straps, and clips used to improve a building's resistance to high winds and earthquakes often show signs of corrosion (see Figure 3-17). Corrosion is affected by many factors, but the primary difference between coastal and inland/Great Lakes areas is the presence of salt spray, tossed into the air by breaking waves and blown onto land by onshore winds. Salt spray accumulates on metal surfaces, accelerating the electrochemical processes that cause corrosion, particularly CROSS REFERENCE in the humid conditions common along the coast. See Chapter 14, Section 14.2, for Corrosion severity varies considerably from community a discussion of salt spray and to community along the coast, from building to building moisture effects. within a community, and even within an individual building. Figure 3-17. Example of corrosion, and resulting failure, of metal connectors SOURCE: SPENCER ROGERS, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 3-25 IDENTIFYING HAZARDS Factors affecting the rate of corrosion include humidity, wind direction and speed, seasonal wave conditions, distance from the shoreline, elevation above the ground, orientation of the building to the shoreline, rinsing by rainfall, shelter and air flow in and around the building, and the component materials. Wood decay is most commonly caused by moisture. Moisture - related decay is prevalent in all coastal areasit is not exclusive to buildings near the shoreline. Protection against moisture - related decay can be accomplished by one or more of the CROSS REFERENCE See FEMA Technical Bulletin 8, Corrosion Protection for Metal Connectors in Coastal Areas (1996), for more information about corrosion and corrosion - resistant connectors. following: use of preservative -treated or naturally durable wood, proper detailing of wood joints to eliminate standing water, avoidance of cavity wall systems, and proper installation of water -resistive barriers. Sunlight, aging, insects, chemicals, and temperature can also lead to decay. FEMA P-499 Fact Sheet 1.7, Coastal Building Materials, has more information on the use of materials to resist corrosion, moisture, and decay (FEMA 2010). 3.3.4.4 Rain Rain presents two principal hazards to coastal residential construction: Penetration of the building envelope during high -wind events (see Section 3.3.1.2) Vertical loads due to rainfall ponding on the roof Ponding usually occurs on flat or low -slope roofs where a parapet or other building element causes rainfall to accumulate, and where the roof drainage system fails. Every inch of accumulated rainfall causes a downward - directed load of approximately 5 pounds per square foot. Excessive accumulation can lead to progressive deflection and instability of roof trusses and supports. 3.3.4.5 Hail Hailstorms develop from severe thunderstorms, and generate balls or lumps of ice capable of damaging agricultural crops, buildings, and vehicles. Severe hailstorms can damage roofing shingles and tiles, metal roofs, roof sheathing, skylights, glazing, and other building components. Accumulation of hail on flat or low - slope roofs, like the accumulation of rainfall, can lead to significant vertical loads and progressive deflection of roof trusses and supports. 3.3.4.6 Termites Infestation by termites is common in coastal areas subject to high humidity and frequent and heavy rains. Improper preservative treatments, improper design and construction, and even poor landscaping practices, can all contribute to infestation problems. The IRC includes a termite infestation probability map, which shows that most coastal areas have a moderate to very heavy probability of infestation (ICC 2012b). Protection against termites can be accomplished by one or more of the following: use of preservative -treated wood products (including field treatment of notches, holes, and cut ends), use of naturally termite -resistant wood species, chemical soil treatment, and installation of physical barriers to termites (e.g., metal or plastic termite shields). 3-26 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS 3..4.7 Wildfire Wildfires can occur virtually everywhere in the United States and can threaten buildings constructed in coastal areas. Topography, the availability of vegetative fuel, and weather are the three principal factors that influence wildfire hazards. FEMA has produced several reports discussing the reduction of the wildfire hazard and the vulnerability of structures to wildfire hazards, including Wildfire Mitigation in the 1998 Florida Wildfires (FEMA 1998) and FEMA P-737, Home Builder's Guide to Construction in Wildfire Zones (FEMA 2008b). Some communities have adopted the International Wildland- Urban Interface Code (ICC 2012c), which includes provisions that address the spread of fire and defensible space for buildings constructed near wildland areas. Experience with wildfires has shown that the use of fire -rated roof assemblies is one of the most effective methods of preventing loss of buildings to wildfire. Experience has also shown that replacing highly flammable vegetation around buildings with minimally flammable vegetation is also an effective way of reducing possible wildfire damage. Clearing vegetation around some buildings may be appropriate, but this action can lead to slope instability and landslide failures on steeply sloping land. Siting and construction on steep slopes requires careful consideration of multiple hazards with sometimes conflicting requirements. 3.3.4.8 Floating Ice Some coastal areas of the United States are vulnerable to problems caused by floating ice. These problems can take the form of erosion and gouging of coastal shorelines, flooding due to ice jams, and lateral and vertical ice loads on shore protection structures and coastal buildings. On the other hand, the presence of floating ice along some shorelines reduces erosion from winter storms and wave effects. Designers should investigate potential adverse and beneficial effects of floating ice in the vicinity of their building site. Although this Manual does not discuss these issues in detail, additional information can be found in Caldwell and Crissman (1983), Chen and Leidersdorf (1988), and USACE (2002). 3.3.4.9 Snow The principal hazard associated with snow is its accumulation on roofs and the subsequent deflection and potential failure of roof trusses and supports. Calculation of snow loads is more complicated than rain loads, because snow can drift and be distributed non -uniformly across a roof. Drainage of trapped and melted snow, like the drainage of rain water, must be addressed by the designer. In addition, particularly in northern climates such as New England and the Great Lakes, melting snow can result in ice dams. Ice dams can cause damage to roof coverings, drip edges, gutters, and other elements along eaves, leaving them more susceptible to future wind damage. 3.3.4.10 Atmospheric Ice Ice can sometimes form on structures as a result of certain atmospheric conditions or processes (e.g., freezing rain or drizzle or in -cloud icing —accumulation of ice as supercooled clouds or fog comes into contact with a structure). The formation and CROSS REFERENCE Chapter 7 of ASCE 7 includes maps and equations for calculating snow loads. It also includes provisions for additional loads due to ice dams (ASCE 2010). -0 CROSS REFERENCE State CZM programs (see Section 5.6, in Chapter 5) are a good source of hazard information, vulnerability analyses, mitigation plans, and other information about coastal hazards. COASTAL CONSTRUCTION MANUAL 3-27 IDENTIFYING HAZARDS accretion of this ice is termed atmospheric ice. Fortunately, typical coastal residential buildings are not considered ice -sensitive structures and are not subject to structural failures resulting from atmospheric ice. However, designers should consider proximity of coastal residential buildings to ice -sensitive structures (e.g., utility towers, utility lines, and similar structures) that may fail under atmospheric ice conditions. Designers should also be aware that ice build-up on structures, trees, and utility lines can result in a falling ice hazard to building occupants. 3.4 Coastal Flood Effects Coastal flooding can originate from a number of sources. Tropical cyclones, other coastal storms, and tsunamis generate the most significant coastal flood hazards, which usually take the form of hydrostatic forces, hydrodynamic forces, wave effects, and flood -borne debris effects. Regardless of the source of coastal flooding, a number of flood parameters must be investigated at a coastal site to correctly characterize potential flnnd ha7nrdz- Origin of flooding Flood frequency Flood depth Flood velocity Flood direction Flood duration Wave effects Erosion and scour Sediment overwash Flood -borne debris CROSS REFERENCE See Section 8.5 for procedures used to calculate flood loads. If a designer can determine each of these parameters for a site, the specification of design flood conditions is straightforward and the calculation of design flood loads will be more precise. Unfortunately, determining some of these parameters (e.g., flood velocity, debris loads) is difficult for most sites, and design flood conditions and loads may be less exact. 3.4.1 Hydrostatic Forces Standing water or slowly moving water can induce horizontal hydrostatic forces against a structure, especially when floodwater levels on different sides of the structure are not equal. Also, flooding can cause vertical hydrostatic forces, or flotation (see Figure 3-18). 3.4.2 Hydrodynamic Forces Hydrodynamic forces on buildings are created when coastal floodwaters move at high velocities. These high -velocity flows are capable of destroying solid walls and dislodging buildings with inadequate foundations. High -velocity flows can also move large quantities of sediment and debris that can cause additional damage. High -velocity flows in coastal areas are usually associated with one or more of the following: Storm surge and wave runup flowing landward, through breaks in sand dunes or across low-lying areas (see Figure 3-19) 1�10) CROSS REFERENCE Predicting the speed and direction of high -velocity flows is difficult. Designers should refer to the guidance contained in Section 8.5.6 and should assume that the flow can originate from any direction. 3-28 COASTAL CONSTRUCTION MANUAL Tsunamis IDENTIFYING HAZARDS Figure 3-18. Intact houses floated off their foundations and carried inland during Hurricane Hugo in 1989 (Garden City, SC) Figure 3-19. Storm surge at Horseshoe Beach, FL, during Tropical Storm Alberto in 2006 SOURCE: NOAA NATIONAL WEATHER SERVICE FORECAST OFFICE NOTE Outflow (flow in the seaward direction) of floodwaters driven into bay or upland areas Storm surge does not correlate to hurricane category according to the earlier Saffir-Simpson Strong currents parallel to the shoreline, driven by the Hurricane Scale, so the scale obliquely incident storm waves was renamed (Saffir Simpson Hurricane Wind Scale) and High -velocity flows can be created or exacerbated by the changed in 2010 to eliminate any presence of manmade or natural obstructions along the reference to storm surge (see shoreline and by weak points formed by shore -normal roads Table 3-1). and access paths that cross dunes, bridges or shore -normal canals, channels, or drainage features. For example, evidence after Hurricane Opal struck Navarre Beach, FL, in 1995 suggests that large engineered buildings channeled flow between them (see Figure 3-20). The channelized flow caused deep scour channels across the island, undermining a pile -supported house between the large buildings (see Figure 3-21), and washing out roads and houses (see Figure 3-22) situated farther landward. COASTAL CONSTRUCTION MANUAL 3-29 IDENTIFYING HAZARDS Figure 3-20. Flow channeled between large buildings during Hurricane Opal in 1995 scoured a deep channel and damaged infrastructure and houses at Navarre Beach, FL SOURCE: FLORIDA DEPARTMENT OF ENVIRONMENTAL PROTECTION, USED WITH PERMISSION Figure 3-21. Pile -supported house in the area of channeled flow shown in Figure 3-20. The building foundation and elevation successfully prevented high -velocity flow, erosion, and scour from destroying this building Figure 3-22. This house, located in an area of channeled flow near that shown in Figure 3-20, was undermined, washed into the bay behind the barrier island, and became a threat to navigation x Large engineered 4k N. ti buildings ' Scour I f ' pop �r Depth of at-orm-induced erosion and scour 3-30 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS 3.4.3 Waves Waves can affect coastal buildings in a number of ways, including breaking waves, wave runup, wave reflection and deflection, and wave uplift. The most severe damage is caused by breaking waves (see Figure 3-23). The force created by waves breaking against a vertical surface is often 10 or more times higher than the force created by high winds during a storm event. Figure 3-23. Storm waves breaking against a seawall in front of a coastal residence at Stinson Beach, CA SOURCE: LESLEY EWING, USED WITH PERMISSION Wave runup occurs as waves break and run up beaches, sloping surfaces, and vertical surfaces. Wave runup (see Figure 3-24) can drive large volumes of water against or around coastal buildings, inducing fluid impact forces (albeit smaller than breaking wave forces), current drag forces, and localized erosion and scour (see Figure 3-25). Wave runup against a vertical wall generally extends to a higher elevation than runup on a sloping surface and is capable of destroying overhanging decks and porches. Wave reflection or deflection from adjacent structures or objects can produce forces similar to those caused by wave runup. Figure 3-24. Wave runup beneath elevated buildings at Scituate, MA, during the December 1992 nor'easter storm SOURCE: JIM O'CONNELL, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 3-31 IDENTIFYING HAZARDS Shoaling waves beneath elevated buildings can lead to wave uplift forces. The most common example of wave uplift damage occurs at fishing piers, where pier decks are commonly lost close to shore, when shoaling storm waves lift the pier deck from the pilings and beams. The same type of damage can sometimes be observed at the lowest floor of insufficiently elevated, but well-founded, residential buildings and underneath slabs -on -grade below elevated buildings (see Figure 3-26). Figure 3-25. The sand underneath this Pensacola Beach, FL, building was eroded due to wave runup and storm surge (Hurricane Ivan, 2004) Figure 3-26. Concrete slab -on -grade flipped up by wave action came to rest against two foundation members, generating large unanticipated loads on the building foundation (Topsail Island, NC, Hurricane Fran, 1996) 3-32 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS 3.4.4 Flood -Borne Debris Flood -borne debris produced by coastal flood events and storms typically includes decks, steps, ramps, breakaway wall panels, portions of or entire houses (see Figure 3-27), heating oil and propane tanks, vehicles, boats, decks and pilings from piers (see Figure 3-28), fences, destroyed erosion control structures, and a variety of smaller objects. Flood -borne debris is often capable of destroying unreinforced masonry walls, light wood -frame construction, and small -diameter posts and piles (and the components of structures they support). Figure 3-29 shows debris generated by destroyed buildings at Pass Christian, MS, that accumulated approximately 1,000 feet inland from the highway. The debris from buildings closest to the Gulf of Mexico undoubtedly accentuated damage to buildings in the area and contributed to their destruction. Debris trapped by cross bracing, closely spaced pilings, grade beams, or other components or obstructions below the BFE is also capable of transferring flood and wave loads to the foundation of an elevated structure. Parts of the country are exposed to more massive debris, such as the drift logs shown in Figure 3-30. Figure 3-27. A pile -supported house at Dauphin Island, AL, was toppled and washed into another house, which suffered extensive damage (Hurricane Georges, 1998) L Ti . 5rr up COASTAL CONSTRUCTION MANUAL 3-33 ti. ._: OEMR i 7 7-4 n � Reduced structural a . damage due to inundation h and small waves (large waves attenuated by debris piles) •'Fil "�F _ %.. .. She. '-4'. i�..� .. �` kK�Y^+" '.� Severe structural damage- ''`'„''` due to waves and debris :5 �lvi Only floor slabs remain Gulf ofMexico. IDENTIFYING HAZARDS Figure 3-30. Drift logs driven into coastal houses at Sandy Point, WA, during a March 1975 storm SOURCE: KNOWLES AND TERICH 1977, SHORE AND BEACH, USED WITH PERMISSION 3.5 Erosion Erosion refers to the wearing or washing away of coastal lands. Although the concept of erosion is simple, erosion is one of the most complex hazards to understand and predict at a given This section reviews basic concepts related to coastal erosion, but cannot provide site. therefore, designers should develop an a comprehensive treatment of the many understanding of erosion fundamentals, but rely aspects of erosion that should be considered on coastal erosion experts (at Federal, State, and in planning, siting, and designing coastal local agencies; universities; and private firms) for residential buildings. specific guidance regarding erosion potential at a site. The term "erosion" is commonly used to refer to the horizontal recession of the shore (i.e., shore erosion), but can apply to other types of erosion. For example, seabed or lakebed erosion (also called downcutting) occurs when fine-grained sediments in the nearshore zone are eroded and carried into deep water. these sediments are lost permanently, resulting in a lowering of the seabed or lakebed. this process has several important consequences: increased local water depths, increased wave heights reaching the shoreline, increased shore erosion, and undermining of erosion control structures. Downcutting has been documented along some ocean -facing shorelines, but also along much of the Great Lakes shoreline NOTE NOTE Erosion is one of the most complex hazards faced by designers. However, given erosion data provided by experts, assessing erosion effects on building design can be reduced to three basic steps: 1. Define the most landward shoreline location expected during the life of the building. 2. Define the lowest expected ground elevation during the life of the building. 3. Define the highest expected BFE during the life of the building. COASTAL CONSTRUCTION MANUAL 3-35 IDENTIFYING HAZARDS (which is largely composed of fine-grained glacial deposits). Designers should refer to Keillor (1998) for more information on this topic. Erosion is capable of threatening coastal residential buildings in a number of ways: Destroying dunes or other natural protective features (see Figure 3-31) Destroying erosion control devices (see Figure 3-32) Lowering ground elevations, undermining shallow foundations, and reducing penetration depth of pile foundations (see Figure 3-33) Transporting beach and dune sediments landward, where they can bury roads and buildings and marshes (see Figure 3-34) Breaching low-lying coastal barrier islands exposing structures on the mainland to increased flood and wave effects (see Figures 3-35 and 3-36) Eroding coastal bluffs that provide support to buildings outside the floodplain itself (see Figure 3-37) Sand that is moved during erosional events can create overwash and sediment burial issues. Further, the potential for landslides and ground failures must also be considered. Figure 3-31. Dune erosion in Ocean City, NJ, caused by the remnants of Hurricane Ida (2009) and a previous nor'easter 3-36 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Figure 3-32. Erosion and seawall damage in New Smyrna Beach, FL, following Hurricane Jeanne in 2007 Figure 3-33. Erosion undermining a coastal residence in Oak Island, NC, caused by Hurricane Floyd in 1999 ELAKLEY COASTAL CONSTRUCTION MANUAL 3-37 IDENTIFYING HAZARDS Figure 3-34. Overwash on Topsail Island, NC, after Hurricane Bonnie in 1998 SOURCE:USGS Figure 3-35. A January 1987 nor'easter cut a breach across Nauset Spit on Cape Cod, MA; the breach grew from an initial width of approximately 20 feet to over a mile within 2 years, exposing the previously sheltered shoreline of Chatham to ocean waves and erosion SOURCE: JIM O'CONNELL, USED WITH PERMISSION 3-38 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Figure 3-36. Undermined house at Chatham, MA, in 1988; nine houses were lost as a result of the formation of the new tidal inlet shown in Figure 3-35 SOURCE: JIM O'CONNELL, USED WITH PERMISSION Figure 3-37. Bluff failure by a combination of marine, terrestrial, and seismic processes led to progressive undercutting of blufftop apartments at Capitola, CA, where six of the units were demolished after the 1989 Loma Prieta earthquake SOURCE: GRIGGS 1994, JOURNAL OF COASTAL RESEARCH, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 3-39 IDENTIFYING HAZARDS 3.5.1 Describing and Measuring Erosion Erosion should be considered part of the larger process of shoreline change. When more sediment leaves a shoreline segment than moves into it, erosion results; when more sediment moves into a shoreline segment than leaves it, accretion results; and when the amounts of sediment moving into and leaving a shoreline segment balance, the shoreline is said to be stable. Care must be exercised in classifying a particular shoreline as erosional, accretional, or stable. A shoreline classified as erosional may experience periods of stability or accretion. Likewise, a shoreline classified as stable or accretional may be subject to periods of erosion. Observed shoreline behavior depends on the time period of analysis and on prevailing and extreme coastal processes during that period. NOTE Most owners and designers worry only about erosion. However, sediment deposition and burial can also be a problem if dunes and windblown sand migrate inland. r_J NOTE Short-term erosion rates can es are classified as short-term exceed long-term rates by a For these reasons, shoreline changes factor of 10 or more. changes and long-term changes. Short-term changes occur over periods ranging from a few days to a few years and can be highly variable in direction and magnitude. Long-term changes occur over a period of decades, during which short-term changes tend to average out to the underlying erosion or accretion trend. Both short-term and long-term shoreline changes should be considered in siting and design of coastal residential construction. Erosion is usually expressed as a rate, in terms of - Linear retreat (e.g., feet of shoreline recession per year) Volumetric loss (e.g., cubic yards of eroded sediment per foot of shoreline frontage per year) The convention used in this Manual is to cite erosion rates as positive numbers, with corresponding shoreline change rates as negative numbers (e.g., an erosion rate of 2 feet per year is equivalent to a shoreline change rate of -2 feet per year). Likewise, accretion rates are listed as positive numbers, with corresponding shoreline change rates as positive numbers (e.g., an accretion rate of 2 feet per year is equivalent to a shoreline change rate of 2 feet per year). Shoreline erosion rates are usually computed and cited as long- term, average annual rates. However, erosion rates are not uniform in time or space. Erosion rates can vary substantially from one location along the shoreline to another, even when the two locations are only a short distance apart. A study by Zhang (1998) examined long-term erosion rates along the east coast of the United States. Results showed the dominant trend along the east coast of the United States is WARNING Proper planning, siting, and design of coastal residential buildings require: (1) a basic understanding of shoreline erosion processes, (2) erosion rate information from the community, State, or other sources, (3) appreciation for the uncertainty associated with the prediction of future shoreline positions, and (4) knowledge that siting a building immediately landward of a regulatory coastal setback line does not guarantee the building will be safe from erosion. Owners and designers should also be aware that shore changes and modifications near to or updrift of a building site can affect the site. 3-40 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS one of erosion (72 percent of the stations examined experienced long-term erosion), with shoreline change rates averaging -3.0 feet per year (i.e., 3.0 feet per year of erosion). However, variability along the shoreline is considerable, with a few locations experiencing more than 20 feet per year of erosion, and over one-fourth of the stations experiencing accretion. A study of the Pacific County, WA, coastline found erosion rates as high as 150 feet per year, and accretion rates as high as 18 feet per year (Kaminsky et al. 1999). Erosion rates can also vary over time at a single location. For example, Figure 3-38 illustrates the shoreline history over a period of 160 years for the region approximately 1.5 miles south of Indian River Inlet, DE. Although the long-term, average annual shoreline change rate is approximately -2 feet per year, short-term shoreline change rates vary from 27 feet per year (erosion resulting from severe storms) to +6 feet per year (accretion associated with post -storm recovery of the shoreline). This conclusion —that erosion rates can vary widely over time —has also been demonstrated by other studies (e.g., Douglas, et al., 1998). Designers should also be aware that some shorelines experience large seasonal fluctuations in beach width and elevation. These changes are a result of seasonal variations in wave conditions and water levels, and should not be taken as indicators of long-term shoreline changes. For this reason, shoreline change calculations at beaches subject to large seasonal fluctuations should be based on shoreline measurements taken at approximately the same time of year. NOTE Apparent erosion or accretion resulting from seasonal fluctuations of the shoreline is not an indication of true shoreline change. Figure 3-38. Shoreline changes through time at a location approximately 1.5 miles south of Indian River Inlet, DE DATA SOURCES: NOAA AND THE STATE OF DELAWARE COASTAL CONSTRUCTION MANUAL 3-41 IDENTIFYING HAZARDS Erosion rates have been calculated by many States and communities to establish regulatory construction setback lines. These rates are typically calculated from measurements made with aerial photographs, historical charts, or beach profiles. However, a number of potential errors are associated with measurements and calculations using each of the data sources, particularly the older data. Some studies have estimated that errors in computed erosion rates can range up to 1 foot or more per year. Therefore, even if published erosion rates are less than 1 foot per year this Manual recommends siting coastal residential structures based on the larger of the published erosion rate, or 1 foot per year, unless there is compelling evidence to support a smaller erosion rate. Basing design on erosion rates of less than 1 foot per year can lead to significant underestimation of the future shoreline and inadequate setback to protect the building from long- term erosion. 3.5.2 Causes of Erosion Erosion can be caused by a variety of natural or manmade actions, including: Storms and coastal flood events, usually rapid and dramatic (also called storm -induced erosion) Natural changes associated with tidal inlets, river outlets, and entrances to bays (e.g., interruption of littoral transport by jetties and channels, migration or fluctuation of channels and shoals, formation of new inlets) Construction of manmade structures and human activities (e.g., certain shore protection structures; damming of rivers; dredging or mining sand from beaches and dunes; and alteration of vegetation, surface drainage, or groundwater at coastal bluffs) Long-term erosion that occurs over a period of decades, due to the cumulative effects of many factors, including CROSS REFERENCE changes in water level, sediment supply, and those factors Chapters 12 and 13 provide mentioned above information about designing and constructing sound pile and Local scour around structural elements, including piles column foundations. and foundation elements Erosion can affect all coastal landforms except highly resistant geologic formations. Low-lying beaches and dunes are vulnerable to erosion, as are most coastal bluffs, banks, and cliffs. Improperly sited buildings even those situated atop coastal bluffs and outside the floodplain—and buildings with inadequate foundation support are especially vulnerable to the effects of erosion. 3.5.2.1 Erosion During Storms Erosion during storms can be dramatic and damaging. Although storm -induced erosion is usually short-lived (usually occurring over a few hours in the case of hurricanes and typhoons, or over a few tidal cycles or days in the case of nor'easters and other coastal storms), the resulting erosion can be equivalent to decades of long- term erosion. During severe storms or coastal flood events, large dunes may be eroded 25 to 75 feet or more (see Figure 3-31) and small dunes may be completely destroyed. 3-42 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Erosion during storms sometimes occurs despite the presence of erosion control devices such as seawalls, revetments, and toe protection. Storm waves frequently overtop, damage, or destroy poorly designed, constructed, or maintained erosion control devices. Lands and buildings situated behind an erosion control device are not necessarily safe from coastal flood forces and storm -induced erosion. Narrow sand spits, barrier islands and low-lying coastal lands can be breached by tidal channels and inlets —often originating from the buildup of water on the back side (see Figure 3-39) or washed away entirely (see Figure 3-40). Storm -induced erosion damage to unconsolidated cliffs and bluffs typically takes the form of large-scale collapse, slumping, and landslides, with concurrent recession of the top of the bluff. j- CROSS REFERENCE FIRMs incorporate the effects of dune and bluff erosion during storms (see Section 3.6.7). Figure 3-39. Breach through barrier island at Pine Beach, AL, before Hurricane Ivan (2001) and after (2004) SOURCE:USGS Figure 3-40. Cape San Blas, Gulf County, FL, in November 1984, before and after storm -induced erosion COASTAL CONSTRUCTION MANUAL 3-43 IDENTIFYING HAZARDS Storm -induced erosion can take place along open -coast shorelines (Atlantic, Pacific, Gulf of Mexico, and Great Lakes shorelines) and along shorelines of smaller enclosed or semi -enclosed bodies of water. If a body of water is subject to increases in water levels and generation of damaging wave action during storms, storm - induced erosion can occur. 3.5.2.2 Erosion Near Tidal Inlets, Harbor, Bay, and River Entrances Many miles of coastal shoreline are situated on or adjacent to connections between two bodies of water. These connections can take the form of tidal inlets (short, narrow hydraulic connections between oceans and inland waters), harbor entrances, bay entrances, and river entrances. The size, location, and adjacent shoreline stability of these connections are usually governed by six factors: WARNING Tidal and freshwater flows through the connection The location of a tidal inlet, harbor Wave climate entrance, bay entrance, or river Sediment supply entrance can be stabilized by jetties or other structures, but the Local geology shorelines in the vicinity can still fluctuate in response to storms, Jetties or stabilization structures waves, and other factors. Channel dredging Temporary or permanent changes in any of these governing factors can cause the connections to migrate, change size, or change configuration, and can cause sediment transport patterns in the vicinity of the inlet to change, thereby altering flood hazards in nearby areas. Construction of jetties or similar structures at a tidal inlet or a bay, harbor, or river entrance often results in accretion on one side and erosion on the other, with a substantial shoreline offset. This offset results from the jetties trapping the littoral drift (wave -driven sediment moving along the shoreline) and preventing it from moving to the downdrift side. Figure 3-41 shows such a situation at Ocean City Inlet, MD, where formation 3-44 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS of the inlet in 1933 by a hurricane and construction of inlet jetties in 1934-1935 led to approximately 800 feet of accretion against the north jetty at Ocean City and approximately 1,700 feet of erosion on the south side of the inlet along Assateague Island as of 1977 (Dean and Perlin 1977). Between 1976 and 1980, shoreline change rates on Assateague Island averaged from 49 feet per year and -33 feet per year (USACE 2009b). In 2004, USACE began the "Long -Term Sand Management" project to restore Assateague Island. Erosion and accretion patterns at stabilized inlets and entrances sometimes differ from the classic pattern occurring at the Ocean City Inlet. In some instances, accretion occurs immediately adjacent to both jetties, with erosion beyond. In some instances, erosion and accretion patterns near a stabilized inlet change over time. Figure 3-42 shows buildings at Ocean Shores, WA, that were threatened by shore erosion shortly after their construction, despite the fact that the buildings were located near an inlet jetty on a beach that was historically viewed as accretional. Development in the vicinity of a tidal inlet or bay, harbor, or river entrance is often affected by lateral migration of the channel and associated changes in sand bars (which may focus waves and erosion on particular shoreline areas). Often, these changes are cyclic in nature and can be identified and forecast through a review of historical aerial photographs and bathymetric data. Those considering a building site near a tidal inlet or a bay, harbor, or river entrance should investigate the history of the connection, associated shoreline fluctuations, migration trends, and impacts of any stabilization structures. Failure to do so could result in increased building vulnerability or building loss to future shoreline changes. NOTE Cursory characterizations of shoreline behavior in the vicinity of a stabilized inlet, harbor, or bay entrance should be rejected in favor of a more detailed evaluation of shoreline changes and trends. WARNING Many State and local siting regulations allow residential development in areas where erosion is likely to occur. Designers should not assume that a building sited in compliance with minimum State and local requirements is safe from future erosion. See Chapter 4. COASTAL CONSTRUCTION MANUAL 3-45 IDENTIFYING HAZARDS Shoreline changes in the vicinity of one of the more notable regulatory takings cases illustrate this point. The upper image in Figure 3-43 is a 1989 photograph of one of the two vacant lots owned by David Lucas, which became the subject of the Lucas vs. South Carolina Coastal Council case when Lucas challenged the State's prohibition of construction on the lots. By December 1997, the case had been decided in favor of Lucas, the State of South Carolina had purchased the lots from Lucas, the State had resold the lots, and a home had been constructed on one of the lots (Jones et al. 1998). The lower image in Figure 3-43 shows a December 1997 photograph of the same area, with erosion undermining the home built on the former Lucas lot (left side of photograph) and an adjacent house (also present in 1989 in upper image). Figure 3-43. July 1989 photoi, of vacant lot owl by Lucas, Isle of Palms, SC (top) photograph take December 1997 lot with new hor (bottom) 3-46 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS 3.5.2.3 Erosion Due to Manmade Structures and Human Activities Human actions along the shoreline can both reduce and increase flood hazards. In some instances, structures built or actions taken NOTE to facilitate navigation cause erosion elsewhere. In other cases, structures built or actions taken to halt erosion and reduce flood More information on beach hazards at one site increase erosion and flood hazards at nearby sites. nourishment is provided at For this reason, evaluation of a potential coastal building site requires http://www.csc.noaa.gov/ consideration of natural and human -caused shoreline changes. beach nourishment. Effects of Shore Protection Structures In performing their intended function, shore protection structures can lead to or increase erosion on nearby properties. This statement CROSS REFERENCE should not be taken as an indictment of all erosion control structures, because many provide protection against erosion and flood Adverse impacts of erosion hazards. Rather, this Manual simply recognizes the potential for control structures can adverse impacts of these structures on nearby properties and offers sometimes be mitigated through beach nourishment. some siting guidance for residential buildings relative to erosion See Section 4.7. control structures (see Section 4.6), where permitted by States and communities. These potential impacts vary from site to site and structure to structure and can sometimes be mitigated by beach nourishment —the placement of additional sediment on the beach —in the vicinity of the erosion control structure. Groins (such as those shown in Figure 2-12, in Chapter 2) are short, shore -perpendicular structures designed to trap available littoral sediments. They can cause erosion to downdrift beaches if the groin compartments are not filled with sand and maintained in a full condition. Likewise, offshore breakwaters (see Figure 3-44) can trap available littoral sediments and reduce the sediment supply to nearby beaches. This adverse effect should be mitigated by combining breakwater construction with beach nourishment —design guidance for offshore breakwater projects typically calls for the inclusion of beach nourishment (Chasten et al. 1993). Figure 3-44. Example of littoral sediments being trapped behind offshore breakwaters on Lake Erie, Presque Isle, PA SOURCE:USACE COASTAL CONSTRUCTION MANUAL 3-47 IDENTIFYING HAZARDS Seawalls, bulkheads, and revetments are shore -parallel structures built, usually along the shoreline or at the base of a bluff, to act as retaining walls and to provide some degree of protection against high water levels, waves, and erosion. The degree of protection they afford depends on their design, construction, and maintenance. They do not prevent erosion of the beach, and in fact, can exacerbate ongoing erosion of the beach. The structures can impound upland sediments that would otherwise erode and nourish the beach, lead to passive erosion (eventual loss of the beach as a structure prevents landward migration of the beach profile), and lead to active erosion (localized scour waterward of the structure and on unprotected property at the ends of the structure). Post -storm inspections show that the vast majority of privately financed seawalls, revetments, and erosion control devices fail during 1-percent-annual-chance, or lesser, events (i.e., are heavily damaged or destroyed, or withstand the storm, but fail to prevent flood damage to lands and buildings they are intended to protect see Figures 3-32 and 3-45). Reliance on these devices to protect inland sites and residential buildings is not a good substitute for proper siting and foundation design. Guidance on evaluating the ability of existing seawalls and similar structures to withstand a 1-percent-annual-chance coastal flood event can be found in Walton et al. (1989). Finally, some communities distinguish between erosion control structures constructed to protect existing development and those constructed to create a buildable area on an otherwise unbuildable site. Designers should investigate any local or State regulations and requirements pertaining to erosion control structures before selecting a site and undertaking building design. Effects of Alteration of Vegetation, Drainage, or Groundwater WARNING Alteration of vegetation, drainage, or groundwater can sometimes make a site more vulnerable to coastal storm or flood events. For regulations require that communities protect example, removal of vegetation (grasses, ground covers, trees, mangrove stands in Zone mangroves) at a site can render the soil more prone to erosion by V from any human -caused wind, rain, and flood forces. Alteration of natural drainage patterns alteration that would increase potential flood damage. 3-48 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS and groundwater flow can lead to increased erosion potential, especially on steep slopes and coastal bluffs. Irrigation and septic systems often contribute to bluff instability problems by elevating groundwater levels and decreasing soil strength. 3.5.2.4 Long -Term Erosion Observed long-term erosion at a site represents the net effect of a combination of factors. The factors that contribute to long-term erosion can include: Sea level rise or subsidence of uplands Lake level rise or lakebed erosion along the Great Lakes (Figure 3-46) Reduced sediment supply to the coast Construction of jetties, other structures, or dredged channels that impede littoral transport of sediments along the shoreline Increased incidence or intensity of storms Alteration of upland vegetation, drainage, or groundwater flows (especially in coastal bluff areas) WARNING Coastal FIRMs (even recently published coastal FIRMs) do not incorporate the effects of long- term erosion. Users are cautioned that mapped Zone V and Zone A areas subject to long-term erosion underestimate the extent and magnitude of actual flood hazards that a coastal building may experience over its lifetime. Regardless of the cause, long-term shore erosion can increase the vulnerability of coastal construction in a number of ways, depending on local shoreline characteristics, construction setbacks, and structure design. Figure 3-47 shows an entire block of buildings that are dangerously close to the shoreline and vulnerable to storm damage due to the effects of long-term erosion. COASTAL CONSTRUCTION MANUAL 3-49 IDENTIFYING HAZARDS Figure 3-47. Long-term erosion at South Bethany Beach, DE, has lowered ground elevations beneath buildings and left them more vulnerable to storm damage SOURCE: CHRIS JONES 1992, USED WITH PERMISSION In essence, long-term erosion acts to shift flood hazard zones landward. For example, a site mapped accurately as Zone A may become exposed to Zone V conditions; a site accurately mapped as outside the 100-year floodplain may become exposed to Zone A or Zone V conditions. Despite the fact that FIRMS do not incorporate long-term erosion, other sources of long-term erosion data are available for much of the country's shorelines. These data usually take the form of historical shoreline maps or erosion rates published by individual States or specific reports (from Federal or State agencies, universities, or consultants) pertaining to counties or other small shoreline reaches. Designers should be aware that more than one source of long-term erosion rate data may be available for a given site and that the different sources may report different erosion rates. Differences in rates may be a result of different study periods, different data sources (e.g., aerial photographs, maps, ground surveys), or different study methods. When multiple sources and long-term erosion rates exist for a given site, designers should use the highest long-term erosion rate in their siting decisions, unless they conduct a detailed review of the erosion rate studies and conclude that a lower erosion rate is more appropriate for forecasting future shoreline positions. 3-50 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS 3.5.2.5 Localized Scour Localized scour can occur when water flows at high velocities past an object embedded in or resting on erodible soil (localized scour can also be caused or exacerbated by waves interacting with the object). The scour is not caused by the flood or storm event, per se, but by the distortion of the flow field by the object; localized scour occurs only around the object itself and is in addition to storm- or flood -induced erosion that occurs in the general area. Flow moving past a fixed object must accelerate, often - forming eddies or vortices and scouring loose sediment from CROSS REFERENCE the immediate vicinity of the object. Localized scour around Refer to Section 8.5 for additional individual piles and similar objects (see Figure 3-48) is generally discussion on scour. limited to small, cone -shaped depressions (less than 2 feet deep and several feet in diameter). Localized scour is capable of undermining slabs and grade -supported structures. However, in severe cases, the depth and lateral extent of localized scour can be much greater, and will jeopardize foundations and may lead to structural failure. Figure 3-49 shows severe local scour that occurred around residential foundations on Bolivar Peninsula, TX, after Hurricane Ike in 2008. This type of scour was widespread during Hurricane Ike. Although some structures were able to withstand the scour and associated flood forces, others were not. Designers should consider potential effects of localized scour when calculating foundation size, depth, or embedment requirements. Figure 3-48. �• • Determination of localized V - t { I. scour from changes in +t"r ?' sand color, texture, and 4xy►- _ f, � A�• � , �.� � • bedding (Hurricane Fran, o x x ` x • -a 1996) 4 ,� : ate ''• .J• I - Sim`` a COASTAL CONSTRUCTION MANUAL 3-51 IDENTIFYING HAZARDS Figure 3-49. Residential foundation that suffered severe scour on Bolivar Peninsula, TX (Hurricane Ike, 2008) i�• �iLj - ?17 s-_ 1L-+ 3.5.3 Overwash and Sediment Burial Sediment eroded during a coastal storm event must travel to one of the following locations: offshore to deeper water, along NOTE the shoreline, or inland. Overwash occurs when low-lying coastal lands are overtopped and eroded by storm surge and Most owners and designers worry waves, such that the eroded sediments are carried landward by only about erosion. However, sediment deposition and burial floodwaters, burying uplands, roads, and at -grade structures can also be a problem. (see Figure 3-50). Depths of overwash deposits can reach 3 to 5 feet, or more, near the shoreline, but gradually decrease with increasing distance from the shoreline. Overwash deposits can extend several hundred feet inland following a severe storm (see Figure 3-34), especially in the vicinity of shore -perpendicular roads. Post -storm aerial photographs and/or videos can be used to identify likely future overwash locations. The physical processes required to create significant overwash deposits (i.e., waves capable of suspending sediments in the water column and flow velocities generally in excess of 3 feet per second) are also capable of damaging buildings. Thus, existing coastal buildings located in Zone A (particularly the seaward portions of Zone A) and built on slab or crawlspace foundations should be considered vulnerable to damage from overwash, high -velocity flows, and waves. 3.5.4 Landslides and Ground Failures Landslides occur when slopes become unstable and loose material slides or flows under the influence of gravity. Often, landslides are triggered by other events such as erosion at the toe of a steep slope, earthquakes, floods, or heavy rains, but can be worsened by human actions such as destruction of vegetation or uncontrolled pedestrian access on steep slopes (see Figure 3-51). An extreme example is Hurricane Mitch in 1998, where heavy rainfall led to flash flooding, numerous landslides, and an estimated 10,000 deaths in Nicaragua. 3-52 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Figure 3-50. Overwash from Hurricane Opal (1995) at Pensacola Beach, FL, moved sand landward from the beach and buried the road, adjacent lots, and some at -grade buildings to a depth of 3 to 4 feet Figure 3-51. Unstable coastal bluff at Beacon's Beach, San Diego, CA SOURCE: LESLEY EWING, USED WITH PERMISSION UNSTABLE CLIFFS ^� STAY 4 BACK' if n 1"I I►uurs �!':.. '..- -J�,a •- �' IF IRS � _ - F.E1tf �1► ►REIEMT EIISIK' , Z Designers should seek and use landslide information and data from State geological survey agencies and USGS (http://Iandslides.usgs.gov/). Designers should also be aware that coastal bluff failures can be induced by seismic activity. Griggs and Scholar (1997) detail bluff failures and damage to residential buildings resulting from several earthquakes, including the March 1964 Alaska earthquake and the October 1989 Loma Prieta earthquake (see Figure 3-37). Coastal bluff failures were documented as far away as 50 miles from the Loma Prieta epicenter and 125 miles from the Alaska earthquake epicenter. In both instances, houses and infrastructure were damaged and destroyed as a result of these failures. 3.6 NAP Flood Hazard Zones Understanding the methods and assumptions underlying Flood Insurance Study (FIS) reports and FIRMS is useful to the designer, especially in the case where the effective FIRM is more than a few years old, and where an updated flood hazard determination is desired. COASTAL CONSTRUCTION MANUAL 3-53 IDENTIFYING HAZARDS FEMA determines flood hazards at a given site based on the following factors: Anticipated flood conditions (stillwater elevation, wave setup, wave runup and overtopping, and wave propagation) during the base flood event (based on the flood level that has a 1-percent chance of being equaled or exceeded in any given year) Potential for storm -induced erosion of the primary dune during the base flood event Physical characteristics of the floodplain, such as vegetation and existing development Topographic and bathymetric information NOTE A detailed discussion of the methodology for computing stillwater elevations, wave heights, and wave runup is beyond the scope of this Manual. Refer to Guidelines and Specifications for Flood Hazard Mapping Partners (FEMA 2003) for more information. Computer models are used to calculate flood hazards and water surface elevations. FEMA uses the results of these analyses to map BFEs and flood hazard zones. 3.6.1 Base Flood Elevations To determine BFEs for areas affected by coastal flooding, FEMA computes 100-year Stillwater elevations and wave setup, and then determines the maximum 100-year wave heights and, in some areas, the maximum 100-year wave runup, associated with those stillwater elevations. Wave heights are the heights, above the wave trough, of the crests of wind -driven waves. Wave runup is the rush of wave water up a slope or structure. Stillwater elevations are the elevations of the water surface resulting solely from storm surge (i.e., the rise in the surface of the ocean due to the action of wind and the drop in atmospheric pressure associated with hurricanes and other storms). u NOTE Note that rounding of coastal BFEs means that it is possible for the wave crest or wave runup elevation to be up to 0.5 foot above the lowest floor elevation. This is another reason to incorporate freeboard into design. The stillwater elevation plus wave setup equals the mean water elevation, which serves as the surface across which waves propagate. Several factors can contribute to the 100-year mean water elevation in a coastal area. The most important factors include offshore bathymetry, astronomical tide, wind setup (rise in water surface as strong winds blow water toward the shore), pressure setup (rise in water surface due to low atmospheric pressure), wave setup (rise in water surface inside the surf zone due to the presence of breaking waves), and, in the case of the Great Lakes, seiches and variations in lake levels. The BFEs shown for coastal flood hazard areas on FIRMs are established not at the stillwater elevation, but at the elevation of either the wave crest or the wave runup (rounded to the nearest foot), whichever is greater. Whether the wave crest elevation or the wave runup elevation is greater depends primarily on upland topography. In general, wave crest elevations are greater where the upland topography is gentle, such as along most of the Gulf, southern Atlantic, and middle -Atlantic coasts, while wave runup elevations are greater where the topography is steeper, such as along portions of the Great Lakes, northern Atlantic, and Pacific coasts. 3-54 COASTAL CONSTRUCTION MANUAL 3.6.2 Flood Insurance Zones The insurance zone designations shown on FIRMs indicate the magnitude and severity of flood hazards. The zone designations that apply to coastal flood hazard areas are listed below, in decreasing order of magnitude and severity. IDENTIFYING HAZARDS #J NOTE Zones AE, VE, and X appear on FIRMs produced since the 'd 1980 O Id FIRM h 11 Zones VE, Vl V30, and V. These zones, collectively referred mi - s. n o er s, t e corresponding zones are Al-A30, to as Zone V, identify the Coastal High Hazard Area, which V1-V30, and B or C, respectively. is the portion of the SFHA that extends from offshore to the inland limit of a primary frontal dune along an open coast and any other portion of the SFHA that is subject to high -velocity wave action from storms or seismic sources. The boundary of Zone V is generally based on wave heights (3 feet or greater) or wave runup depths (3 feet or greater). Zone V can also be mapped based on the wave overtopping rate (when waves run up and over a dune or barrier). Zones AE, AI—A30, AO, and A. These zones, collectively referred to as Zone A or AE, identify portions of the SFHA that are not within the Coastal High Hazard Area. Zones AE, AI—A30, AO, and A are used to designate both coastal and non -coastal SFHAs. Regulatory requirements of the NFIP for buildings located in Zone A are the same for both coastal and riverine flooding hazards. Limit of Moderate Wave Action (LiMWA). Zone AE in coastal areas is divided by the LiMWA. The LiMWA represents the landward limit of the 1.5-foot wave. The area between the LiMWA and the Zone V limit is known as the Coastal A Zone for building code and standard purposes and as the Moderate Wave Action (MoWIA) area by FEMA flood mappers. This area is subject to wave heights between 1.5 and 3 feet during the base flood. The area between the LiMWA and the landward limit of Zone A due to coastal flooding is known as the Minimal WlaveAction (MiWIA) area, and is subject to wave heights less than 1.5 feet during the base flood. The LiMWA is now included on preliminary DFIRMs provided to communities; however, if a community does not want to delineate the LiMWA on its final DFIRM, it can provide a written request to FEMA, with justification, to remove it. There presently are no NFIP floodplain management requirements or special insurance ratings associated with the designation of the LiMWA. However, in areas designated with a LiMWA, there are requirements imposed by the I -Codes. Aside from I -Code requirements, NOTE communities are encouraged to adopt Zone V requirements rather than the minimum NFIP requirements in these areas to address the increased risks associated with waves and velocity action. The Community Rating System (CRS) awards credit points to communities that extend Zone V design and construction requirements to the LiMWA, and additional points to communities that extend Zone V requirements landward of the LiMWA. COASTAL CONSTRUCTION MANUAL 3-55 IDENTIFYING HAZARDS Zones X, B, and C. These zones identify areas outside the SFHA. Zone B and shaded Zone X-500 identify areas subject to inundation by the flood that has a 0.2-percent chance of being equaled or exceeded during any given year, often referred to as the 500-year flood. Zone C and unshaded Zone X identify areas outside the 500-year floodplain. Areas protected by accredited levee systems are mapped as shaded Zone X. U TERMINOLOGY SPECIAL FLOOD HAZARD AREA (SFHA) defines an area with a 1-percent chance, or greater, of flooding in any given year. This is commonly referred to as the extent of the 100-year floodplain. COASTAL SFHA is the portion of the SFHA where the source of flooding is coastal surge or inundation. It includes Zone VE and Coastal A Zone. ZONE VE is that portion of the coastal SFHA where base flood wave heights are 3 feet or greater, or where other damaging base flood wave effects have been identified, or where the primary frontal dune has been identified. COASTAL A ZONE (MoWA AREA) is that portion of the coastal SFHA referenced by building codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many NFIP-compliant structures on shallow or solid wall foundations. MiWA AREA is that portion of the Coastal SFHA where base flood wave heights are less than 1.5 feet. UMWA is the boundary between the MoWA and the MiWA. RIVERINE SFHA is that portion of the SFHA mapped as Zone AE and where the source of flooding is riverine, not coastal. ZONE AE is the portion of the SFHA not mapped as Zone VE. It includes the MoWA, the MiWA, and the Riverine SFHA. 3.6.3 FIRMs, DFIRMs, and FISs Figure 3-52 shows a typical paper FIRM that a designer might encounter for some coastal areas. Three flood hazard zones are shown on this FIRM: Zone V, Zone A, and Zone X. Figure 3-53 shows an example of a transect perpendicular to the shoreline. Since the early 2000s, FEMA has been preparing Digital FIRMs (DFIRMs) to replace the paper maps. Figure 3-54 shows a typical DFIRM that a designer is likely to encounter in many coastal areas. The DFIRM uses a photographic base and shows either the results of a recent FIS or the results of a digitized paper FIRM (possibly with a datum conversion from National Geodetic Vertical Datum [NGVD] to North American Vertical Datum [NAVD]). The flood hazard zones and BFEs on a DFIRM are delineated in a manner consistent with those on a paper FIRM, although they may reflect updated flood hazard calculation procedures. CROSS REFERENCE See Section 3.3 for a brief discussion of coastal flood hazards and FIRMs. NOTE Additional information about FIRMs is available in FEMA's 2006 booklet How to Use a Flood Map to Protect Your Property, FEMA 258 (FEMA 2006b). 3-56 COASTAL CONSTRUCTION MANUAL Limit of moderate wave action (LiMWA) Zone X Zone X (shaded) Zone AE (EL9) (MiWA) COASTAL Zane AE (MoWA) (EL10) O C ...Zone VE El (EL11), Zone VE (EL12) Zone VE (EL13) Zone VE (EL15) Shoreline IDENTIFYING HAZARDS L" Figure 3-52. Portion of a paper FIRM showing coastal flood insurance rate zones. The icons on the right indicate the associated flood hazard zones for design and construction purposes. The LiMWA is not shown on older FIRMs, but is shown on newer FIRMs and DFIRMs COASTAL CONSTRUCTION MANUAL 3-57 IDENTIFYING HAZARDS r, ZON EfuFAI:: p. ZONE VE �►; n .�� ;..�. . f �* z• �_ EL 11 � � � ( ) ZONE AE 1 - DEL g) ..•L- MIT OFMODERATE iIN WCOA Y OP ZONE X ZONE VE i ZONE X (EL .12) - ZON E AE # � . ZONE VE ,,*` ;S: i[EL 8y rt (EL 11 ) ti 3 r LEGEND 9 .. .. .. .. Limit of Mocierale wave Actio't - + . - ! '7 -: - ■ ,s, . N ZONE AE NOTES TO USERS STRAhID •.,r STREET 1 OZONE AK "j'{ELr11j .—' 1heAE Zone category has been dmded by a Urn It dt Mnderale Wave Actlon ,-•Jr �{ll.t $T {LIMWA) The. LrA{WA represents the approxlmare land+ and lirrlrT Of The t fool s breaAinF; wave Rase flood cond,tions he Moen the VE Zone and the LrMWA w.1C he. �45 •fir : i�i .� _ similar to but less severe Chan those +n the VE lone Conlacr the FEMA Map Service Center al 1-800-358-9616 rot information on "1 'L-IMI, Q�WODERATE ' available products assocraled ,with Chas FIRA1 Available products may includa _ WAVE ACTION prevroualy+ssued Letters of Map Change a Flood dnsurance Study report. and!or digital versions of I h i s map 1 he FEMA Map $ervrte Center may a15p be reached by Fax at 1 8W-363-9620 and Its websde at htlp rrww.v Cems govlmsc a� p C Z If you have questions about this map or questions concemmg the National Flood � , Lit Insu ranee Program mgenera l ❑Iea se call 1-877-FE MA- FAA t 1 - a Yl-336-2521)or i - G'y visit ICre FEMA Weil sit e ar fill' �fvNV'x le ma uv ZQNE ,•VE' ,=:1 1' hiFr. N N {EL.12].. Figure 3-54. Example DFIRM for a coastal area that shows the LiMWA SOURCE: FEMA 2008c A coastal FIS is completed with FEMA-specified techniques and procedures (see FEMA 2007) to determine mean water levels (stillwater elevation plus wave setup) and wave elevations along transects drawn perpendicular to the shoreline (see Figure 3-53). The determination of the 100-year mean water elevation (and elevations associated with other return intervals) is usually accomplished through the statistical analysis of historical tide and water level data, and/or by the use of numerical storm surge and wave models. Wave heights and elevations on land are computed from mean water level and topographic data with established procedures and models that account for wave dissipation by obstructions (e.g., sand dunes, buildings, vegetation) and wave regeneration across overland fetches. 3-58 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Building codes and standards —and FEMA building science publications —refer to the Coastal A Zone and have specific requirements or recommendations for design and construction in this zone. Post -disaster damage inspections consistently show the need for such a distinction. Figure 3-53 shows how the Coastal A Zone can be inferred from FIS transects and maps. Detailed FEMA coastal mapping guidance is contained in Appendix D of Guidelines and Specifications for Flood Hazard Mapping Partners (FEMA 2003). Designers need not be familiar with all of these guidelines, but they may be useful on occasion. Appendix D is divided into several documents, one for the Atlantic and Gulf of Mexico coasts, one for the Pacific coast, and one NOTE for the Great Lakes coast. These documents have been and continue to be updated and revised, so designers should refer to the FEMA mapping Web site for the latest versions: http://www.fema. gov/plan/prevent/fhm/dl_vzn.shtm#3. Guidance on mapping the LiMWA is contained in Procedure Memorandum No. 50 at http://www.fema.gov/ I i brary/viewRecord.do? id =3481. 3.6.4 Wave Heights and Wave Crest Elevations FEMNs primary means of establishing BFEs and distinguishing between Zone V, Zone A, and Zone X is wave height. Wave height is simply the vertical distance between the crest and trough of a wave propagating over the water surface. BFEs in coastal areas are usually set at the elevation of the crest of the wave as it propagates inland. The maximum wave crest elevation (used to establish the BFE) is determined by the maximum wave height, which depends lij TERMINOLOGY: WAVE HEIGHT Wave height is the vertical distance between the wave crest and wave trough (see Figure 3-55). Wave crest elevation is the elevation of the crest of a wave, referenced to the NGVD, NAVD, or other datum. COASTAL CONSTRUCTION MANUAL 3-59 IDENTIFYING HAZARDS largely on the 100-year stillwater depth (dioo). This depth is the difference between the 100-year stillwater elevation (Eioo) (including wave setup) and the ground elevation (noted as GS in Figure 3-55). Note that ground elevation in this use is not the existing ground elevation, but is the ground elevation that will result from the erosion expected to occur during the base flood (or in some cases, it may be appropriate to take it as the eroded ground elevation expected over the life of a building). In shallow waters the maximum height of a breaking wave (Hb) is usually taken to be 78 percent of the stillwater depth ds, and determined by the equation Hb = 0.78d, However, designers should be aware that where steep slopes exist immediately seaward of a building, wave heights can exceed 0.78d,,, (and a reasonable alternative is to set Hb = 1.00ds in such instances). The wave form in shallow water is distorted so that the crest and trough are not equidistant from the stillwater level; for NFIP CROSS REFERENCE flood mapping purposes, the wave crest lies at 70 percent of the wave height above the stillwater elevation (the wave trough See Equation 8.1 and Example 8.1 for calculations pertaining to lies a distance equal to 30 percent of the wave height, below stillwater depth K). the stillwater elevation). Thus, the maximum elevation of a breaking wave crest above the stillwater elevation is equal to 0.55d, In the case of the 1-percent-annual-chance (base) flood, Hb = 0.78d,00 and the maximum height of a breaking wave above the 100-year stillwater elevation = 0.55d,00 (see Figure 3-55). Note that for wind -driven waves, water depth is only one of three parameters that determine the actual wave height at a particular site (wind speed and fetch length are the other two). In some instances, actual wave heights may be below the depth -limited maximum height. Figure 3-55. BFE determination for coastal flood hazard areas where wave crest elevations exceed wave runup elevations (Zones A and V) 3-60 COASTAL CONSTRUCTION MANUAL For a coastal flood hazard area where the ground slopes up gently from the shoreline, and there are few obstructions such as houses and vegetation, the BFE shown on the FIRM is approximately equal to the ground elevation plus the 100-year stillwater depth (dloo) plus 0.55d100. For example, where the ground elevation is 4 feet NAVD and dloo is 6 feet, the BFE is equal to 4 feet plus 6 feet plus 3.3 feet, or 13.3 feet NAVD, rounded to 13 feet NAVD. 3.6.5 Wave Runup On steeply sloped shorelines, the rush of water up the surface of the natural beach (including dunes and bluffs) or the surface of a manmade structure (such as a revetment or vertical wall) can result in flood elevations higher than those of the crests of wind -driven waves. For a coastal flood hazard area where this situation occurs, the BFE shown on the FIRM is equal to the highest elevation reached by the water (see Figure 3-56). 3.6.6 Primary Frontal Dune IDENTIFYING HAZARDS #j NOTE FEMA maps Zone V based on wave heights where the wave height (vertical distance between wave crest and wave trough) is greater than or equal to 3 feet. NOTE FEMA maps Zone V based on wave runup where the vertical distance between the runup elevation and the ground (the runup "depth") is greater than or equal to 3 feet. The NFIP has other parameters used to establish Zone V delineations besides wave heights and wave runup depths. In some cases, the landward limit of the primary frontal dune will determine the landward limit of Zone V. This Zone V designation is based on dune morphology, as opposed to base flood conditions. Consult the Guidelines and Specifications for Flood Hazard Mapping Partners (FEMA 2003) for details regarding the NFIP primary frontal dune delineation. Note that some States and communities may have different dune definitions, but these will not be used by the NFIP to map Zone V. Figure 3-56. Where wave runup elevations exceed wave crest elevations, the BFE is equal to the runup elevation COASTAL CONSTRUCTION MANUAL 3-61 IDENTIFYING HAZARDS �j TERMINOLOGY WAVE RUNUP is the rush of water up a slope or structure. WAVE RUNUP DEPTH at any point is equal to the maximum wave runup elevation minus the lowest eroded ground elevation at that point. WAVE RUNUP ELEVATION is the elevation reached by wave runup, referenced to NGVD or other datum. WAVE SETUP is an increase in the stillwater surface elevation near the shoreline, due to the presence of breaking waves. Wave setup typically adds 1.5 to 2.5 feet to the 100-year stillwater flood elevation. MEAN WATER ELEVATION is the sum of the stillwater elevation and wave setup. 3.6.7 Erosion Considerations and Flood Hazard Mapping Proper design requires two types of erosion to be considered: dune and bluff erosion during the base flood event, and long-term erosion. Newer FIRMS account for the former, but no FIRMS account for the latter. Dune/Bluff Erosion. Current FIS procedures account for the potential loss of protective dunes and bluffs during the 100-year flood. However, this factor was not considered in coastal FIRMs prepared prior to May 1988, which delineated Zone V without any consideration for storm -induced erosion. Zone V boundaries were drawn at the crest of the dune solely on the basis of the elevation of the ground and without regard for the erosion that would occur during a storm. Long -Term Erosion. Designers, property owners, and floodplain managers should be careful not to assume that flood hazard zones shown on FIRMs accurately reflect current flood hazards, especially if there has been a significant natural hazard event since the FIRM was published. For example, flood hazard restudies completed after Hurricane Opal (1995, Florida Panhandle) and Fran (1996, Topsail Island, NC) have produced FIRMs that are dramatically different from the FIRMs in effect prior to the hurricanes. Figure 3-57 provides an example of the effects of both dune erosion and long-term erosion changes. The figure compares pre- and post -storm FIRMs for Surf City, NC. The map changes are attributable to two factors: (1) pre -storm FIRMs did not show the effects of erosion that occurred after the FIRMs were published and did not meet technical standards currently in place, and (2) Hurricane Fran caused significant changes to the topography of the barrier island. Not all coastal FIRMs would be expected to undergo such drastic revisions after a flood restudy; however, many FIRMs may be in need of updating, and designers should be aware that FIRMs may not accurately reflect present flood hazards at a site. 3.6.8 Dune Erosion Procedures Current Zone V mapping procedures (FEMA 2003) require that a dune have a minimum frontal dune reservoir (dune cross-section above 100-year stillwater level and seaward of dune peak) of 540 square feet in order to be considered substantial enough to withstand erosion during a base flood event. According to FEMA procedures, a frontal dune reservoir less than 540 square feet will result in dune removal (dune disintegration), while a frontal dune reservoir greater than or equal to 540 square feet generally will result in dune retreat (see Figure 3-58). 3-62 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Figure 3-58. Current FEMA treatment of dune removal and dune retreat SOURCE: FEMA 2003 COASTAL CONSTRUCTION MANUAL 3-63 IDENTIFYING HAZARDS The current procedure for calculating the post -storm profile in the case of dune removal is relatively simple: a straight line is drawn from the pre -storm dune toe landward at an upward slope of 1 on 50 (vertical to horizontal) until it intersects the pre -storm topography landward of the dune. Any sediment above the line is assumed to be eroded. This Manual recommends that the size of the frontal dune reservoir used by designers to prevent dune removal during a 100-year storm be increased to 1,100 square feet. This recommendation is made for three reasons: (1) The 540 square feet rule used by FEMA reflects dune size at the time of mapping and does not account for future conditions, when beaches and dunes may be compromised by long-term erosion; (2) The 540 square feet rule does not account for the cumulative effects of multiple storms that may occur within short periods of time, such as in 1996, when Hurricanes Bertha and Fran struck the North Carolina coast within 2 months of each other (see Figure 4-6 in Chapter 4); and (3) even absent long-term erosion and multiple storms, use of the median frontal dune reservoir underestimates dune erosion 50 percent of the time. Dune erosion calculations at a site should also take dune condition into account. A dune that is not covered by well -established vegetation (i.e., vegetation that has been in place for two or more growing seasons) is more vulnerable to wind and flood damage than one with well -established vegetation. A dune crossed by a road or pedestrian path offers a weak point that storm waves and flooding exploit; to reduce potential weak points, elevated dune walkways are recommended. Post -storm damage inspections frequently show that dunes are breached at these weak points and structures landward of them are more vulnerable to erosion and flood damage. 3.6.9 Levees and Levee Protection The floodplain area landward of a levee system for which the levee system provides a certain level of risk reduction is known CROSS REFERENCE as the levee -impacted area. Some levees include interior drainage systems that provide for conveyance of outflow Section 2.6.2 provides additional of streams and runoff. Levee -impacted areas protected b detail g the risks i siting a P P y building in alevee-impacted area. accredited levees meeting NFIP requirements are mapped as Zone X (shaded) and the interior drainage areas are designated as Zone A. For levees not meeting NFIP requirements, both sides of the levee are mapped as Zone A. Levees on older FIRMs may not have been evaluated against NFIP criteria, and may not offer the designed level of protection due to deterioration, changed hydrology or channel characteristics, or partial levee failure. 3.7 Flood Hazard Assessments for Design Purposes Designers may sometimes be faced with a FIRM and FIS that are several years old, or older. As such, designers should determine whether the FIRM still accurately represents flood hazards associated with the site under present day base flood conditions. If not, the designer may need to pursue updating the information in order to more accurately understand the hazard conditions at the site. WARNING Some sites lie outside flood hazard areas shown on FIRMs, but may be subject to current or future flood and erosion hazards. These sites, like those within mapped flood hazard areas, should be evaluated carefully. 3-64 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS 3.7.1 Determine If Updated or More Detailed Flood Hazard Assessment is Needed Two initial questions drive the decision to update or complete a more detailed flood hazard assessment: 1. Does the FIRM accurately depict present flood hazards at the site of interest? 2. Will expected shore erosion render the flood hazard zones shown on the FIRM obsolete during the projected life of the building or development at the site? The first question can be answered with a brief review of the FIRM, the accompanying FIS report, and site conditions. The answer to the second question depends upon whether or not the site is experiencing long- term shore erosion. If the shoreline at the site is stable and is not experiencing long-term erosion, then the FIRM does not require revision for erosion considerations. However, because FIRMS are currently produced without regard to long-term erosion, if a shoreline fluctuates or experiences long-term erosion, the FIRM will cease to provide the best available data at some point in the future (if it has not already) and a revised flood hazard assessment will be necessary. Updated and revised flood hazard assessments are discussed with siting and design purposes in mind, not in the context of official changes to FIRMs that have been adopted by local communities. The official FEMA map change process is a separate issue that is not addressed by this Manual. Moreover, some siting and design recommendations contained in this Manual exceed minimum NFIP requirements, and are not tied to a community's adopted FIRM and its associated requirements. 3.7.1.1 Does the FIRM Accurately Depict Present Flood Hazards? In order to determine whether a FIRM represents current flood hazards, and whether an updated or more detailed flood hazard assessment is needed, the following steps should be carried out: NOTE Obtain copies of the latest FIRM and FIS report for the The date of the effective (i.e., site of interest. If the effective date precedes the critical newest) FIRM for a community can be found on FEMNs Web site milestones listed in Section 3.8, an updated flood hazard under the heading "Community assessment may be needed. Status Book," at http://www. fema.gov/fema/csb.shtm. Review the legend on the FIRM to determine the history of the panel (and revisions to it), and review the study methods described in the FIS. If the revisions and study methods are not consistent with current study methods (FEMA 2007), an updated flood hazard assessment may be needed. If the FIS calculated dune erosion using the 540 square feet criterion (refer to Section 3.5.8) and placed the Zone V boundary on top of the dune, check the dune cross-section to see if it has a frontal dune reservoir of at least 1,100 square feet above the 100-year stillwater elevation. If not, consider shifting the Zone V boundary to the landward limit of the dune and revising other flood hazard zones, as needed. Review the description in the FIS report of the storm, water level, and flood source data used to generate the 100-year stillwater elevation and BFEs. If significant storms or flood events have affected the area since the FIS report and FIRM were completed, the source data may need to be revised and an updated flood hazard assessment may be needed. COASTAL CONSTRUCTION MANUAL 3-65 IDENTIFYING HAZARDS Determine whether there have been significant physical changes to the site since the FIS and FIRM were completed (e.g., erosion of dunes, bluffs, or other features; opening of a tidal inlet; modifications to drainage, groundwater, or vegetation on coastal bluffs; construction or removal of shore protection structures; filling or excavation of the site). If there have been significant changes in the physical configuration and condition since the FIS and FIRM were completed, an updated and more detailed flood hazard assessment may be needed. Determine whether adjacent properties have been significantly altered since the FIS and FIRM were completed (e.g., development, construction, excavation, etc.) that could affect, concentrate, or redirect flood hazards on the site of interest. If so, an updated and more detailed flood hazard assessment may be needed. NOTE Where a new FIRM exists (i.e., based on the most recent FEMA study procedures and topographic data), long-term erosion considerations can be approximated by shifting all flood hazard zones landward a distance equal to the long-term annual erosion rate multiplied by the life of the building or development (use 50 years as the minimum life). The shift in the flood hazard zones results from a landward shift of the profile. If, after following the steps above, it is determined that an updated flood hazard assessment may be needed, see Section 3.7.2 for more information on updating and revising flood hazard assessments. 3.7.1.2 Will Long -Term Erosion Render a FIRM Obsolete? Designers should determine whether a FIRM is likely to become obsolete as a result of long-term erosion considerations, and whether a revised flood hazard assessment is needed. First, check with local or State CZM agencies for any information on long-term erosion rates or construction setback lines. If such rates have been calculated, or if construction setback lines have been established from historical shoreline changes, long-term erosion considerations may necessitate a revised flood hazard assessment. In cases where no long-term erosion rates have been published, and where no construction setback lines have been established based on historical shoreline movements, designers should determine whether the current shoreline has remained in the same approximate location as that shown on the FIRM (e.g., has there been any significant shore erosion, accretion, or fluctuation?). If there has been significant change in the shoreline location or orientation since the FIS and FIRM were completed, a revised flood hazard assessment may be needed. 3.7.1.3 Will Sea Level Rise Render a FIRM Obsolete? Sea level rise has two principal effects: (1) it increases storm tide elevations and allows for larger wave heights to reach a coastal site, and (2) it leads to shoreline erosion. For these reasons, designers should investigate potential sea level rise and determine whether projected sea level changes will increase flood hazards at a site. Relying on the FIRM to project future site and base flood conditions may not be adequate in many cases. The NOAA site http://tidesandcurrents.noaa.gov/sltrends/sltrends.html provides historical information that a designer can extrapolate into the future. Designers may also wish to consider whether accelerated rates of rise will occur in the future. 3-66 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS A USACE Engineering Circular (USACE 2009a) provides guidance on sources of sea level change data and projections, and discusses how the data and projections can be used for planning purposes. The guidance is useful for planning and designing coastal residential buildings. 3.7.2 Updating or Revising Flood Hazard Assessments Updating or revising an existing flood hazard assessment for siting and design purposes —can be fairly simple or highly complex, depending upon the situation. A simple change may involve shifting a Zone A or Zone X boundary, based upon topographic data that is better than those used to generate the FIRM. A complex change may involve a detailed erosion assessment and significant changes to mapped flood hazard zones. If an assessment requires recalculating local flood depths and wave conditions on a site, FEMA models (Erosion, Runup, and WHAFIS) can be used for the site (bearing in mind the recommended change to the required dune reservoir to prevent dune loss, described in 35.8). NOTE Coastal hazard analysis models (Erosion, Runup, WHAFIS) used by FEMA's FIS contractors are available for use by others. However, those performing updates or revising flood hazard assessments are advised to obtain the assistance of an experienced coastal professional. FEMA has also issued its Coastal Hazard Modeling Program (CHAMP) to facilitate the use of standard FEMA models for flood hazard mapping. If an assessment requires careful consideration of shore erosion, the checklist, flowchart, and diagram shown in Chapter 4 can be a guide, but a qualified coastal professional should be consulted. Much of the information and analyses described in the checklist and flowchart is likely to have already been developed and carried out previously by others, and should be available in reports about the area; designers are advised to check with the community. Cases for which information is unavailable and basic analyses have not been completed are rare. The final result of the assessment should be a determination of the greatest flood hazards resulting from a I -percent -annual -chance coastal flood event that the site will be exposed to over the anticipated life of a building or development. The determination should account for short- and long-term erosion, bluff stability, sea level rise, and storm -induced erosion; in other words, both chronic and catastrophic flood and erosion hazards, along with future water level conditions, should be considered. 3.8 Milestones of FEMA Coastal Flood Hazard Mapping Procedures and FIRMs Designers are reminded that FEMA's flood hazard mapping procedures have evolved over the years (the coastal mapping site, http://www.fema.gov/plan/prevent/fhm/dl_vzn.shtm, provides links to current coastal mapping guidance and highlights many of these changes). Thus, a FIRM produced today might differ from an earlier FIRM, not only because of physical changes at the site, but also because of changes in FEMA hazard zone definitions, revised models, and updated storm data. Major milestones in the evolution of FEMA flood hazard mapping procedures, which can render early FIRMs obsolete, include: COASTAL CONSTRUCTION MANUAL 3-67 IDENTIFYING HAZARDS In approximately 1979, a FEMA storm surge model replaced NOAA tide frequency data as the source of storm tide stillwater elevations for the Atlantic and Gulf of Mexico coasts. In approximately 1988, coastal tide frequency data from the USACE New England District replaced earlier estimates of storm tide elevations for New England. In approximately 1988, return periods for Great Lakes water levels from the USACE Detroit District replaced earlier estimates of lake level return periods. There have been localized changes in flood elevations. For example, after Hurricane Opal (1995), a revised analysis of historical storm tide data in the Florida panhandle raised 100-year stillwater flood elevations and BFEs by several feet (Dewberry & Davis 1997). Prior to Hurricane Frederic in 1979, BFEs in coastal areas were set at the storm surge stillwater elevation, not at the wave crest elevation. Beginning in the early 1980s, FIRMS have been produced with Zone V, using the WHAFIS model and the 3-foot wave height as the landward limit of Zone V. Beginning in approximately 1980, tsunami hazard zones on the Pacific coast were mapped using procedures developed by the USACE. These procedures were revised in approximately 1995 for areas subject to both tsunami and hurricane effects. Before May 1988, flood hazard mapping for the Atlantic and Gulf of Mexico coasts was based solely on ground elevations and without regard for erosion that would occur during the base flood event; this practice resulted in Zone V boundaries being drawn near the crest of the primary frontal dune. Changes in mapping procedures in May 1988 accounted for storm -induced dune erosion and shifted many Zone V boundaries to the landward limit of the primary frontal dune. After approximately 1989, FIRMS were produced using a revised WHAFIS model, a runup model, and wave setup considerations to map flood hazard zones. Beginning in approximately 1989, a Great Lakes wave runup methodology (developed by the USACE Detroit District and modified by FEMA) was employed. Beginning in approximately 1989, a standardized procedure for evaluating coastal flood protection structures (Walton et al. 1989) was employed. Beginning in approximately 2005, FEMA began mapping the 2-percent exceedance wave runup elevation during the base flood instead of the mean runup elevation. In 2005, FEMA issued its Final Draft Guidelines for Coastal Flood Hazard Analysis and Mapping for the Pacific Coast of the United States. Beginning in 2005, FEMA began using advanced numerical storm surge (ADCIRC) and offshore wave (STWAVE and SWAN) models for Atlantic and Gulf of Mexico coastal flood insurance studies (conventional dune erosion procedures and WHAFIS are still used on land). Studies completed using these models should be considered the most accurate and reliable. In 2007, FEMA issued its Atlantic Ocean and Gulf of Mexico Coastal Guidelines Update. 3-68 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS In 2007, FEMA issued guidance for mapping the 500-year (0.2-percent-annual-chance) wave envelope in coastal studies. In 2008, FEMA issued guidance for mapping coastal flood hazards in sheltered waters. In December 2008, FEMA issued mapping guidance for the LiMWA (FEMA 2008c), which delineates the 1.5-foot wave height location, and thus, defines the landward limit of the Coastal A Zone. In 2009, FEMA issued its Great Lakes Coastal Guidelines Update (FEMA 2009). 3.9 References ASCE (American Society of Civil Engineers). 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. Blake, E.S., E.N. Rappaport, J.D. Jarell, and C.W. Landsea. 2005. The Deadliest, Costliest, and Most Intense United States Hurricanes from 1851 to 2004 (and Other Frequently Requested Hurricane Facts). NOAA Technical Memorandum. NWS TPC-4, 48 pp. Caldwell, S. R.; R. D. Crissman. 1983. Design for Ice Forces. A State of the Practice Report. Technical Council on Cold Regions Engineering. American Society of Civil Engineers. Camfield, F. E. 1980. Tsunami Engineering. Special Report No. 6. U.S. Army, Coastal Engineering Research Center. Chasten, M. A.; J. D. Rosati; J. W. McCormick; R. E. Randall. 1993. Engineering Design Guidance for Detached Breakwaters as Shoreline Stabilization Structures. Technical Report CERC 93-13. U.S. Army Corps of Engineers, Coastal Engineering Research Center. Chen, A. 1; C. B. Leidersdor£ 1988. Arctic Coastal Processes and Slope Protection Design. Monograph. Technical Council on Cold Regions Engineering. American Society of Civil Engineers. Dean, R. G.; M. Perlin. 1977. "Coastal Engineering Study of Ocean City Inlet, Maryland." Proceedings of the ASCE Specialty Conference, Coastal Sediments '77. American Society of Civil Engineers. New York. pp. 520-542. Dewberry & Davis, Inc. 1997. Executive Summary of Draft Report, Coastal Flood Studies of the Florida Panhandle. Douglas, B. C.; M. Crowell; S. P. Leatherman. 1998. "Considerations for Shoreline Position Prediction." Journal of Coastal Research. Vol. 14, No. 3, pp. 1025-1033. FEMA (Federal Emergency Management Agency). 1996. Corrosion Protection for Metal Connectors in Coastal Areas for Structures Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program. Technical Bulletin 8-96. FEMA. 1997. Multi -Hazard Identification and Risk Assessment, A Cornerstone of the National Mitigation Strategy. COASTAL CONSTRUCTION MANUAL 3-69 IDENTIFYING HAZARDS FEMA. 1998. Wildfire Mitigation in the 1998 Florida Wildfires. Wildfire Report FEMA-1223-DR-FL. FEMA, Region IV. FEMA. 2003. Guidelines and Specifications for Flood Hazard Mapping Partners. April. FEMA. 2005. Final Draft Guidelines for Coastal Flood Hazard Analysis and Mapping for the Pacific Coast of the United States. January. FEMA. 2006a. Homebuilders' Guide to Earthquake Resistant Design and Construction. FEMA 232. June. FEMA. 2006b. How to Use a Flood Map to Protect Your Property. FEMA 258. FEMA. 2007. Atlantic Ocean and Gulf of Mexico Coastal Guidelines Update. Final Draft. February. FEMA. 2008a. Taking Shelter From the Storm: Building a Safe Room For Your Home or Small Business. FEMA 320. August. FEMA. 2008b. Home Builder's Guide to Construction in Wildfire Zones. FEMA P-737. FEMA. 2008c. Procedure Memorandum No. 50 - Policy and Procedures for Identifying and Mapping Areas Subject to Wave Heights Greater than 1.5 feet as an Informational Layer on Flood Insurance Rate Maps (FIRMS). FEMA. 2009. GreatLakes Coastal Guidelines Update.:%:`��.E�=c=s.:<,c.tci":cr. lakes-guidelines.pd£ March. FEMA. 2010. Fact Sheet 1.7 "Coastal Building Materials." Home Builder's Guide to Coastal Construction. FEMA P-499. December. Griggs, G. B. 1994. "California's Coastal Hazards." Coastal Hazards Perception, Susceptibility and Mitigation, Journal of Coastal Research Special Issue No. 12. C. Finkl, Jr., ed., pp. 1-15. Griggs, G. B.; D. C. Scholar. 1997. Coastal Erosion Caused by Earthquake -Induced Slope Failure. Shore and Beach. Vol. 65, No. 4, pp. 2-7. Harris -Galveston Subsidence District. 2010. "Subsidence 1906-2000." Data Source National Geodetic Survey. http://www.hgsubsidence.org/assets/pdfdocuments/HGSD%20Subsidence%2OMap%20 1906-2000.pdf. Retrieved 1/18/2010. Last modified 1/19/2010. Horning Geosciences. 1998. Illustration showing principal geologic hazards acting along typical sea cliff in Oregon. ICC (International Code Council). 2012a. International Building Code. Birmingham, AL. ICC. 2012b. International Residential Code. Birmingham, AL. ICC. 2012c. International Wildland- Urban Interface Code. Birmingham, AL. IPCC (Intergovernmental Panel on Climate Change). 2007. Climate Change 2007 The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. 3-70 COASTAL CONSTRUCTION MANUAL IDENTIFYING HAZARDS Jarrell, J.D., B.M. Mayfield, E.N. Rappaport, and C.W. Landsea. 2001. The Deadliest, Costliest, and Most Intense United States Hurricanes from 1900 to 2000 (and Other Frequently Requested Hurricane Facts). NOAA Technical Memorandum. NWS TPC-3, 30 pp. Jones, C. P.; D. L. Hernandez; W. C. Eiser. 1998. "Lucas vs. South Carolina Coastal Council, Revisited." Proceedings of the 22nd Annual Conference of the Association of State Floodplain Managers. Kaminsky, G. M.; R. C. Daniels; R. Huxford; D. McCandless; P. Rugegiero. 1999. "Mapping Erosion Hazard Areas in Pacific County, Washington." Coastal Erosion Mapping and Management, journal of Coastal Research. Special Issue No. 28, M. Crowell and S. P. Leatherman, eds. Keillor, J. P. 1998. Coastal Processes Manual.• How to Estimate the Conditions of Risk to Coastal Property from Extreme Lake Levels, Storms, and Erosion in the Great Lakes Basin. 2nd Edition. WISCU-H-98-003. University of Wisconsin Sea Grant Institute. Knowles, S.; T. A. Terich. 1977. "Perception of Beach Erosion Hazards at Sandy Point, Washington." Shore and Beach, Vol. 45, No. 3, pp. 31-35. Larsen, C.E. 1994. "Beaches ridges as monitors of isostatic uplift in the Upper Great Lakes." journal of Great Lakes Research. Internat. Assoc. Great Lakes Res. 20(1):108-134. NOAA (National Oceanic and Atmospheric Administration). 2010. "The Saffir-Simpson Hurricane Wind Scale." http://www.nhc.noaa.gov/pdf/sshws.pdf. Accessed December 16, 2010. NOAA. 2011a. Atlantic Oceanographic and Meteorological Laboratory. "Hurricane Research Division: Frequently Asked Questions." http://www.aoml.noaa.gov/hrd/tcfaq/tcfagHED.html. Version 4.4. June. Accessed June 24, 2011. NOAA. 2011b. Center for Operational Oceanographic Products and Services. "Mean Sea Level Trend 8534720 Atlantic City, New Jersey" http://tidesandcurrents.noaa.gov/sltrends/sltrends—station. shtml?stnid=8534720. Accessed June 16, 2011. National Research Council. 1990. Managing Coastal Erosion. National Academy Press. Shepard, F. P.; H. L. Wanless. 1971. Our Changing Coastlines. McGraw-Hill, Inc. Sparks, P. R.; S. D. Schiff; T. A. Reinhold. 1994. "Wind Damage to Envelopes of Houses and Consequent Insurance Losses." journal of Wind Engineering and Industrial Aerodynamics. Vol. 53, pp. 145-155. TTU (Texas Tech University).2004. A Recommendation for an Enhanced Fujita Scale. Wind Science and Engineering Center. June. USACE (U.S. Army Corps of Engineers). 1971. Report on the National Shoreline Study. USACE. 2002. Ice Engineering. Engineering Manual EM-1110-2-1612. USACE. 2008. Coastal Engineering Manual. Engineering Manual EM-1110-2-1100. USACE. 2009a. Water Resource Policies and Authorities Incorporating Sea -Level Change Considerations in Civil Works Program. Engineering Circular No. 1165-2-211. COASTAL CONSTRUCTION MANUAL 3-71 IDENTIFYING HAZARDS USACE. 2009b. Dynamic Sustainability: Shoreline Management on Maryland s Atlantic Coast. Tales of the Coast. November. Walton, T. L.; J. P. Ahrens; C. L. Truitt; R. G. Dean. 1989. Criteria for Evaluating Coastal Flood -Protection Structures. Technical Report CERC 89-15. U.S. Army Corps of Engineers, Coastal Engineering Research Center Zhang, K. 1998. Storm Activity and Sea Level Rise along the US East Coast during the 20th Century, and Their Impact on Shoreline Position. Ph.D. Dissertation. University of Maryland at College Park, 3-72 COASTAL CONSTRUCTION MANUAL Siting residential buildings to minimize their vulnerability to coastal hazards should be one of the most important aspects of the development (or redevelopment) process. Informed decisions regarding siting, design, and construction begin with a complete and detailed understanding of the advantages and disadvantages of potential sites for coastal construction. Gaining this knowledge prior to the purchase of coastal property and the initiation of design is important to ensure that coastal residential buildings are properly sited to minimize risk. i r"I CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/ mat/fema55.shtm). Experience has shown that not all coastal lands are suitable for development, or at least not the type and intensity of development that has occurred on some coastal lands in the past. Prudent siting has often been overlooked or ignored in the past; properties have been developed and buildings have been constructed close to the shoreline, near bluff edges, and atop steep coastal ridges. Unfortunately, many similar siting and development decisions are still made every day based on site conditions at the time of purchase or on an incomplete or inaccurate assessment of existing and future conditions. Too often, these decisions leave property owners and local governments struggling with a number of avoidable problems: Damage to, or loss of, buildings Damage to attendant infrastructure NOTE Buildings located on public beaches as shorelines erode One of the principal objectives Vulnerable buildings and infrastructure that require of this Manual is to improve site emergency or permanent protection measures and/or selection for coastal buildings. relocation COASTAL CONSTRUCTION MANUAL 4-1 SITING Emergency evacuation Injuries and loss of life A thorough evaluation of coastal property for development purposes involves four steps (see Figure 4-1): 1. Compile lot/parcel information for one or more candidate properties; for each property, follow steps 2 through 4. 2. Identify hazards and assess risk. 3. Determine whether the risk can be reduced through siting, design, or construction and whether the residual risks to the site and the building are acceptable. Figure 4-1. Evaluation of coastal property • Location and dimensions • Zoning and land use requirements (including setbacks) • Topography and drainage • Prior damage to site/building • Cost of hazard insurance • Legal and regulatory constraints • Existing building or structure • Flood • Wind • Storm -induced erosion • Earthquake • Utilities and Infrastructure • Soils and vegetation • Prior erosion control efforts • Flood, erosion, landslide, wind, seismic, and other hazards • Property access (e.g., vulnerability of roads to storm damage, alternative access routes) • Landslide • Long-term erosion • Subsidence • Other YES to the last question Find and evaluate other properties NO to the last question 4-2 COASTAL CONSTRUCTION MANUAL SITING 4. Either proceed with the purchase or development of a property, or reject the candidate properties, and find and WARNING evaluate other properties. Many coastal property buyers A building or development site need not be vacant or undeveloped fail to investigate potential risk land. Indeed, much of the construction occurring in coastal to their land and buildings.Designers should work communities today involves replacement of existing buildings, with owners to identify and infill development between adjacent buildings, or redevelopment mitigate those risks. of previously developed property (refer to Figure 4-2). This chapter addresses property evaluation broadly and applies to the following types of development: Development of raw land. Development on large, vacant parcels, usually without existing on -site access roads and WARNING utilities. Some severe coastal hazards Development on previously subdivided lots. Development cannot be mitigated through on previously subdivided or platted lots or small parcels, design and construction. usuallywith roads and utilities in lace and surrounded b p y A design and construction "success" can be rendered a or adjacent to residential structures. Lots may or may not failure by poor siting. be vacant. This category includes infill development and redevelopment. Today, there are relatively few places along the shoreline where there is insufficient information to make rational, informed siting decisions. Following the lessons and procedures described in this Volume of the Manual will help designers, purchasers, owners, developers, and community officials identify those locations where coastal residential development and buildings can be sited so that the risks are minimized. An otherwise successful design can be negated by failure to site a building properly. The North Carolina house shown in Figure 4-3 illustrates this type of failure; while the house appears to be a structural success, long-term erosion has left it standing permanently in the water and uninhabitable. In contrast, a siting COASTAL CONSTRUCTION MANUAL 4-3 SITING Figure 4-3. Long-term erosion left this well-built Kitty Hawk, NC, house standing in the ocean (Hurricane Dennis, 1999) SOURCE: D. GATLEY, FEMA Figure 4-4. Although sited away from the shore, winds from Hurricane Floyd (1999) tore off the large overhanging roof of this house in Wrightstville Beach, NC success can be overshadowed by poor design, construction, or maintenance. The North Carolina house shown in Figure 4-4 was set back from the shoreline and safe from long-term erosion, but, it could not resist winds from Hurricane Floyd in 1999. 4.1 Identifying Suitable Property for Coastal Residential Structures The first step in the coastal development or construction process involves the purchase of a vacant or previously developed lot or parcel. This step, in many ways, constrains subsequent siting, design, and construction decisions and determines the long-term vulnerability of coastal residential buildings. Prospective property buyers who fail to fully investigate properties before acquiring them may subsequently be faced with a variety ofproblems that are difficult, costly, or essentially impossible to solve. Although this Manual does not address the initial identification of candidate properties in detail, buyers and design professionals who assist them with property evaluations should keep the following in mind as they narrow their search for a suitable building/development site: 4-4 COASTAL CONSTRUCTION MANUAL SITING The geographic region or area a buyer is interested in determines the hazards to which the property is exposed. WARNING An existing erosion control structure on or near a lot or Before any purchase, each parcel is an indication of prior erosion, but the structure buyer should, in consultation cannot be assumed to be adequate to protect a building or with experts and local officials, determine the acceptable level of development in the future. residual risk and decide how to manage the actual risks expected The vulnerability of coastal building generally over the life of the building or increases with time, as a result of one or more of the development. Note that risk following: gradual weakening or deterioration of the assessment, risk tolerance, building itself., sea level or lake level rise; or erosion- and risk reduction issues are not simple —property acquisition induced shoreline recession, which affects the majority of and development decisions coastal areas in the United States. should be based on a wide range of information. Future development activities and patterns on adjacent and nearby properties may affect the vulnerability of buildings or development on any given property. Any given lot or parcel may not be suitable for the CROSS REFERENCE purchaser's intended use of the property. Refer to Chapter 3 for Land use, zoning, setbacks, public health regulations, discussion of coastal hazards, floodplain management, building code, and related including flooding, erosion, requirements generally determine development densities, wind, earthquake, and other environmental considerations. building size and location limitations, minimum design and construction practices, and allowable responses Refer to Chapter 6 for descriptions of risk assessment, to erosion hazards; however, compliance with these risk tolerance, and residual risk. requirements does not ensure the future safety of the building or development. Development practices that perpetuate or duplicate historical siting, design, or construction practices do not ensure the future safety of new buildings and/or development. Many historical practices are inadequate by today's standards; further, changing shoreline conditions may render those practices obsolete. Property selection —along with subsequent siting, design, construction, and maintenance decisions determines the vulnerability of and risk to any building or improvements. Narrowing the search for coastal property suitable for development or redevelopment requires careful consideration of a variety of property and area characteristics, including the nature and success of previous erosion control efforts (e.g., groins and revetments). Note that some communities and States restrict or prohibit the construction or reconstruction of revetment, seawall, and groin structures such as those shown in Figure 4-5. A number of States require that residential real estate transactions be accompanied by a disclosure of information pertaining to flood hazards and other hazards (if the seller or agent knows of such hazards). However, the requirements concerning the form and timing of disclosures differ. Therefore, the type and amount of information that must be disclosed varies widely. Taken collectively, the disclosure requirements COASTAL CONSTRUCTION MANUAL 4-5 SITING Figure 4-5. Groins were installed in an attempt to stop erosion (note narrower beaches downdrift of groins, as shown also in Figure 2-12) SOURCE: BONNIE M. BENDELL, NORTH CAROLINA DIVISION OF COASTAL MANAGEMENT, USED WITH PERMISSION (in force and as proposed) provide a good indication of the types of information that prospective property buyers and designers should seek, whether or not their State requires such disclosure. Builders should contact a real estate agent or real estate attorney for a list of real estate natural hazard disclosure laws in their State. 4.2 Compiling Information on Coastal Property After candidate properties are identified, the next step is to compile a wide range of information for each property. This is no trivial matter; this step may require considerable time and effort. Table 4-1 is a list of general information that should be compiled. Information listed in Table 4-1 is usually available from local, regional, State, or Federal governments, from universities, or from knowledgeable professionals; however, the availability and quality of the information will vary by State and community. 4-6 COASTAL CONSTRUCTION MANUAL SITING Table 4-1. General Information Needed to Evaluate Coastal Property • Township/county/jurisdiction • Special zoning or land use districts • Street address • Other hazard area designation • Parcel designation/tax map ID • Natural resource protection area designation • Subdivision information • Total acreage • Water -ward property boundary (platted or fixed line; moving line [e.g., mean high water line, mean low water line, or other datum, elevation, feature]) • Property shape • Property elevations and topography • Location relative to adjacent properties • Configuration of adjacent properties • Shoreline frontage (i.e., dimension parallel to shoreline) • Property depth (i.e., dimension perpendicular to shoreline) • Acreage landward/outside of natural, physical, or regulatory construction or development limits (i.e., usable f acreage) • Hazard Mitigation Plan • Land use designation at property and adjacent properties • Zoning classification and resulting restrictions on use • Building code and local amendments • Flood hazard area: elevation and construction requirements • Erosion hazard area: construction setbacks and regulations • Natural resource protection area: siting, construction, or use restrictions • Easements and rights -of -way on property (including beach access locations for nearby properties or the general public) • Local and State siting and construction regulations • Regulatory front, back, and side setbacks • Local and State permitting procedures and requirements • Local and State regulations regarding use, construction, and repair of erosion control measures • Riparian rights • Local and State restrictions on cumulative repairs or improvements • Conditions or other requirements attached to building or zoning permits • Subdivision plat covenants and other restrictions imposed by developers and homeowner's associations • Hazard disclosure requirements for property transfer, including geologic hazard reports • Soils, geology, and vegetation - site and regional • Topography of nearshore (including nearshore slope), beach, dune, bluff, uplands • Site drainage - surface water and groundwater • Littoral sediment supply and sediment budget • Storm, erosion, and hazard history of property • Erodibility of the nearshore bottom • Erosion control structure on site - type, age, condition, and history • Proximity to inlets and navigation structures • Previous or planned community/regional beach/dune restoration projects • Relative sea level/water level changes - land subsidence or uplift • Access road (s) • Emergency evacuation route(s) • Electric, gas, water, telephone, and other utilities - onsite or offsite lines and hookups • Sewer or septic requirements/limitations • Limitations imposed by utility/infrastructure locations on property use COASTAL CONSTRUCTION MANUAL 4-7 SITING Table 4-1. General Information Needed to Evaluate Coastal Property (concluded) • Intended use - owner -occupied or rental property • Real estate taxes • Development impact fees • Permit fees • Hazard insurance - availability, premiums, deductibles, and exclusions • Property management fees • Special assessments for community/association projects (e.g., private roads and facilities, dune preservation) • Maintenance and repair of private erosion control structures • Increased building maintenance and repairs in areas subject to high winds, wind -driven rain, and/or salt spray • Building damage costs (insured and uninsured) from previous storms Communities participating in the NFIP should have a FIRM and FIS on file for the community (see Section 3.6.3). The FIS includes detailed flood hazard data for parts of the community and usually includes a narrative of the flood history of a community. The best source of current hazard information is at the local level due to the local officials' knowledge of local hazards, policies, codes, and regulations. Many States and communities produce brochures or publications to help property owners and prospective buyers evaluate coastal property. The publications listed below are examples of the types of information available. Natural Hazard Considerations for Purchasing Coastal Real Estate in Hawai'i: A Practical Guide of Common Questions andAnswers (University of Hawaii Sea Grant College Program 2006), answers common questions that are considered when purchasing developed and undeveloped coastal real estate. It includes a strong focus on long-term erosion, which is the most common coastal hazard in Hawaii. Living on the Coast: Protecting Investments in Shore Property on the Great Lakes (University of Wisconsin Sea Grant Program 2004) contains a description of natural processes that affect the Great Lakes coast from glacial melt and lake level rise to local erosion. It also includes information on risk management and protecting coastal properties that is relevant to all coastal areas. The FEMA Residential Coastal Construction Web page includes a list of Web resources relevant to Great Lakes hazards adapted from the University of Wisconsin Sea Grant Program. n\ NOTE Owners and prospective buyers of coastal property should contact their community or State officials for publications and data that will help them evaluate the property. A Manual for Researching Historical Coastal Erosion (Fulton 1981) describes in detail how to use historical weather data, local government records, and historical maps and photographs to understand and quantify shoreline, sea bluff, and cliff retreat. Two communities in San Diego County, CA are used as case studies to illustrate the research methods presented. Questions andAnswers on Purchasing Coastal Real Estate in South Carolina (South Carolina Sea Grant Extension Program 2001) provides prospective property owners with basic information on a variety of topics, including shoreline erosion, erosion control, high winds, and hazard insurance (including earthquakes). 4-8 COASTAL CONSTRUCTION MANUAL SITING 4 In the absence of current hazard information, historical records can be used to preduct future hazard conditions, impacts, and frequencies. However, natural and manmade changes at a site may render simple extrapolation of historical patterns inaccurate. 4.3 Evaluating Hazards and Potential Vulnerability Evaluating hazards and the potential vulnerability of a building is perhaps most crucial when evaluating the suitability of coastal lands for development or redevelopment. Basing hazard and vulnerability analyses solely on building code requirements, the demarcation of hazard zones or construction setback lines, and the location and design of nearby buildings is inadequate. A recommended procedure for performing such an evaluation is outlined in the next section. .3.1 Define Coastal Hazards Affecting the Property Defining the coastal hazards affecting a property under consideration for development requires close examination of both historical and current hazard information. This Manual recommends the following steps: Step 1: Use all available information to characterize the type, severity, and frequency of hazards (e.g., flood, storm -induced and long-term erosion, accretion or burial, wind, seismic, tsunami, landslide, wildfire, and other natural hazards) that have affected or could affect the property. Step 2: Examine the record for long-term trends (> 50-100 years), short-term trends (< 10-20 years), and periodic or cyclic variations (both spatial and temporal) in hazard events. Determine whether particularly severe storms are included in the short-term or long-term records and what effects those storms had on the overall trends. If cyclic variations are observed, determine the periods and magnitudes of the variations. Step 3: Determine whether or not extrapolation of historical trends and hazard occurrences is reasonable. Examine the record for significant changes to the coastal system or inland and upland areas that will reduce, intensify, or modify the type, severity, and frequency of hazard occurrence at the property. The following are examples of events or processes that preclude simple extrapolation of historical trends: �J NOTE This Manual is intended primarily for design professionals, coastal specialists, and others with the expertise to evaluate coastal hazards and the vulnerability of sites and buildings to those hazards, and to design buildings in coastal areas. Readers not familiar with hazard and vulnerability evaluations are encouraged to seek the services of qualified professionals. CROSS REFERENCE Chapter 3 presents additional information about natural hazards in coastal areas and the effects of those hazards. Chapter 6 provides information about recurrence intervals. Loss of a protective dune or bluff feature that had been there for a long time may lead to increased incidence and severity of flood or erosion damage. Loss of protective natural habitats, such as marshes, swamps, coral reefs, and shoreline vegetation, can increase vulnerability to erosion and flooding. COASTAL CONSTRUCTION MANUAL 4-9 SITING Significant increases in sea, bay, or lake levels generally increase vulnerability to flooding and coastal storm events. Erosion or storms may create weak points along the shoreline that are predisposed to future breaching, inlet formation, and accelerated erosion, or may expose geologic formations that are more resistant to future erosion. Recent or historical modifications to an inlet (e.g., construction or modification of jetties, creation or deepening of a dredged channel) may alter the supply of littoral sediments and modify historic shoreline change trends. Formation or closure of an inlet during a storm alters local tide, wave, current, and sediment transport patterns and may expose previously sheltered areas to damaging waves (see Figures 3-39 and 3-41 in Chapter 3). Widespread construction of erosion control structures may reduce the input of sediments to the littoral system and cause or increase local erosion. Recent seismic events may have caused uplift, settlement, submergence, or fracturing of a region, altering its hazard vulnerability to flood and other hazards. Changes in surface water flows, drainage patterns, or groundwater movements, and reduction in vegetative cover may increase an area's susceptibility to landslides. Topographic changes resulting from the retreat of a sea cliff or coastal bluff may increase wind speeds at a site. Exposure changes, such as the removal of trees to create future development, can increase wind pressures on existing buildings at a site. Step 4: Forecast the type, severity, and frequency of future hazard events likely to affect the property over a suitably long period of time, say over at least 50-70 years. This forecast should be based on either: (1) extrapolation of observed historical trends, modified to take into account those factors that will cause deviations from historical trends; or (2) detailed statistical and modeling studies calibrated to reflect basic physical and meteorological processes, and local conditions. Extrapolation of trends should be possible for most coastal sites and projects. Detailed statistical and modeling studies may be beyond the scope and capabilities of many coastal development projects. 4.3.2 Evaluate Hazard Effects on the Property WARNING Compliance with minimum siting requirements administered by local and State governments does not guarantee a building will be safe from hazard effects. To reduce risks from coastal hazards to an acceptable level, exceeding minimum siting requirements may be necessary. Once the type, severity, and frequency of future hazard events have been forecast, designers should use past events as an indication of the nature and severity of effects likely to occur during those forecast events. Information about past events at the site of interest and at similar sites should be considered. This historical 4-10 COASTAL CONSTRUCTION MANUAL SITING 4 information should be combined with knowledge about the site and local conditions to estimate future hazard effects on the site and any improvements. Designers should consider the effects of low -frequency, rare events (e.g., major storms, extreme water levels, tsunamis, earthquakes), and multiple, successive lesser events (see Figure 4-6). For example, many of the post -storm damage assessments summarized in Chapter 2 show that the cumulative erosion and damage caused by a series of minor coastal storms can be as severe as the effects of a single, major storm. AFTER HURRICANE BERTHA _ �,� 1 :--=act=3• . - _ AFTER HURRICANE FRAN �-w 4.4 General Siting Considerations Figure 4-6. Cumulative effects of storms occurring within a short period at one housing development in Jacksonville, NC, July —September 1996 SOURCE: JOHN ALTHOUSE, USED WITH PERMISSION It is always best to build in lower risk areas. However, when building in more vulnerable areas, a variety of factors must be considered in selecting a specific site and locating a building on that site. These factors are outlined in Figure 4-1 and include: Building code and land use requirements Local floodplain management requirements adopted to participate in the NFIP COASTAL CONSTRUCTION MANUAL 4-11 SITING Other regulatory requirements Presence and location of infrastructure Previous development and/or subdivision of property Physical and natural characteristics of the property Vulnerability of the property to coastal hazards When siting the foundation of a building in two different flood insurance zones, design and regulatory requirements of the most restrictive zone apply. For example, even though the majority of the foundation of the building illustrated in Figure 4-7 is located in Zone A, Zone V requirements would apply to the entire building. Regulatory controls do not necessarily prevent imprudent siting of coastal buildings. Figure 4-8 shows flood and debris damage to new construction sited in Zone A that could have been avoided had the site been designated a Coastal A Zone, and had the structure been elevated on an open foundation. Because there are situations where minimum requirements do not address site -specific hazards, prospective buyers should Figure 4-7. When siting a foundation in two different flood zones, requirements for the most restrictive zone apply to the whole building 4-12 COASTAL CONSTRUCTION MANUAL SITING 4 evaluate a site for its suitability for purchase, development, or redevelopment prior to acquiring the property. However, property owners often undertake detailed studies only after property has been acquired. Designers should recognize situations in which poor siting is allowed or encouraged, and should work with property owners to minimize risks to coastal buildings. Depending on the scale of the project, this could involve one or more of the following: Locating development on the least hazardous portion of the site Rejecting the site and finding another Transferring development rights to another parcel better NOTE able to accommodate development Proper siting and design should Combining lots or parcels take into account both slow -onset hazards (e.g., long-term erosion, Reducing the footprint of the proposed building and multiple minor storms) and rapid - shifting the footprint away from the hazard onset hazards (e.g., extreme storm events). Shifting the location of the building on the site by modifying or eliminating ancillary structures and development Seeking variances to lot line setbacks along the landward and side property lines (in the case of development along a shoreline) Moving roads and infrastructure Modifying the building design and site development to facilitate future relocation of the building on the same site Altering the site to reduce its vulnerability Construction of protective structures, if allowed by the community 4.5 Raw Land Development Guidelines Large, undeveloped parcels available for coastal development generally fall into two classes: Parcels well -suited to development, but vacant due to the desires of a former owner, lack of access, or lack of demand for development. Such parcels include those with deep lots, generous setbacks, and avoidance of dune areas —these attributes should afford protection against erosion and flood events for years to come (see Figure 4-9). Parcels difficult to develop, with extensive areas of sensitive or protected resources, with topography or site conditions requiring extensive alteration, or with other special site characteristics that make development expensive relative to nearby parcels. Increasingly, coastal residential structures are planned and constructed as part of mixed -use developments, such as the marina/townhouse development shown in Figure 4-10. Such projects can involve complicated environmental and regulatory issues, as well as more difficult geotechnical conditions and increased exposure to flood hazards. COASTAL CONSTRUCTION MANUAL 4-13 SITING Figure 4-9. Example of parcels well -suited to coastal development in Louisiana SOURCE:USGS Figure 4-10. Example of parcels difficult to develop (mixed -use marina/ townhouse development) Development in both circumstances should satisfy planning and site development guidelines such as those listed in Table 4-2 (adapted from recommended subdivision review procedures for coastal development in California [California Coastal Commission 1994]). Development of raw land in coastal areas should consider the effects of all hazards known to exist and the effects of those hazards on future property owners. Similarly, such development should consider local, State, or Federal policies, regulations, or plans that will affect the abilities of future property owners to protect, transfer, or redevelop their properties (e.g., those dealing with erosion control, coastal setback lines, post - disaster redevelopment, landslides, and geologic hazards). 4-14 COASTAL CONSTRUCTION MANUAL Table 4-2. Planning and Site Development Guidelines for Raw Land DO determine whether the parcel is suitable for subdivision or should remain a single parcel. DO ensure that the proposed land use is consistent with local, regional, and State planning and zoning requirements. DO ensure that all aspects of the proposed development consider and integrate topographic and natural features into the design and layout. DO avoid areas that require extensive grading to ensure stability. SITING 4 DON'T rely on engineering solutions to correct poor planning decisions. DO identify and avoid, or set back from, all sensitive DON'T rely on relocation or restoration efforts resources and prominent land features. to replace resources impacted by poor planning decisions DO account for all types of erosion (e.g., long-term DON'T overlook the effects to surface and erosion, storm -induced erosion, erosion due to inlets) groundwater hydrology from modifications to the and governing erosion control policies when laying parcel. out lots and infrastructure near a shoreline. DO use a multi -hazard approach to planning and DON'T forget to consider future site and hazard design. conditions on the parcel. 4.5.1 Road Placement near Shoreline Based on studies and observations of previous coastal development patterns and resulting damage, there are several subdivision and lot layout practices that should be avoided. The first of these is placing a road close to the shoreline in an area of small lots. WARNING In the case of an eroding shoreline, placing a road close to the shoreline and creating small lots between the road and the shoreline results in buildings, the roadway itself, and utilities being extremely vulnerable to erosion and storm damage, and can lead to future conflicts over shore protection and buildings occupying public beaches. Figure 4-11 is a view along a washed-out, shore -parallel road in Garcon Point, FL, after Hurricane Ivan in 2004. Homes Proper lot layout and siting of building along an eroding shoreline are critical. Failure to provide deep lots and to place roads and infrastructure well away from the shoreline ensures future conflicts over building reconstruction and shore protection. COASTAL CONSTRUCTION MANUAL 4-15 SITING to the left have lost inland access. Figure 4-12 shows a recommended lot layout that provides sufficient space to comply with State/local setback requirements and avoid damage to dunes. Some communities have land development regulations that help achieve this goal. For example, the Town of Nags Head, NC, modified its subdivision regulations in 1987 to require all new lots to extend from the ocean to the major shore -parallel highway (Morris 1997). Figure 4-13 compares lots permitted in Nags Head prior to 1987 with those required after 1987. The town also has policies and regulations governing the combination of nonconforming lots (Town of Nags Head 1988). Figure 4-11. Roads placed near shorelines can wash out, causing access problems for homes such as these located at Garcon Point, FL (Hurricane Ivan, 2004) Figure 4-12. Recommended lot layout for road setback near the shoreline 4-16 COASTAL CONSTRUCTION MANUAL SITING Figure 4-13. Comparison of Nags Head, NC, oceanfront lot layouts permitted before and after 1987 SOURCE: ADAPTED FROM MORRIS 1997 COASTAL CONSTRUCTION MANUAL 4-17 SITING Figure 4-14. Problematic versus recommended layouts for shore -parallel roadways and associated utilities 4-18 COASTAL CONSTRUCTION MANUAL SITING Figure 4-15. Problematic versus recommended layouts for shoreline lots COASTAL CONSTRUCTION MANUAL 4-19 SITING Figure 4-17. Lots created in line with natural or manmade features can concentrate floodwaters 4-20 COASTAL CONSTRUCTION MANUAL SITING Figure 4-18. Coastal lot development scenarios SOURCE: ADAPTED FROM CALIFORNIA COASTAL COMMISSION 1994 COASTAL CONSTRUCTION MANUAL 4-21 SITING Figure 4-19. As buildings in this Humbolt County, CA, community are threatened by bluff erosion along the Pacific Ocean, they are moved to other sites on the jointly owned parcel In extreme cases, entire communities have been threatened by erosion and have elected to relocate. For example, the village of Shishmaref, AK, voted in November 1998 to relocate their community of 600 after storm erosion threatened several houses and after previous shore protection efforts failed. More information on specific examples of relocation of threatened buildings can be found in FEMA 257, Mitigation of Flood and Erosion Damage to Residential Buildings in Coastal Areas (FEMA 1994). The report also presents several examples of flood and erosion mitigation through other measures (e.g., elevation, foundation alterations). 4.5.3 Lot Configurations rear Tidal Inlets, Ray Entrances, and River Mouths Layout of lots and infrastructure along shorelines near tidal inlets, bay entrances, and river mouths is especially problematic. The three South Carolina houses in Figure 4-20 were built between January 1995 and January 1996, approximately 2 years before the photograph was taken in July 1997. They were built 100 or more feet landward of the vegetation line, but rapid erosion associated with a nearby tidal inlet left the houses standing on the beach only two years after construction. The shoreline will probably return to its former location, taking several years to do so. Although the buildings are structurally intact, their siting can be considered a failure. CROSS REFERENCE Section 3.5 also describes instances where the subdivision and development of oceanfront parcels near ocean -bay connections led to buildings being threatened by inlet -caused erosion. Figure 4-21 shows condominiums built adjacent to the shore in Havre de Grace, MD, where the mouth of the Susquehanna River meets the head of the Chesapeake Bay. Although the buildings are elevated, they are subject to storm surge and flood -borne debris. Infrastructure development and lot layout in similar cases should be preceded by a detailed study of historical shoreline changes, including development of (at least) a conceptual model of shoreline changes. Potential future shoreline positions should be projected, and development should be sited sufficiently landward of any areas of persistent or cyclic shoreline erosion. 4-22 COASTAL CONSTRUCTION MANUAL SITING 4 Figure 4-20. Three 2-year-old South Carolina houses left standing on the beach as a result of rapid erosion associated with a nearby tidal inlet (July 1997) Figure 4-21. Condominiums built along the shoreline at the mouth of the Susquehanna River on the Chesapeake Bay were subjected to flood -borne debris after Hurricane Isabel (Havre de Grace, MD, 2003) 4.6 Development Guidelines for Existing Lots Many of the principles discussed in the raw land scenario also apply to the construction or reconstruction of buildings on existing lots. Builders siting on a specific lot should take site dimensions, site features (e.g., topographic, drainage, soils, vegetation, sensitive resources), coastal hazards, and regulatory factors into consideration. However, several factors must be considered at the lot level; these are not a primary concern at the subdivision level: COASTAL CONSTRUCTION MANUAL 4-23 SITING Buildable area limits imposed by lot -line setbacks, hazard setbacks, and sensitive resource protection requirements Effects of coastal hazards on lot stability Location and extent of supporting infrastructure, utility lines, septic tanks and drain fields, etc. Impervious area requirements for the lot Prior development of the lot Future building repairs, relocation, or protection Regulatory restrictions or requirements for on -site flood or erosion control Although the local regulations, lot dimensions, and lot characteristics generally define the maximum allowable building footprint on a lot, designers should not assume that constructing a building to occupy the entire buildable area is a prudent siting decision. Designers should consider all the factors that can affect an owner's ability to use and maintain the building and site in the future (see Table 4-3). Table 4-3. Guidelines for Siting Buildings on Existing Lots DO study the lot thoroughly for all possible resource DON'T assume that siting a new building in a and hazard concerns - seek out all available previous building footprint or in line with adjacent information on hazards affecting the area and prior buildings will protect the building against coastal coastal hazard impacts on the lot. hazards. DON'T overlook the constraints that site topography, infrastructure and ancillary structures (e.g., utility DO avoid lots that require extensive grading to lines, septic tank drain fields, swimming pools), trees achieve a stable building footprint area. and sensitive resources, and adjacent development plane on site development, and (if necessary) future landward relocation of the building. DO identify and avoid, or set back from, all sensitive DON'T overlook the effects to surface and resources. groundwater hydrology from development of the lot. 4-24 COASTAL CONSTRUCTION MANUAL SITING 4 4.6.1 Building on Lots Close to Shoreline Experience shows that just as developers should avoid certain subdivision development practices in hazardous coastal areas, they should also avoid certain individual lot siting and development practices. One of the most common siting errors is placing a building as close to the water as allowed by local and State regulations. Although such siting is permitted by law, it can lead to a variety of avoidable problems, including increased building vulnerability, damage to the building, and eventually encroachment onto a beach. On an eroding shoreline, this type of siting often results in the building owner being faced with one of three options: loss of the building, relocation of the building, or (if permitted) protection of the building through an erosion control measure. Alternatives to this practice include siting the building farther landward than required by minimum setbacks, and designing the building so it can be easily relocated. Siting a building farther landward also allows (in some cases) for the natural episodic cycle of dune building and storm erosion without jeopardizing the building itself. Siting a building too close to a coastal bluff edge can result in building damage or loss (see Figures 3-37 and 3-46, in Chapter 3). Keillor (1998) provides guidance regarding selecting appropriate construction setbacks for bluffs on the Great Lakes shorelines; these general concepts are applicable elsewhere. Some sites present multiple hazards, which designers and owners may not realize without careful evaluation. Figure 4-22 shows northern California homes constructed along the Pacific shoreline at the top and bottom of a coastal bluff. These homes may be subject to several hazards, including storm waves and erosion, landslides, and earthquakes. Designers should consider all hazards and avoid them to the extent possible when siting a building. Figure 4-22. Coastal building site in Aptos, CA, provides an example of a coastal building site subject to multiple hazards SOURCE:CHERYL HAPKE,USGS,USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 4-25 SITING 4.6.2 Siting near Erosion Control Structures Siting a building too close to an erosion control structure, or failing to allow sufficient room for such a structure to be built, is another problematic siting practice. Figure 4-23 shows an example of buildings constructed near the shoreline behind a rock revetment. Although this revetment likely provided some protection to the buildings, they would have been better protected were they sited farther inland from the revetment. As shown in the figure, storm waves can easily overtop the revetment and damage the buildings. CROSS REFERENCE For more discussion on erosion and erosion control structures, see Section 3.5. Section 3.5.2.3 specifically discusses the effects of shore protection structures. A related siting problem that is commonly observed along ocean shorelines as well as along bay or lake shorelines, canals, manmade islands, and marina/townhouse developments is the construction of buildings immediately adjacent to bulkheads. The bulkhead along the shoreline in front of the building in Figure 4-24 was completely destroyed from a subtropical storm. Had the building in the left of the photograph not been supported by an adequate pile foundation, it would likely have collapsed. Buildings sited close to an erosion control structure should not rely on the structure to prevent undermining. Bulkheads are rarely designed to withstand a severe coastal flood and are easily overtopped by floodwaters and waves. During severe storms, landward buildings receive little or no protection from the bulkheads. In fact, if such a bulkhead fails, the building foundation can be undermined and the building may be damaged or be a total loss. Where buildings are constructed too close to an erosion control structure or immediately adjacent to bulkheads, it may be difficult to repair the erosion control structure in the future because of limitations on construction access and equipment operation. If erosion control structures are permitted and are employed, they should be sited far enough away from any nearby buildings to provide sufficient access to the site to complete repairs. Figure 4-23. Damage to buildings sited behind a rock revetment close to an eroding shoreline at Garden City Beach, SC (Hurricane Hugo,1989) 4-26 COASTAL CONSTRUCTION MANUAL SITING 4 Figure 4-24. Beach erosion and damage due to a destroyed bulkhead at Bonita Beach, FL, from a subtropical storm SOURCE: JUDSON HARVEY, JUNE 1982, USED WITH PERMISSION 4.6.3 Siting Adjacent to Large Trees Although preservation of vegetation and landscaping are an important part of the siting process, designers should avoid siting and design practices that can lead to building damage. For example, designs that "notch" buildings and rooflines to accommodate the presence or placement of large trees should be avoided (see Figure 4-25). This siting practice may lead to avoidable damage to the roof and envelope during a high -wind event due to the unusual roof shape and additional sharp corners where wind pressure is greater. Additionally, the potential consequences of siting a building immediately adjacent to existing large trees should be evaluated carefully. The condition and species of the existing trees should be considered. The combination of wind and rain can weaken diseased trees, causing large branches to become wind-borne debris during high -wind events. Some shallow -rooted species topple when their roots pull out of rain - saturated soils. Pine trees common to the southern United States are prone to snapping in half during high -wind events. 4.6.4 Siting of Pedestrian Access The siting of pedestrian access between a coastal building and the shoreline often gets inadequate attention when siting decisions and plans are made. Experience shows, however, that uncontrolled access can damage coastal vegetation and landforms, providing weak points upon which storm forces act. Dune blowouts and breaches of these weak points during storms often result, and buildings landward of the weak points can be subject to increased flood, wave, erosion, or overwash effects. Several options exist for controlling pedestrian (and vehicular access) to shorelines. Guidance for the planning, layout, and construction of access structures and facilities can be found in a number of publications (additional dune walkover guidance is available on the FEMA Residential Coastal Construction Web page). COASTAL CONSTRUCTION MANUAL 4-27 SITING Figure 4-25. (below) Notching the building and roofline around a tree can lead to roof and envelope damage during a high - wind event Influence ri t and Dune Restoration on Siting Decisions Beach nourishment can be a means of mitigating potential adverse effects of shore protection structures. Beach nourishment and dune restoration can also be carried out alone, as a way of replacing beach or dune sediments already lost to erosion or of providing nourishment in anticipation of future erosion (National Research Council 1995). Beach nourishment projects typically involve dredging or excavating hundreds of thousands to millions of cubic yards of sediment, and placing it along the shoreline. Beach nourishment projects are preferred over hardened erosion control structures by many States and communities, largely because the projects add sediment to the littoral system and provide recreational beach space. The longevity of a beach nourishment project depends upon several factors: project length, project volume, native beach and borrow site sediment characteristics, background erosion rate, and the incidence and severity of storms following project implementation. Thus, most projects are designed to include an initial beach nourishment phase, followed by periodic maintenance nourishment (usually at an interval of 5 to 10 years). WARNING Beach nourishment and dune restoration projects are temporary. Although they can mitigate some storm and erosion effects, their presence should not be a substitute for sound siting, design, and construction practices. 4-28 COASTAL CONSTRUCTION MANUAL SITING 4 The projects can provide protection against erosion and storm effects, but future protection is tied to a community's commitment to future maintenance efforts. Beach nourishment projects are expensive and often controversial (the controversy usually arises over environmental concerns and the use of public monies to fund the projects). That controversy is beyond the scope of this Manual, but planning and construction of these projects can take years to carry out, and economic considerations usually restrict their use to densely populated shorelines. Therefore, as a general practice, designers and owners should not rely upon future beach nourishment to compensate for poor siting decisions. As a practical matter, however, beach nourishment is the only viable option available to large, highly developed coastal communities, where both inland protection and preservation of the recreational beach are vital. Beach nourishment programs are ongoing in many of these communities and infill development and redevelopment continue landward of nourished beaches. Although nourishment programs reduce potential storm and erosion damage to inland development, they do not eliminate all damage, and sound siting, design, and construction practices must be followed. Dune restoration projects typically involve placement of hundreds to tens of thousands of cubic yards of sediment along an existing or damaged dune. The projects can be carried out in concert with beach nourishment, or alone. Smaller projects may fill in gaps or blowouts caused by pedestrian traffic or minor storms, while large projects may reconstruct entire dune systems. Dune restoration projects are often accompanied by dune revegetation efforts in which native dune grasses or ground covers are planted to stabilize the dune against windblown erosion, and to trap additional windblown sediment. WARNING Although dune vegetation serves many valuable functions, such as stabilizing existing dunes and building new dunes, it is not very resistant to coastal flood and erosion forces. The success of dune restoration and revegetation projects depends largely on the condition of the beach waterward of the dune. Property owners and designers are cautioned that the protection provided by dune restoration and revegetation projects along an eroding shoreline is short -lived —without a protective beach, high tides, high water levels, and minor storms will erode the dune and wash out most of the planted vegetation. In some instances, new buildings have been sited such that there is not sufficient space waterward to construct and maintain a viable dune. In many instances, erosion has placed existing development in the same situation. A dune restoration project waterward of such structures will not be effective and therefore, those buildings in greatest need of protection will receive the least protection. Hence, as in the case of beach nourishment, dune restoration and revegetation should not be used as a substitute for proper siting, design, and construction practices. COASTAL CONSTRUCTION MANUAL 4-29 SITING 4.8 Decision Time The final step in evaluating a lot or parcel for potential development or redevelopment is to answer two questions: 1. Can the predicted risks be reduced through siting, design, and construction? 2. Are the residual risks to the site and building/development acceptable? Unless both questions can be answered affirmatively, the property should be rejected (at least for its intended use) and other properties should be identified and evaluated. Alternatively, the intended use of the property might be modified so that it is consistent with predicted hazard effects and other constraints. Ultimately, however, reducing the long-term risks to coastal residential buildings requires comprehensive evaluation of the advantages and disadvantages of a given site based on sound siting practices as described in this chapter. 4.9 References CROSS REFERENCE Section 6.2.1 discusses reducing risk through design and construction. Chapter 6 also discussses residual risk. California Coastal Commission. 1994. Land Form Alteration Policy Guidance. FEMA (Federal Emergency Management Agency). 1994. Mitigation of Flood and Erosion Damage to Residential Buildings in CoastalAreas. FEMA 257. May. Fulton, K. 1981. A Manual for Researching Historical Coastal Erosion. California Sea Grant Publication T-CSGCP-003. Griggs, G. B. 1994. "California's Coastal Hazards." Coastal Hazards — Perception, Susceptibility and Mitigation, Special Issue No. 12. C. Finkl, ed. Prepared for the journal of Coastal Research, An International Forum for the Littoral Sciences. Keillor, J. P. 1998. Coastal Processes Manual.• How to Estimate the Conditions of Risk to Coastal Property from Extreme Lake Levels, Storms, and Erosion in the Great Lakes Basin. WISCU-H-98-003. University of Wisconsin Sea Grant Institute. Morris, M. 1997. Subdivision Design in Flood Hazard Areas. Planning Advisory Service Report Number 473. American Planning Association. National Research Council. 1995. Beach Nourishment and Protection. South Carolina Sea Grant Extension Program. 2001. Questions andAnswers on Purchasing Coastal Real Estate in South Carolina. CR-003559. May. Town of Nags Head. 1988. Hurricane and Post -Storm Mitigation and Reconstruction Plan. 4-30 COASTAL CONSTRUCTION MANUAL SITING 4 Tuttle, D. 1987. "A Small Community's Response to Catastrophic Coastal Bluff Erosion." Proceedings of the ASCE Specialty Conference, Coastal Zone '87. American Society of Civil Engineers. New York. University of Hawaii Sea Grant College Program. 2006. Natural Hazard Considerations for Purchasing Coastal Real Estate in Hawai'i: A Practical Guide of Common Questions and Answers. UNHI- SEAGRANT-BA-06-03. August. University of Wisconsin Sea Grant Program. 2004. Living on the Coast: Protecting Investments in Shore Property on the Great Lakes. COASTAL CONSTRUCTION MANUAL 4-31 i P"I stigating Regulatory - - ,uirements States and communities throughout the United States enforce regulatory requirements that determine CROSS REFERENCE where and how buildings may be sited, designed, and constructed. These requirements include those For resources that augment the guidance associated with regulatory programs established by and other information in this Manual, see the Residential Coastal Construction Federal and State statutes and locally adopted floodplain Web site (http://www.fema.gov/rebuild/ management ordinances, building codes, subdivision mat/fema55.shtm). regulations, and other land use ordinances and laws. Applicable regulatory programs include the NFIP, which is intended to reduce the loss of life and damage caused by natural hazards, and programs established to protect wetlands and other wildlife habitat, which seek to minimize degradation of the environment. In addition, States and communities enforce requirements aimed specifically at the regulation of construction along the shorelines of oceans, bays, and lakes. Federal, State, and local regulatory requirements can have a significant effect on the siting, design, construction, and cost of buildings. Therefore, designers, property owners, and builders engaged in residential construction projects in the coastal environment should conduct a thorough investigation to identify all regulations that may affect their properties and projects. COASTAL CONSTRUCTION MANUAL 5-1 INVESTIGATING REGULATORY REQUIREMENTS 5.1 Land Use Regulations State and local governments establish regulations governing the development and use of land within their jurisdictions. The goal of these land use regulations is generally to promote sound physical, social, and economic development. The regulations take many forms zoning and floodplain management ordinances, subdivision regulations, utility codes, impact fees, historic preservation requirements, and environmental regulations —and they are WARNING often incorporated into and implemented under comprehensive Designers and floodplain or master plans developed by local jurisdictions in coordination managers are cautioned with their State governments and under State statutory authority. that major natural hazard events can change shoreline With land use regulations, communities can prohibit or locations, ground elevations, restrict development in specified areas. They can also establish and site conditions. Information developed for the area before a requirements for lot size, clearing and grading, and drainage, significant event, including data as well as the siting of buildings, floodplain management, shown on FIRMs and associated construction of access roads, installation of utility lines, planting development regulations, may of vegetative cover, and other aspects of the land development provide less -than -base flood and building construction processes. Land use regulations protection after the event. Extreme care should be taken in enacted and enforced by State and local governments across the siting and designing residential country vary in content and complexity according to the needs buildings in post -disaster and concerns of individual jurisdictions; therefore, it is beyond situations. the scope of this Manual to list or describe specific regulations. However, such regulations can have a significant effect on the construction and improvement of residential and other types of buildings in both coastal and non -coastal areas. Therefore, designers, builders, and property owners must be aware of the regulations that apply to their projects. The best sources of information about land use regulations are State and local planning, land management, economic development, building code, floodplain management, and community affairs officials. Professional organizations such as the American Planning Association (APA) and its State chapters are also excellent sources of information. Community officials may be interested in several APA projects and guidance publications (described on the APA Web site at http://www.planning.org): Subdivision Design in Flood Hazard Areas (Morris 1997), APA Planning Advisory Service Report Number 473. This report provides information and guidance on subdivision design appropriate for SFHAs and includes several examples of State and local subdivision requirements in coastal flood hazard areas. The report was prepared under a cooperative agreement with FEMA. Growing Smart Legislative Guidebook (APA 2002). Growing Smart is a major initiative launched by the APA in 1994 to examine statutory reform under the philosophy that there is no "one -size -fits - all" approach. The guidebook contains model planning statutes and commentary that highlight key issues in their use for State and local planning agencies. Chapter 7 of the guidebook includes a model "Natural Hazards Element" for incorporation into local government comprehensive plans. Planning for Post -Disaster Recovery and Reconstruction (Schwab et al. 1998), APA Planning Advisory Service Report Number 483/484. This report provides guidance regarding all hazards for local planners. 5-2 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS It includes a model ordinance for regulating hazard areas and includes case studies for five hazard scenarios (flood, hurricane, wildfire, earthquake, and tornado). The report includes the model "Natural Hazards Element" from the Growing Smart Legislative Guidebook that can be incorporated into local comprehensive plans. The report was prepared under a cooperative agreement with FEMA. Hazard Mitigation: Integrating Best Practices into Planning (Schwab 2010), APA Planning Advisory Service Report Number 560. This report introduces hazard mitigation as a critical area of practice for planners. It provides guidance on how to integrate hazard mitigation strategies into planning activities and shows where hazard mitigation can fit into zoning and subdivision codes. The report was prepared by APA and supported by FEMA. 5.1.1 Coastal Barrier Resource Areas and Other Protected Areas The CBRA of 1982 was enacted to protect vulnerable coastal barriers from development; minimize the loss of life; reduce expenditures of Federal revenues; and protect fish, wildlife, and other natural resources. This law established the Coastal Barrier Resources System (CBRS), which is managed by the U.S. Department of the Interior (DOI), U.S. Fish and Wildlife Service. The law restricts Federal NOTE expenditures and financial assistance that could encourage development of coastal barriers. The CBRA does not prohibit Additional information about privately financed development; however, it does prohibit most CBRS regulations and areas new Federal financial assistance, including Federally offered included in the CBRS is available at the U.S. Fish flood insurance, in areas within the CBRS (also referred to as and Wildlife Service Web CBRA areas). Flood insurance may not be sold for buildings in site at http://www.fws.gov/ the CBRS that were constructed or substantially improved after habitatconservation/coastal_ October 1, 1983. The financial risk of building in these areas is barrier.html. transferred from Federal taxpayers directly to those who choose to live in or invest in these areas. The Coastal Barrier Improvement Act (CBIA), passed in 1991, tripled the size of the CBRS to over 1.1 million acres. The CBIA also designated otherwise protected areas (OPA) that include lands that are under some form of public ownership. The CBIA prohibits the issuance of flood insurance on buildings constructed or substantially improved after November 16, 1991, for the areas added to the CBRS, including OPAs. An exception is made to allow insurance for buildings located in OPAs that are used in a manner consistent with the purpose for which the area is protected. Examples include research buildings, buildings that support the operation of a wildlife refuge, and similar buildings. CBRS boundaries are shown on a series of maps produced by DOI. OPA designations discourage development of privately owned inholdings and add a layer of Federal protection to coastal barriers already held for conservation or recreation, such as national wildlife refuges, national parks and seashores, State NOTE Any building within a CBRS area that is constructed or substantially improved after October 1, 1983, or the date of designation for areas added to the system in 1991, is not eligible for Federal flood insurance or other Federal financial assistance. The same restriction applies to substantially damaged buildings in a CBRS area that are repaired or renovated after those dates. However, all buildings within the CBRS must still comply with the NFIP siting, design, and construction requirements in their communities. COASTAL CONSTRUCTION MANUAL 5-3 INVESTIGATING REGULATORY REQUIREMENTS and county parks, and land owned by private groups for conservation or recreational purposes. The CBRS currently includes 271 OPAs, which add up to approximately 1.8 million acres of land and associated aquatic habitat. FEMA shows approximate CBRS boundaries on FIRMS so that insurance agents and underwriters may determine eligibility for flood insurance coverage. Before constructing a new building, substantially improving an existing building, or repairing a substantially damaged building, the designer or property owner should review the FIRM to determine whether the property is located near or within CBRS or OPA boundaries. In situations where the FIRM does not allow for a definitive determination, the designer or property owner should request a determination from the U.S. Fish and Wildlife Service based on the DOI maps. 5.1.2 Coastal Zone Management Regulations The CZMA of 1972 encourages adoption of coastal zone policies by U.S. coastal States in partnership with the Federal Government. CZMA regulations have been adopted by 28 of the 30 coastal States and the five island territories. For current information concerning the status of State and national CZM programs, refer to the Web site of the NOAA, National Ocean Service, Office of Ocean and Coastal Resource Management, at http://coastalmanagement.noaa.gov/programs/czm.html. Each State's CZM program contains provisions to: Protect natural resources Manage development in high hazard areas Manage development to achieve quality coastal waters Give development priority to coastal -dependent uses Establish orderly processes for the siting of major facilities Locate new commercial and industrial development in or adjacent to existing developed areas Provide public access for recreation Redevelop urban waterfronts and ports, and preserve and restore historic, cultural, and aesthetic coastal features Simplify and expedite governmental decision -making actions Coordinate State and Federal actions Give adequate consideration to the views of Federal agencies Ensure that the public and local government have a say in coastal decision -making Comprehensively plan for and manage living marine resources Coastal zone regulations vary greatly. Many States, such as Washington, Oregon, and Hawaii, provide guidelines for development while leaving the enactment of specific regulatory requirements up to county and local governments. Most State CZM regulations control construction seaward of a defined boundary line, such as a dune or road. Many States, though not all, regulate or prohibit construction seaward of a second line based on 5-4 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS erosion. Some of these lines are updated when new erosion mapping becomes available; lines that follow physical features such as dune lines are not fixed and "float" as the physical feature shifts over time. Examples of other types of State coastal regulations include requirements concerning the placement or prohibition of shore protection structures and the protection of dunes. Some States not only control new construction, but also regulate renovations and repairs of substantially damaged buildings to a greater degree than required by the NFIP. These regulations help limit future damage in coastal areas by requiring that older buildings be brought up to current standards when they are renovated or repaired. In addition to regulating the construction of buildings near the coast, many jurisdictions regulate the construction of accessory structures, roads and infrastructure, and other development -related activities. 5.2 National Flood Insurance Program The NFIP, which is administered by FEMA, is a voluntary program with the goals of reducing the loss of life and damage caused by flooding, helping victims recover from floods, and promoting an equitable distribution of costs among those who are protected by flood insurance and the general public. The NFIP operates through a partnership between the Federal Government and individual communities such as States, counties, parishes, and incorporated cities, towns, townships, boroughs, and villages. Participation in the NFIP is voluntary. Lower cost, federally backed flood insurance is made available to property owners and renters in participating communities. In return, each community adopts and enforces a floodplain management ordinance or law that meets or exceeds the minimum requirements of the NFIP for new construction, substantial improvement of existing buildings, and repairs of substantially damaged buildings. As part of administering the NFIP, FEMA conducts flood hazard studies and provides each community with FIRM and FIS reports, which together present flood hazard information, including the boundaries of the SFHA—the area subject to inundation by the flood that has a 1 percent chance of being equaled or exceeded in any given yearBFEs, and flood insurance zones. FEMA also provides State and local agencies with technical assistance and funding in support of flood hazard mitigation. Unless the community as a whole practices adequate flood hazard mitigation, the potential for loss will not be reduced significantly. Discussed below is a history of the NFIP, and some components of the NFIP that allow for community -wide mitigation: FEMA flood hazard studies, minimum regulatory requirements enforced by communities participating in the NFIP, and the NFIP CRS program. TERMINOLOGY SUBSTANTIAL IMPROVEMENT: Improvement of a building (such as reconstruction, rehabilitation, or addition) is considered a substantial improvement if its cost equals or exceeds 50 percent of the market value of the building before the start of construction of the improvement. SUBSTANTIAL DAMAGE: Damage to a building (regardless of the cause) is considered substantial damage if the cost of restoring the building to its before -damage condition would equal or exceed 50 percent of the market value of the structure before the damage occurred. COASTAL CONSTRUCTION MANUAL 5-5 INVESTIGATING REGULATORY REQUIREMENTS 5.2.1 History of the NFIP Congress created the NFIP in 1968 when it passed the National Flood Insurance Act. The primary purposes of the Act are to: Indemnify individuals for flood losses through insurance CROSS REFERENCE Reduce future flood losses through floodplain management regulations For additional information on the NFIP and its mapping products, Reduce Federal expenditures for disaster assistance and see Section 3.6. flood control FEMA is prohibited from providing flood insurance to a community under the 1968 Act if a community does not adopt and enforce floodplain management regulations that meet or exceed the floodplain management criteria established in accordance with Section 1361(c) of the 1968 Act. Subsidizing flood insurance for existing buildings was not incentive enough for communities to voluntarily participate in the NFIP. The same held true for individuals purchasing flood insurance. In 1973, Congress passed the Flood Disaster Protection Act. The 1973 Act prohibits Federal agencies from providing financial assistance for acquisition or construction of buildings in a SFHA in a community that does not participate in the NFIP. Certain disaster assistance for these non -participating communities is also prohibited. Another key provision of the 1973 Act was the "Mandatory Flood Insurance Purchase Requirement," which requires federally insured or regulated lenders to require flood insurance on all grants and loans for buildings purchased or constructed in the SFHA. To further the efforts of the NFIP, Congress amended the 1968 and 1973 Acts with the National Flood Insurance Reform Act in 1994. The 1994 Act: (1) increased the amount of flood insurance coverage allowed to be purchased, (2) codified the NFIP CRS, (3) added the Increased Cost of Compliance coverage for individual property owners who had to comply with floodplain management regulations, (4) established the Flood Mitigation Assistance grant program to assist States and communities to develop mitigation plans and implement measures to reduce future flood damage to structures, and (5) added a requirement that FEMA assess its flood hazard map inventory at least once every 5 years. Congress amended the 1994 Act with the Flood Insurance Reform Act of 2004. The 2004 Act established the Repetitive Flood Claims and Severe Repetitive Loss grant programs to reduce or eliminate future losses to properties in the NFIP. 5.2.2 FEMA Flood Hazard Studies To provide communities with the information needed to enact and enforce floodplain management ordinances or laws consistent with the requirements of the NFIP, FEMA conducts flood hazard studies for communities throughout the United States and publishes the results in FIRMS and FIS reports. The information provided by FIS reports and FIRMs includes the names and locations of flooding sources; the sizes and frequencies of past floods; the limits of the SFHA in areas subject to riverine, lacustrine, and coastal flooding; flood insurance zone CROSS REFERENCE For an explanation of how BFEs, flood zones, and LiMWAs are determined for coastal flood hazard areas and how they affect coastal construction, see Section 3.6. 5-6 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS designations; and BFE contours throughout the SFHA. FIRMS in coastal areas may also show the LiMWA. Communities can use the information provided in FIS reports and FIRMS to manage SFHA development. At the same time, FEMA uses the FIS and FIRMS to establish insurance premiums for houses and other buildings. The information pertaining to the BFE and the flood zone at the building site are of particular importance for a coastal construction project. 5.2.3 Minimum Regulatory Requirements The floodplain management ordinances or laws adopted by communities that participate in the NFIP must meet or exceed the minimum NFIP regulatory requirements set forth at Title 44 of the Code of Federal Regulations (CFR) Section 60.3 (44 CFR § 60.3). Community floodplain management regulations include requirements in the SFHA that apply WARNING to new construction, substantially improved buildings, and substantially damaged buildings in both Zone A and Zone V. Communities participating in Additional requirements apply to new subdivisions and other the NFIP are encouraged to development in the SFHA. adopt and enforce floodplain management ordinances or The minimum NFIP requirements for new construction, laws more stringent than the minimum requirements of the substantially improved, and substantially damaged buildings NFIP regulations. For example, affect the type of foundation that can be used, establishes some States and communities the required height of the lowest floor to or above the BFE, require that buildings be establishes the criteria for the installation of building utility elevated above rather than systems, requires the use of flood damage -resistant materials, and simply to the BFE. The additional elevation is referred limits the use of the area below the lowest floor. In recognition of to as freeboard (see Figure 5-4). the greater hazard posed by breaking waves 3 feet high or higher, Check with local floodplain FEMA has established minimum NFIP regulatory requirements managers and building officials for Zone V buildings that are more stringent than the minimum concerning such requirements. requirements for Zone A buildings. Therefore, the location of a building in relation to the Zone A/Zone V boundary on a FIRM can affect the design of the building. In that regard, it is important to note that if a building or other structure has any WARNING portion of its foundation in Zone V, it must be built to comply with Zone V requirements. The guidance in this Manual was not specifically developed The following sections summarize the minimum NFIP for manufactured housing. For NFIP requirements concerning requirements (for the exact wording of the regulations, refer manufactured housing, refer to to 44 CFR g 60.3): Section 5.2.3.1 describes the minimum 44 CFR Section 60.3 and FEMA requirements that apply throughout the SFHA. Sections 5.2.3.2 P-85, Protecting Manufactured and 5.2.3.3 describe requirements specific to Zone A and Homes from Flood and Other Hazards, A Multi -Hazard Zone V, respectively. Foundation and Installation Guide (FEMA 2009a). 5.2.3.1 Minimum Requirements in All SFHAs The minimum NFIP floodplain management requirements for all SFHAs affect buildings, subdivisions and other new development, new and replacement water supply systems, and new and replacement sanitary sewage systems. These requirements, set forth at 44 CFR § 60.3(a) and (b), are summarized in Table 5-1. COASTAL CONSTRUCTION MANUAL 5-7 INVESTIGATING REGULATORY REQUIREMENTS Table 5-1. General NFIP Requirements • Communities shall require permits for development in SFHAs and shall review permit applications to determine whether proposed building sites will be reasonably safe from flooding. • Buildings shall be designed (or modified) and anchored to prevent flotation, collapse, and lateral movement resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy. • Buildings shall be constructed with materials resistant to flood damage. • Buildings shall be constructed with methods and practices that minimize flood damage. • Buildings shall be constructed with electrical, heating, ventilation, plumbing, and air conditioning equipment and other service facilities that are designed and/or located to prevent water from entering or accumulating within their components during flooding. • Communities shall obtain and reasonably use any BFE and floodway data available from other sources for SFHAs for which the FIRM does not provide BFEs or floodways. • Communities shall review proposals for subdivisions and other new developments to determine whether such proposals will be consistent with the need to minimize flood damage within flood -prone area. • Proposals for new subdivisions and other new developments greater than 50 lots or 5 acres, whichever is less, and for which BFEs are not shown on the effective FIRM shall include BFE data. • Public utilities and facilities, such as sewer, gas, electrical, and water systems for new subdivisions and other new developments shall be located and constructed to minimize or eliminate flood damage. • Adequate drainage shall be provided for new subdivisions and new developments to reduce exposure to flood hazards. • New and replacement water supply systems shall be designed to minimize or eliminate infiltration of flood waters into the systems. • New and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of flood waters into the systems and discharges from the systems into flood waters. • On -site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding. Floodplain management regulations apply to new construction, substantially improved buildings, and substantially damaged buildings located within the SFHA. FEMA has two resources to assist State and local officials with NFIP requirements: FEMA P-758, Substantial Improvement/Substantial Damage (SI/SD) Desk Reference (FEMA 2010a) and the FEMA P-784 Substantial Damage Estimator (SDE) software (FEMA 2010b). FEMA P-758 is intended to be used by local officials responsible for administering local codes and ordinances, including requirements related to substantial improvement and substantial damage. It also is intended for State officials who provide NFIP technical assistance to communities. FEMA P-758 provides practical guidance and suggested procedures to implement the NFIP requirements for substantial improvement and repair of substantial damage. 5-8 COASTAL CONSTRUCTION MANUAL The SDE software was developed to assist State and local officials in determining substantial damage in accordance with a local floodplain management ordinance meeting the requirements of the NFIR Data collected during the evaluation process and entered into the SDE software provides an inventory of potentially substantially damaged buildings, including both residential and non-residential structures. For more information, consult the local floodplain management official in the area where the building is being constructed. FEMA 213, Answers to Questions About Substantially Damaged Buildings (FEMA 1991; currently being updated as of the publication of this Manual) provides answers to commonly asked questions about substantial improvement and substantial damage. INVESTIGATING REGULATORY REQUIREMENTS WARNING In addition to the floodplain management requirements discussed in this Manual, the NFIP regulations include requirements specific to floodplains along rivers and streams. Because this Manual focuses on the construction of residential buildings in coastal areas, it does not discuss these additional requirements. For more information about these requirements, consult local floodplain management officials. Also refer to FEMA 259, Engineering Principles and Practices for Retrofitting Flood -Prone Residential Structures (FEMA 2011). 5.2.3.2 Additional Minimum Requirements for Buildings in Zone A The additional minimum requirements specific to buildings in Zones AE, AI—A30, AO, and A pertain to the elevation of the lowest floor, including basement, in relation to the BFE or the depth of the base flood, and to the enclosed areas below the lowest floor. Note that these requirements are the same for Coastal A Zones and Zone A. Building Elevation in Zones AE and A1—A30 The top of the lowest floor, including the basement floor, of all new construction, substantially improved, and substantially damaged buildings must be at or above the BFE. The lowest floors of buildings in Zones AE, AI—A30, and A must be at or above the BFE. Foundation walls below the BFE must have openings that allow the entry of flood waters so that interior and exterior hydrostatic pressures can equalize. Note that some damage is likely to be sustained if building construction meets only the minimum NFIP requirements because the structure under the top of the lowest floor will be inundated during the base flood. Building Elevation in Zone A FIRMs do not show BFEs in SFHAs designated Zone A (i.e., unnumbered Zone A) because detailed flood hazard studies in those areas have not been performed. The lowest floors of buildings in Zone A must be elevated to or above the BFE whenever BFE data are available from other sources. The IBC and IRC both authorize the local official to require an applicant to use BFE data from other sources or to determine the BFE. If no BFE data are available, communities must ensure that buildings are constructed with methods and practices that minimize flood damage. COASTAL CONSTRUCTION MANUAL 5-9 INVESTIGATING REGULATORY REQUIREMENTS Building Elevation in Zone AO Zone AO designates areas where flooding is characterized by shallow depths (averaging 1-3 feet) and/or unpredictable flow paths. In Zone AO, the top of the lowest floor, including the basement floor, of all new construction, substantially improved, and substantially damaged buildings must be above the highest grade adjacent to the building by at least the depth of flooding in feet shown on the FIRM. For example, if the flood depth shown on the FIRM is 3 feet, the top of the lowest floor must be at least 3 feet above the highest grade adjacent to the building. If no depth is shown on the FIRM, the minimum required height above the highest adjacent grade is 2 feet. Enclosures Below the Lowest Floor in Zones AE, Al—A30, AO, and A Enclosed space below the lowest floors of new construction, substantially improved, and substantially damaged buildings may be used only for parking of vehicles, access to the building, or storage. The walls of such areas must have openings designed to allow the automatic entry and exit of flood waters so that interior and exterior hydrostatic pressures equalize during flood events. To satisfy this requirement, non -engineered openings may be used to provide a total net open area of 1 square inch per square foot of enclosure. Designs for engineered openings must be certified by a registered professional engineer or architect as providing the required performance (see Section 2.6.2 of ASCE 24, Flood Resistant Design and Construction). The installation of openings must meet the following ASCE 24 criteria: 1. Each enclosed area must have openings. 2. There must be a minimum of two openings on different sides of each enclosed area, and 3. The bottom of each opening must be no more than 1 foot above the higher of the final interior grade or floor and the finished exterior grade immediately under each opening. For more information about openings requirements for the walls of enclosures below the lowest floors of buildings in Zone A, refer to FEMA NFIP Technical Bulletin 1, Openings in Foundation Walls and Walls of Enclosures Below Elevated Buildings in Special Flood Hazard Areas in accordance with the National Flood Insurance Program (FEMA 2008d). 5.2.3.3 Additional Minimum Requirements for Buildings in Zone V WARNING Even waves less than 3 feet high can impose large loads on foundation walls. This Manual recommends that buildings in the Coastal A Zone be designed and constructed to meet Zone V requirements (see Section 5.4.2 and Chapter 11). WARNING Flood vents must be unobstructed in order to perform as intended. For example, flood vents backed with interior gypsum board finish do not allow for the automatic entry and exit of flood waters. The additional minimum requirements enforced by participating communities regarding new construction, substantially improved buildings, and substantially damaged buildings in Zones VE, Vl V30, and V pertain to the siting of the building, the elevation of the lowest floor in relation to the BFE, the foundation design, enclosures below the lowest floor, and alterations of sand dunes and mangrove stands (refer to 44 CFR g 60.3(e)). 5-10 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS Siting All new construction must be located landward of the reach of mean high tide (i.e., the mean high water line). In addition, manmade alterations of sand dunes or mangrove stands are prohibited if those alterations would increase potential flood damage. Removing sand or vegetation from, or otherwise altering, a sand dune or removing mangroves may increase potential flood damage; therefore, such actions must not be carried out without the prior study and approval from a local floodplain official. Building Elevation All new construction, substantially improved, and substantially damaged buildings must be elevated on pilings, posts, piers, or columns so that the bottom of the lowest horizontal structural member of the lowest floor (excluding the vertical foundation members) is at or above the BFE. In Zone V, buildings must be elevated on an open foundation (e.g., pilings, posts, piers, or columns). Foundation Design The piling or column foundations for all new construction, substantially improved, and substantially damaged buildings, as well as the buildings attached to the foundations, must be anchored to resist flotation, collapse, and lateral movement due to the effects of wind and water loads acting simultaneously on all components of the building. A registered engineer or architect must develop or review the structural design, construction specifications, and plans for construction and must certify that the design and methods of construction to be used are in accordance with accepted standards of practice for meeting the building elevation and foundation design standards described above. In addition, erosion control structures and other structures such as bulkheads, seawalls, and retaining walls may not be attached to the building or its foundation. CROSS REFERENCE For more information about enclosures, the use of space below the lowest floor, and breakaway walls, refer to Section 8.5.8, 8.5.10, 12.4, and 13.1.10 of this Manual and to the following FEMA NFIP Technical Bulletins: a Design and Construction Guidance for Breakaway Walls Below Elevated Buildings Located in Coastal High Hazard Areas in accordance with the National Flood Insurance Program, Technical Bulletin 9 (FEMA 2008a) ® Flood Damage -Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program, Technical Bulletin 2 (FEMA 2008b) a Free -of -Obstruction Requirements for Buildings Located in Coastal High Hazard Areas in accordance with the National Flood Insurance Program, Technical Bulletin 5 (FEMA 2008c) L'J NOTE For more information about the use of fill in Zone V, refer to Free -of -Obstruction Requirements for Buildings Located in Coastal High Hazard Areas in accordance with the National Flood Insurance Program, FEMA NFIP Technical Bulletin 5 (FEMA 2008c). COASTAL CONSTRUCTION MANUAL 5-11 INVESTIGATING REGULATORY REQUIREMENTS Use of Fill Fill may not be used for the structural support of any building within Zones VE, Vl V30, and V. Minor grading and the placement of minor quantities of fill is permitted for landscaping and drainage purposes under and around buildings and for support of parking slabs, pool decks, patios and walkways. Fill may be used in Zone V for minor landscaping and site drainage purposes (consult local officials for specific guidance or requirements). Space Below the BFE The space below all new construction, substantially improved, and substantially damaged buildings must either be free of obstructions or enclosed only by non -supporting breakaway walls, open wood latticework, or insect screening intended to collapse under water loads without causing collapse, displacement, or other structural damage to the elevated portion of the building or the supporting foundation system. Furthermore, NFIP requirements specify permitted uses below the BFE, use of flood damage -resistant materials below 5-12 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS COASTAL CONSTRUCTION MANUAL 5-13 INVESTIGATING REGULATORY REQUIREMENTS the BFE (see NFIP Technical Bulletin 2, FEMA 2008b), and placement of mechanical/utility equipment below the BFE. WARNING Compliance with these requirements for the space below the BFE will minimize flood damage. This has been confirmed Although the NFIP regulations permit below-BFE enclosures by post -damage assessments of buildings following disaster that meet the criteria presented events. Failure to comply with these requirements violates the here, many communities may local floodplain management ordinance and NFIP regulations, have adopted ordinances that and can lead to higher flood insurance premiums and prohibit all such enclosures or uninsured losses. that establish more stringent criteria, such as an enclosure size limitation. Check with The current NFIP regulatory requirements regarding breakaway local officials about such walls are set forth at 44 CFR § 60.3(e)(5). The regulations specify requirements. a design safe loading resistance for breakaway walls of not less than 10 pounds per square foot and not more than 20 pounds per square foot. However, the regulations also provide guidance for the use of alternative designs that do not meet the specified loading requirements. In general, breakaway walls built according to such designs are permitted if a registered engineer or architect certifies that the walls will collapse under a water load less than that of the base flood and that the elevated portion of the building and supporting foundation system will not be subject to collapse, displacement, or other structural damage due to the simultaneous effects of wind and water loads on all components of the building. Additional requirements apply to the use of an enclosed area below the lowest floor —it may be used only for parking, building access, or storage and it must be constructed of flood damage -resistant materials. The current NFIP regulations do not provide specifications or other detailed guidance for the design and construction of alternative types of breakaway walls. However, the results of research conducted for FEMA and the National Science Foundation by North Carolina State University and Oregon State University, including full-scale tests of breakaway wall panels, provide the basis for prescriptive criteria for the design and construction of breakaway wall panels that do not meet the requirement for a loading resistance of 10 to 20 pounds per square foot. These criteria are presented in the NFIP Technical Bulletin 9 (FEMA 2008a). The criteria address breakaway wall construction materials, including wood framing, light -gauge steel framing, and masonry; attachment of the walls to floors and foundation members; utility lines; wall coverings such as interior and exterior sheathing, siding, and stucco; and other design and construction issues. In addition, the bulletin describes the results of the testing. The test results are described in greater detail in Behavior of Breakaway Walls Subjected to Wave Forces: Analytical and Experimental Studies (Tung et al. 1999). 5.2.4 Community Rating System Although a participating community's floodplain management ordinance or law must, at a minimum, meet the requirements of the NFIP regulations, FEMA encourages communities to establish additional or more stringent requirements as they see fit. In 1990, to provide incentives for communities to adopt more stringent requirements, FEMA established the NFIP CRS, a program through which FEMA encourages and recognizes community floodplain management activities that exceed the minimum NFIP requirements. Under the CRS, flood insurance premiums within participating communities are adjusted to reflect the reduced flood risk resulting from community activities that meet the three goals of the CRS: (1) reducing flood losses, (2) facilitating accurate insurance ratings, and (3) promoting awareness of the importance of flood insurance. 5-14 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS Through the CRS, a community is awarded credit points for carrying out floodplain management activities in the areas of public information, mapping and regulations, flood damage reduction, and flood preparedness. The number of points awarded determines the community's CRS class (from 1 to 10), which, in turn, determines the community's discount in flood insurance premiums for structures within and outside the SFHA. Participation in the CRS is voluntary; any community compliant with the rules and regulations of the NFIP may apply for a CRS classification. In addition to helping communities obtain insurance premium discounts, the CRS promotes floodplain management activities that help save lives, reduce property damage, and promote sustainable, more livable communities. 5.3 Building Codes and Standards Many States and communities regulate the construction of buildings by adopting and enforcing building codes. Building codes set forth minimum requirements for structural design, materials, fire safety, exits, natural hazard mitigation, sanitary facilities, light and ventilation, environmental control, fire protection, and energy conservation. The purpose of a code is to establish the minimum acceptable requirements necessary for protecting the public health, safety, and welfare in the built environment. Building codes apply primarily to new construction, but may also apply to existing buildings that are being repaired, altered, or added to and when a building is undergoing a change of occupancy as defined by the code. Numerous standards related to design and construction practices and construction materials are incorporated into a building code by reference rather than by inclusion of all of the text of the standard in the code. For example, ASCE 7 is a reference standard for both the IBC and IRC, where applicable provisions of ASCE 7 are enacted by reference, in lieu of directly incorporating text of ASCE 7 into the IBC and IRC. Most locally adopted building codes in the United States are based on model building codes. Examples of model building codes are the series of codes promulgated by the International Code Council (ICC) including: International Building Code (IBC), (ICC 2012a) International Residential Code for One- and Two -Family Dwellings (IRC), (ICC 2012b) NOTE As of May 1, 2010, 1,138 communities throughout the United States were receiving flood insurance premium discounts through the CRS as a result of implementing local mitigation, outreach, and educational activities that exceed the minimum NFIP requirements. For more information about the CRS, contact the State NFIP Coordinating Agency or the appropriate FEMA Regional Office (listed on the FEMA Residential Coastal Construction Web page). NOTE The adoption and enforcement of building codes and standards is not consistent across the United States. Codes and standards in some States and communities may be more restrictive than those in others. In addition, some communities have not adopted a building code. In communities where building codes have not been adopted or where the existing codes are not applied to one- and two-family residential buildings, design professionals, contractors, and others engaged in the design and construction of coastal residential buildings are encouraged to follow the requirements of a model building code and the best practices presented in this Manual. COASTAL CONSTRUCTION MANUAL 5-15 INVESTIGATING REGULATORY REQUIREMENTS International Existing Building Code (IEBC) (ICC 2012c) #J International Mechanical Code (IMC) (2012d) International Plumbing Code (IPC) (2012e) International Private Sewage Disposal Code (IPSDC) (2012f) International Fuel Gas Code (IFGC) (2012g) International Fire Code (IFC) (2012h) Provisions of the IBC and IRC are the model building codes of most interest for this Manual because they address primary requirements for design and construction of coastal residential buildings and because of their wide -spread use in the United States. The National Fire Protection Association's NFPA 5000 (NFPA 2012), Building Construction and Safety Code, is used by some jurisdictions instead of the IBC and IRC. While model codes are widely used, States and local jurisdictions often incorporate amendments and revisions to meet specific needs. Variations in code provisions from one State or jurisdiction to the next, coupled with potential code revisions, make it imperative that the designer work with local officials to identify applicable codes, standards, and construction requirements. NOTE When the 2000 I -Codes were first published, many components of the NFIP were not included. After freeboard requirements were added to the 2006 I -Codes, NFIP requirements were represented in the minimum requirements of building codes. By referencing ASCE 24, the I -Codes include some requirements more restrictive than the NFIP. U NOTE Provisions of the IBC, IRC, IMC, IPC, IPSDC, IFGC, IFC and NFPA 5000 are consistent with applicable provisions of NFIP regulations. Even in cases where amendments are minimal and where the commonly used model codes are adopted, questions often arise regarding the applicability of IBC and IRC code provisions to the design of residential buildings. As stated in the scoping language of the 2009 IBC (ICC 2009a): Detached one- and two-family dwellings and multiple single-family dwellings (townhouses) not more than three stories above grade plane in height with a separate means of egress and their accessory structures shall comply with the International Residential Code. Therefore, primary guidance for regulatory requirements for the design and construction of buildings of interest in this Manual (e.g., one -and two-family detached dwellings) are based on the requirements specified in the IRC. Generally, construction of residential buildings under the IRC need not involve a registered design professional, unless required by State law for the jurisdiction where the building is constructed. However, the building designer should be aware that engineered design is broadly permitted in the IRC and applicable even for a building structure with requirements contained entirely within the IRC, as stated in Section R301.1.3 (ICC 2009b): Engineered design in accordance with the International Building Code is permitted for all buildings and structures, and parts thereof, included in the scope of this code. 5-16 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS In certain cases and most coastal areas, however, the IRC requires structural elements to be "designed in accordance with accepted engineering practice." For example, engineered design of structural elements which fall outside the scope of requirements in the IRC such as building systems of excessive weight, elements of excessive length or height, or products not specifically addressed in the IRC is required. IRC Section R322.3.6 requires that construction documents be prepared and sealed by a registered design professional, and include documentation that the design and methods of construction to be used meet the applicable criteria of the IRC. Buildings in regions of high wind, seismic, snow, and flood hazards as well as building elements outside of the range of limitations in the IRC require design beyond the IRC prescriptive provisions as follows: Wind. Buildings located where the basic wind speed equals or exceeds I10 miles per hour or where the IRC indicates special design for wind is required (wind speed triggers for the hurricane -prone region are based on mapped wind speeds in the 2012 IRC). Seismic. Buildings located in Seismic Design Category E. �J NOTE The 2012 IRC replaces the previous basic wind speed map, Figure R301.2(4), with three new figures. ® Figure R301.2(4)A presents a new map of basic wind speeds based on the ASCE 7-10 wind map data but converted to allowable -stress design (ASD) levels. ® Figure R301.2(4)B provides shaded regions that indicate where wind speeds equal or exceed the scope of the IRC and use of recognized standards for wind design is required. ® Figure R301.2(4)C indicates where the openings of buildings must be protected from wind- borne debris in accordance with ASTM E1996. Wind speed maps and triggers in the 2012 IRC are on an ASD basis, while wind speed maps and triggers in ASCE 7-10 are on a strength basis. Snow. Buildings in regions with ground snow loads greater than 70 pounds per square foot. Flood. Buildings and structures constructed in whole or in part in coastal high hazard areas (including Zone V). In addition to provisions of the IBC, applicable standards specifically recognized as accepted engineering practice for wind design within the IRC are: American Forest and Paper Association (AF&PA), Wood Frame Construction Manual for One- and Two -Family Dwellings (AF&PA 2012); ICC 600, Standard for Residential Construction in High -Wind Regions (ICC 2008a); ASCE 7-10, Minimum Design Loads for Buildings and Other Structures (ASCE 2010); and American Iron and Steel Institute (AISI), Standard for Cold -Formed Steel Framing —Prescriptive Method For One- and Two -Family Dwellings with Supplement (AISI 2007). For flood, ASCE 24-05, Flood Resistant Design and Construction (ASCE 2005), is specifically recognized within the IRC as an alternative to the flood design provisions of the IRC. Engineered design requirements within both the IRC and IBC recognize ASCE 7 as the standard reference for minimum design loads due to hazards such as wind, flood, and seismic. As a result, within this Manual, provisions of ASCE 7 are used extensively for determination of minimum loads in accordance with engineered design requirements of the codes. For many portions of the Pacific, Great Lakes, and New England coasts, construction will generally fall within the prescriptive limits of the 2012 IRC and not require engineered design. COASTAL CONSTRUCTION MANUAL 5-17 INVESTIGATING REGULATORY REQUIREMENTS 5.4 Best Practices for Exceeding Minimum NAP Regulatory Requirements This section presents best practices for exceeding NFIP minimum requirements. These best practices address the significant hazards present in Coastal A Zone and Zone V and are aimed at increasing the ability of coastal residential buildings to withstand natural hazard events. Refer to Section 5.2 for the minimum requirements of the NFIP regulations concerning buildings in Zone A and Zone V. Table 5-2 in Section 5.4.3 summarizes the NFIP requirements and the best practices of this Manual regarding buildings in Zone A, Coastal A Zone, and Zone V. 5.4.1 Zone A This Manual includes discussion of best practices for the design and construction of buildings in areas subject to coastal flooding, but focuses on Zone V and the Coastal A Zone (the portion of Zone A seaward of the LiMWA). However, development in the portion of Zone A landward of the LiMWA can benefit from many of the Zone V and Coastal A Zone design and construction practices included in this Manual. Designers seeking guidance regarding good practice for the design and construction of such buildings should consult local floodplain management, building, or code officials. Additional guidance can be found in FEMA 259, Engineering Principles and Practices for Retrofitting Flood -Prone Residential Structures (FEMA 2011); the IBC (ICC 2012a) and IRC (ICC 2012b); and the FEMA NFIP Technical Bulletins (available at http://www. This Manual recommends the provisions of ASCE 24 as best practices. These include, but are not limited to, the addition of freeboard in elevation requirements in Zone A (Figure 5-1). 5.4.2 Coastal A Zone and Zone V As explained in Chapters 1 and 3 of this Manual, the NFIP regulations do not differentiate between the Coastal A Zone and the portion of Zone A that is landward of the LiMWA. Because Coastal A Zones may be subject to the types of hazards present in Zone V, such as wave effects, velocity flows, erosion, scour, and high winds, this Manual recommends that buildings in Coastal A Zones meet the NFIP regulatory requirements for Zone V buildings (i.e., the performance requirements concerning resistance to flotation, collapse, and lateral movement and the prescriptive requirements concerning elevation, foundation type, engineering certification of design and construction, enclosures below the lowest floor, and use of structural fill —see Section 5.2.3.3). To provide a greater level of protection against the hazards in Coastal A Zone and Zone V, this Manual recommends the following as good practice for the siting, design, and construction of buildings in those zones: The building should be located landward of both the long-term erosion setback and the limit of base flood storm erosion, rather than simply landward of the reach of mean high tide. The bottom of the lowest horizontal structural member should be elevated above, rather than to, the BFE (i.e., provide freeboard —see Figure 5-2[b]). 5-18 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS Figure 5-1. Recommended elevation for buildings in Zone A compared to minimum requirements COASTAL CONSTRUCTION MANUAL 5-19 INVESTIGATING REGULATORY REQUIREMENTS Figure 5-2. 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E0Q)0) §/� § \ 0 r— (1) 1 ^ w u—§ ALL E(9z; c /« F g F @ w a </ zo m G z2 2 \ k cmLL« . .cn I < L « " v v 0 �LL z m 2 LL JLr g? \ 27 cz =t7 §� ` E\ Cƒ\\ 00 C) §= .\///a2@= __ _ c0)0 >=-0 ©c==o>== ?® E-coo 0 2 e E=o—ten=moo cc o#=°a=%®% wuo\\\g«=> �\32z> COASTAL CONSTRUCTION MANUAL 5-31 INVESTIGATING REGULATORY REQUIREMENTS Table 5-2 Notes: (a) Individual States and communities may enforce more stringent requirements that supersede those summarized here. Exceeding minimum NFIP requirements will provide increased flood protection and may result in lower flood insurance premiums. (b) The references in this section cite the latest available publications at the time of publication of this Manual. The specific editions of these references are: • ASCE 7: ASCE 7-10, Minimum Design Loads for Buildings and Other Structures • ASCE 24: ASCE 24-05, Flood Resistant Design and Construction • IBC: 2012 International Building Code. Appendix G includes provisions for flood -resistant construction. The provisions in IBC Appendix G are not mandatory unless specifically referenced in the adopting ordinance. Many States have not adopted Appendix G. Section references are the same as 2009 IBC. • ICC 700: National Green Building Standard (ICC 2008b) • IRC: 2012 International Residential Code for One- and Two -Family Dwellings. Section references are the same as 2009 IRC. • FEMA P-55: Specific sections or chapters of this Manual; FEMA P-55, Coastal Construction Manual (2011) • FEMA P-348: 1999 Edition of FEMA P-348, Protecting Building Utilities from Flood Damage • FEMA P-499: Specific fact sheets in the 2010 edition of FEMA P-499, Home Builder's Guide to Coastal Construction Technical Fact Sheet Series • FEMA P-550: FEMA P-550, Recommended Residential Construction for Coastal Areas (Second Edition, 2009) • FEMA P-798: Natural Hazards and Sustainability for Residential Buildings (2010) • FEMA TB: Specific numbered FEMA NFIP Technical Bulletins (available at http., � k,,- t, ,-�i.g. )la ll"pI shtm) • NFIP: U.S. Code of Federal Regulations - 44 CFR § 60.3 "Flood plain management criteria for flood -prone areas." Current as of June 30, 2011. • NFIP Evaluation Study: Evaluation of the National Flood Insurance Program's Building Standards (American Institutes for Research 2006) • NFIP FMB 467-1: Floodplain Management Bulletin on the NFIP Elevation Certificate. Note that this bulletin was published in 2004, while the Elevation Certificate (FEMA Form 81-31) has been updated since 2004, and is updated periodically. (c) State or community may regulate to a higher elevation (DFE). (d) LHSM = Lowest horizontal structural member. (e) Some coastal communities require open foundations in Zone A. (f) There are some differences between what is permitted under floodplain management regulations and what is covered by NFIP flood insurance. Building designers should be guided by floodplain management requirements, not by flood insurance policy provisions. (g) Some coastal communities prohibit breakaway walls and allow only open lattice or screening. (h) Placement of nonstructural fill adjacent to buildings in Zone AO in coastal areas is not recommended. (i) Some communities may allow encroachments to cause a 1-foot rise in the flood elevation, while others may allow no rise. 5-32 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS 5.5 References AF&PA (American Forest & Paper Association). 2012. Wood Frame Construction Manual for One- and Two -Family Dwellings. WFCM-12. AISI (American Iron and Steel Institute). 2007. Standard for Cold -Formed Steel Framing - Prescriptive Method for One- and Two -Family Dwellings with Supplement. (AISI S230-07w/S2-08). American Institutes for Research. 2006. Evaluation of the National Flood Insurance Program's Building Standards. October. APA (American Planning Association). 2002. Growing Smart Legislative Guidebook, Model Statutes for Planning and the Management of Change. January. ASCE (American Society of Civil Engineers). 2005. Flood Resistant Design and Construction. ASCE Standard ASCE 24-05. ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. ASTM (ASTM International). 1996. Standard Specification for Performance ofExterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes. ASTM E1996. FEMA (Federal Emergency Management Agency). 1991. Answers to Questions About Substantially Damaged Buildings. National Flood Insurance Program Community Assistance Series. FEMA 213. May. FEMA. 1996. Corrosion Protection for Metal Connectors in Coastal Areas for Structures Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program. Technical Bulletin 8-96. FEMA. 1999. Protecting Building Utilities from Flood Damage. FEMA P-348. FEMA. 2004. Floodplain Management Bulletin on the Elevation Certificate. NFIP Bulletin 467-1. May. FEMA. 2008a. Design and Construction Guidance for Breakaway Walls Below Elevated Buildings Located in Coastal High Hazard Areas. NFIP Technical Bulletin 9. FEMA. 2008b. Flood Damage -Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas. NFIP Technical Bulletin 2. FEMA. 2008c. Free -of -Obstruction Requirements for Buildings Located in Coastal High Hazard Areas. NFIP Technical Bulletin 5. FEMA. 2008d. Openings in Foundation Walls and Walls of Enclosures Below Elevated Buildings in Special Flood Hazard Areas. NFIP Technical Bulletin 1. FEMA. 2009a. Protecting Manufactured Homes from Floods and Other Hazards, A Multi -Hazard Foundation and Installation Guide. FEMA P-85. November. COASTAL CONSTRUCTION MANUAL 5-33 INVESTIGATING REGULATORY REQUIREMENTS FEMA. 2009b. Recommended Residential Construction for Coastal Areas: Building on Strong and Safe Foundations. FEMA P-550. December. FEMA. 2010a. Substantiallmprovement/Substantial Damage Desk Reference. FEMA P-758. May. FEMA. 2010b. The FEMA Substantial Damage Estimator (SDE). FEMA P-784. June. FEMA. 2010c. Home Builder's Guide to Coastal Construction Technical Fact Sheet Series. FEMA P-499. December. FEMA. 2010d. Natural Hazards and Sustainability for Residential Buildings. FEMA P-798. September. FEMA. 2011. Engineering Principles and Practices for Retrofitting Flood -Prone Residential Structures. FEMA P-259,Third Edition. ICC (International Code Council). 2008a. Standard for Residential Construction in High -Wind Regions, ICC 600. Birmingham, AL. ICC. 2008b. National Green Building Standard, ICC 700. Birmingham, AL. ICC. 2009a. International Building Code. Birmingham, AL. ICC. 2009b. International Residential Code for One- and Two -Family Dwellings. Birmingham, AL. ICC. 2012a. International Building Code. Birmingham, AL. ICC. 2012b. International Residential Code for One- and Two -Family Dwellings. Birmingham, AL. ICC. 2012c. International Existing Building Code. Birmingham, AL. ICC. 2012d. International Mechanical Code. Birmingham, AL. ICC. 2012e. International Plumbing Code. Birmingham, AL. ICC. 2012£ International Private Sewage Disposal Code. Birmingham, AL. ICC. 2012g. International Fuel Gas Code. Birmingham, AL. ICC. 2012h. International Fire Code. Birmingham, AL. Morris, M. 1997. Subdivision Design in Flood Hazard Areas. Planning Advisory Service Report Number 473. American Planning Association. NFPA (National Fire Protection Association). 2012. Building Construction and Safety Code. NFPA 5000. Schwab, J.; K C. Topping; C. C. Eadie; R. E. Deyle; R. A. Smith. 1998. Planning for Post -Disaster Recovery and Reconstruction. Planning Advisory Service Report Number 483/484. American Planning Association. Schwab, J. 2010. Hazard Mitigation: Integrating Best Practices into Planning. APA Planning Advisory Service Report Number 560. 5-34 COASTAL CONSTRUCTION MANUAL INVESTIGATING REGULATORY REQUIREMENTS Tung, C. C.; B. Kasal; S. M. Rogers, Jr.; S. C. Yeh. 1999. Behavior of Breakaway Walls Subjected to Wave Forces: Analytical and Experimental Studies. UNC-SG-99-03. North Carolina Sea Grant, North Carolina State University. Raleigh, NC. Code of Federal Regulations "Flood plain management criteria for flood -prone areas." 44 CFR § 60.3. June 30, 2011. COASTAL CONSTRUCTION MANUAL 5-35 i P"I 000000 IF)d4almentals of Risk Analysis and Risk Reduction A successful building design incorporates elements of risk assessment, risk reduction, and risk management. Building success as defined in Chapter 1 can be met through various CROSS REFERENCE methods, but they all have one thing in common: careful consideration of natural hazards and use of siting, design, For resources that augment the construction, and maintenance practices to reduce damage guidance and other information in this Manual, see the Residential to the building. Designing in areas subject to coastal hazards Coastal Construction Web site requires an increased standard of care. Designers must also be (http://www.fema.gov/rebuild/ knowledgeable about loading requirements in coastal hazard mat/fema55.shtm). areas and appropriate ways to handle those loads. Failure to address even one of these concerns can lead to building damage, destruction, or loss of use. Designers should remember that the lack of building damage during a high -probability (low -intensity) wind, flood, or other event cannot be construed as a building success success can only be measured against a design event or a series of lesser events with the cumulative effect of a design event. A critical component of successful building construction in coastal environments is accurately assessing the risk from natural hazards and then reducing that risk as much as possible. Accurate risk assessment and risk reduction are directly tied to correctly identifying natural hazards relevant to the building site. Before beginning the design process, it is important to understand and identify the natural hazard risks associated with a particular site, determine the desired level of protection from those hazards, and determine how best to manage residual risk. Design professionals must communicate these concepts to building owners so COASTAL CONSTRUCTION MANUAL 6-1 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION they can determine if the level of residual risk is acceptable or whether it would be cost -beneficial to further increase the hazard resistance of the building, and thereby reduce the residual risk. Once the desired level of protection and the residual risk have been evaluated by the designer and the owner, the information in Volume II can be used to incorporate appropriate forces and loads into a successful hazard -resistant design. 6.1 Assessing Risk 1� TERMINOLOGY RISK: Potential losses associated with a hazard, defined in terms of expected probability and frequency, exposure, and consequences. RESIDUAL RISK: The level of risk that is not offset by hazard - resistant design or insurance, and that must be accepted by the property owner. A hazard -resistant building design begins with a proper risk assessment. Building success can only be achieved by successfully identifying and managing natural hazard risks. Designing a successful building requires an understanding of the magnitude of the hazards and how frequently the building may be subjected to these hazards. This information is used to assess the potential exposure of the building to these hazards, i.e., the risk to the building. For the purposes of this Manual, risk assessment is the process of quantifying the total risk to a coastal building from all significant natural hazards that may impact the building. Designers should be well informed with current hazard and risk information and understand how risk affects their design decisions and the requirements of the client. Designers should: Obtain the most up-to-date published hazard data to assess the vulnerability of a site, following the steps outlined in Section 4.3. Conduct or update a detailed risk assessment if there is reason to believe that physical site conditions have changed significantly since the hazard data were published or published hazard data is not representative of a site. Review or revise an existing risk assessment if there is reason to believe that physical site conditions will change significantly over the expected life of a structure or development of the site (see Section 3.7). After a risk assessment is completed, the designer should review siting and design options that will mitigate the effects of the identified hazards. The building owner may not find the amount of damage or loss of function acceptable, and the designer should work with the building owner to mitigate the risk to an acceptable level. 6.1.1 Identifying Hazards for Design Criteria Coastal areas are subject to many hazards, including distinct events such as hurricanes, coastal storms, earthquakes, and earthquake -induced landslides and tsunamis. Coastal hazards also include continuous, less obvious coastal phenomena, such as long-term erosion, shoreline migration, and the corrosion and decay of building materials. The effects of hazards associated with distinct events are often immediate, severe, CROSS REFERENCE Chapter 7 presents an introduction to Volume II and a summary of the insurance and financial implications of design decisions. 6-2 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION and easily visible, while those associated with slow -onset, long-term processes are more likely to become apparent only over time. Manmade structures such as bulkheads, dams, dikes, groins, jetties, levees, and seawalls may also be present in coastal areas and the effects of these structures on nearby buildings must be considered. CROSS REFERENCE For information on identifying coastal hazards, refer to Chapter 3. For siting considerations, refer to Chapter 4. The designer must determine which specific hazards will For discussion of codes and affect a particular site and the vulnerability of the site to standards, refer to Chapter 5. the identified natural hazards. Not all sites have the same hurricane exposure, erosion exposure, or seismic risk. The exposure of the building to these natural hazards should be evaluated and incorporated into the design criteria. The designer must first focus on code compliance. By following code provisions and NFIP regulations for flood, wind, and seismic design, the immediately understood and quantified hazards are mitigated to a certain degree. To fully understand the risk at a particular site, the designer should then study the risk associated with an above -design -level event. Finally, the designer should consider mitigation solutions to long-term issues such as erosion, subsidence, and sea level rise. The designer should also address the possibility of unlikely events such as a levee failure (when appropriate). While such events may seem very unlikely or improbable to the owner, it is important that designers review flood maps, flood studies, and historical events to understand the risks to the building and how to best manage them. Additionally, cumulative effects of multiple hazards should be considered. For example, hurricane -induced wind and flooding impacts may be exacerbated by sea level rise or subsidence. Designing buildings to resist these forces may present numerous challenges and therefore, these issues should be carefully evaluated. 6.1.2 Probability of Hazard Occurrence and Potential Consequences Understanding the probabilities and the consequences of building damage or failure will help designers determine the level of natural hazard resistance they seek in the building design and better quantify the risk. Flood, wind, and seismic events have been studied and modeled with varying degrees of accuracy for centuries. Careful study of each of these hazards has resulted in a notable historical record of both the frequency and intensity of those events. The historic frequency of events with different intensities allows mathematical analysis of the events and the development of probabilities of future events. The probability of future events occurring can be used to predict the potential consequences of building design choices. For instance, understanding the probability that a site will experience a specific wind speed allows a designer to carefully design the building for that wind speed and understand the wind risk to that building. The designer can also consult with the owner on the level of wind protection incorporated into the building design and help them determine how to manage the residual risk. Residual risk will be present because storm events that result in greater -than -design wind speeds can occur. Based on the owner's level of acceptance to risk, the owner may then decide to seek a higher level of building performance or purchase insurance to reduce the residual risk. Designers must determine the probability of occurrence of each type of hazard event over the life of the structure and evaluate how often it might occur. The frequency of the occurrence of a natural hazard is COASTAL CONSTRUCTION MANUAL 6-3 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION referred to in most design codes and standards as the recurrence interval. The probability of the occurrence of severe events should be evaluated over the life of the structure, and the consequences of their occurrence should be addressed in the design. While more frequent and less severe events may not have the same drastic consequences as less frequent but more severe events, they should still be identified and assessed in the risk assessment. In contrast, some events may be so severe and infrequent that it is likely not cost-effective to design the building to withstand them. In most coastal areas of the United States, buildings must meet minimum regulatory and code requirements intended to provide protection from natural hazard events of specified magnitudes. These events are usually identified according to their recurrence intervals. For instance, the base flood used by the NFIP is associated with a recurrence interval of 100 years, the basic wind speed for Risk Category 11 structures in ASCE 7-10 is associated with a recurrence interval of 700 years, and the return interval for earthquake design is 2,500 years. After identifying the recurrence interval of a natural hazard event or design event (through codes, standards, or other design criteria) the designer can determine the probability of one or more occurrences of that event or a larger event during a specified period, such as the expected lifespan of the building. Table 6-1 illustrates the probability of occurrence for natural hazard events with recurrence intervals of 10, 25, 50, 100, 500, and 700 years. Of particular interest in this example is the event with a 100-year recurrence interval because it serves as the basis for the floodplain management and insurance requirements of the NFIP regulations, and floodplain regulations enforced by local governments. The event with a 100-year recurrence interval WARNING has a 1 percent probability of being equaled or exceeded over Designers of structures along the course of 1 year (referred to as the 1-percent-annual-chance Great Lakes shorelines, if they are flood event). As the period increases, so does the probability using Table 6-1 to evaluate flood that an event of this magnitude or greater will occur. For probabilities, should be aware example, if a house is built to the 1-percent-annual-chance that the table may underestimate actual probabilities during flood level (often referred to as the 100-year flood level), the periods of high lake levels. For house has a 26 percent chance of being flooded during a 30- example, Potter (1992) calculated year period, equivalent to the length of a standard mortgage that during rising lake levels in (refer to the bolded cells in Table 6-1). Over a 70-year period, 1985, Lake Erie had a 10 percent which may be assumed to be the useful life of many buildings, probability of experiencing a 100-year flood event in the next the home has a 51 percent chance of being flooded (refer to the 12 months (versus 1 percent as bolded cells in Table 6-1). The same principle applies to other shown in Table 6-1). natural hazard events with other recurrence intervals. 6-4 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION Table 6-1. Probability of Natural Hazard Event Occurrence for Various Periods of Time The percentages shown represent the probabilities of one or more occurrences of an event of a given magnitude or larger within the specified period. The formula for determining these probabilities is Pn = 1-(1-Pa)n, where Pa = the annual probability and n = the length of the period. The bold blue text in the table reflects the numbers used in the example in this section. 6.2 Reducing Risk Once the risk has been assessed, the next step is to decide how to best mitigate the identified hazards. The probability of a hazard event occurrence is used to evaluate risk reduction strategies and determine the level of performance to incorporate into the design. The chance of severe flooding, high -wind events, or a severe earthquake can dramatically affect the design methodology, placement of the building on the site, and materials selected. Additionally, the risk assessment and risk reduction strategy must account for the short- and long-term effects of each hazard, including the potential for cumulative effects and the combination of effects from different hazards. Overlooking a hazard or underestimating its long-term effects can have disastrous consequences for the building and its owner. WARNING Meeting minimum regulatory and code requirements for the siting, design, and construction of a building does not guarantee that the building will be safe from all hazard effects. Risk to the building still exists. It is up to the designer and building owner to determine the amount of acceptable risk to the building. Although designers have no control over the hazard forces, the siting, design, construction, and maintenance of the building are largely within the control of the designer and owner. The consequences of inadequately addressing these design items are the impetus behind the development of this Manual. Risk reduction is comprised of two aspects: physical risk reduction and risk management through insurance. Eliminating all risk is impossible. Risk reduction, therefore, also includes determining the acceptable level of residual risk. Managing risk, including identifying acceptable levels of residual risk, underlies the entire coastal construction process. The initial, unmitigated risk is reduced through a combination COASTAL CONSTRUCTION MANUAL 6-5 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION of floodplain ordinances, building codes, best practices construction, and insurance. Each risk reduction element decreases the residual risk; the more elements that are applied, the smaller the remaining residual risk. Figure 6-1 shows the general level of risk reduction after each risk reduction element is applied. Figure 6-1. Initial risk is reduced to residual risk through physical and financial risk reduction elements 6-6 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION Design decisions including elevation, placement and orientation of the building on the site, size and shape of the building, and the materials and methods used in its construction all affect a building's vulnerability to natural hazard events. However, these decisions can also affect initial and long-term costs (see Section 7-5), aesthetic qualities (e.g., the appearance of the finished building, views from within), and convenience for the homeowner (e.g., accessibility). The tradeoffs among these factors involve objective and subjective considerations that are often difficult to quantify and likely to be assessed differently by developers, builders, homeowners, and community officials. The cost of siting and design decisions must be balanced with the amount of protection from natural hazards provided. 6.2.1.1 Factors of Safety and Designing for Events that Exceed Design Minimums Codes and standards require minimum levels of protection from natural hazards, including a minimum factor of safety. Factors of safety are designed to account for unknowns in the prediction of natural hazards and variability in the construction process and construction materials. Since the designer may have limited control over these factors it is important that they not only embrace the minimum factors of safety, but determine whether a higher factor of safety should be incorporated into the design to improve the hazard resistance of buildings. Such decisions can often result in other benefits besides increased risk reduction such as potential reduced insurance premiums and improved energy efficiency (see Chapter 7). The designer should also evaluate what the consequences would be to the building if the minimum design conditions were exceeded by a natural hazard event. When beginning the design process, it is important to determine the building's risk category as defined in ASCE 7-10 and the 2012 IBC. A building's risk category is based on the risk to human life, health, and welfare associated with potential damage or failure of the building. The factors of safety incorporated into the design criteria increase as the risk category increases. These risk categories dictate which design event is used when calculating performance expectations of the building, specifically the loads the building is expected to resist. The risk categories from ASCE 7-10 are summarized as: Category I. Buildings and structures that are normally unoccupied, such as barns and storage sheds, and would likely result in minimal risk to the public in the event of failure. NOTE ASCE 7-10 and the 2012 IBC introduced the term risk categories. Risk categories are called "occupancy categories" in previous editions. The broad categories in ASCE 7-10 are intended to represent the specific listings in the 2012 IBC. The descriptions provided in this Manual are broad, and both ASCE 7-10 and the 2012 IBC should be consulted to determine risk category. Category II. All buildings and structures that are not classified by the other categories. This includes a majority of residential, commercial, and industrial buildings. Category III. Buildings and structures that house a large number of people in one place, and buildings with occupants having limited ability to escape in the event of failure. Such buildings include theaters, elementary schools, and prisons. This category also includes structures associated with utilities and storage of hazardous materials. Category IV. Buildings and structures designated as essential facilities, such as hospitals and fire stations. This category also includes structures associated with storage of hazardous materials considered COASTAL CONSTRUCTION MANUAL 6-7 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION a danger to the public and buildings associated with utilities required to maintain the use of other buildings in this category. Performance expectations for buildings vary widely depending on the type of hazard being resisted. Selection of the design event in the I -Codes is determined by the hazard type, the risk category of building, and the type of building damage expected. Selecting a higher risk category for most residential buildings should result in a higher final design wind pressure for design and should improve building performance in high -wind events. It can also result in additional freeboard in Zone V and Coastal A Zone if using ASCE 24 in flood design. For flood hazard design, the building is divided into two distinct parts: the foundation and the main structure. For the NOTE foundation, standard methods of design target an essentially elastic response of the foundation for the design event such that Designing to only minimum code little or no structural damage is expected. The main structure and regulatory requirements may result in designs based on is designed to be constructed above the DFE to eliminate the different levels of risk for different need for designing it to resist flood loads. If flooding occurs hazards. The importance of each at an elevation higher than the DFE, flood loads can be hazard level addressed by such significant where flood waters impact solid walls (as opposed requirements, and whether an to open foundation elements). Additionally, a water level only acceptable level of residual risk remains, should therefore be a few inches above the minimum floor elevation can result in carefully considered during the damage to walls and floors, and the loss of floor insulation, design process. wiring, and ductwork. The IRC incorporates freeboard for houses in Zone V and Coastal A Zone, and the IBC incorporates freeboard for buildings by virtue of using ASCE 24. Including freeboard in the building design provides a safety factor against damage to the main structure and its contents caused by flood elevations in excess of the design flood. While codes and standards set minimum freeboard requirements, a risk assessment may indicate the merits of incorporating additional freeboard above the minimum requirements (see Sections 6.2.1.3 and 6.3). For wind hazard design, standard methods of design also target an essentially elastic response of the building structure for the design event (i.e., 700-year wind speed, 3-second gust per ASCE 7-10) such that little or no structural damage is expected. For wind speeds in excess of the design event, wind pressures increase predictably with wind velocity, and factors of safety associated with material resistances provide a margin against structural failure. For seismic hazard design, life safety of the occupants is the primary focus rather than preventing any damage to the building. All portions of the building should be designed to resist the earthquake loads. Buildings are designed using the Maximum Considered Earthquake (i.e., 1 percent in 50 years) and include factors such as ground motion and peak ground acceleration. Adjustment factors are applied to design criteria based on the risk category for the building. For erosion hazard design for bluff -top buildings, the ratio of soil strength to soil stresses is commonly used as the safety factor by geotechnical engineers when determining the risk of �J NOTE In the past, little thought was given to mitigation. Homeowners relied on insurance for replacement costs when a natural hazard event occurred, without regard to the inconvenience and disruption of their daily lives. Taking a mitigation approach can reduce these disruptions and inconveniences. 6-8 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION slope failures. The choice of a safety factor depends on the type and importance of bluff -top development, the bluff height, the nature of the potential bluff failure (e.g., deep rotational failure versus translational failure), and the acceptable level of risk associated with a bluff failure. Studies in the Great Lakes provide guidance for the selection of appropriate geotechnical safety factors (Valejo and Edil 1979, Chapman et al. 1996, and Terraprobe 1994). 6.2.1.2 Designing above Minimum Requirements and Preparing for Events That Exceed Design Events In addition to incorporating factors of safety into design, homeowners, developers, and builders can make siting and design decisions that further manage risks by increasing the level of hazard resistance for the building. For example, hazard resistance can be improved by the following measures: A building can be sited further landward than the minimum distance specified by State or local setback requirements A building can be elevated above the level required by NFIP, State, and local requirements (refer to Section 6.2.1.3 for example) Supporting piles can be embedded deeper than required by State or local regulations Structural members and connections that exceed code requirements for gravity, uplift, and/or lateral forces can be used Improved roofing systems that provide greater resistance to wind than that required by code can be used Roof shapes (e.g., hip roofs) that reduce wind loads can be selected Openings (e.g., windows, doors) can be protected with permanent or temporary shutters or covers, whether or not such protection is required by code Enclosures below an elevated building can be eliminated or minimized NOTE While some coastal construction techniques have the combined effect of improving hazard resistance and energy efficiency, some design decisions make these considerations incompatible (see FEMA P-798, Natural Hazards and Sustainability for Residential Buildings [FEMA 2010]). Designers should discuss the implications and overall financial impacts of design decisions with homeowners so they can make an informed decision. The combination of insurance, maintenance, energy costs, and flood and wind resistance requires careful consideration and an understanding of the tradeoffs. Incorporating above -code design can result in many benefits, such as reduced insurance premiums, reduced building maintenance, and potentially improved energy efficiency. These design decisions can sometimes offset the increased cost of constructing above the code minimums. 6.2.1.3 Role of Freeboard in Coastal Construction The IRC and IBC (through ASCE 24) incorporate a minimum amount of freeboard. Including freeboard beyond that required by the NFIP and the building code should be seriously considered when designing for a homeowner with flooding risks. As of 2009, the IRC requires I foot of freeboard in Zone V and Coastal A COASTAL CONSTRUCTION MANUAL 6-9 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION Zone. In most locations, designing for at least the freeboard requirements in ASCE 24, which requires more freeboard than the IRC in many cases, may establish the level of care expected of a design professional. Freeboard that exceeds the minimum NFIP requirements can be a valuable tool in maintaining NFIP compliance and lessening potential flood damage. Some benefits of incorporating freeboard are: Allows lower flood insurance premiums Provides additional protection for floods exceeding the BFE Provides some contingency if future updates to FIRMS raise the BFE CROSS REFERENCE Section 7.5.2 includes a discussion of freeboard, BFE, and DFE. Helps account for changes within the SFHA that are not represented in the current FIRM or FIS Provides some contingency for surveying benchmarks that may have moved Provides some contingency for errors in the lowest floor elevation during construction without compromising the elevation above the BFE Provides some contingency for changes in water levels due to sea level change or subsidence Even if a freeboard policy is not in force by the State or local jurisdiction, constructing a building to an elevation greater than the BFE reduces the homeowner's flood insurance premium. A FEMA report titled Evaluation of the National Flood Insurance Program' Building Standards (American Institutes for Research 2006) evaluates the benefits of freeboard. The report finds that freeboard is a cost-effective method for reducing risk in many instances and provides some guidance on the comparison of the percent increase in cost of construction with the reduced risk of flooding. Additionally, it evaluates the cost of construction for implementing freeboard and compares it to the flood insurance premium savings. A reevaluation of this study in December of 2009 validated that freeboard is still a cost-effective option in many coastal areas. 6.2.2 Managing Residual Risk through Insurance Once all of the regulatory and physical risk reduction methods are incorporated into a building design, there will still be a level of residual risk to the building that must be assumed by homeowners. One way to minimize the financial exposure to the residual risk is through insurance. Insurance can be divided into a number of categories based on the type of hazard, and whether the insurance is private or purchased through a pool of other policy holders on a State or Federal level. While it is not the role of the designer to discuss insurance policies with an owner, it is important to understand the types of insurance available to an owner and the effect of building design decisions on various insurance programs. The following sections summarize of the types of hazard insurance and discuss how some design decisions can affect insurance premiums. 6-10 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION 6.2.2.1 Types of Hazard Insurance For houses in coastal areas, residual risks associated with flooding, high winds, and in some areas, earthquakes, are of particular concern. The financial risks can be mitigated through a variety of insurance mechanisms, including the NFIP, homeowners wind or earthquake insurance, insurance pools, and self-insurance plans. National Flood Insurance Program Federally backed flood insurance is available for both existing and new construction in communities that participate in the NFIP. To be insurable under the NFIP, a building must have a roof, have at least two walls, and be at least 50 percent above grade. Like homeowners insurance, flood insurance is obtained from private insurance companies. Flood insurance, because it is federally backed, is available for buildings in all coastal areas of participating communities, regardless of how high the flood hazard is. The following exceptions apply: Buildings constructed after October 1, 1982, that are entirely over water or seaward of mean high tide New construction, substantially improved, or substantially damaged buildings constructed after October 1, 1983, that are located on designated undeveloped coastal barriers included in the CBRS (see Section 5.1.1 of this Manual) Portions of boat houses located partially over water (e.g., the ceiling and roof over the area where boats are moored) WARNING Purchasing insurance is not a substitute for a properly designed and constructed building. Insurance is a way of reducing financial exposure to residual risk. CROSS REFERENCE For more information on hazard insurance, see Section 7.6. liiz; COST CONSIDERATION The NFIP places a cap on the amount of coverage for the building and its contents, which may not cover the entire cost of high value properties. Additional flood insurance will be required to insure losses above this limit. The flood insurance rates for buildings in NFIP-participating communities vary according to the physical characteristics of the buildings, the date the buildings were constructed, and the magnitude of the flood hazard at the site of the buildings. The flood insurance premium for a building is based on the rate, standard per -policy fees, the amount of the deductible, applicable NFIP surcharges and discounts, and the amount of coverage obtained. Wind Insurance Homeowners insurance policies normally include coverage for wind. However, insurance companies that issue homeowner policies occasionally deny wind coverage to buildings in areas where the risks from these hazards are high, especially in coastal areas subject to a significant hurricane or typhoon risk. At the time of publication of this Manual, underwriting associations, COASTAL CONSTRUCTION MANUAL 6-11 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION or "pools," are a last resort for homeowners who need wind coverage but cannot obtain it from private companies. Seven States have beach and wind insurance plans: Alabama, Florida, Louisiana, Mississippi, North Carolina, South Carolina, and Texas. Georgia and New York provide this kind of coverage for windstorms and hail in certain coastal communities through other property pools. In addition, New Jersey operates the Windstorm Market Assistance Program (Wind -MAP; http:// www.njiva.org) to help residents in coastal communities find homeowners insurance in the voluntary market. When Wind - MAP does not identify an insurance carrier for a homeowner, the homeowner may apply to the New Jersey Insurance Underwriting Association, known as the FAIR Plan, for a perils -only policy. Earthquake Insurance WARNING Hurricanes cause damage through wind and flooding; however, flood insurance policies only cover flood damage, and wind insurance policies only cover damage from wind and wind -driven rain. For more comprehensive insurance protection, property owners should invest in both flood and wind insurance. A standard homeowners insurance policy can often be modified through an endorsement to include earthquake coverage. However, like wind coverage, earthquake coverage may not be available in areas where the earthquake risk is high. Moreover, deductibles and rates for earthquake coverage (of typical coastal residential buildings) are usually much higher than those for flood, wind, and other hazard insurance. Self -Insurance Where wind and earthquake insurance coverage is not available from private companies or insurance pools —or where homeowners choose to forego available insurance —owners with sufficient financial reserves may be able to assume complete financial responsibility for the risks not offset through siting, design, construction, and maintenance (i.e., self -insure). Homeowners who contemplate self-insurance must understand the true level of risk they are assuming. 6.2.2.2 Savings, Premium, and Penalties Design and siting decisions can often have a dramatic effect on both flood and wind insurance premiums. The primary benefit of the guidance in this Manual is the reduction of damage, disruption, and risk to the client. However, the reduction of insurance costs is a secondary benefit. Siting a building farther from the coastline could result in moving a building from Zone V into Zone A, thereby reducing premiums. Additionally, the height of the structure can affect flood insurance premiums. Raising the first floor elevation above the BFE (adding freeboard) reduces premiums in all flood zones. Some design decisions increase, rather than decrease, insurance premiums. For instance, while the NFIP allows for enclosures below the lowest floor, their presence may increase flood insurance premiums. Breakaway walls and floor systems 6-12 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION elevated off the ground can raise premiums. Although these are allowed by the program, these types of design elements should WARNING be considered carefully and discussed with homeowners in light of their overall long-term cost implications. Improper construction of enclosures below elevated In some States, building a house stronger than required by code residential buildings in Zone V and post -construction conversion results in reduced wind insurance premiums. For example, of enclosed space to habitable Florida requires insurance companies to offer discounts or use (in Zone A and Zone V) are credits for design and construction techniques that reduce common compliance violations of damage and loss in windstorms. Stronger roofs and wall the NFIR For more guidance on systems and improved connections may reduce premiums. enclosures, see Section 2.3.5 of this Manual. Conversely, the addition of large overhangs and other building elements that increase the building's wind exposure can increase premiums. Building a structure stronger than the minimum code can have the dual benefit of reducing insurance premiums and decreasing damage during a flood or wind event. COASTAL CONSTRUCTION MANUAL 6-13 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION 6.3.1 Misconceptions about the 100-Year Flood Event Homeowners commonly misunderstand the 1-percent-annual-chance flood, often called the 100 year flood. There is a 1 percent chance each year of the occurrence of a flood that equals or exceeds the BFE. By contrast, the chance of burglary in 2005 was only 0.6 percent nationwide, but homeowners are concerned enough by this threat that they use security systems and buy homeowners insurance to cover their belongings. Many homeowners believe that being in the 1-percent-annual-chance floodplain means that there is only a 1 percent chance of ever being flooded, which they deem a very small risk. Another misconception is that the "100-year" flood only happens once every 100 years. Unfortunately, these misconceptions result in a gross underestimation of their flood risk. In reality, a residential building within the SFHA has a 26 percent chance of being damaged by a flood over the course of a 30-year mortgage, compared to a 10 percent chance of fire or 17 percent chance of burglary. 6.3.2 Misconceptions about Levee Protection Another common misconception involves levee protection. Many homeowners behind a levee believe that the levee will CROSS REFERENCE protect their property from flood so they believe they are not at risk. Since each levee is constructed to provide protection Section 2.3.2 discusses building against a specific flood frequency, the level of protection behind a levee. must be identified before the risk can be identified. Owners and designers must understand that because levees are only designed to withstand certain storm event recurrence intervals, they may fail when a greater -than -design event occurs. Additional risk factors include the age of the levee and whether the level of protection provided by it may have changed over time. Designers must also understand that levees may have been designed for a specific level of protection, but if flood data changes over time due to an improved understanding of flood modeling, the current level of protection may be less than the designed level of protection. If a levee should fail or is overtopped, the properties behind the levee will be damaged by flooding, which could be as damaging as if there were no levee there at all. Therefore, even in levee -protected areas, homeowners need to be aware of the risk and should consider elevation and other mitigation techniques to minimize their flood risk. 6-14 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION COASTAL CONSTRUCTION MANUAL 6-15 FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION 6-16 COASTAL CONSTRUCTION MANUAL FUNDAMENTALS OF RISK ANALYSIS AND RISK REDUCTION 6.4 References American Institutes for Research. 2006. Evaluation of the National Flood Insurance Program's Building Standards. October. American Society of Civil Engineers (ASCE). 2005. Flood Resistant Design and Construction. ASCE Standard ASCE 24-05. ASCE. 2010. Minimum Design Loads of Buildings and Other Structures. ASCE Standard ASCE 7-10. Chapman, J. A.; T. B. Edil; and D. M. Mickelson. 1996. Effectiveness ofAnalysis Methods for Predicting Long Term Slope Stability on the Lake Michigan Shoreline. Final report of the Lake Michigan, Wisconsin, Shoreline Erosion and Bluff Stability Study. December. FEMA (Federal Emergency Management Agency). 2010. Natural Hazards and Sustainability for Residential Buildings. FEMA P-798. September. FEMA. 2011. Flood Insurance Manual. May. Potter, K. W. 1992. "Estimating the Probability Distribution of Annual Maximum Levels on the Great Lakes." journal of Great Lakes Research, International Association of Great Lakes Research. (18)1, pp. 229-235. Terraprobe. 1994. Geotechnical Principles for Stable Slopes. Great Lakes -St. Lawrence River Shoreline Policy. Prepared for the Ontario Ministry of Natural Resources. Terraprobe, Ltd., Brampton, Ontario. March. Valejo, L. E.; T. B. Edil. 1979. "Design Charts for Development and Stability of Evolving Slopes." journal of Civil Engineering Design. Marcel Dekker, Inc., publisher, 1(3), pp. 232-252. COASTAL CONSTRUCTION MANUAL 6-17 Acronyms I:1 AF&PA American Forest & Paper Association AIA American Institute of Architects AISI American Iron and Steel Institute APA American Planning Association ASCE American Society of Civil Engineers ASD allowable -stress design ASFPM Association of State Floodplain Managers ASLA American Society of Landscape Architects I: BCEGS Building Code Effectiveness Grading Schedule BFE base flood elevation BOCA Building Officials and Code Administrators International, Inc. BPAT Building Performance Assessment Team C CBIA Coastal Barrier Improvement Act CBRA Coastal Barrier Resources Act CBRS Coastal Barrier Resources System COASTAL CONSTRUCTION MANUAL A-1 ACRONYMS Volume I CFR Code of Federal Regulations CRS Community Rating System CZM Coastal Zone Management CZMA Coastal Zone Management Act DFE design flood elevation DFIRM Digital Flood Insurance Rate Map DOI Department of the Interior EF Enhanced Fujita EHP Earthquake Hazards Program ENSO El Nino/La Nina -Southern Oscillation F FBC Florida Building Code FEMA Federal Emergency Management Agency FIRM Flood Insurance Rate Map FIS Flood Insurance Study GSA General Services Administration HUD Department of Housing and Urban Development A-2 COASTAL CONSTRUCTION MANUAL Volume I ACRONYMS IBC International Building Code IBHS Insurance Institute for Business and Home Safety ICBO International Conference of Building Officials ICC International Code Council IEBC International Existing Building Code IFC International Fire Code IFGC International Fuel Gas Code IMC International Mechanical Code IPC International Plumbing Code IPCC Intergovernmental Panel on Climate Change IPSDC International Private Sewage Disposal Code IRC International Residential Code ISO Insurance Services Office LiMWA Limit of Moderate Wave Action Tj MAT Mitigation Assessment Team MiWA Minimal Wave Action MMI Modified Mercalli Intensity MoWA Moderate Wave Action NAHB National Association of Home Builders COASTAL CONSTRUCTION MANUAL A-3 ACRONYMS Volume I NAVD North American Vertical Datum NBC National Building Code NEHRP National Earthquake Hazards Reduction Program NFIP National Flood Insurance Program NFPA National Fire Protection Association NGVD National Geodetic Vertical Datum NIST National Institute of Standards and Technology NOAA National Oceanic and Atmospheric Administration NRCA National Roofing Contractors Association NRCS Natural Resources Conservation Service NSPE National Society of Professional Engineers NWS National Weather Service 0 OCRM Office of Ocean and Coastal Resource Management OPA Otherwise Protected Area L J SBC Standard Building Code SBCCI Southern Building Code Congress International SDE Substantial Damage Estimator SFHA Special Flood Hazard Area SFIP Standard Flood Insurance Policy SI/SD Substantial Improvement/Substantial Damage SSHWS Saffir-Simpson Hurricane Wind Scale A-4 COASTAL CONSTRUCTION MANUAL Volume I ACRONYMS UBC Uniform Building Code USACE U.S. Army Corps of Engineers USGS U.S. Geological Survey Wind -MAP Windstorm Market Assistance Program (New Jersey) COASTAL CONSTRUCTION MANUAL A-5 Glossary 0-9 100-year flood — See Base flood. 500-year flood — Flood that has as 0.2-percent probability of being equaled or exceeded in any given year. "MI Acceptable level of risk — The level of risk judged by the building owner and designer to be appropriate for a particular building. Adjacent grade — Elevation of the natural or graded ground surface, or structural fill, abutting the walls of a building. See also Highest adjacent grade and Lowest adjacentgrade. Angle of internal friction (soil) — A measure of the soil's ability to resist shear forces without failure. Appurtenant structure — Under the National Flood Insurance Program, an "appurtenant structure" is "a structure which is on the same parcel of property as the principal structure to be insured and the use of which is incidental to the use of the principal structure." Barrier island — A long, narrow sand island parallel to the mainland that protects the coast from erosion. Base flood — Flood that has as 1-percent probability of being equaled or exceeded in any given year. Also known as the 100-year flood. Base Flood Elevation (BFE) — The water surface elevation resulting from a flood that has a 1 percent chance of equaling or exceeding that level in any given year. Elevation of the base flood in relation to a specified datum, such as the National Geodetic Vertical Datum or the North American Vertical Datum. The Base Flood Elevation is the basis of the insurance and floodplain management requirements of the National Flood Insurance Program. COASTAL CONSTRUCTION MANUAL G-1 GLOSSARY Volume I Basement — Under the National Flood Insurance Program, any area of a building having its floor subgrade on all sides. (Note: What is typically referred to as a "walkout basement," which has a floor that is at or above grade on at least one side, is not considered a basement under the National Flood Insurance Program.) Beach nourishment — A project type that typically involve dredging or excavating hundreds of thousands to millions of cubic yards of sediment, and placing it along the shoreline. Bearing capacity (soils) — A measure of the ability of soil to support gravity loads without soil failure or excessive settlement. Berm — Horizontal portion of the backshore beach formed by sediments deposited by waves. Best Practices — Techniques that exceed the minimum requirements of model building codes; design and construction standards; or Federal, State, and local regulations. Breakaway wall — Under the National Flood Insurance Program, a wall that is not part of the structural support of the building and is intended through its design and construction to collapse under specific lateral loading forces without causing damage to the elevated portion of the building or supporting foundation system. Breakaway walls are required by the National Flood Insurance Program regulations for any enclosures constructed below the Base Flood Elevation beneath elevated buildings in Coastal High Hazard Areas (also referred to as Zone V). In addition, breakaway walls are recommended in areas where flood waters flow at high velocities or contain ice or other debris. Building code — Regulations adopted by local governments that establish standards for construction, modification, and repair of buildings and other structures. Building use — What occupants will do in the building. The intended use of the building will affect its layout, form, and function. Building envelope — Cladding, roofing, exterior walls, glazing, door assemblies, window assemblies, skylight assemblies, and other components enclosing the building. Building systems — Exposed structural, window, or roof systems. Built-up roof covering — Two or more layers of felt cemented together and surfaced with a cap sheet, mineral aggregate, smooth coating, or similar surfacing material. Bulkhead — Wall or other structure, often of wood, steel, stone, or concrete, designed to retain or prevent sliding or erosion of the land. Occasionally, bulkheads are used to protect against wave action. C Cladding — Exterior surface of the building envelope that is directly loaded by the wind. Closed foundation — A foundation that does not allow water to pass easily through the foundation elements below an elevated building. Examples of closed foundations include crawlspace foundations and stem wall foundations, which are usually filled with compacted soil, slab -on -grade foundations, and continuous perimeter foundation walls. G-2 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY Coastal A Zone — The portion of the coastal SFHA referenced by building codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many NFIP-compliant structures on shallow or solid wall foundations. Coastal barrier — Depositional geologic feature such as a bay barrier, tombolo, barrier spit, or barrier island that consists of unconsolidated sedimentary materials; is subject to wave, tidal, and wind energies; and protects landward aquatic habitats from direct wave attack. Coastal Barrier Resources Act of 1982 (CBRA) — Act (Public Law 97-348) that established the Coastal Barrier Resources System (CBRS). The act prohibits the provision of new flood insurance coverage on or after October 1, 1983, for any new construction or substantial improvements of structures located on any designated undeveloped coastal barrier within the CBRS. The CBRS was expanded by the Coastal Barrier Improvement Act of 1991. The date on which an area is added to the CBRS is the date of CBRS designation for that area. Coastal flood hazard area — An area subject to inundation by storm surge and, in some instances, wave action caused by storms or seismic forces. Usually along an open coast, bay, or inlet. Coastal geology — The origin, structure, and characteristics of the rocks and sediments that make up the coastal region. Coastal High Hazard Area — Under the National Flood Insurance Program, an area of special flood hazard extending from offshore to the inland limit of a primary frontal dune along an open coast and any other area subject to high -velocity wave action from storms or seismic sources. On a Flood Insurance Rate Map, the Coastal High Hazard Area is designated Zone V, VE, or Vl V30. These zones designate areas subject to inundation by the base flood, where wave heights or wave runup depths are 3.0 feet or higher. Coastal processes — The physical processes that act upon and shape the coastline. These processes, which influence the configuration, orientation, and movement of the coast, include tides and fluctuating water levels, waves, currents, and winds. Coastal sediment budget — The quantification of the amounts and rates of sediment transport, erosion, and deposition within a defined region. Coastal Special Flood Hazard Area — The portion of the Special Flood Hazard Area where the source of flooding is coastal surge or inundation. It includes Zone VE and Coastal A Zone. Code official — Officer or other designated authority charged with the administration and enforcement of the code, or a duly authorized representative, such as a building, zoning, planning, or floodplain management official. Column foundation — Foundation consisting of vertical support members with a height -to -least -lateral - dimension ratio greater than three. Columns are set in holes and backfilled with compacted material. They are usually made of concrete or masonry and often must be braced. Columns are sometimes known as posts, particularly if they are made of wood. Components and Cladding (C&C) — American Society of Civil Engineers (ASCE) 7-10 defines C&C as "... elements of the building envelope that do not qualify as part of the MWFRS [Main Wind Force Resisting System]." These elements include roof sheathing, roof coverings, exterior siding, windows, doors, soffits, fascia, and chimneys. COASTAL CONSTRUCTION MANUAL G-3 GLOSSARY Volume I Conditions Greater than Design Conditions — Design loads and conditions are based on some probability of exceedance, and it is always possible that design loads and conditions can be exceeded. Designers can anticipate this and modify their initial design to better accommodate higher forces and more extreme conditions. The benefits of doing so often exceed the costs of building higher and stronger. Connector — Mechanical device for securing two or more pieces, parts, or members together, including anchors, wall ties, and fasteners. Consequence — Both the short- and long-term effects of an event for the building. See Risk. Constructability — Ultimately, designs will only be successful if they can be implemented by contractors. Complex designs with many custom details may be difficult to construct and could lead to a variety of problems, both during construction and once the building is occupied. Continuous load paths — The structural condition required to resist loads acting on a building. The continuous load path starts at the point or surface where loads are applied, moves through the building, continues through the foundation, and terminates where the loads are transferred to the soils that support the building. Corrosion -resistant metal — Any nonferrous metal or any metal having an unbroken surfacing of nonferrous metal, or steel with not less than 10 percent chromium or with not less than 0.20 percent copper. Dead load — Weight of all materials of construction incorporated into the building, including but not limited to walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items and fixed service equipment. See also Loads. Debris — Solid objects or masses carried by or floating on the surface of moving water. Debris impact loads — Loads imposed on a structure by the impact of floodborne debris. These loads are often sudden and large. Though difficult to predict, debris impact loads must be considered when structures are designed and constructed. See also Loads. Deck — Exterior floor supported on at least two opposing sides by an adjacent structure and/or posts, piers, or other independent supports. Design event — The minimum code -required event (for natural hazards, such as flood, wind, and earthquake) and associated loads that the structure must be designed to resist. Design flood — The greater of either (1) the base flood or (2) the flood associated with the flood hazard area depicted on a community's flood hazard map, or otherwise legally designated. Design Flood Elevation (DFE) — Elevation of the design flood, or the flood protection elevation required by a community, including wave effects, relative to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum. The DFE is the locally adopted regulatory flood elevation. If a community regulates to minimum National Flood Insurance Program (NFIP) requirements, the G-4 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY DFE is identical to the Base Flood Elevation (BFE). If a community chooses to exceed minimum NFIP requirements, the DFE exceeds the BFE. Design flood protection depth — Vertical distance between the eroded ground elevation and the Design Flood Elevation. Design stillwater flood depth — Vertical distance between the eroded ground elevation and the design stillwater flood elevation. Design stillwater flood elevation — Stillwater elevation associated with the design flood, excluding wave effects, relative to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum. Development — Under the National Flood Insurance Program, any manmade change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation, or drilling operations or storage of equipment or materials. Dry floodproofing — A flood retrofitting technique in which the portion of a structure below the flood protection level (walls and other exterior components) is sealed to be impermeable to the passage of floodwaters. Dune — See Frontal dune and Primary frontal dune. Dune toe — Junction of the gentle slope seaward of the dune and the dune face, which is marked by a slope of 1 on 10 or steeper. E Effective Flood Insurance Rate Map — See Flood Insurance Rate Map. Elevation — Raising a structure to prevent floodwaters from reaching damageable portions. Enclosure — The portion of an elevated building below the lowest floor that is partially or fully shut in by rigid walls. Encroachment — The placement of an object in a floodplain that hinders the passage of water or otherwise affects the flood flows. Erodible soil — Soil subject to wearing away and movement due to the effects of wind, water, or other geological processes during a flood or storm or over a period of years. Erosion — Under the National Flood Insurance Program, the process of the gradual wearing away of land masses. Erosion analysis — Analysis of the short- and long-term erosion potential of soil or strata, including the effects of flooding or storm surge, moving water, wave action, and the interaction of water and structural components. Exterior -mounted mechanical equipment — Includes, but is not limited to, exhaust fans, vent hoods, air conditioning units, duct work, pool motors, and well pumps. COASTAL CONSTRUCTION MANUAL G-5 GLOSSARY Volume I F Federal Emergency Management Agency (FEMA) — Independent agency created in 1979 to provide a single point of accountability for all Federal activities related to disaster mitigation and emergency preparedness, response, and recovery. FEMA administers the National Flood Insurance Program. Federal Insurance and Mitigation Administration (FIMA) — The component of the Federal Emergency Management Agency directly responsible for administering the flood insurance aspects of the National Flood Insurance Program as well as a range of programs designed to reduce future losses to homes, businesses, schools, public buildings, and critical facilities from floods, earthquakes, tornadoes, and other natural disasters. Fill — Material such as soil, gravel, or crushed stone placed in an area to increase ground elevations or change soil properties. See also Structural fill. Flood — Under the National Flood Insurance Program, either a general and temporary condition or partial or complete inundation of normally dry land areas from: (1) the overflow of inland or tidal waters; (2) the unusual and rapid accumulation or runoff of surface waters from any source; (3) mudslides (i.e., mudflows) that are proximately caused by flooding as defined in (2) and are akin to a river of liquid and flowing mud on the surfaces of normally dry land areas, as when the earth is carried by a current of water and deposited along the path of the current; or (4) the collapse or subsidence of land along the shore of a lake or other body of water as a result of erosion or undermining caused by waves or currents of water exceeding anticipated cyclical levels or suddenly caused by an unusually high water level in a natural body of water, accompanied by a severe storm, or by an unanticipated force of nature, such as flash flood or abnormal tidal surge, or by some similarly unusual and unforeseeable event which results in flooding as defined in (1), above. Flood -damage -resistant material — Any construction material capable of withstanding direct and prolonged contact (i.e., at least 72 hours) with flood waters without suffering significant damage (i.e., damage that requires more than cleanup or low-cost cosmetic repair, such as painting). Flood elevation — Height of the water surface above an established elevation datum such as the National Geodetic Vertical Datum, North American Vertical Datum, or mean sea level. Flood hazard area — The greater of the following: (1) the area of special flood hazard, as defined under the National Flood Insurance Program, or (2) the area designated as a flood hazard area on a community's legally adopted flood hazard map, or otherwise legally designated. Flood insurance — Insurance coverage provided under the National Flood Insurance Program. Flood Insurance Rate Map (FIRM) — Under the National Flood Insurance Program, an official map of a community, on which the Federal Emergency Management Agency has delineated both the special hazard areas and the risk premium zones applicable to the community. (Note: The latest FIRM issued for a community is referred to as the "effective FIRM" for that community.) G-6 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY Flood Insurance Study (FIS) — Under the National Flood Insurance Program, an examination, evaluation, and determination of flood hazards and, if appropriate, corresponding water surface elevations, or an examination, evaluation, and determination of mudslide (i.e., mudflow) and flood -related erosion hazards in a community or communities. (Note: The National Flood Insurance Program regulations refer to Flood Insurance Studies as "flood elevation studies.") Flood -related erosion area or flood -related erosion prone area — A land area adjoining the shore of a lake or other body of water, which due to the composition of the shoreline or bank and high water levels or wind -driven currents, is likely to suffer flood -related erosion. Flooding — See Flood. Floodplain — Under the National Flood Insurance Program, any land area susceptible to being inundated by water from any source. See also Flood. Floodplain management — Operation of an overall program of corrective and preventive measures for reducing flood damage, including but not limited to emergency preparedness plans, flood control works, and floodplain management regulations. Floodplain management regulations — Under the National Flood Insurance Program, zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances (such as floodplain ordinance, grading ordinance, and erosion control ordinance), and other applications of police power. The term describes State or local regulations, in any combination thereof, that promulgate standards for the purpose of flood damage prevention and reduction. Floodwall — A flood retrofitting technique that consists of engineered barriers designed to keep floodwaters from coming into contact with the structure. Footing — Enlarged base of a foundation wall, pier, post, or column designed to spread the load of the structure so that it does not exceed the soil bearing capacity. Footprint — Land area occupied by a structure. Freeboard — Under the National Flood Insurance Program, a factor of safety, usually expressed in feet above a flood level, for the purposes of floodplain management. Freeboard is intended to compensate for the many unknown factors that could contribute to flood heights greater than the heights calculated for a selected size flood and floodway conditions, such as the hydrological effect of urbanization of the watershed. Freeboard is additional height incorporated into the Design Flood Elevation, and may be required by State or local regulations or be desired by a property owner. Frontal dune — Ridge or mound of unconsolidated sandy soil extending continuously alongshore landward of the sand beach and defined by relatively steep slopes abutting markedly flatter and lower regions on each side. Frontal dune reservoir — Dune cross-section above 100-year stillwater level and seaward of dune peak. COASTAL CONSTRUCTION MANUAL G-7 GLOSSARY Volume I G Gabion — Rock -filled cage made of wire or metal that is placed on slopes or embankments to protect them from erosion caused by flowing or fast-moving water. Geomorphology — The origin, structure, and characteristics of the rocks and sediments that make up the coastal region. Glazing — Glass or transparent or translucent plastic sheet in windows, doors, skylights, and shutters. Grade beam — Section of a concrete slab that is thicker than the slab and acts as a footing to provide stability, often under load -bearing or critical structural walls. Grade beams are occasionally installed to provide lateral support for vertical foundation members where they enter the ground. H High -velocity wave action — Condition in which wave heights or wave runup depths are 3.0 feet or higher. Highest adjacent grade — Elevation of the highest natural or regraded ground surface, or structural fill, that abuts the walls of a building. Hurricane — Tropical cyclone, formed in the atmosphere over warm ocean areas, in which wind speeds reach 74 miles per hour or more and blow in a large spiral around a relatively calm center or "eye." Hurricane circulation is counter -clockwise in the northern hemisphere and clockwise in the southern hemisphere. Hurricane clip or strap — Structural connector, usually metal, used to tie roof, wall, floor, and foundation members together so that they resist wind forces. Hurricane -prone region — In the United States and its territories, hurricane -prone regions are defined by The American Society of Civil Engineers (ASCE) 7-10 as: (1) The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed for Risk Category II buildings is greater than 115 mph, and (2) Hawaii, Puerto Rico, Guam, the Virgin Islands, and American Samoa. Hydrodynamic loads — Loads imposed on an object, such as a building, by water flowing against and around it. Among these loads are positive frontal pressure against the structure, drag effect along the sides, and negative pressure on the downstream side. Hydrostatic loads — Loads imposed on a surface, such as a wall or floor slab, by a standing mass of water. The water pressure increases with the square of the water depth. Initial costs — Include property evaluation, acquisition, permitting, design, and construction. G-8 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY Interior mechanical equipment — Includes, but is not limited to, furnaces, boilers, water heaters, and distribution ductwork. LJ Jetting (of piles) — Use of a high-pressure stream of water to embed a pile in sandy soil. See also Pile foundation. Jetty — Wall built from the shore out into the water to restrain currents or protect a structure. Joist — Any of the parallel structural members of a floor system that support, and are usually immediately beneath, the floor. L Lacustrine flood hazard area — Area subject to inundation from lakes. Landslide — Occurs when slopes become unstable and loose material slides or flows under the influence of gravity. Often, landslides are triggered by other events such as erosion at the toe of a steep slope, earthquakes, floods, or heavy rains, but can be worsened by human actions such as destruction of vegetation or uncontrolled pedestrian access on steep slopes. Levee — Typically a compacted earthen structure that blocks floodwaters from coming into contact with the structure, a levee is a manmade structure built parallel to a waterway to contain, control, or divert the flow of water. A levee system may also include concrete or steel floodwalls, fixed or operable floodgates and other closure structures, pump stations for rainwater drainage, and other elements, all of which must perform as designed to prevent failure. Limit of Moderate Wave Action (LiMWA) — A line indicating the limit of the 15-foot wave height during the base flood. FEMA requires new flood studies in coastal areas to delineate the LiMWA. Littoral drift — Movement of sand by littoral (longshore) currents in a direction parallel to the beach along the shore. Live loads — Loads produced by the use and occupancy of the building or other structure. Live loads do not include construction or environmental loads such as wind load, snow load, rain load, earthquake load, flood load, or dead load. See also Loads. Load -bearing wall — Wall that supports any vertical load in addition to its own weight. See also Non - load -bearing wall. Loads — Forces or other actions that result from the weight of all building materials, occupants and their possessions, environmental effects, differential movement, and restrained dimensional changes. Loads can be either permanent or variable. Permanent loads rarely vary over time or are of small magnitude. All other loads are variable loads. COASTAL CONSTRUCTION MANUAL G-9 GLOSSARY Volume I Location — The location of the building determines the nature and intensity of hazards to which the building will be exposed, loads and conditions that the building must withstand, and building regulations that must be satisfied. See also Siting. Long-term costs — Include preventive maintenance and repair and replacement of deteriorated or damaged building components. A hazard -resistant design can result in lower long-term costs by preventing or reducing losses from natural hazards events. Lowest adjacent grade (LAG) — Elevation of the lowest natural or regraded ground surface, or structural fill, that abuts the walls of a building. See also Highest adjacent grade. Lowest floor — Under the National Flood Insurance Program (NFIP), "lowest floor" of a building includes the floor of a basement. The NFIP regulations define a basement as "... any area of a building having its floor subgrade (below ground level) on all sides." For insurance rating purposes, this definition applies even when the subgrade floor is not enclosed by full -height walls. Lowest horizontal structural member — In an elevated building, the lowest beam, joist, or other horizontal member that supports the building. Grade beams installed to support vertical foundation members where they enter the ground are not considered lowest horizontal structural members. 1�1 Main Wind Force Resisting System (MWFRS) — Consists of the foundation; floor supports (e.g., joists, beams); columns; roof raters or trusses; and bracing, walls, and diaphragms that assist in transferring loads. The American Society of Civil Engineers (ASCE) 7-10 defines the MWFRS as "... an assemblage of structural elements assigned to provide support and stability for the overall structure." Manufactured home — Under the National Flood Insurance Program, a structure, transportable in one or more sections, built on a permanent chassis and designed for use with or without a permanent foundation when attached to the required utilities. Does not include recreational vehicles. Marsh — Wetland dominated by herbaceous or non -woody plants often developing in shallow ponds or depressions, river margins, tidal areas, and estuaries. Masonry — Built-up construction of building units made of clay, shale, concrete, glass, gypsum, stone, or other approved units bonded together with or without mortar or grout or other accepted methods of joining. Mean return period — The average time (in years) between landfall or nearby passage of a tropical storm or hurricane. Mean water elevation — The surface across which waves propagate. The mean water elevation is calculated as the stillwater elevation plus the wave setup. Mean sea level (MSL) — Average height of the sea for all stages of the tide, usually determined from hourly height observations over a 19-year period on an open coast or in adjacent waters having free access to the sea. See also National Geodetic Vertical Datum. G-10 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY Metal roof panel — Interlocking metal sheet having a minimum installed weather exposure of 3 square feet per sheet. Minimal Wave Action area (MiWA) — The portion of the coastal Special Flood Hazard Area where base flood wave heights are less than 1.5 feet. Mitigation — Any action taken to reduce or permanently eliminate the long-term risk to life and property from natural hazards. Mitigation Directorate — Component of the Federal Emergency Management Agency directly responsible for administering the flood hazard identification and floodplain management aspects of the National Flood Insurance Program. Moderate Wave Action area (MoWA) — See Coastal A Zone. IL National Flood Insurance Program (NFIP) — Federal program created by Congress in 1968 that makes flood insurance available in communities that enact and enforce satisfactory floodplain management regulations. National Geodetic Vertical Datum (NGVD) — Datum established in 1929 and used as a basis for measuring flood, ground, and structural elevations, previously referred to as Sea Level Datum or Mean Sea Level. The Base Flood Elevations shown on most of the Flood Insurance Rate Maps issued by the Federal Emergency Management Agency are referenced to NGVD or, more recently, to the North American Vertical Datum. Naturally decay -resistant wood — Wood whose composition provides it with some measure of resistance to decay and attack by insects, without preservative treatment (e.g., heartwood of cedar, black locust, black walnut, and redwood). New construction — For the purpose of determining flood insurance rates under the National Flood Insurance Program, structures for which the start of construction commenced on or after the effective date of the initial Flood Insurance Rate Map or after December 31, 1974, whichever is later, including any subsequent improvements to such structures. (See also Post -FIRM structure.) For floodplain management purposes, new construction means structures for which the start of construction commenced on or after the effective date of a floodplain management regulation adopted by a community and includes any subsequent improvements to such structures. Non -load -bearing wall — Wall that does not support vertical loads other than its own weight. See also Load -bearing wall. Nor'easter — A type of storm that occurs along the East Coast of the United States where the wind comes from the northeast. Nor'easters can cause coastal flooding, coastal erosion, hurricane -force winds, and heavy snow. North American Vertical Datum (NAVD) — Datum established in 1988 and used as a basis for measuring flood, ground, and structural elevations. NAVD is used in many recent Flood Insurance Studies rather than the National Geodetic Vertical Datum. COASTAL CONSTRUCTION MANUAL G-11 GLOSSARY Volume I ,J Open foundation — A foundation that allows water to pass through the foundation of an elevated building, which reduces the lateral flood loads the foundation must resist. Examples of open foundations are pile, pier, and column foundations. Operational costs — Costs associated with the use of the building, such as the cost of utilities and insurance. Optimizing energy efficiency may result in a higher initial cost but save in operational costs. Oriented strand board (OSB) — Mat -formed wood structural panel product composed of thin rectangular wood strands or wafers arranged in oriented layers and bonded with waterproof adhesive. Overwash — Occurs when low-lying coastal lands are overtopped and eroded by storm surge and waves such that the eroded sediments are carried landward by floodwaters, burying uplands, roads, and at -grade structures. Pier foundation — Foundation consisting of isolated masonry or cast -in -place concrete structural elements extending into firm materials. Piers are relatively short in comparison to their width, which is usually greater than or equal to 12 times their vertical dimension. Piers derive their load -carrying capacity through skin friction, end bearing, or a combination of both. Pile foundation — Foundation consisting of concrete, wood, or steel structural elements driven or jetted into the ground or cast -in -place. Piles are relatively slender in comparison to their length, which usually exceeds 12 times their horizontal dimension. Piles derive their load -carrying capacity through skin friction, end bearing, or a combination of both. Platform framing — A floor assembly consisting of beams, joists, and a subfloor that creates a platform that supports the exterior and interior walls. Plywood — Wood structural panel composed of plies of wood veneer arranged in cross -aligned layers. The plies are bonded with an adhesive that cures when heat and pressure are applied. Post -FIRM structure — For purposes of determining insurance rates under the National Flood Insurance Program, structures for which the start of construction commenced on or after the effective date of an initial Flood Insurance Rate Map or after December 31, 1974, whichever is later, including any subsequent improvements to such structures. This term should not be confused with the term new construction as it is used in floodplain management. Post foundation — Foundation consisting of vertical support members set in holes and backfilled with compacted material. Posts are usually made of wood and usually must be braced. Posts are also known as columns, but columns are usually made of concrete or masonry. Precast concrete — Structural concrete element cast elsewhere than its final position in the structure. See also Cast -in -place concrete. G-12 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY Pressure -treated wood — Wood impregnated under pressure with compounds that reduce the susceptibility of the wood to flame spread or to deterioration caused by fungi, insects, or marine borers. Premium — Amount of insurance coverage. Primary frontal dune — Under the National Flood Insurance Program, a continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and subject to erosion and overtopping from high tides and waves during major coastal storms. The inland limit of the primary frontal dune occurs at the point where there is a distinct change from a relatively steep slope to a relatively mild slope. Rating factor (insurance) — A factor used to determine the amount to be charged for a certain amount of insurance coverage (premium). Recurrence interval — The frequency of occurrence of a natural hazard as referred to in most design codes and standards. Reinforced concrete — Structural concrete reinforced with steel bars. Relocation — The moving of a structure to a location that is less prone to flooding and flood -related hazards such as erosion. Residual risk — The level of risk that is not offset by hazard -resistant design or insurance, and that must be accepted by the property owner. Retrofit — Any change or combination of adjustments made to an existing structure intended to reduce or eliminate damage to that structure from flooding, erosion, high winds, earthquakes, or other hazards. Revetment — Facing of stone, cement, sandbags, or other materials placed on an earthen wall or embankment to protect it from erosion or scour caused by flood waters or wave action. Riprap — Broken stone, cut stone blocks, or rubble that is placed on slopes to protect them from erosion or scour caused by flood waters or wave action. Risk — Potential losses associated with a hazard, defined in terms of expected probability and frequency, exposure, and consequences. Risk is associated with three factors: threat, vulnerability, and consequence. Risk assessment — Process of quantifying the total risk to a coastal building (i.e., the risk associated with all the significant natural hazards that may impact the building). Risk category — As defined in American Society of Civil Engineers (ASCE) 7-10 and the 2012 International Building Code, a building's risk category is based on the risk to human life, health, and welfare associated with potential damage or failure of the building. These risk categories dictate which design event is used when calculating performance expectations of the building, specifically the loads the building is expected to resist. Risk reduction — The process of reducing or offsetting risks. Risk reduction is comprised of two aspects: physical risk reduction and risk management through insurance. COASTAL CONSTRUCTION MANUAL G-13 GLOSSARY Volume I Risk tolerance — Some owners are willing and able to assume a high degree of financial and other risks, while other owners are very conservative and seek to minimize potential building damage and future costs. Riverine SFHA — The portion of the Special Flood Hazard Area mapped as Zone AE and where the source of flooding is riverine, not coastal. Roof deck — Flat or sloped roof surface not including its supporting members or vertical supports. 0 Sand dunes — Under the National Flood Insurance Program, natural or artificial ridges or mounds of sand landward of the beach. Scour — Removal of soil or fill material by the flow of flood waters. Flow moving past a fixed object accelerates, often forming eddies or vortices and scouring loose sediment from the immediate vicinity of the object. The term is frequently used to describe storm -induced, localized conical erosion around pilings and other foundation supports, where the obstruction of flow increases turbulence. See also Erosion. Seawall — Solid barricade built at the water's edge to protect the shore and prevent inland flooding. Setback — For the purpose of this Manual, a State or local requirement that prohibits new construction and certain improvements and repairs to existing coastal buildings in areas expected to be lost to shoreline retreat. Shearwall — Load -bearing wall or non -load -bearing wall that transfers in -plane lateral forces from lateral loads acting on a structure to its foundation. Shoreline retreat — Progressive movement of the shoreline in a landward direction; caused by the composite effect of all storms over decades and centuries and expressed as an annual average erosion rate. Shoreline retreat is essentially the horizontal component of erosion and is relevant to long-term land use decisions and the siting of buildings. Single -ply membrane — Roofing membrane that is field -applied with one layer of membrane material (either homogeneous or composite) rather than multiple layers. The four primary types of single -ply membranes are chlorosulfonated polyethylene (CSPE) (Hypalon), ethylene propylene diene monomer (EPDM), polyvinyl chloride (PVC), and thermoplastic polyolefin (TPO). Siting — Choosing the location for the development or redevelopment of a structure. Special Flood Hazard Area (SFHA) — Under the National Flood Insurance Program, an area having special flood, mudslide (i.e., mudflow), or flood -related erosion hazards, and shown on a Flood Hazard Boundary Map or Flood Insurance Rate Map as Zone A, AO, Al-A30, AE, A99, AH, V, Vl V30, VE, M, or E. The area has a 1 percent chance, or greater, of flooding in any given year. Start of construction (for other than new construction or substantial improvements under the Coastal Barrier Resources Act) — Under the National Flood Insurance Program, date the building permit was issued, provided the actual start of construction, repair, reconstruction, rehabilitation, addition placement, or other improvement was within 180 days of the permit date. The actual start means either the first placement of permanent construction of a structure on a site such as the pouring of slab or footings, G-14 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY the installation of piles, the construction of columns, or any work beyond the stage of excavation; or the placement of a manufactured home on a foundation. Permanent construction does not include land preparation, such as clearing, grading, and filling; nor the installation of streets or walkways; excavation for a basement, footings, piers, or foundations or the erection of temporary forms; or the installation on the property of accessory buildings, such as garages or sheds not occupied as dwelling units or not part of the main structure. For a substantial improvement, the actual start of construction means the first alteration of any wall, ceiling, floor, or other structural part of a building, whether or not that alteration affects the external dimensions of the building. State Coordinating Agency — Under the National Flood Insurance Program, the agency of the State government, or other office designated by the Governor of the State or by State statute to assist in the implementation of the National Flood Insurance Program in that State. Stillwater elevation — The elevations of the water surface resulting solely from storm surge (i.e., the rise in the surface of the ocean due to the action of wind and the drop in atmospheric pressure association with hurricanes and other storms). Storm surge — Water pushed toward the shore by the force of the winds swirling around a storm. It is the greatest cause of loss of life due to hurricanes. Storm tide — Combined effect of storm surge, existing astronomical tide conditions, and breaking wave setup. Structural concrete — All concrete used for structural purposes, including plain concrete and reinforced concrete. Structural fill — Fill compacted to a specified density to provide structural support or protection to a structure. See also Fill. Structure — For floodplain management purposes under the National Flood Insurance Program (NFIP), a walled and roofed building, gas or liquid storage tank, or manufactured home that is principally above ground. For insurance coverage purposes under the NFIP, structure means a walled and roofed building, other than a gas or liquid storage tank, that is principally above ground and affixed to a permanent site, as well as a manufactured home on a permanent foundation. For the latter purpose, the term includes a building undergoing construction, alteration, or repair, but does not include building materials or supplies intended for use in such construction, alteration, or repair, unless such materials or supplies are within an enclosed building on the premises. Substantial damage — Under the National Flood Insurance Program, damage to a building (regardless of the cause) is considered substantial damage if the cost of restoring the building to its before -damage condition would equal or exceed 50 percent of the market value of the structure before the damage occurred. Substantial improvement — Under the National Flood Insurance Program, improvement of a building (such as reconstruction, rehabilitation, or addition) is considered a substantial improvement if its cost equals or exceeds 50 percent of the market value of the building before the start of construction of the improvement. This term includes structures that have incurred substantial damage, regardless of the actual repair work performed. The term does not, however, include either (1) any project for improvement of a structure to correct existing violations of State or local health, sanitary, or safety code specifications which have been identified by the local code enforcement official and which are the minimum necessary to ensure COASTAL CONSTRUCTION MANUAL G-15 GLOSSARY Volume I safe living conditions, or (2) any alteration of a "historic structure," provided that the alteration will not preclude the structure's continued designation as a "historic structure." Super typhoons — Storms with sustained winds equal to or greater than 150 mph. �I Threat — The probability that an even of a given recurrence interval will affect the building within a specified period. See Risk. Tornado — A rapidly rotating vortex or funnel of air extending groundward from a cumulonimbus cloud Tributary area — The area of the floor, wall, roof, or other surface that is supported by the element. The tributary area is generally a rectangle formed by one-half the distance to the adjacent element in each applicable direction. Tropical cyclone — A low-pressure system that generally forms in the tropics, and is often accompanied by thunderstorms. Tropical depression — Tropical cyclone with some rotary circulation at the water surface. With maximum sustained wind speeds of up to 39 miles per hour, it is the second phase in the development of a hurricane. Tropical disturbance — Tropical cyclone that maintains its identity for at least 24 hours and is marked by moving thunderstorms and with slight or no rotary circulation at the water surface. Winds are not strong. It is a common phenomenon in the tropics and is the first discernable stage in the development of a hurricane. Tropical storm — Tropical cyclone that has 1-minute sustained wind speeds averaging 39 to 74 miles per hour (mph). Tsunami — Long -period water waves generated by undersea shallow -focus earthquakes, undersea crustal displacements (subduction of tectonic plates), landslides, or volcanic activity. Typhoon — Name given to a hurricane in the area of the western Pacific Ocean west of 180 degrees longitude. Underlayment — One or more layers of felt, sheathing paper, non -bituminous saturated felt, or other approved material over which a steep -sloped roof covering is applied. Undermining — Process whereby the vertical component of erosion or scour exceeds the depth of the base of a building foundation or the level below which the bearing strength of the foundation is compromised. Uplift — Hydrostatic pressure caused by water under a building. It can be strong enough lift a building off its foundation, especially when the building is not properly anchored to its foundation. G-16 COASTAL CONSTRUCTION MANUAL Volume I GLOSSARY V Variance — Under the National Flood Insurance Program, grant of relief by a community from the terms of a floodplain management regulation. Violation — Under the National Flood Insurance Program (NFIP), the failure of a structure or other development to be fully compliant with the community's floodplain management regulations. A structure or other development without the elevation certificate, other certifications, or other evidence of compliance required in Sections 60.3(b)(5), (c)(4), (c)(10), (d)(3), (e)(2), (e)(4), or (e)(5) of the NFIP regulations is presumed to be in violation until such time as that documentation is provided. Vulnerability — Weaknesses in the building or site location that may result in damage. See Risk. Water surface elevation — Under the National Flood Insurance Program, the height, in relation to the National Geodetic Vertical Datum of 1929 (or other datum, where specified), of floods of various magnitudes and frequencies in the floodplains of coastal or riverine areas. Wave — Ridge, deformation, or undulation of the water surface. Wave height — Vertical distance between the wave crest and wave trough. Wave crest elevation is the elevation of the crest of a wave, referenced to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum. Wave overtopping — Occurs when waves run up and over a dune or barrier. Wave runup — Is the rush of water up a slope or structure. Wave runup occurs as waves break and run up beaches, sloping surfaces, and vertical surfaces. Wave runup depth — At any point is equal to the maximum wave runup elevation minus the lowest eroded ground elevation at that point. Wave runup elevation — Is the elevation reached by wave runup, referenced to the National Geodetic Vertical Datum or other datum. Wave setup — Increase in the stillwater surface near the shoreline due to the presence of breaking waves. Wave setup typically adds 1.5 to 2.5 feet to the 100-year stillwater flood elevation and should be discussed in the Flood Insurance Study. Wave slam — The action of wave crests striking the elevated portion of a structure. Wet floodproofing — A flood retrofitting technique that involves modifying a structure to allow floodwaters to enter it in such a way that damage to a structure and its contents is minimized. COASTAL CONSTRUCTION MANUAL G-17 GLOSSARY Volume I Z Zone A — Under the National Flood Insurance Program, area subject to inundation by the 100-year flood where wave action does not occur or where waves are less than 3 feet high, designated Zone A, AE, Al- A30, A0, AH, or AR on a Flood Insurance Rate Map. Zone AE — The portion of the Special Flood Hazard Area (SFHA) not mapped as Zone VE. It includes the Moderate Wave Action area, the Minimal Wave Action area, and the riverine SFHA. Zone B — Areas subject to inundation by the flood that has a 0.2-percent chance of being equaled or exceeded during any given year, often referred to the as 500-year flood. Zone B is provided on older flood maps, on newer maps this is referred to as "shaded Zone X." Zone C — Designates areas where the annual probability of flooding is less than 0.2 percent. Zone C is provided on older flood maps, on newer maps this is referred to as "unshaded Zone X." Zone V — See Coastal High Hazard Area. Zone VE — The portion of the coastal Special Flood Hazard Area where base flood wave heights are 3 feet or greater, or where other damaging base flood wave effects have been identified, or where the primary frontal dune has been identified. Zone X — Under the National Flood Insurance Program, areas where the flood hazard is lower than that in the Special Flood Hazard Area. Shaded Zone X shown on recent Flood Insurance Rate Maps (Zone B on older maps) designate areas subject to inundation by the 500-year flood. Unshaded Zone X (Zone C on older Flood Insurance Rate Maps) designate areas where the annual probability of flooding is less than 0.2 percent. Zone X (Shaded) — Areas subject to inundation by the flood that has a 0.2-percent chance of being equaled or exceeded during any given year, often referred to the as 500-year flood. Zone X (Unshaded) — Designates areas where the annual probability of flooding is less than 0.2 percent. G-18 COASTAL CONSTRUCTION MANUAL Index, Volume Bold text indicates chapter titles or major headings. Italicized text indicates a figure or table. A Alaska Coast, 2-13, 3-20 Coastal environment, 3-7 All -hazards approach, 2-16, 4-14, 4-15, 4-25, 5-2 ASCE (see Building codes and standards) Atlantic Coast, 2-4, 3-5, 3-5, 3-10, 3-21, 3-54, 3-68 Map and timeline of milestones, significant events, regulations, codes, andpractices, 2-2 Mid - Delineation of coastline, 3-5 Environment, 3-5 Flood and wind events, 2-7 North Delineation of coastline, 3-5 Environment, 3-5 Flood and wind events, 2-4 South Delineation of coastline, 3-5 Environment, 3-5 Flood and wind events, 2-8 B Barrier island, construction on, 3-43, 3-62, 4-19 Erosion of, 3-36, 3-43 Exposure of homes to coastal effects, 2-8, 2-17, 2-19, 3-30, 3-43 Location of, 3-5, 3-6 Base flood, 1-10, 3-54, 3-60, 6-4 (see also 100-year flood; Zones) Base flood elevation (BEE), 1-6, 3-54 Elevating above (see Freeboard) Establishing based on wave height, 2-9, 3-59, 3-60 Establishing based on wave runup, 3-61, 3-68 Mapping, 3-54, 3-56, 5-9 NFIP requirements, 5-7, 5-20 Relationship with design flood elevation (DFE), 2-9, 2-10 Rounding of, 3-54 Terminology box, 2-9 Use of space below, 2-26, 5-12 (see also Enclosures) Wave height, 1-10 Dune and bluff erosion during, 3-62, 3-68 Relationship to sea level rise, 3-66 Wave heights, relationship to flood hazard zones, 3-56, 3-59 Basement, 2-21, 5-9 NFIP definition, 2-21 Zone AE, Al-A30 minimum requirements, 5-9 Zone AO, 5-10 Basic wind speed, 3-12, 5-17 (see also Wind speed) Design levels, 3-12, 6-8, 5-17 Map, ASCE 7-10 wind speed map, 3-13 Risk Category II structures, recurrence interval for, 6-4 Topographic influences, 2-15, 2-18, 3-12, 3-15 Wind speed map, IRC and ASCE, about, 3-12, 5-17 Bays, 3-5 Construction regulation near, 5-1 Damage in, 2-8, 2-12, 2-27 3-20, 4-23 Development in, 3-45, 4-10, 4-26 Erosion, relationship to, 3-42, 3-44 Exposure of homes to coastal effects of, 2-17, 2-19 High velocity flows, 3-29 Lot configurations near, 4-22 (see also Siting) Storm surge, 3-11 Wave amplification, in, 3-20 Beach erosion, examples of, 3-37 through 3-39, 4-27 Beach nourishment, 3-3, 3-47 Related to siting decisions, 4-28 Bearing capacity of soils, loss of during liquefaction, 3-18 Berm, siting near, 2-19 Best practices, 1-5, 2-23, 2-24, 3-17, 5-3, 5-15, 5-18, 5-21 through 5-32, 6-6 Coastal A Zone, 2-16, 5-18, 5-20 COASTAL CONSTRUCTION MANUAL I-1 INDEX Volume I Planning, Growing Smart, APA, 5-2, 5-3 Summary table, with NFIP requirements, 5-21 through 5-32 Zone A, 5-18 Zone V, 5-18, 5-20 Bluffs, 2-13, 2-14, 2-17, 3-3, 3-5, 3-6, 3-23, 3-36, 3-42, 4-24 Building on lots close to shoreline, 4-25 (see also Siting) Damage on or related to, 3-39, 3-49, 3-53, 4-22 Effect of altering vegetation or drainage on, 3-49 Effect of siting on wind speeds, 2-18, 3-15 Erosion, in relationship to FIS/FIRM, 3-62, 3-66, 3-67 Great Lakes, setbacks, 4-25 Vulnerability to erosion, erodible, 2-19 Vulnerability to seismic activity, 3-53 Wave runup, 3-61 Breakaway walls, 2-10, 2-25, 2-26, 2-27 2-28, 3-33, 5-10, 5-12, 5-19 Alternatives, in Zone V, 5-19 Effect on insurance premiums, 2-26, 6-12, 6-13 Foundations, relationship to, 5-14 NFIP requirements, 5-14, 5-22 through 5-32 Recommendations relating to, 5-22 through 5-32 Building codes and standards, 1-1, 5-15 AF&PA, 5-17 AISI, 5-17 ASCE 7 Basic wind speed, 3-12, 3-13, 5-17, 6-4, 6-8 Reference standard, as a, 5-15, 5-17 Risk Categories, 6-7 Seismic load provisions, 3-17 Snow loads, 3-27 Summary table, with NFIP requirements, 5-21 through 5-32 Wind-borne debris requirements, 2-23 Wind speedup due to topographic effects, calculating, 3-15 ASCE 24, 6-8, 6-9 Best practices, as guidance for, 5-18 Coastal A Zone, 1-6, 6-8 Flood openings, 5-10 Freeboard, 5-18, 6-8, 6-9 Reference standard, as a, 5-16, 5-17, 6-8, 6-9 Summary table, with NFIP requirements, 5-21 through 5-32 Engineered design, 5-17 IBC BFE data source, 5-9 Coastal A Zone, 1-6 Freeboard requirements, 6-8, 6-9 Model building code, as, 5-15 Reference standards, 1-6, 5-15, 5-16, 5-17, 6-9 Risk Category, 6-7 Seismic load provisions, 3-17 Summary table, with NFIP requirements, 5-21 through 5-32 Zone A, 5-18 ICC, 5-17 IEBC, 5-16 IFC, 5-16 IFGC, 5-16 IMC, 5-16 International Code Series (I -Codes), 1-1 IPC, 5-16 IPSDC, 5-16 IRC Basic wind speed, 3-12, 5-17 Best practices, as guidance for, 1-5 BFE data source, 5-9 Engineered design, 5-17, 5-18 Freeboard, 1-5, 6-8, 6-9 Model building code, as, 5-15 Reference standards, 5-15, 5-16, 5-17 Seismic load provisions, 3-17 Summary table, with NFIP requirements, 5-21 through 5-32 Termites map, 3-26 Zone A, 5-18 NFPA 5000, 5-16 Prescriptive design, 5-17, 5-18 Breakaway walls, 5-14 Building envelope, 1-3, 2-16, 2-23, 3-12, 3-15 Damage examples, 3-14, 3-15 Effect on, when sited near large trees, 4-27 High wind effect on, 2-10, 2-17, 2-23, 2-25, 3-12, 3-16 Maintenance of, 2-30 Building Performance Assessment Team (BPAT), 2-1, 2-4 Building (see also Elevation of buildings) Historical performance of, 2-1 Identifying suitable property for, 4-4 Relocation, when threatened, 4-22 Successful practices, 1-3, 1-4, 2-16 Type focused on in this Manual, 1-2 Use, 1-5 Use of moveable, in erosion -prone areas, 4-20 Warning box, poor siting, 4-3 Bulkheads (see Erosion control structures) CFR Section 60.3, Title 44, 5-7, 5-10, 5-17 (see also NFIP; Regulatory requirements) Cluster development, 4-20, 4-21 (see also Siting, Developing raw land) I-2 COASTAL CONSTRUCTION MANUAL Volume I INDEX Coastal A Zone, 1-10, 3-55, 5-18 (see also Zone A; MoWA; LiMWA; NFIP flood hazard zones) Best practices in, 2-16, 2-21, 3-59, 4-12, 5-18, 5-20, 5-21 through 5-32 Enclosures, 2-26, 5-10, 5-12 Freeboard in, 1-5, 6-8, 6-9 Mapping and the LiMWA, 3-55, 3-57, 3-69 Recommendations for more stringent requirements in, 1-6, 2-8, 2-9, 2-11 Terminology box, 3-56 Warning box, building in, 5-10 Coastal Barrier Improvement Act of 1991 (CBIA), 5-3 Coastal Barrier Resources Act of 1982 (CBRA), 5-3 Coastal barrier resource areas, 5-3 FIRM mapping, 5-4 Coastal Barrier Resources System (CBRS), 5-3 Coastal flood hazard area, 1-2 BFEs, 3-54, 3-60, 3-61 Design in, 2-20 Flood hazard zones, 3-55 Wave runup, 3-61 Coastal environment, 3-2 Alaska, 3-7 Atlantic, 3-5 Coastal processes, 3-3 Geology and geomorphology, 3-2 Great Lakes, 3-6 Gulf of Mexico, 3-6 Hawaii and Pacific Territories, 3-7 Pacific, 3-6 Reducing risk in, 6-1 Requirements in, 5-1 Sediment budget, 3-3 Siting in, 2-18 (see also Siting) U.S. Caribbean Territories, 3-6 Coastal hazards, 3-12 Earthquakes, 3-17 (see also Seismic hazard; Tsunami) Erosion, 3-35 Flooding (see Flood hazard) Future conditions and events, forecasting, 4-10, 6-3 (see also Recurrence interval) Hail, 3-26 High wind, 3-12 Ice, Atmospheric, 3-27 Ice, Floating, 3-27 Information sources, 4-8 Landslides and ground failures, 3-52 Probability ofoccurrence, 6-5 Rain, 3-26 Salt spray and moisture, 3-25 Sea and lake level rise, 3-21 Sediment deposition and burial, 3-52 Siting considerations, 4-5, 4-9 Snow, 3-27 Spring tide, effect on hazard, 3-8 Subsidence and uplift (land), 3-24 Termites, 3-26 Tsunamis, 3-19 Warning box, effects of combined natural hazards, 3-1 Wildfire, 3-27 Coastal High Hazard Area, 1-1, 3-55, 5-10 (see also Zone V) CZMA, 5-4 Designation on FIRM, 3-55 IRC provisions, 5-17 NFIP definition, 3-55 Coastal processes (see Coastal environment) Coastal sediment budget (see Coastal environment) Coastal storms, 3-7 El Nino Southern Oscillation, 2-14, 3-11 Examples of damage, 2-7 2-14 Great Lakes, 3-11 Hurricanes, 3-8 Nor'easters, 3-10 Saffir-Simpson Hurricane Wind Scale, 3-9 Tropical cyclones, 3-8 Typhoons, 3-8 Coastal flood effects, 3-21, 3-28 Flood -borne debris, 3-33 Hydrodynamic forces, 3-28 Hydrostatic forces, 3-28 Storm surge, 3-28 (see Storm surge) Waves, 3-31 Coastal Zone Management Act of 1972 (CZMA), 5-4 Column foundation (see Foundation) Community rating system (CRS), 3-55, 5-6, 5-14 Connections Best practices, 6-9, 6-13 Corrosion, 2-22, 3-25, 3-25 Failure, 2-8, 2-10, 2-22, 2-25, 2-25, 3-15, 3-18 Salt spray, effect on, 2-23 Construction, 2-24 Best practices, 2-24 Constructability, 1-5 Land use regulations, pertaining to, 5-2 NFIP regulations, pertaining to, 5-5 Planning for, 1-3 Poor, consequences of, 2-8, 2-9, 2-11, 2-15 Pre- and post -FIRM, performance of, 2-6 Seismic area, in, 3-17 Tsunami area, in, 3-18 Continuous load paths (see Loads) Costs, long-term, 1-5, 6-7, 6-16 Cross -shore sand transport, terminology box, 3-3 COASTAL CONSTRUCTION MANUAL I-3 INDEX Volume I D Debris (see Loads; Flood -borne debris; Wind-borne debris) Deck, 2-23, 3-31, 3-33 (for Roof decks, see Roof) Examples of loss of, 2-7 NFIP requirements, 5-11, 5-29, 5-30 Design, 2-20, 5-21 Above minimum requirements, 6-9 Elevating, example of, 6-15 Certifications, 5-27 Conditions, greater than, 1-5, 6-7, 6-9 Earthquake hazard, for, 3-17 Effect on insurance savings, premiums, and penalties, 6-12 Engineered, 5-17, 5-18 Erosion hazard, factors of safety for, 6-8 Event, terminology box, 1-4 Flood elevation (DFE), 6-10 Relationship to BFE, 2-9 Terminology box, 2-9 Flood hazard, factors of safety for, 6-8 Framework for success, 1-4 Levels Events below, 2-10, 2-11, 3-12, 3-14, 3-15 Exceeding, 3-12, 3-14, 6-3, 6-7 Seismic hazard, factors of safety for, 6-8 Sustainable, 1-6, 5-31 Warning, importance of proper planning, siting, and design, 3-40 Wind hazard, factors of safety for, 6-8 Wind speed (see Basic wind speed; Wind speed) Development guidelines (see Siting, Developing raw land; Siting, Developing existing lots) Digital FIRM (DFIRM), 3-55, 3-56 (see also Flood Insurance Rate Map [FIRM]; National Flood Insurance Program [NFIP]) Example of, 3-58 Dunes, 2-16, 3-3, 3-29 Avoidance of building on, 4-13, 4-15, 4-17 Avoidance of damage to, 4-16, 4-17 Buildings sited on, 2-19 Effect on wind speeds, 3-15 Erosion considerations, in relationship to FIRM, 2-17, 3-43, 3-62 Erosion example, 3-36, 3-63 Erosion mapping procedures, NFIP, 3-62, 3-63, 3-64, 3-68 Erosion of, 2-19, 3-3, 3-36, 3-40, 3-42, 3-62 Frontal reservoir, NFIP mapping requirement, 3-62, 3-67 Great Lakes, 3-6 Loss, effect of, 4-9 Primary frontal dune (NFIP), 3-54, 3-55, 3-56, 3-61, 3-68 Restoration, related to siting considerations, 4-28 Vegetation of, 3-63, 4-29, 5-11 Wave runup, 3-61 Zone V, alterations in, 5-10, 5-11 Zone V boundary, 3-65, 3-68 E Earthquakes (see Seismic hazard) Effects of multiple storms, 2-7 2-13, 2-17, 2-18, 3-64, 4-11 Elevation certificate, 5-32 Elevation of buildings (see also Freeboard; Lowest floor; Lowest horizontal structural member) Above minimum requirements, 2-16, 5-18, 5-19, 5-20, 5-23, 6-9, 6-14, 6-15 Corrosion rates, affecting, 3-26 Example of success, 2-22, 3-30 Seismic effects, 3-18 Zone A NFIP requirements, 5-9 Zone AE and Al-A30 NFIP requirements, 5-9 Zone AO NFIP requirements, 5-10 Zone V NFIP requirements, 5-11 El Nino Southern Oscillation, 2-13, 2-14, 3-11 Enclosures, 1-4, 2-26, 6-9 (see also Breakaway walls) ASCE 24 criteria, 5-10 BFE, below, 5-14 Breakaway walls in, 2-10, 2-26, 2-27 Coastal A Zone recommendations, 2-26, 5-12, 5-18 Cost implications of, 6-12 Effect on insurance savings, premiums, and penalties, 2-26, 6-12, 6-13 Elevated, 2-29, 2-29 Examples, 2-27 2-28, 2-29, 2-30 Flood -borne debris, as source of, 2-26 Louvers and lattice, made of, 2-26, 2-28 NFIP requirements, Zone A, 2-26, 5-10, 6-13 NFIP requirements, Zone V, 2-26, 5-10, 5-18, 6-13 Summary table, with NFIP requirements, 5-25 Swimming pools, in, 2-24 Terminology box, 2-26 Two-story, 2-29, 2-30 Use of, 2-26 Warning box, below-BFE, 5-14, 6-13 Enhanced Fujita Scale (tornado), 3-16 EF Scale with wind speeds, 3-16 Erosion, 3-35 (see also Erosion control structures) Barrier islands, of, 3-43 Causes, 3-42 During storms, 3-42 Effects of alteration of vegetation, draining, or groundwater, 3-48 I-4 COASTAL CONSTRUCTION MANUAL Volume I INDEX Effects of shore protection structures, 3-47 Examples of, 2-3, 2-13, 3-11, 3-30, 3-36, 3-37 3-38, 3-39, 3-43, 3-44 3-45, 3-46, 4-11, 4-22, 4-23, 4-27 Factor of safety for design, 6-9 FIRM, incorporating effects on, 2-16, 3-43, 3-49, 3-50, 3-62,3-68 Great Lakes, 2-12, 3-35, 3-44, 3-49 Historical events, 2-6, 2-7, 2-9, 2-10, 2-12, 2-13, 2-14 Landslides and ground failures (see Landslides and ground failures) Long-term (see Long-term erosion) Manmade structures, due to, 2-19, 2-20, 3-47 (see also Erosion control structures) Measuring, 3-40 Overwash and sediment burial, 3-52 Passive, 3-48 Rates, 3-23, 3-40, 3-41 Rocky coastline, 3-4 Scour (see Scour) Seasonal fluctuations, 3-41 Threats due to, 2-21, 3-36, 4-10, 4-22 Tidal inlets, harbors, bays, river entrances, 3-44, 4-22 Warning box, minimum local regulations, 3-45 Erosion control structures, 3-47 Bulkheads, 3-48, 4-26, 4-27 5-11 Erosion, related to, 2-19, 3-35, 3-43, 3-47, 4-10 Failure of, 3-48 Groins, 2-19, 3-47, 2-20, 4-6 High -velocity flow, effects on, 3-28 Maintenance, 2-30 Offshore breakwaters, 3-47, 3-47 Restrictions, related to, 4-5, 5-11 Revetments, 2-19, 3-43, 3-48 Examples, 3-45, 4-26 Wave runup, 3-61 Seawalls, 2-19, 3-43, 3-48 Examples, 3-31, 3-37, 3-48 Great Lakes, 2-12, 2-13 Siting near, 2-19, 4-5, 4-26, 6-3 F 500-year flood, 2-12, 3-56, 3-69, 6-5, 6-15 Factors of safety, 6-7 Federal Emergency Management Agency (FEMA), 1-1 (see also NFIP) Contact information, 1-10 Hazard mitigation milestones, 2-2 through 2-5 Reports (see BPAT; MAT) Fetch, 3-11, 3-58, 3-60 Fill (see Structural fill) Flood -borne debris, 3-28, 3-33 Breakaway walls, as, 2-26 Examples, 2-10, 3-33, 4-23 Siting consideration, 4-22, 4-23 Summary table, with NFIP requirements, 5-21 through 5-32 Flood damage -resistant materials, 5-11 Requirements for use of, 5-7, 5-12, 5-14, 5-22 Flood hazard 100 year floodplain, 3-50, 3-56 100 year flood (see 100-year flood) 500-year flood (see 500-year flood) Adequacy of existing mapping, 3-65 Assessment for design, 3-64 Determining if FIRM accurately depicts flood hazard,3-65 Flood -borne debris, 3-33 Future conditions and events, forecasting, 4-10, 6-3 (see also Recurrence interval) IRC, 5-17 Loads, 3-28, 6-8 Long-term erosion effect on, 2-17, 3-42, 3-49, 3-66, 5-18 NFIP mapping, 3-62, 3-67 Probability ofoccurrence, 6-5 Recurrence intervals, 6-4 Siting considerations, 4-9 Updating flood hazard assessments, 3-67 Zones, 3-53 (see also NFIP flood hazard zones) Flood hazard zones, NFIP (see Zones) Flood insurance (see National Flood Insurance Program [NFIP]) Flood Insurance Rate Map (FIRM), 5-6 Assessing adequacy of, 3-65, 5-2 BEE on, 3-54, 3-61, 6-10 CBRS boundaries, 5-4 Coastal flood zones, 3-55 Digital (see DFIRM) Dune erosion procedures, 3-62 Erosion considerations, 3-62 Erosion, dune and bluff, inclusion on, 3-43, 3-62 Erosion, long-term, mapping considerations, 2-16, 3-23, 3-48, 3-50, 3-62, 3-66 Example of, 3-57 3-58, 3-63 FIRMS, DFIRMs, and FISs, 3-56 Insurance zone designations, 3-55, 5-9 Levee and levee protection, 3-64 Limitations for medium- to long-term planning, 3-23 LiMWA on, 3-57 3-58 Methods and assumptions underlying, 3-53 Milestones in mapping procedures and products, 3-67 COASTAL CONSTRUCTION MANUAL I-5 INDEX Volume I Minimum regulatory requirements, use of to determine, 5-7 NFIP, as part of, 5-5, 5-6 Older, 2-17, 3-55, 3-64 Pre- and Post-, 2-6, 2-8, 2-10, 2-21, 2-22, 5-12 Relationship to DFIRM, 3-56 Revising after a storm, 2-11 3-62, 3-63 Sea level rise, mapping considerations, 2-16, 3-23, 3-66 Warning boxes, in relationship to sea level rise, long- term erosion, and recent events, 2-16, 3-49, 3-64, 5-2 Flood Insurance Study (FIS), 3-56, 5-6 (see also FIRM and NFIP) Property information, source of information, 4-8 Flood openings, 2-26, 2-27 2-29, 5-9, 5-10 Summary table, with NFIP requirements, 5-21 through 5-32 Flood vents, warning box, 5-10 Flooding (see Flood hazard) Florida Building Code, 2-10 Florida Keys, 2-8, 2-9, 3-5, 3-6, 3-9 Footing, 2-21, 2-25 (see also Loads) Forces (see Loads) Foundation, 2-4, 2-11 Breakaway walls, relationship to, 5-14 (see also Breakaway walls) Damage, 2-7, 2-10, 2-15, 2-21, 2-25, 3-28, 3-32, 3-55, 4-12 Design, requirements in Zone A, 2-16 Design, requirements in Zone V, 5-10, 5-11 Earthquake effects on, 3-18 Erosion, effects on, 3-36, 3-42 (see also Foundation, scour) Loads Continuous load paths to, 1-4, 2-9, 2-10, 2-21, 2-22, 5-21 Flood -borne debris, 3-33 Wave, 5-10 Scour, effects of, 3-30, 3-51, 3-52 Siting, in two different flood zones, 4-12, 5-7 Substantial improvement and substantial damage, requirements related to, 5-12 Successful design, 1-3, 2-6, 2-13, 2-21, 3-30, 4-26, 6-8 Summary table, with NFIP requirements, 5-21 through 5-32 Swimming pools, effect of, 2-24 Types Column, 2-19 Continuous perimeter wall, 2-21, 2-21 Closed, 2-26 Masonry pier, 2-11 Open, 2-21 Pile, embedded, 2-21, 2-22, 2-25, 3-30, 4-25 Shallow spread, 2-21 Slab, 2-21, 3-32, 3-52 Undermining, 2-14, 2-19, 2-21, 3-37 4-26 Walls below BFE, 5-9 Freeboard, 1-6, 6-9 Coastal A Zone, in, 6-8 Effect on insurance savings, premiums, and penalties, 6-12 Exceeding NFIP requirements, 5-19, 5-23 IRC requirements, 1-5, 5-16, 5-23 Reasons to adopt, 2-21, 3-54 Relationship to BFE and DFE, 5-7 Role in coastal construction, 6-9 Safety factor, as, 6-8 Terminology box, 1-6 Free -of -obstruction requirements, 2-26, 2-27, 5-11, 5-12, 5-22 Frequency of hazard events, determining, 3-28, 4-9, 4-10, 6-3, 6-5 (see also Probability of hazard occurrence) G Gable ends, failure of, 2-24, 3-15 Geology and geomorphology, coastal, 3-2 Glazing, requirements in wind-borne debris regions, 2-23 Great Lakes Coast, 2-12, 3-6 Bluff setbacks, 4-25 Building on lots close to shoreline, 4-25 (see also Siting) Delineation of coastline, 3-5 Environment, 3-6, 3-10, 3-11 Erosion, 3-35, 3-44, 3-49 FIRMS, related to, 3-23, 3-59, 3-68 Flood and wind, 2-12 Probabilities, flooding, 6-5 Safety factors, 6-9 Siting, 4-8, 4-25 Snow and ice dams, 3-27 Warning box, probabilities during high lake levels, 6-4 Water level variations, 3-21, 3-22, 3-23, 3-25, 3-54 Wave runup elevations, 3-54, 3-68 Groins (see Erosion control structures) Ground failure, 3-20, 3-52 (see also Landslides and ground failures) Earthquake, result of, 3-17 Erosion, result of, 3-36 Ground motion and ground shaking, seismic, 3-17, 3-18, 6-8 Ground rupture, seismic, 3-17 Groundwater Effect of altering, 3-42, 3-48, 3-66, 4-10 Elevated, effects of, 2-12, 2-17 Great Lakes, 3-6, 3-11 I-6 COASTAL CONSTRUCTION MANUAL Volume I INDEX Siting considerations, 4-15, 4-24 Withdrawal resulting in subsidence (land), 3-24 Gulf of Mexico Coast Delineation ofcoastline, 3-5 Environment, 3-6 Flood and wind events, 2-9 H Hail, as hazard, 3-26 Insurance, 6-12 Harbors, 3-44 Damage to, 2-12, 3-19 Erosion near, 3-44 Tsunami wave amplification and resonance in, 3-20 Warning box, shoreline fluctuations near inlets, harbors etc., 3-44 Hawaii Delineation of coastline, 3-5 Design wind speeds, 3-12, 3-13 Environment, 3-7 Erosion, 4-8 Flood and wind events, 2-15 Tsunami events, 3-20 Hazards (see also Coastal hazards) Defining at site, 4-9 Disclosure of, 4-5 Evaluating effect for site, 4-10 Future conditions and events, forecasting, 4-10, 6-3 (see also Recurrence interval) Identification, 2-16, 3-1, 4-2, 6-3 Multiple, 3-27, 4-25, 6-3 Probability ofoccurrence, 6-5 Reducing, by good siting decisions, 4-11 Resisting, 1-5 Warning box, long-term changes can magnify hazards, 3-1 High -velocity flow, 2-17, 3-7, 3-28, 3-30 High -velocity wave action, 1-10, 3-55 High wind (see Wind hazard) Human activity, effect on erosion, 3-47 (see also Erosion control structures) Hurricane (see also Hurricanes, named) High -wind hazard, 3-12 Probability of occurrence, 6-5 Saffir-Simpson Hurricane Wind Scale, 3-9 Statistics, 3-9, 3-10 Tropical cyclones, 3-8 Typhoons and super typhoons, 3-8 Wind speeds, 3-8 Hurricanes, named, summary of, 2-2 through 2-5 Agnes, 3-9 Alicia, 2-10, 3-9 Andrew, 2-8, 2-8, 2-9, 2-10, 3-9, 3-14, 3-16 Bertha, 3-64, 4-11 Bob, 2-6, 3-9 Camille, 2-9, 3-9 Carla, 2-9 Charley, 2-10, 2-23, 2-23 Dennis, 4-4 Dolly, 3-9 Earl, 3-9 Floyd, 2-9, 3-37 4-4 Fran, 2-9, 2-21, 2-21, 3-32, 3-51, 3-62, 3-63, 3-64, 4-11 Frances, 3-9 Frederic, 2-9, 3-68 Georges, 2-10, 2-11, 3-33 Gloria, 2-6, 2-7 Hugo, 2-8, 2-11, 3-9, 3-16, 3-29, 4-26 Ike, 2-11, 2-17, 2-17, 2-18, 2-26 2-27 3-8, 3-9, 3-12, 3-14, 3-15, 3-51, 3-52 Iniki, 2-15, 3-14 Isabel, 2-8, 4-23 Ivan, 2-10, 2-22, 3-9, 3-32, 3-43, 4-16, 4-16 Katrina, 2-10, 2-11, 2-20, 2-21, 2-22, 2-24, 2-25, 2-25, 3-8, 3-9, 3-34 4-3, 4-17, 4-19 Long Island Express, 2-6, 2-6 Marilyn, 2-11, 2-12, 3-9 Mitch, 3-52 Opal, 2-10, 3-29, 3-30, 3-34 3-48, 3-53, 3-62, 3-68, 4-12 Hydrodynamic forces, 3-28 NFIP requirements, 5-8 Summary table, with NFIP requirements, 5-21 through 5-32 Hydrostatic forces, 3-28 NFIP requirements, 5-8, 5-9, 5-10 Summary table, with NFIP requirements, 5-21 through 5-32 Ice, 3-27 Atmospheric, 3-27 Floating, 3-27 Loads, 3-27 Increased Cost of Compliance, NFIP, 5-6 Insurance, hazard Earthquake, 6-12 Flood, National Flood Insurance Program, 6-11 (see also NFIP) Premiums and penalties, 6-12 Self, 6-12 Warning boxes COASTAL CONSTRUCTION MANUAL I-7 INDEX Volume I Coverage, 6-12 Relationship to design and construction, 6-11 Wind, 6-11 International Code Council (ICC) (see Building codes and standards) International Code Series (I -Codes) (see Building codes and standards) L Lake level rise, 3-21, 3-49, 4-5 (see also Subsidence) Land use regulations, 4-5, 4-15, 5-2 Source of information on, 5-2 Landslides and ground failures, 3-52 Bluff failure, 3-43 Coastal hazard, as, 2-17, 3-11, 3-20, 6-2 Earthquake, related to, 3-18 Erosion, related to, 3-36 Events, historical, 2-13, 2-14, 2-14 Siting, considerations in, 4-9, 4-10, 4-17, 4-25 Tsunami, related to, 3-19, 3-20 Vegetation removal, as cause of, 3-52 Wildfire, related to, 3-27 Levee and levee protection, 3-64 Accredited, 3-56 Failures, 2-10, 2-20, 6-3 Misconceptions about protection, 6-14 Related to NFIP, 3-56, 3-64 Risks of siting within, 2-19, 6-3, 6-14 Terminology box, 2-19 Limit of Moderate Wave Action (LiMWA), 3-55, 5-18 (see also Coastal A Zone) Example of, 3-57 3-58 FIRMS, shown on, 3-69, 5-7 Terminology box, 3-56 Liquefaction, soil, 3-17, 3-18 Littoral sediments, 3-4, 3-42, 3-44. 3-47, 3-47, 3-49, 4-10, 4-28 Loads Continuous load path, 1-4, 2-9, 2-10, 2-21, 2-22, 5-21 Debris, 3-19, 3-28, 3-33, 5-22, 5-24 Flood, 3-28, 6-8 Foundation, on, 5-11, 5-12 Hydrodynamic, 3-28 Hydrostatic, 3-28 Ice, 3-27 NFIP requirements, 5-14 Rain and hail, 3-26 Seismic, 3-17, 3-19, 6-8 Snow, 3-27, 5-17 Summary table, with NFIP requirements, 5-21 through 5-32 Swimming pool, transferred, 2-24 Tornado, weak, 3-17 Wave, 3-33, 5-10 Warning box, Coastal A Zone, 5-10 Wind, on buildings, 2-23, 3-12, 3-15, 6-9 Location (see Siting) Longshore sand transport, terminology box, 3-3 Long-term erosion, 2-7 2-17, 3-40, 3-42, 3-49, 3-49, 3-50, 3-65, 3-66, 4-4 5-18 Effect on wind speed, 3-15 NFIP mapping considerations, 3-62 Siting considerations, 2-18, 2-19, 4-5, 5-18 Vegetation, removal as cause of, 3-49 Warning, effects of on FIRM, 2-16, 3-49 Long-term hazards (see listing for each hazard: Erosion; Lake -level rise; Salt spray; Moisture; Sea level rise; Subsidence [land]; Uplift [land]) Not shown on FIRMS, 3-23 Siting considerations, 2-17, 4-4, 4-9 Lot layout, configuration, and design (see also Siting) Examples, 4-16through 4-21 Lowest floor (see also Elevation of buildings; Lowest horizontal structural member) Summary table, with NFIP requirements, 5-21 through 5-32 Terminology box, 2-21 Use of space below (see Enclosure) Zone A, requirements in, 5-9 Lowest horizontal structural member (see also Elevation of buildings) Elevating above minimum, 5-18, 6-15 Summary table, with NFIP requirements, 5-21 through 5-32 Use of space below (see Enclosure) Zone V, requirements in, 5-11, 5-12, 5-20 M Maintenance, 2-30, 4-5, 4-8 Mangrove stands Alterations of, in Zone V, 5-10, 5-11, 5-21 Warning box, 3-48 Manufactured homes, 2-9, 2-10, Warning box, 5-7 Mapping guidance, FEMA, 3-59, 3-67 Mean water elevation, 3-54, 3-58 Terminology box, 3-62 Mid -Atlantic Coast (see Atlantic Coast) Minimal Wave Action area (MiWA), 3-55, 3-57 Terminology box, 3-56 Mitigation Assessment Team (MAT), 2-1, 2-4 Moderate Wave Action area (MOWN), 3-55 3-57 (see also I-8 COASTAL CONSTRUCTION MANUAL Volume I INDEX Coastal A Zone) Terminology box, 3-56 Modified Mercalli Index (MMI) Scale, 3-18 Moisture, effect of, 3-25 Corrosion, 3-26 Wood decay, 3-26 Moveable buildings in erosion -prone areas, 4-20 Multiple storms, effect of, 2-7 2-13, 2-17, 2-18, 3-64, 4-11 N National Flood Insurance Program (NFIP), 5-5, 6-11 Base flood elevation, 2-10, 3-54 Community Rating System, 5-14 Dune (see also Dunes) Erosion procedures, 3-62 Primary frontal dune, 3-61 Exceeding minimum NFIP requirements, 5-18, 5-21, 5-21 through 5-32 Flood Disaster Protection Act, 2-7, 5-6 Flood hazard mapping, 3-62 Flood hazard studies, 5-5, 5-6 (see also Flood Insurance Study) Flood hazard zones, 3-53 (see also Zone A, etc.) Flood Insurance Rate Maps (FIRMS), 3-56, 5-6 (see also Flood Insurance Rate Maps) Flood Insurance Reform Act of 2004, 5-6 Flood Insurance Studies (FIS), 3-56, 5-6 (see also Flood Insurance Study) Flood insurance zones, 3-55 (see also Zone A, etc.) Flood Mitigation Assistance grant program, 5-6 History, 5-6 Increased cost of compliance, 5-6 Insurance restrictions, 5-6 CBRS, 5-3 Contents of enclosures, 2-26 Coverage, cap on, 6-11 Non -participating communities, 5-6 Warning box, buildings over water or below ground, 4-3 Levee, 3-64 LiMWA, 3-55 Mapping requirements Dune erosion procedures, 3-62, 3-63 Frontal dune reservoir, 3-62 National Flood Insurance Act of 1968, 5-6 National Flood Insurance Reform Act of 1994, 5-6 Regulatory requirements, minimum, 5-7, 5-8, 5-21 through 5-32 Repetitive Flood Claims grant program, 5-6 Severe Repetitive Loss grant program, 5-6 SFHA, related to NFIP, 5-5, 5-6 Minimum requirements, 5-7 Substantial damage and substantial improvement, 5-5, 5-12, 5-13 Minimum requirements, 5-7 Summary of regulatory requirements, 5-21 through 5-32 Vegetation, related to NFIP mapping, 3-54, 3-58, 3-61, 3-66 Warning boxes Buildings over water or below ground, 4-3 Exceeding requirements, 5-7 Zone A (see also Zone A) Exceeding minimum requirements, 5-18 Minimum requirements, 5-7, 5-9 Zone V (see also Zone V) Exceeding minimum requirements, 5-18 Minimum requirements, 5-7, 5-10 NFIP flood hazard zones (see also Zone A; Zone B; etc.) Base flood elevations, 3-54 North Atlantic Coast (see Atlantic Coast; Coastal storms, Nor'easters) 0 100 year flood (see also Base flood) Misconceptions about, 6-14 Probability ofoccurrence, 6-5 Relationship to 1-percent annual -chance -flood, 6-4 Occupancy category (see Risk, Categories) Offshore breakwaters (see Erosion control structures) Open space, to reduce hazards in lot layout, 4-20 Otherwise Protected Area (OPA), 5-3 (see also Coastal Barrier Improvement Act of 1991 [CBIA] and CBRA) FIRM mapping, 5-4 NFIP insurance restrictions within, 5-3 Overhangs, roof, 2-23, 2-24, 4-4, 6-13 Overwash, 3-36, 3-52 Examples of, 3-11, 3-38, 3-53 Pedestrian access, 4-27 Sediment budget, as part of, 3-3 Siting considerations, 4-17 P Pacific Coast Delineation of coastline, 3-5 Environment, 3-6 Flood and wind events, 2-13 Passive erosion, 3-48 (see also Erosion) Patio (see Deck) Pedestrian access, siting of, 4-27 Pier, 3-32 COASTAL CONSTRUCTION MANUAL I-9 INDEX Volume I Post -disaster performance and recommendations Construction, 2-24 Design, 2-20 Enclosures, 2-26 Hazard identification, 2-16 Maintenance, 2-30 Siting, 2-18 Premiums and penalties, insurance, 6-12 Basis of, 6-11 Building above minimum requirements, effect on, 6-9, 6-10 CRS, related to, 5-14 Design choices, effect on, 6-12, 6-15 Elevation, effect on, 6-12, 6-15, 6-16 Enclosures, 2-26 through 2-29, 6-12, 6-13 Factors of safety, related to, 6-7 FIRM, relationship to, 5-7 Freeboard, effect on, 1-6, 6-10, 6-16 Siting considerations, 4-8 Space below the BFE, 5-14 Wind, 6-13 Prescriptive design, 5-17 Breakaway walls, 5-14 Primary frontal dune, 3-54, 3-56, 3-61, 3-68 Zone V, 1-10, 3-55 Probability of hazard occurrence, 6-3 (see also Recurrence interval) Frequency - recurrence intervals, 6-5 R Rain Events, 2-7, 2-8, 2-9, 2-10, 2-13, 2-14 Hazard, 3-26 Penetration of building envelope, 2-23, 3-15 Raw land, developing (see Siting) Recurrence interval, 6-4 (see also Seismic hazard; Flood hazard, etc.) Frequency - recurrence intervals, 6-5 Future conditions and events, forecasting, 4-10, 6-3 Regulatory requirements, 5-1, 5-21 through 5-32 (see also Codes and standards; NFIP) Repetitive Flood Claims grant program, 5-6 Residual risk, 6-1, 6-3, 6-5, 6-6, 6-10 Communicating to clients, 6-13 Managing through insurance, 6-10 Relationship to minimum regulatory and code requirements, 6-6, 6-7, 6-8 Siting decision, related to, 4-2, 4-30 (see also Siting) Terminology box, 6-2 Warning box, determining acceptable level, 4-5, 6-5 Retrofit Flood, 2-9 Insurance savings, 6-11 Seismic, 3-19 Revetment (see Erosion control structures) Richter Scale, 3-17 Risk (see also Residual risk) Acceptable level of, 6-5 Analysis, 6-1 Assessing, 4-2, 6-2 Benefits of elevating above minimum requirements, example, 6-15 Categories per ASCE 7-10 and 2012 IBC, 6-7 Communicating to clients, 6-13, 6-15 Multiple hazards, cumulative effect of, 6-3 Predicted, 4-30, 6-3 Reduction, 4-2, 6-1, 6-5, 6-6 Design and construction, through, 6-5, 6-6 Factors of safety, 6-7 Management through insurance, 6-10 Siting decision, related to, 4-30 (see also Siting) Terminology box, 6-2 Tolerance for, 1-5 Warning boxes Acceptable levels of actual and residual risk, 4-5 Importance of investigating potential risk to sites, 4-3 River entrances, 3-44 Lot configurations near, 4-22 (see also Siting) Warning box, stabilization by jetties, 3-44 Riverine Riverine floodplain requirements, 5-9 SFHA, terminology box, 3-56 Warning box, riverine floodplain requirements, 5-9 Road near shoreline, 4-15 (see also Siting) Shore -normal, high -velocity flows related to, 3-29 Shore -parallel, 4-16, 4-17, 4-18 Roof, 2-10, 2-11, 2-15, 2-23, 2-25, 6-9 Damage to, examples, 2-8, 2-12, 2-18, 2-24, 3-14 Fire -rated, use of, 3-27 Hail, effect on, 3-26 Notching, around tree, 4-27, 4-28 Overhangs, damage to, 4-4 Pressurization of building, effect on, 2-23 Rain, loads on, 3-26 Snow, loads on, 3-27 Tornado, effect on, 3-17 Wind-borne debris, effect on, 3-15 S Saffir-Simpson Hurricane Wind Scale, 3-8, 3-9 Salt spray, 2-23, 3-25, 4-8 Scour, 2-19, 3-42, 3-51, 3-52 I-10 COASTAL CONSTRUCTION MANUAL Volume I INDEX Channelized flow, 3-29, 3-30 Coastal A Zone, in, 5-18 Examples of, 2-21, 3-30, 3-32, 3-51, 3-52 Protective structures, near, 2-19, 3-48 Shallow spread footing and slab foundation, potential for, 2-21, 2-21 Swimming pools, near, 2-24 Sea level rise Discussion of, 1-1, 3-21 Effect on FIRM accuracy, 3-66 Siting considerations, 4-5 Warning box, accounting for on FIRMS, 2-16 Seawall (see Erosion control structures) Sediment Budget, 3-3, 4-7 Burial, 3-40, 3-52 Seismic hazard Bluff failure, cause of, 3-53 Construction considerations, 2-18, 3-17 Earthquake, discussion of, 3-17 Earthquake insurance, 6-12 Effects Ground motion, shaking, rupture, 3-17 Liquefaction of soil, 3-17, 3-18 Rapid uplift, 3-17 Soil consolidation, 3-17 Elevation of building, effects on, 3-18 Future conditions and events, forecasting, 4-10, 6-3 (see also Seismic hazard, Return period for design) Load, 3-17, 3-19, 6-8 Measuring Modified Mercalli Index (MMI) Scale, 3-18 Richter Scale, 3-17 Return period for design, 6-4 Seismic Design Category E, 5-17 Siting considerations, 4-9 Subsidence, 3-17 Tsunami, discussion of, 3-19 Self insurance, 6-12 Septic systems, effect on stabilization, 2-17, 3-49 Setback, 1-2 Construction, 1-2, 3-49 Erosion considerations, 3-42, 3-66, 5-18 Exceeding minimum requirements, 6-9 Siting considerations, 4-5, 4-7 4-9, 4-13, 4-15, 4-16, 4-24, 4-25 Warning box, 3-40 Severe Repetitive Loss grant program, 5-6 Shore protection structures, 3-47 (see also Erosion control structures) Shoreline -parallel road (see Siting, Road placement near shoreline) Siting, 1-5, 2-18, 4-1 Beach nourishment and dune restoration considerations, 4-28 Compiling information, 4-6, 4-7 Decisions Effect on insurance savings, premiums, and penalties, 6-12 Final, 4-30 Defining coastal hazards, 4-9 Developing existing lots, 4-3, 4-23 Adjacent to Large Trees, 4-27, 4-28 Guidelines for Building on Existing Lots, 4-24 Lots close to shoreline, 4-25 Near erosion control structures, 4-5, 4-26 Pedestrian access, 4-27 Developing raw land, 4-3, 4-13 Guidelines for Developing Raw Sites, 4-15 Lot layouts, examples, 4-16through 4-21 Moveable buildings in erosion -prone areas, 4-20 Lot configurations near shoreline, 4-17 Lot configurations near tidal inlets, bay entrances, river mouths, 4-22 Road placement near shoreline, 4-15 Evaluating coastal hazards, 4-10 Evaluating hazards and potential vulnerabilities, 4-9 Evaluation ofproperty, 4-2 Future development, 4-5 Great Lakes, 4-8, 4-25 Identifying suitable property, 4-4 Land use regulations, 5-2 Long-term increase of vulnerability, 4-5 Multiple zones, on, 4-12 Near rocky shorelines, 2-19 Near shoreline, 2-18 Reducing hazards by siting decision, 4-13 Regulations and requirements, 4-5 Vulnerabilities related to, 6-3 Warning boxes Beach nourishment and dune restoration in relationship to siting, 4-28, 4-29 Future flood and erosion hazards, 3-64 Importance of proper planning, siting, and design, 3-40 Lot layout and siting along eroding shorelines, 4-15 Poor, 4-3 Post -disaster changes in hazards, 5-2 Regulations in relationship to hazards, 3-45, 4-10, 6-5 Zone V NFIP requirements, 5-10 Slope stability (see also Landslides and ground failures) Hazards, 2-17 Siting considerations, 4-9 Vegetation removal, 3-27 Snow hazard, 3-27 Loads greater than 70 pounds per square foot, 5-17 Soil COASTAL CONSTRUCTION MANUAL I-11 INDEX Volume I Liquefaction, 3-17, 3-18 Seismic consolidation, 3-17 South Atlantic Coast (see Atlantic Coast) Special Flood Hazard Area (SFHA), 1-10, 2-10, 5-5, 5-7 Designing of buildings in, 5-2, 5-7 Flood insurance zones, in relationship to, 3-55 History of, 5-6 Minimum NFIP requirements, 5-7, 5-8 NFIP/FIS, related to, 5-5, 5-6, 5-7 Relationship to MiWA and LiMWA, 3-56 Siting and land use in, 5-2 Substantial improvement and substantial damage, NFIP requirements, 5-12 Terminology box, 1-10, 3-56 Zone A requirements, 5-9 Zone V requirements, 5-10 Stillwater elevation, 3-54, 3-57 Accuracy in FIRM/FIS, 3-65 Mean water levels, relationship to, 3-58, 3-62 NFIP consideration, 3-54 Relationship to wave height, 3-60 Source of, 3-68 Storm surge Damage, 2-6, 2-7, 2-8, 2-9, 2-10, 2-11, 2-11, 2-12, 2-13, 2-17, 2-20, 2-21, 2-22, 3-7 3-29, 3-32, 3-34 Great Lakes, 3-6, 3-11 Modeling, 3-68 Pacific coast, 3-6, 3-11 Relationship to Saffir-Simpson Scale, 2-1, 2-11, 3-8, 3-29 Stillwater elevation, 3-54, 3-68 Storm tide, 3-66, 3-68 Structural fill Elevation on, 2-21, 3-18 Requirements in Zone V, 5-11, 5-12 Summary table, with NFIP requirements, 5-21 through 5-32 Subsidence (land) Freeboard, as contingency for, 6-10 Long-term, 3-24, 3-49 Relative to water levels, 3-23 Risk, long-term, 6-3 Seismic related, 3-17 Siting considerations, 4-7 Substantial damage Coastal zone management, 5-5 NFIP requirements, general, 5-5, 5-7, 5-8 Terminology box, 5-5 Zone V requirements, 5-12, 5-13 Substantial improvement CBRS insurance restrictions, 5-3 Coastal zone management, 5-5 NFIP requirements, general, 5-5, 5-7, 5-8 Terminology box, 5-5 Zone V requirements, 5-12, 5-13 Super typhoon, 3-8 Sustainable building design, 1-6, 5-31 Swimming pools, 1-8, Below elevated buildings, 2-24 Building performance, related to, 2-24 Recommendations and NFIP requirements regarding, 5-30 Siting considerations, 4-24 T Termites, 3-26 Tidal inlets, 3-5, 3-44, 3-66, 4-23 Buildings located near, 2-19 Erosion near, 3-38, 3-42, 3-44 Lot configurations near, 4-22 (see also Siting) Warning box, shoreline fluctuations near inlets, harbors etc., 3-44 Topography Effect on tsunami runup, 3-19 Effect on wildfire hazard, 3-27 Effect on wind speed estimation, 2-17, 2-18, 3-12 Relationship to BEE, 3-54 Siting, 4-7, 4-13, 4-24 Tornado,3-16 Enhanced Fujita Scale, 3-16 High wind hazard, 3-12 Tree, siting building adjacent to large, 4-27, 4-28 Tropical cyclones, 3-8 (see also Tropical storms; Hurricanes; Typhoons) Tropical storms Agnes, 2-7 Alberto, 3-29 Allison, 2-10, 3-7 Definition of, 3-8 High wind hazard, 3-12 Probability ofoccurrence, 6-5 Wind speeds, 3-8 Tsunami Discussion of, 3-19 Examples of damage, 2-13, 2-15, 3-19 High -velocity flow, 3-29 Mapping, 3-68 Typhoon, 2-15, 3-8 Erosion during, 3-42 High wind hazard, 3-12 Paka, 2-15 Probability ofoccurrence, 6-5 Wind speeds, 3-8 I-12 COASTAL CONSTRUCTION MANUAL Volume I INDEX U Uplift (land) (see also Wave, Uplift forces) Long-term, 3-24, 4-7 Rapid, seismic, 3-17, 4-10 U.S. Caribbean Territories Delineation of coastline, 3-5 Environment, 3-6 Flood and wind events, 2-11 U.S. Pacific Territories Delineation of coastline, 3-5 Environment, 3-7 Flood and wind events, 2-15 Utilities, 4-3, 4-7 4-15, 4-15, 6-8 ASCE risk categories, 6-7 NFIP requirements, 5-8 Shore -parallel roads, on, 4-17, 4-18 Summary table, with NFIP requirements, 5-21 through 5-32 V Vegetation Dune, 3-64, 4-29, 5-11 Warning box, resistance of dune vegetation to coastal hazards, 4-29 Effects of removal of, 2-17, 3-12, 3-42, 3-48, 4-9 Landslides and ground failures, as cause of, 3-52 Long-term erosion, as cause of, 3-49 Flammable, 3-27 NFIP flood mapping, related to, 3-54, 3-58, 3-61, 3-66 Siting considerations, 4-7 4-23, 4-27 Vents, flood, 5-10 W Wave, 3-31 Coastal effect, 3-31 Crest elevation, 3-57 3-59 Relationship to wave height, 3-60 Terminology box, 3-59 Deflection, 3-31 Height, 3-54, 3-59 (see also Stillwater elevation) Calculation of, 3-60 Flood zones and BFE, 1-10, 2-9, 2-17, 3-55, 3-56, 3-61, 3-68, 5-7 Terminology box, 3-59 Loads, 3-33, 5-10 Overtopping, 3-55, 4-26 Reflection, 3-31 Runup, 3-31, 3-54, 3-61 High -velocity flow, 3-28 Revetment, against, 3-61 Terminology box, 3-62 Setup, 3-54 Terminology box, 3-62 Uplift forces, 3-32 Wildfire hazard, 3-27, 4-9 Wind-borne debris, 2-23, 3-15, 4-27 Wind hazard, 3-12 Building envelope, effect on, 3-16, 4-27 Damage examples, 242-12, 2-18, 2-23, 2-24 3-14, 3-15, 4-4 Future conditions and events, forecasting, 4-10, 6-3 (see also Recurrence interval) High -wind effects on buildings, 2-17, 3-12 Load, on buildings, 2-10, 2-23, 3-12, 3-15, 6-9 Map, ASCE 7-10 wind speed map, 3-13 Rainfall penetration, 3-15 Siting considerations, 4-9 Topography effect on wind speed, 2-18, 3-15, 4-10 Tornado, 3-16 Wind insurance, 6-11, 6-13 Warning box, 6-12 Wind load, 1-5, 2-10, 2-23, 3-15, 6-9 Wind speed, 3-12, 6-3 (see also Basic wind speed) Design (see Basic wind speed) Design beyond prescriptive provisions of IRC, 5-17 Enhanced Fujita Scale, as shown on, 3-16 Greater -than -design, 6-3, 6-8 Map, ASCE 7-10 wind speed map, 3-13 Sajfir-Simpson Hurricane Wind Scale, as shown on, 3-9 Topographic influences, 2-15, 2-18, 3-15, 4-10 Tornado, 3-16 Wind speed map, IRC and ASCE, about, 3-12, 5-17 Z Zone A, 1-10, 3-55 (see also Coastal A Zone) Best practices in, 1-5, 2-16, 5-18, 5-21 through 5-32 Breakaway walls in, 2-26 Coastal hazards in, 2-16, 3-52 Elevation Recommended, 5-19, 5-20 Required, 5-9 Enclosures in, 2-26, 2-29 Failures in, 2-10, 2-21, 4-12 FIRM example, 3-57 Foundation design, requirements in, 2-16 Levees, 3-64 (see also Levee and levee protection) Long-term erosion, not mapped on, 3-49 Minimum NFIP requirements in, 5-9 Siting in, 4-12 COASTAL CONSTRUCTION MANUAL I-13 INDEX Volume I Substantially damaged, related to, 5-7, 5-12 Summary table, with NFIP requirements, 5-21 through 5-32 Two-story enclosures in, 2-29, 2-30 Wave height, 3-59 Zone AI-A30 Elevation, required, 5-9 Enclosures in, 5-10 Zone AE, 3-55 Basement, in, 5-9 Elevation, required, 5-9 Enclosures in, 5-10 Terminology box, 3-56 Zone AO, 5-10 Basement, in, 5-9 Elevation, required, 5-10 Enclosures in, 5-10 Zone A, Coastal (see Coastal A Zone) Zone B, 3-56 Zone C, 3-56 Zone V, 1-10, 3-55 (see also Coastal A Zone) Best practices in, 5-18, 5-20 BEE, space below, 5-12 Breakaway walls in, 2-26 Building elevation in, 5-11 Enclosures in, 2-26, 5-11 (see also Enclosures) Erosion control structures in, 5-11 Fill, use of, 5-12 Foundation design in, 5-11 Freeboard, 1-5 Levee mapping, 3-64 Lowest horizontal structural member requirements, 5-20 Minimum NFIP requirements, 5-10 Siting in, 5-11 Substantial improvement and substantial damage, 5-12 Summary table, with NFIP requirements, 5-21 through 5-32 Wave height, 2-17, 3-61 Wave runup, 3-61 Zone VE, 3-55 Terminology box, 3-56 Zone X, 1-10, 3-56, 3-59, 3-67 Levee mapping, 3-56, 3-64 Unshaded, 1-10, 3-56 I-14 COASTAL CONSTRUCTION MANUAL FEMA P-55 Catalog No. 08352-1 o •l.� — fit.. AT Via' i � f I II Coastal Construction Manual Principles and Practices of Planning, Siting, Designing, Constructing, and Maintaining Residential Buildings in Coastal Areas (Fourth Edition) FEMA P-55 / Volume II / August 2011 �w�ax1 yr: FEMA All illustrations in this document were created by FEMA or a FEMA contractor unless otherwise noted. All photographs in this document are public domain or taken by FEMA or a FEMA contractor, unless otherwise noted. I L r�� ref I � � Ali ��!� �► - � � � . � - .�� Preface The 2011 Coastal Construction Manual, Fourth Edition (FEMA P-55), is a two -volume publication that provides a comprehensive approach to planning, siting, designing, constructing, and maintaining homes in the coastal environment. Volume I of the Coastal Construction Manual provides information about hazard identification, siting decisions, regulatory requirements, economic implications, and risk management. The primary audience for Volume I is design professionals, officials, and those involved in the decision -making process. Volume II contains in-depth descriptions of design, construction, and maintenance practices that, when followed, will increase the durability of residential buildings in the harsh coastal environment and reduce economic losses associated with coastal natural disasters. The primary audience for Volume II is the design professional who is familiar with building codes and standards and has a basic understanding of engineering principles. Volume II is not a standalone reference for designing homes in the coastal environment. The designer should have access to and be familiar with the building codes and standards that are discussed in Volume II and listed in the reference section at the end of each chapter. The designer should also have access to the building codes and standards that have been adopted by the local jurisdiction if they differ from the standards and codes that are cited in Volume II. If the local jurisdiction having authority has not adopted a building code, the most recent code should be used. Engineering judgment is sometimes necessary, but designers should not make decisions that will result in a design that does not meet locally adopted building codes. The topics that are covered in Volume II are as follows: Chapter 7 — Introduction to the design process, minimum design requirements, losses from natural hazards in coastal areas, cost and insurance implications of design and construction decisions, sustainable design, and inspections. COASTAL CONSTRUCTION MANUAL PREFACE Volume II Chapter 8 — Site -specific loads, including from snow, flooding, tsunamis, high winds, tornadoes, seismic events, and combinations of loads. Example problems are provided to illustrate the application of design load provisions of ASCE 7-10, Minimum Design Loads for Buildings and Other Structures. Chapter 9 — Load paths, structural connections, structural failure modes, breakaway walls, building materials, and appurtenances. Chapter 10 — Foundations, including design criteria, requirements and recommendations, style selection (e.g., open, closed), pile capacity in soil, and installation. Chapter 11— Building envelope, including floors in elevated buildings, exterior doors, windows and skylights, non -loading -bearing walls, exterior wall coverings, soffits, roof systems, and attic vents. Chapter 12 — Installing mechanical equipment and utilities. Chapter 13 — Construction, including the foundation, structural frame, and building envelope. Common construction mistakes, material selection and durability, and techniques for improving resistance to decay and corrosion are also discussed. Chapter 14 — Maintenance of new and existing buildings, including preventing damage from corrosion, moisture, weathering, and termites; building elements that require frequent maintenance; and hazard -specific maintenance techniques. Chapter 15 — Evaluating existing buildings for the need for and feasibility of retrofitting for wildfire, seismic, flood, and wind hazards and implementing the retrofitting. Wind retrofit packages that can be implemented during routine maintenance are also discussed (e.g., replacing roof shingles). For additional information on residential coastal construction, see the FEMA Residential Coastal Construction Web site at http://www.fema.gov/rebuild/mat/fema55.shtm. ii COASTAL CONSTRUCTION MANUAL Fourth Edition Authors and Key Contributors William Coulbourne, Applied Technology Council Christopher P. Jones, Durham, NC Omar Kapur, URS Group, Inc. Vasso Koumoudis, URS Group, Inc. Philip Line, URS Group, Inc. David K. Low, DK Low and Associates Acknowledgments Glenn Overcash, URS Group, Inc. Samantha Passman, URS Group, Inc. Adam Reeder, Atkins Laura Seitz, URS Group, Inc. Thomas Smith, TLSmith Consulting Scott Tezak, URS Group, Inc. — Consultant Project Manager Fourth Edition Volume II Reviewers and Contributors Katy Goolsby -Brown, FEMA Region IV John Ingargiola, FEMA Headquarters — Technical Assistance and Research Contracts Program Manager John Plisich, FEMA Region IV Paul Tertell, FEMA Headquarters — Project Manager Ronald Wanhanen, FEMA Region VI Gregory P. Wilson, FEMA Headquarters Brad Douglas, American Forest and Paper Association Gary Ehrlich, National Association of Home Builders Dennis Graber, National Concrete Masonry Association David Kriebel, United States Naval Academy Marc Levitan, National Institute of Standards and Technology Tim Mays, The Military College of South Carolina Sam Nelson, Texas Department of Insurance Janice Olshesky, Olshesky Design Group, LLC Michael Powell, Delaware Department of Natural Resources and Environmental Control David Prevatt, University of Florida Timothy Reinhold, Insurance Institute for Business & Home Safety Tom Reynolds, URS Group, Inc. Michael Rimoldi, Federal Alliance for Safe Homes Randy Shackelford, Simpson Strong -Tie John Squerciati, Dewberry Keqi Zhang, Florida International University Fourth Edition Technical Editing, Layout, and Illustration Diana Burke, URS Group, Inc. Lee -Ann Lyons, URS Group, Inc. Susan Ide Patton, URS Group, Inc. Billy Ruppert, URS Group, Inc. COASTAL CONSTRUCTION MANUAL iii Contents Chapter 7. Pre -Design Considerations.....................................................................................................7-1 7.1 Design Process............................................................................................................................ 7-2 7.2 Design Requirements................................................................................................................. 7-3 7.3 Determining the Natural Hazard Risk....................................................................................... 7-3 7.4 Losses Due to Natural Hazards in Coastal Areas........................................................................ 7-5 7.5 Initial, Long -Term, and Operational Costs................................................................................. 7-6 7.5.1 Cost Implications of Siting Decisions..............................................................................7-7 7.5.2 Cost Implications of Design Decisions............................................................................7-7 7.5.3 Benefits and Cost Implications of Siting, Design, and Construction Decisions .............7-11 7.6 Hazard Insurance..................................................................................................................... 7-12 7.6.1 Flood Insurance............................................................................................................7-13 7.6.1.1 Rating Factors...............................................................................................7-13 7.6.1.2 Coverage.......................................................................................................7-17 7.6.1.3 Premiums...................................................................................................... 7-18 7.6.1.4 Designing to Achieve Lower Flood Insurance Premiums...............................7-20 7.6.2 Wind Insurance............................................................................................................7-21 7.6.2.1 Territory.......................................................................................................7-22 7.6.2.2 Fire Protection Class.....................................................................................7-22 7.6.2.3 Building Code Effectiveness Grading Schedule............................................7-22 7.6.2.4 Construction Type........................................................................................7-23 7.6.2.5 Protective Devices.........................................................................................7-23 7.6.3 Earthquake Insurance...................................................................................................7-24 7.7 Sustainable Design Considerations........................................................................................... 7-24 7.8 Inspection Considerations......................................................................................................... 7-25 7.9 References.................................................................................................................................7-26 COASTAL CONSTRUCTION MANUAL v CONTENTS Yo|umeU Chapter 8.Determining Site -Specific Loads ........................................................................................... 8'l 8.1 Dead Loads ................................................................................................................................ 8'5 8.2 Live Loads .................................................................................................................................. 8'5 8.5 Concept of Tributary or Effective Area and Application oFLoads noxBuilding --------..8'4 8'4 Snow Loads ................................................................................................................................ 8'5 8.5 Flood Loads ................................................................................................................................ 8'5 8.5.1 Design Flood ................................................................................................................. 8'5 8.5.2 Design Flood Elevation .................................................................................................. 8'6 8.5.5 Design Stillwater Flood Depth ....................................................................................... 8'9 8.5.5 Design Breaking Wave Height ...................................................................................... 8'l5 8.5.6 Design Flood Velocity ---------------------------------8'l5 8.5.7 Hydrostatic Loads ......................................................................................................... 8'l7 8.5.8 Wave Loads .................................................................................................................. 8-20 8.5.8.1 Breaking Wave Loads ouVertical Piles ......................................................... 8-2l 8.5.8.2 Breaking Wave Loads ouVertical Walls ....................................................... 8-22 8.5.8.5 Wave Slam .---------------------------------8-25 8.5.9 Hydrodynamic Loads ................................................................................................... 8-28 8.5.10 Debris Impact Loads .................................................................................................... 8'5l 8.5.11 Localized Scour ............................................................................................................ 8'54 8.5.12 Flood Load Combinations ------------------------------.8'57 8.6 Tsunami Loads ......................................................................................................................... 8'47 8'7 Wind Loads .............................................................................................................................. 8'47 8.7.1 Determining Wind Loads ............................................................................................ 8'49 8.7.2 Main Wind Force -------------------------..8'52 8.7.5 Components and Cladding ------------------------------8'6l 8.8 Tornado Loads .......................................................................................................................... 8'67 8.9 Seismic Loads ........................................................................................................................... 8'68 8.10 Load Combinations --------------------------------------8'75 v/ COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Chapter 9. Designing the Building 9-1 9.1 Continuous Load Path................................................................................................................ 9-1 9.1.1 Roof Sheathing to Framing Connection (Link #1)......................................................... 9-4 9.1.2 Roof Framing to Exterior Wall (Link #2)....................................................................... 9-8 9.1.3 Wall Top Plate to Wall Studs (Link#3).........................................................................9-10 9.1.4 Wall Sheathing to Window Header (Link #4).............................................................. 9-12 9.1.5 Window Header to Exterior Wall (Link #5)................................................................. 9-12 9.1.6 Wall to Floor Framing (Link #6)..................................................................................9-15 9.1.7 Floor Framing to Support Beam (Link #7)...................................................................9-17 9.1.8 Floor Support Beam to Foundation (Pile) (Link#8)......................................................9-18 9.2 Other Load Path Considerations.............................................................................................. 9-21 9.2.1 Uplift Due to Shear Wall Overturning..........................................................................9-21 9.2.2 Gable Wall Support...................................................................................................... 9-24 9.2.3 Connection Choices..................................................................................................... 9-24 9.2.4 Building Eccentricities................................................................................................. 9-27 9.2.5 Framing System........................................................................................................... 9-27 9.2.5.1 Platform Framing......................................................................................... 9-27 9.2.5.2 Concrete/Masonry........................................................................................9-27 9.2.5.3 Moment -Resisting Frames............................................................................ 9-28 9.2.6 Roof Shape................................................................................................................... 9-30 9.3 Breakaway Wall Enclosures 9-30 9.4 Building Materials.................................................................................................................... 9-33 9.4.1 Materials Below the DFE............................................................................................. 9-34 9.4.2 Materials Above the DFE............................................................................................. 9-35 9.4.3 Material Combinations................................................................................................ 9-35 9.4.4 Fire Safety Considerations............................................................................................ 9-36 9.4.5 Corrosion.....................................................................................................................9-37 9.5 Appurtenances ..........................................................................................................................9-38 9.5.1 Decks and Covered Porches Attached to Buildings...................................................... 9-38 9.5.1.1 Handrails..................................................................................................... 9-39 9.5.1.2 Stairways...................................................................................................... 9-39 9.5.2 Access to Elevated Buildings........................................................................................ 9-39 9.5.3 Pools and Hot Tubs...................................................................................................... 9-40 9.6 References 9-43 COASTAL CONSTRUCTION MANUAL vii CONTENTS Volume II Chapter 10. Designing the Foundation...................................................................................................10-1 10.1 Foundation Design Criteria...................................................................................................... 10-2 10.2 Foundation Styles..................................................................................................................... 10-2 10.2.1 Open Foundations....................................................................................................... 10-3 10.2.2 Closed Foundations...................................................................................................... 10-3 10.2.3 Deep Foundations........................................................................................................ 10-4 10.2.4 Shallow Foundations.................................................................................................... 10-4 10.3 Foundation Design Requirements and Recommendations........................................................10-4 10.3.1 Foundation Style Selection........................................................................................... 10-5 10.3.2 Site Considerations....................................................................................................... 10-5 10.3.3 Soils Data..................................................................................................................... 10-5 10.3.3.1 Sources of Published Soils Data.................................................................... 10-6 10.3.3.2 Soils Data from Site Investigations............................................................... 10-6 10.4 Design Process........................................................................................................................ 10-10 10.5 Pile Foundations..................................................................................................................... 10-11 10.5.1 Compression Capacity of Piles — Resistance to Gravity Loads.....................................10-12 10.5.2 Tension Capacity of Piles............................................................................................10-15 10.5.3 Lateral Capacity of Piles..............................................................................................10-18 10.5.4 Pile Installation.......................................................................................................... 10-20 10.5.5 Scour and Erosion Effects on Pile Foundations...........................................................10-21 10.5.6 Grade Beams for Pile Foundations............................................................................. 10-23 10.6 Open/Deep Foundations........................................................................................................ 10-25 10.6.1 Treated Timber Pile Foundations................................................................................10-25 10.6.1.1 Wood Pile -to -Beam Connections............................................................... 10-26 10.6.1.2 Pile Bracing.................................................................................................10-27 10.6.1.3 Timber Pile Treatment................................................................................10-31 10.6.2 Other Open/Deep Pile Foundation Styles..................................................................10-31 10.7 Open/Shallow Foundations....................................................................................................10-34 10.8 Closed/Shallow Foundations.................................................................................................. 10-35 10.9 Pier Foundations ........................................ 10.9.1 Pier Foundation Design Examples. 10.9.2 Pier Foundation Summary ........... 10.10 References ......................... 10-36 10-37 10-45 10-46 viii COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Chapter 11. Designing the Building Envelope.........................................................................................11-1 11.1 Floors in Elevated Buildings..................................................................................................... 11-4 11.2 Exterior Doors.......................................................................................................................... 11-4 11.2.1 High Winds..................................................................................................................11-6 11.2.1.1 Loads and Resistance....................................................................................11-6 11.2.1.2 Wind -Borne Debris.......................................................................................11-7 11.2.1.3 Durability.....................................................................................................11-7 11.2.1.4 Water Infiltration..........................................................................................11-7 11.3 Windows and Sklylights........................................................................................................... 11-9 11.3.1 High Winds..................................................................................................................11-9 11.3.1.1 Loads and Resistance.....................................................................................11-9 11.3.1.2 Wind -Borne Debris.................................................................................... 11-10 11.3.1.3 Durability....................................................................................................11-13 11.3.1.4 Water Infiltration....................................................................................... 11-14 11.3.2 Seismic........................................................................................................................11-15 11.3.3 Hail............................................................................................................................11-15 11.4 Non -Load -Bearing Walls, Wall Coverings, and Soffits............................................................11-15 11.4.1 High Winds................................................................................................................11-16 11.4.1.1 Exterior Walls.............................................................................................. 11-16 11.4.1.2 Flashings..................................................................................................... 11-21 11.4.1.3 Soffits..........................................................................................................11-22 11.4.1.4 Durability....................................................................................................11-23 11.4.2 Seismic........................................................................................................................11-24 11.5 Roof Systems...........................................................................................................................11-24 11.5.1 Asphalt Shingles..........................................................................................................11-25 11.5.1.1 High Winds................................................................................................11-25 11.5.1.2 Hail.............................................................................................................11-36 11.5.2 Fiber -Cement Shingles...............................................................................................11-36 11.5.2.1 High Winds................................................................................................11-37 11.5.2.2 Seismic........................................................................................................11-37 11.5.2.3 Hail.............................................................................................................11-37 11.5.3 Liquid -Applied Membranes.........................................................................................11-37 11.5.3.1 High Winds................................................................................................11-37 11.5.3.2 Hail.............................................................................................................11-38 11.5.4 Tiles............................................................................................................................11-38 COASTAL CONSTRUCTION MANUAL ix CONTENTS Volume II 11.5.4.1 High Winds................................................................................................11-38 11.5.4.2 Seismic.......................................................................................................11-43 11.5.4.3 Hail.............................................................................................................11-45 11.5.5 Metal Panels and Metal Shingles.................................................................................11-45 11.5.5.1 High Winds................................................................................................11-45 11.5.5.2 Hail.............................................................................................................11-46 11.5.6 Slate............................................................................................................................11-46 11.5.6.1 High Winds................................................................................................11-46 11.5.6.2 Seismic........................................................................................................11-47 11.5.6.3 Hail.............................................................................................................11-47 11.5.7 Wood Shingles and Shakes.........................................................................................11-47 11.5.7.1 High Winds................................................................................................11-47 11.5.7.2 Hail.............................................................................................................11-48 11.5.8 Low -Slope Roof Systems.............................................................................................11-48 11.5.8.1 High Winds................................................................................................11-49 11.5.8.2 Seismic........................................................................................................11-49 11.5.8.3 Hail.............................................................................................................11-49 11.6 Attic Vents.............................................................................................................................. 11-49 11.7 Additional Environmental Considerations...............................................................................11-52 11.7.1 Sun............................................................................................................................. 11-52 11.7.2 Wind -Driven Rain...................................................................................................... 11-52 11.8 References................................................................................................................................11-52 Listof Figures.......................................................................................................................... 11-58 Listof Tables...........................................................................................................................11-60 Chapter 12. Installing Mechanical Equipment and Utilities................................................................... 12-1 12.1 Elevators................................................................................................................................... 12-1 12.2 Exterior -Mounted Mechanical Equipment................................................................................ 12-2 12.2.1 High Winds................................................................................................................. 12-2 12.2.2 Flooding...................................................................................................................... 12-3 12.2.3 Seismic Events.............................................................................................................. 12-6 12.3 Interior Mechanical Equipment 12.4 Electric Utility, Telephone, and Cable TV Systems 12.4.1 Emergency Power ...................................... 12-6 12-6 12-9 x COASTAL CONSTRUCTION MANUAL Volume II CONTENTS 12.5 Water and Wastewater Systems............................................................................................... 12-10 12.5.1 Wells...........................................................................................................................12-10 12.5.2 Septic Systems.............................................................................................................12-11 12.5.3 Sanitary Systems.........................................................................................................12-11 12.5.4 Municipal Water Connections....................................................................................12-12 12.5.5 Fire Sprinkler Systems.................................................................................................12-12 12.6 References...............................................................................................................................12-12 Chapter 13. Constructing the Building 13-1 13.1 Foundation Construction......................................................................................................... 13-2 13.1.1 Layout..........................................................................................................................13-2 13.1.2 Pile Foundations.......................................................................................................... 13-5 13.1.3 Masonry Foundation Construction.............................................................................. 13-8 13.1.4 Concrete Foundation Construction.............................................................................13-10 13.1.5 Wood Foundation Construction.................................................................................13-12 13.1.6 Foundation Material Durability..................................................................................13-13 13.1.7 Field Preservative Treatment........................................................................................13-17 13.1.8 Substitutions...............................................................................................................13-18 13.1.9 Foundation Inspection Points......................................................................................13-18 13.1.10 Top Foundation Issues for Builders.............................................................................13-18 13.2 Structural Frame..................................................................................................................... 13-19 13.2.1 Structural Connections...............................................................................................13-19 13.2.2 Floor Framing............................................................................................................ 13-23 13.2.2.1 Horizontal Beams and Girders................................................................... 13-24 13.2.2.2 Substitution of Floor Framing Materials......................................................13-25 13.2.2.3 Floor Framing Inspection Points.................................................................13-25 13.2.3 Wall Framing..............................................................................................................13-25 13.2.3.1 Substitution of Wall Framing Materials...................................................... 13-27 13.2.3.2 Wall Framing Inspection Points................................................................. 13-27 13.2.4 Roof Framing............................................................................................................. 13-27 13.2.4.1 Substitution of Roof Framing Materials...................................................... 13-28 13.2.4.2 Roof Frame Inspection Points..................................................................... 13-28 13.2.5 Top Structural Frame Issues for Builders.................................................................... 13-28 13.3 Building Envelope..................................................................................................................13-29 13.3.1 Substitution of Building Envelope Materials.............................................................. 13-30 COASTAL CONSTRUCTION MANUAL xi CONTENTS Volume II 13.3.2 Building Envelope Inspection Points...........................................................................13-31 13.3.3 Top Building Envelope Issues for Builders...................................................................13-31 13.4 References...............................................................................................................................13-32 Chapter 14. Maintaining the Building.....................................................................................................14-1 14.1 Effects of Coastal Environment................................................................................................ 14-2 14.1.1 Corrosion......................................................................................................................14-2 14.1.2 Moisture...................................................................................................................... 14-3 14.1.3 Weathering...................................................................................................................14-4 14.1.4 Termites....................................................................................................................... 14-4 14.2 Building Elements That Require Frequent Maintenance........................................................... 14-5 14.2.1 Glazing.........................................................................................................................14-7 14.2.2 Siding............................................................................................................................14-7 14.2.3 Roofs............................................................................................................................14-8 14.2.4 Exterior -Mounted Mechanical and Electrical Equipment ............................................. 14-9 14.2.5 Decks and Exterior Wood............................................................................................ 14-9 14.2.6 Metal Connectors.......................................................................................................14-10 14.3 Hazard -Specific Maintenance Techniques 14.3.1 Flooding ..................................... 14.3.2 Seismic and Wind ....................... 14.4 References ......................... 14-11 14-12 14-12 14-13 Chapter 15. Retrofitting Buildings for Natural Hazards..........................................................................15-1 15.1 Wildfire Mitigation.................................................................................................................. 15-2 15.2 Seismic Mitigation.................................................................................................................... 15-5 15.3 Flood Mitigation......................................................................................................................15-8 15.3.1 Elevation......................................................................................................................15-8 15.3.2 Relocation...................................................................................................................15-10 15.3.3 Dry Floodproofing......................................................................................................15-11 15.3.4 Wet Floodproofing......................................................................................................15-12 15.3.5 Floodwalls and Levees.................................................................................................15-13 15.3.6 Multihazard Mitigation...............................................................................................15-14 15.4 High -Wind Mitigation............................................................................................................15-15 xii COASTAL CONSTRUCTION MANUAL Volume II CONTENTS 15.4.1 Evaluating Existing Homes.........................................................................................15-16 15.4.2 Wind Retrofit Mitigation Packages.............................................................................15-16 15.4.2.1 Basic Mitigation Package............................................................................. 15-17 15.4.2.2 Intermediate Mitigation Package.................................................................15-19 15.4.2.3 Advanced Mitigation Package......................................................................15-19 15.4.2.4 Additional Mitigation Measures..................................................................15-19 15.4.3 FEMA Wind Retrofit Grant Programs........................................................................15-19 15.5 References................................................................................................................................15-21 Acronyms................................................................................................................................................ A-1 Glossary................................................................................................................................................. G-1 Index........................................................................................................................................................ I-1 List of Figures Chapter 7 Figure 7-1. Design framework for a successful building, incorporating cost, risk tolerance, use, location, materials, and hazard resistance.................................................................7-3 Figure 7-2. Average damage per structure vs. distance from the Florida Coastal Construction Control Line for Bay County, FL................................................................................... 7-4 Figure 7-3. Basic benefit -cost model................................................................................................7-12 Chapter 8 Figure 8-1. Summary of typical loads and characteristics affecting determination of design load ..... 8-2 Figure 8-2. Examples of tributary areas for different structural elements .......................................... 8-4 Figure 8-3. Flowchart for estimating maximum likely design stillwater flood depth at the site ......... 8-7 Figure 8-4. Erosion's effects on ground elevation.............................................................................. 8-8 Figure 8-5. Parameters that are determined or affected by flood depth ............................................. 8-9 Figure 8-6. Velocity versus design stillwater flood depth..................................................................8-17 Figure 8-7. Lateral flood force on a vertical component...................................................................8-19 COASTAL CONSTRUCTION MANUAL xiii CONTENTS Volume II Figure 8-8. Vertical (buoyant) flood force....................................................................................... 8-20 Figure 8-9. Breaking wave pressure distribution against a vertical wall ........................................... 8-23 Figure 8-10. Wave crests not parallel to wall..................................................................................... 8-24 Figure 8-11. Water depth versus wave height, and water depth versus breaking wave force against, a vertical wall.................................................................................................. 8-25 Figure 8-12. Lateral wave slam against an elevated building............................................................. 8-26 Figure 8-13. Hydrodynamic loads on a building.............................................................................. 8-28 Figure 8-14. Scour at single vertical foundation member, with and without underlying scour resistantstratum........................................................................................................... 8-34 Figure 8-15. Deep scour around foundation piles, Hurricane Ike ..................................................... 8-35 Figure 8-16. Scour around a group of foundation piles..................................................................... 8-36 Figure 8-17. Effect of wind on an enclosed building and a building with an opening ....................... 8-48 Figure 8-18. Distribution of roof, wall, and internal pressures on one-story, pile -supported building....................................................................................................................... 8-49 Figure 8-19. Variation of maximum negative MWFRS pressures based on envelope procedures for low-rise buildings...................................................................................8-51 Figure 8-20. Components and cladding wind pressures.................................................................... 8-62 Figure 8-21. Effect of seismic forces on supporting piles................................................................... 8-69 Chapter 9 Figure 9-1. Load path failure at gable end........................................................................................ 9-2 Figure 9-2. Load path failure in connection between home and its foundation ................................. 9-2 Figure 9-3. Roof framing damage and loss due to load path failure at top of wall/roof structureconnection...................................................................................................... 9-3 Figure 9-4. Load path failure in connections between roof decking and roof framing ...................... 9-3 Figure 9-5. Newer home damaged from internal pressurization and inadequate connections ........... 9-4 Figure 9-6. Example load path for case study building..................................................................... 9-5 Figure 9-7. Connection of the roof sheathing to the roof framing (Link#1)..................................... 9-6 Figure 9-8. Connection of roof framing to exterior wall (Link #2)................................................... 9-8 Figure 9-9. Connection of truss to wood -frame wall.......................................................................9-10 xiv COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Figure 9-10. Roof truss -to -masonry wall connectors embedded into concrete -filled or grouted masonrycell..................................................................................................................9-11 Figure 9-11. Connection of wall top plate -to -wall stud (Link#3)......................................................9-11 Figure 9-12. Wall top plate -to -wall stud metal connector................................................................. 9-12 Figure 9-13. Connection of wall sheathing to window header (Link #4)...........................................9-13 Figure 9-14. Connection of window header to exterior wall (Link #5)..............................................9-13 Figure 9-15. Connection of wall to floor framing (Link #6)..............................................................9-15 Figure 9-16. Connection of floor framing to support beam (Link #7)...............................................9-17 Figure 9-17. Metal joist -to -beam connector.......................................................................................9-17 Figure 9-18. Connection of floor support beam to foundation (Link #8)..........................................9-19 Figure 9-19. Diaphragm stiffening and corner pile bracing to reduce pile cap rotation ..................... 9-20 Figure 9-20. Shear wall holddown connector with bracket attached to a wood beam ....................... 9-24 Figure 9-21. Gable -end failure.......................................................................................................... 9-25 Figure 9-22. Gable -end bracing detail; nailing schedule, strap specification, brace spacing, and overhang limits should be adapted for the applicable basic wind speed ......................... 9-26 Figure 9-23. Example of two-story platform framing on a pile -and -beam foundation ...................... 9-28 Figure 9-24. Two-story masonry wall with wood floor and roof framing .......................................... 9-29 Figure 9-25. Steel moment frame with large opening....................................................................... 9-29 Figure 9-26. Gable -end failure caused by high winds........................................................................9-31 Figure 9-27. Hip roof that survived high winds with little to no damage..........................................9-31 Figure 9-28. Typical failure mode of breakaway wall beneath an elevated building .......................... 9-32 Figure 9-29. Breakaway wall panel prevented from breaking away cleanly by utility penetrations .... 9-32 Figure 9-30. Lattice beneath an elevated house in Zone V................................................................ 9-33 Figure 9-31. House being constructed with a steel frame on wood piles ........................................... 9-36 Figure 9-32. Townhouse framing system.......................................................................................... 9-37 Figure 9-33. Recommendations for orientation of in -ground pools .................................................. 9-41 Figure 9-34. Recommended contraction joint layout for frangible slab -on -grade below elevatedbuilding..........................................................................................................9-42 COASTAL CONSTRUCTION MANUAL xv CONTENTS Volume II Chapter 10 Figure 10-1. Closed foundation failure due to erosion and scour undermining ................................. 10-4 Figure 10-2. Near collapse due to insufficient pile embedment........................................................10-13 Figure 10-3. Surviving pile foundation............................................................................................10-13 Figure 10-4. Deflected pile shape for an unbraced pile....................................................................10-19 Figure 10-5. Pier installation methods............................................................................................ 10-20 Figure 10-6. Scour and erosion effects on piling embedment...........................................................10-21 Figure 10-7. Column connection failure.........................................................................................10-24 Figure 10-8. Scour around grade beam............................................................................................10-25 Figure 10-9. Profile of timber pile foundation type......................................................................... 10-26 Figure 10-10. Diagonal bracing using dimensional lumber.............................................................. 10-28 Figure 10-11. Diagonal bracing schematic........................................................................................ 10-28 Figure10-12. Knee bracing.............................................................................................................. 10-30 Figure 10-13. Section view of a steel pipe pile with concrete column and grade beam foundationtype...........................................................................................................10-32 Figure 10-14. Section view of a foundation constructed with reinforced concrete beams and columns to create portal frames...................................................................................10-33 Figure 10-15. Profile of an open/shallow foundation........................................................................ 10-34 Figure 10-16. Stem wall foundation design...................................................................................... 10-36 Figure 10-17. Performance comparison of pier foundations.............................................................. 10-37 Figure 10-18. Pier foundation and spread footing under gravity loading .......................................... 10-38 Figure 10-19. Pier foundation and spread footing exposed to uplift forces ........................................ 10-38 Figure 10-20. Pier foundation and spread footing exposed to uplift and lateral forces ...................... 10-39 Chapter 11 Figure 11-1. Good structural system performance but the loss of shingles, underlayment, siding, housewrap, and soffts resulted in significant interior water damage....................11-2 Figure 11-2. Numerous wind-borne debris scars and several missing asphalt shingles ........................11-3 xvi COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Figure 11-3. House that survived a wildfire due in part to fire-resistant walls and roof while surrounding houses were destroyed...............................................................................11-3 Figure 11-4. Plywood panels on the underside of a house that blew away because of excessive nailspacing...................................................................................................................11-5 Figure 11-5. Sliding glass doors pulled out of their tracks by wind suction........................................11-5 Figure 11-6. Garage door blown from its track as a result of positive pressure...................................11-6 Figure 11-7. A 3/8-inch gap between the threshold and door which allowed wind -driven rain toenter the house..........................................................................................................11-8 Figure 11-8. Window frame pulled out of the wall because of inadequate window frame attachment....................................................................................................................11-9 Figure 11-9. Very old building with robust shutters constructed of 2x4lumber, bolted connections, and heavy metal hinges........................................................................... 11-10 Figure 11-10. Unprotected cupola window that was broken.............................................................. 11-11 Figure 11-11. Design pressure and impact -resistance information in a permanent window label ....... 11-12 Figure 11-12. Roll -up shutter slats that detached from the tracks......................................................11-12 Figure 11-13. Shutter punctured by roof tile..................................................................................... 11-13 Figure 11-14. House in Puerto Rico with metal jalousie louvers........................................................ 11-14 Figure 11-15. Blown -off vinyl siding and foam sheathing; some blow -off of interior gypsum board........................................................................................................................... 11-17 Figure 11-16. Blown -off fiber cement siding; broken window............................................................ 11-18 Figure 11-17. Four brick veneer failure modes; five corrugated ties that were not embedded in themortar joints......................................................................................................... 11-18 Figure 11-18. Typical EIFS assemblies.............................................................................................. 11-19 Figure 11-19. Blown -off EIFS, resulting in extensive interior water damage; detachment of the gypsum board or stud blow off; two windows broken by debris..................................11-20 Figure 11-20. Collapse of the breakaway wall, resulting in EIFS peeling...........................................11-21 Figure 11-21. EIFS with a barrier design: blown-offroofdecking; severely rotted OSB due to leakageat windows......................................................................................................11-22 Figure 11-22. Blown -away soffit, which allowed wind -driven rain to enter the attic ..........................11-23 Figure 11-23. Blow -off of several newer shingles on a roof that had been re-covered by installing new asphalt shingles on top of old shingles..................................................................11-25 COASTAL CONSTRUCTION MANUAL xvii CONTENTS Volume II Figure 11-24. Small area of sheathing that was exposed after loss of a few shingles and some underlayment..............................................................................................................11-26 Figure 11-25. Typical underlayment attachment...............................................................................11-26 Figure 11-26. Enhanced underlayment Option 1, first variation: self -adhering modified bitumen over the sheathing.........................................................................................11-27 Figure 11-27. Enhanced underlayment Option 1, second variation: self -adhering modified bitumenover the felt...................................................................................................11-28 Figure 11-28. House that used enhanced underlayment Option 3 with taped sheathing joints. the self -adhering modified bitumen tape was stapled because of bonding problems .... 11-29 Figure 11-29. Underlayment that was not lapped over the hip...........................................................11-30 Figure 11-30. Loss of shingles and underlayment along the eave and loss of a few hip shingles .......... 11-31 Figure 11-31. Loss of shingles and underlayment along the rake.......................................................11-31 Figure 11-32. Incorrect installation of the starter course...................................................................11-32 Figure 11-33. Uplift loads along the rake that are transferred to the ends of the rows of self-sealing adhesive.....................................................................................................11-33 Figure 11-34. A bleeder strip that was used at a rake blow-off...........................................................11-34 Figure 11-35. Inadequate sealing of the self-sealing adhesive at a hip................................................11-34 Figure 11-36. Proper and improper location of shingle fasteners (nails).............................................11-35 Figure 11-37. Proper and improper location of laminated shingle fasteners (nails).............................11-35 Figure 11-38. Shingles that unzipped at the band lines.....................................................................11-36 Figure 11-39. Blow -off of eave and hip tiles and some broken tiles in the field of the roof.................11-39 Figure 11-40. Large area of blown -off underlayment on a mortar -set tile roof...................................11-39 Figure 11-41. Blow -off of wire -tied tiles installed over a concrete deck..............................................11-39 Figure 11-42. Extensive blow -off of mortar -set tiles...........................................................................11-40 Figure 11-43. Blown-offadhesive-set tile............................................................................................11-40 Figure 11-44. Adhesive that debonded from the cap sheet.................................................................11-41 Figure 11-45. Blow -off of mechanically attached tiles........................................................................11-41 Figure 11-46. Blow -off of hip tiles that were nailed to a ridge board and set in mortar ......................11-42 xviu COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Figure 11-47. Damage to field tiles caused by tiles from another area of the roof, including a hiptile.........................................................................................................................11-42 Figure 11-48. The fastener heads on this mechanically attached tile roof had corroded .....................11-43 Figure 11-49. Area of the roof where tiles were not nailed to batten strips Figure 11-50. Tiles that were nailed to thin wood sheathing Figure 11-51. Figure 11-52. Figure 11-53. Figure 11-54. Figure 11-55. Figure 11-56. Chapter 12 Figure 12-1. Figure 12-2. Tile that slipped out from under the hip tiles ................................................ Blow -off of one of the nailers caused panels to progressively fail; cantilevered condenser platform; broken window.............................................................. Damaged slate roof with nails that typically pulled out of the deck ............... Loss of wood shingles due to fastener corrosion ............................................. 11-44 11-44 11-45 11-46 11-47 11-48 Method for maintaining a continuous load path at the roof ridge by nailing roof sheathing.....................................................................................................................11-5C Holes drilled in roof sheathing for ventilation and roof diaphragm action is maintained.................................................................................................................. 11-51 Condenser damaged as a result of insufficient elevation, Hurricane Georges (U.S. Gulf Coast, 1998)...............................................................................................12-4 Proper elevation of an air-conditioning condenser in a floodprone area; additional anchorage is recommended.......................................................................... 12-4 Figure 12-3. Small piles supporting a platform broken by floodborne debris .................................... 12-5 Figure 12-4. Electric service meters and feeders that were destroyed by floodwaters during HurricaneOpal(1995)................................................................................................. 12-7 Figure 12-5. Recommended installation techniques for electric and plumbing lines and utilityelements............................................................................................................. 12-8 Figure 12-6. Damage caused by dropped overhead service, Hurricane Marilyn (U.S. Virgin Islands, 1995)........................................................................................... 12-9 Chapter 13 Figure13-1. Site layout.................................................................................................................... 13-3 Figure 13-2. Typical pile notching process........................................................................................ 13-4 Figure 13-3. Improper overnotched wood pile.................................................................................. 13-4 COASTAL CONSTRUCTION MANUAL xix CONTENTS Volume II Figure 13-4. Properly notched pile.................................................................................................... 13-5 Figure 13-5. Typical wood pile foundation.......................................................................................13-6 Figure 13-6. Open masonry foundation..........................................................................................13-10 Figure 13-7. Concrete foundation...................................................................................................13-11 Figure13-8. Concrete house............................................................................................................13-11 Figure 13-9. Wood decay at the base of a post supported by concrete..............................................13-14 Figure 13-10. Examples of minimizing the least dimension of wood contact surfaces .......................13-15 Figure 13-11. Drip cut to minimize horizontal water movement along the bottom surface of a wood member...........................................................................................13-15 Figure 13-12. Exposure of end grain in stair stringer cuts..................................................................13-16 Figure 13-13. Deterioration in a notched stair stringer......................................................................13-16 Figure 13-14. Alternative method of installing stair treads................................................................13-17 Figure 13-15. Connector failure caused by insufficient nailing......................................................... 13-20 Figure 13-16. Reinforcement of overnotched piles.............................................................................13-21 Figure 13-17. Beam support at misaligned piles............................................................................... 13-22 Figure 13-18. Proper pile notching for two -member and four -member beams .................................. 13-22 Figure 13-19. Proper use of metal twist strap ties; solid blocking between floor joists ....................... 13-23 Figure 13-20. Engineered joists used as floor joists with proper metal brace to keep the bottoms of the joists from twisting; engineered wood beam ....................................... 13-24 Figure 13-21. Acceptable locations for splices in multiple -member girders.........................................13-25 Figure 13-22. Full -height sheathing to improve transfer of shear ...................................................... 13-26 Chapter 14 Figure 14-1. Pile that appears acceptable from the exterior but has interior decay..............................14-1 Figure 14-2. Wood decay behind a metal beam connector............................................................... 14-3 Figure 14-3. Severely corroded deck connectors..............................................................................14-11 Figure 14-4. Deteriorated wood sill plate.........................................................................................14-12 xx COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Chapter 15 Figure 15-1. The three concentric zones of defensible space...............................................................15-2 Figure 15-2. The building envelope...................................................................................................15-3 Figure 15-3. Fire spreads vertically through vegetation......................................................................15-3 Figure 15-4. FEMA P-737, Home Builder's Guide to Construction in Wildlife Zones: Technical Fact Sheet Series............................................................................................. 15-4 Figure 15-5. FEMA 232, Homebuilders Guide to Earthquake Resistant Design and Construction ......... 15-5 Figure 15-6. A house with severe damage due to cripple wall failure ................................................. 15-6 Figure 15-7. Common open -front configurations in one- and two- family detached houses..............15-7 Figure 15-8. FEMA 530, Earthquake Safety Guide for Homeowners .................................................. 15-8 Figure 15-9. Home elevated on piles..................................................................................................15-9 Figure 15-10. Preparing a building for relocation..............................................................................15-10 Figure 15-11. Dry floodproofed structure......................................................................................... 15-11 Figure 15-12. Wet floodproofed structure.........................................................................................15-13 Figure 15-13. Home protected by a floodwall and a levee..................................................................15-15 Figure 15-14. FEMA P-804, Wind Retrofit Guide for Residential Buildings ........................................ 15-15 Figure 15-15. Wind Retrofit Mitigation Packages............................................................................. 15-17 Figure 15-16. Bracing gable end overhangs........................................................................................15-18 Figure 15-17. Sprayed polyurethane foam adhesive to secure roof deck panels..................................15-18 Figure 15-18. Continuous load path for wind -uplift of a residential, wood -frame building ...............15-20 Figure 15-19. HMA grant process.....................................................................................................15-21 List of Tables Chapter 7 Table 7-1. Examples of Flood and Wind Mitigation Measures........................................................ 7-8 Table 7-2. Sample NFIP Flood Insurance Premiums for Buildings in Zone A ............................... 7-19 COASTAL CONSTRUCTION MANUAL xxi CONTENTS Volume II Table 7-3. Sample NFIP Flood Insurance Premiums for Buildings in Zone V Free of Obstruction Below the Lowest Floor............................................................................. 7-19 Table 7-4. Sample NFIP Flood Insurance Premiums for Buildings in Zone V with Obstruction Below the Lowest Floor.............................................................................7-20 Chapter 8 Table 8-1. Value of Dynamic Pressure Coefficient (Cp) as a Function of Probability ofExceedance.............................................................................................................. 8-23 Table 8-2. Drag Coefficients for Ratios of Width to Depth (w/d) and Width to Height (w/h)....... 8-29 Table 8-3. Depth Coefficient (Q by Flood Hazard Zone and Water Depth ................................ 8-33 Table 8-4. Values of Blockage Coefficient CB................................................................................. 8-33 Table 8-5. Selection of Flood Loads for F in ASCE 7-10 Load Combinations for a GlobalForces............................................................................................................... 8-37 Table 8-6. Roof Uplift Connector Loads at Building Edge Zones ................................................. 8-53 Table 8-7. Lateral Diaphragm Load from Wind Perpendicular to Ridge ....................................... 8-53 Table 8-8. Roof and Wall Sheathing Suction Loads...................................................................... 8-63 Table 8-9. Lateral Connector Loads from Wind at Building End Zones ....................................... 8-63 Chapter 9 Table 9-1. General Guidance for Selection of Materials................................................................ 9-33 Chapter 10 Table 10-1. Foundation Styles in Coastal Areas.............................................................................. 10-3 Table 10-2. ASTM D2487 10-Soil Classifications.......................................................................... 10-8 Table 10-3. Advantages and Special Considerations of three Types of Pile Materials .....................10-12 Table 10-4. Bearing Capacity Factors (Nq )...................................................................................10-14 Table 10-5. Earth Pressure Coefficients..........................................................................................10-14 Table 10-6. Friction Angle Between Soil and Pile(8).....................................................................10-15 Table 10-7. Allowable Compression and Tension of Wood Piles Based on Varying Diameters, Embedments, and Installation Methods......................................................................10-18 Table 10-8. Values of nh Modulus of Subgrade Reaction................................................................10-19 xxii COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Table 10-9. Advantages and Special Considerations of Pile Installation Methods...........................10-21 Table 10-10. Example Analysis of the Effects of Scour and Erosion on a Foundation ...................... 10-23 Chapter 11 Table 11-1. Allowable Basic Wind Speed as a Function of Class....................................................11-31 Chapter 13 Table 13-1. Table 13-2. Table 13-3. Table 13-4. Chapter 14 Table 14-1. Chapter 15 Table 15-1. Table 15-2. Table 15-3. Table 15-4. Table 15-5. Foundation and Floor Framing Inspection Points Wall Inspection Points ......................................... Roof Frame Inspection Points .............................. Building Envelope Inspection Points .................... Maintenance Inspection Checklist .................................................13-18 ................................................ 13-27 ................................................ 13-29 .................................................13-31 Advantages and Disadvantages of Elevation .................. Advantages and Disadvantages of Relocation ................ Advantages and Disadvantages of Dry Floodproofing ... Advantages and Disadvantages of Wet Floodproofing ... Advantages and Disadvantages of a Floodwall or Levee. List of Equations Chapter 8 Equation 8.1. Design Stillwater Flood Depth ................. Equation 8.2. Design Flood Velocity .............................. Equation 8.3. Lateral Hydrostatic Load .......................... Equation 8.4. Vertical (Buoyant) Hydrostatic Force ....... Equation 8.5. Breaking Wave Load on Vertical Piles ...... 14-5 ........................................15-9 ......................................15-10 ......................................15-12 ......................................15-13 ......................................15-14 ............................................................ 8 -10 ............................................................ 8 -16 8-18 8-19 8-21 COASTAL CONSTRUCTION MANUAL xxiii CONTENTS Volume II Equation 8.6. Breaking Wave Load on Vertical Walls........................................................................ 8-22 Equation 8.7. Lateral Wave Slam........................................................................................................ 8-26 Equation 8.8. Hydrodynamic Load (for All Flow Velocities).............................................................. 8-29 Equation8.9. Debris Impact Load..................................................................................................... 8-32 Equation 8.10. Localized Scour Around a Single Vertical Pile.............................................................. 8-35 Equation 8.11. Total Localized Scour Around Vertical Piles................................................................ 8-36 Equation 8.12. Total Scour Depth Around Vertical Walls and Enclosures ........................................... 8-37 Equation 8.13. Velocity Pressure.......................................................................................................... 8-50 Equation 8.14. Design Wind Pressure for Low -Rise Buildings 1 Equation 8.15. Seismic Base Shear by Equivalent Lateral Force Procedure ........................................... 8-69 Equation 8.16. Vertical Distribution of Seismic Forces......................................................................... 8-70 Chapter 10 Equation 10.1. Sliding Resistance.......................................................................................................10-10 Equation 10.2. Ultimate Compression Capacity of a Single Pile..........................................................10-14 Equation 10.3. Ultimate Tension Capacity of a Single Pile..................................................................10-15 Equation 10.4. Load Application Distance for an Unbraced Pile.........................................................10-19 Equation 10.5. Determination of Square Footing Size for Gravity Loads ........................................... 10-40 Equation 10.6. Determination of Soil Pressure................................................................................... 10-43 Chapter 13 Equation 13.1. Pile Driving Resistance for Drop Hammer Pile Drivers ................................................ 13-8 List of Examples Chapter 8 Example 8.1. Design Stillwater Flood Depth Calculations.................................................................8-11 Example 8.2. Wave Slam Calculation................................................................................................ 8-27 Example 8.3. Hydrodynamic Load on Piles versus Breaking Wave Load on Piles .............................. 8-30 xxiv COASTAL CONSTRUCTION MANUAL Volume II CONTENTS Example 8.4. Flood Load Example Problem Example 8.5. Roof Uplift Connector Loads .................................................. Example 8.6. Lateral Diaphragm Loads from Wind Perpendicular to Ridge Example 8.7. Roof Sheathing Suction Loads ................................................ Example 8.8. Lateral Connection Framing Loads from Wind 8-38 8-54 8-57 8-64 8-66 Example8.9. Seismic Load................................................................................................................ 8-70 Example 8.10. Load Combination Example Problem.......................................................................... 8-75 Chapter 9 Example 9.1. Example 9.2. Example 9.3. Example 9.4. Example 9.5. Example 9.6. Example 9.7. Chapter 10 Roof Sheathing Nail Spacing for Wind Uplift................................................................ 9-6 Roof -to -Wall Connection for Uplift............................................................................... 9-9 Uplift and Lateral Load Path at Window Header..........................................................9-14 Uplift and Lateral Load Path at Wall -to -Floor Framing................................................9-15 Uplift Load Path at Floor to Support Beam Framing....................................................9-18 Uplift Load Path for Support Beam-to-Pile...................................................................9-19 Uplift and Compression Due to Shear Wall Overturning.............................................9-21 Example 10.1. Calculation for Allowable Capacities of Wood Piles 10-16 Example 10.2. Diagonal Brace Force..................................................................................................10-29 Example 10.3. Pier Footing Under Gravity Load............................................................................... 10-40 Example 10.4. Pier Footing Under Uplift Load................................................................................. 10-42 Example 10.5. Pier Footing Under Uplift and Lateral Loads............................................................. 10-44 List of Worksheets Chapter 8 Worksheet 1. Flood Load Computation Non Tsunami Coastal A Zones (Solid Foundation) ............. 8-44 COASTAL CONSTRUCTION MANUAL xxv CONTENTS Volume II Worksheet 2. Flood Load Computation Non Tsunamic Zone V and Coastal A Zone (Open Foundation)......................................................................................................8-46 Worksheet 3. Load Combination Computation................................................................................. 8-80 xxvi COASTAL CONSTRUCTION MANUAL i P"I )esign Considerations This chapter provides an overview of the issues that should be considered before the building is designed. CROSS REFERENCE Coastal development has increased in recent years, and some For resources that augment of the sites that are chosen for development have higher risks of the guidance and other impact from natural hazards than in the past. Examples of sites information in this Manual, with higher risks are those that are close to the ocean, on high see the Residential CoastalConstruction Web site (http:// bluffs that are subject to erosion, and on artificial fill deposits. www.fema.gov/rebuild/mat/ In addition, many of the residential buildings constructed today fema55.shtm). are larger and more costly than before, leading to the potential for larger economic losses if disaster strikes. However, studies conducted by the Federal Emergency Management Agency (FEMA) and others after major coastal disasters have consistently shown that coastal residential buildings that are properly sited, designed, and constructed have generally performed well during natural hazard events. Important decisions need to be made prior to designing the building. The decisions should be based on an understanding of regulatory requirements, the natural hazard and other risks associated with constructing a building on a particular site (see Chapter 4), and the financial implications of the decisions. The financial implications of siting decisions include the cost of hazard insurance, degree of hazard resistance and sustainability in the design, and permits and inspections. COASTAL CONSTRUCTION MANUAL 7-1 7 PRE -DESIGN CONSIDERATIONS Volume II Once a site has been selected, decisions must be made concerning building placement, orientation, and design. These decisions are driven primarily by the following: Owner, designer, and builder awareness of natural hazards Risk tolerance of the owner Aesthetic considerations (e.g., building appearance, proximity to the water, views from within the building, size and number of windows) Building use (e.g., full-time residence, part-time residence, rental property) Requirements of Federal, State, and local regulations and codes Initial and long-term costs The interrelationships among aesthetics, building use, regulatory and code requirements, and initial cost become apparent during siting and design, and decisions are made according to the individual needs or goals of the property owner, designer, or builder. However, an understanding of the effect of these decisions on long-term and operational costs is often lacking. The consequences of the decisions can range from increased maintenance and utility costs to the ultimate loss of the building. The goal of this Manual is to provide the reader with an understanding of these natural hazards and provide guidance on concepts for designing a more hazard -resistant residential building. 7.1 Design Process The design process includes a consideration of the types of natural hazards that occur in the area where the building site is located and the design elements that allow a building to effectively withstand the potential damaging effects of the natural hazards (see Figure 7-1). The intent of this Manual is to provide sufficient technical information, including relevant examples, to help the designer effectively design a coastal residential building. This Manual does not describe all combinations of loads, types of material, building shapes and functions, hazard zones, and elevations applicable to building design in the coastal environment. The designer must apply engineering judgment to a range of problems. In addition, good design by itself is not enough to guarantee a high -quality structure. Although designing building components to withstand site -specific loads is important, a holistic approach that also includes good construction, inspection, and maintenance practices can lead to a more resilient structure. Before designing a building and to optimize the usefulness of Volume II of this Manual, the designer should obtain the codes and standards, such as ASCE 7 and ASCE 24, that are listed in the reference section of each chapter and other relevant information such as locally adopted building codes and appropriate testing protocols. Although codes and standards provide minimums, the designer may pursue a higher standard. Many decisions require the designer's judgment, but it is never appropriate to use a value or detail that will result in a building that is not constructed to code. 7-2 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 Figure 7-1. Design framework for a successful building, incorporating cost, risk tolerance, use, location, materials, and hazard resistance Volume II contains many design equations, but they do not cover all of the design calculations that are necessary and are provided only as examples. 7.2 Design Requirements The minimum design requirements for loads, materials, and material resistances for a given building design are normally specified in the locally adopted building code. Nothing in this Manual is intended to recommend the use of materials or systems outside the uses permitted in building code requirements. The loads used in this Manual are based on ASCE 7-10, which is the reference load standard in model building codes. Material and material resistance requirements cited in this Manual are based on the minimum requirements of applicable building codes. However, designers are encouraged throughout the Manual to seek out information on loads and materials that exceed the minimum requirements of the building code. Other sources of information for loads and materials are also provided. 7.3 Determining the Natural Hazard Risk Assessing risk to coastal buildings and building sites requires identifying or delineating hazardous areas and considering the following factors: Types of hazards known to affect a region Geographic variations in hazard occurrence and severity Methods and assumptions underlying existing hazard identification maps or products COASTAL CONSTRUCTION MANUAL 7-3 7 PRE -DESIGN CONSIDERATIONS Volume II "Acceptable" level of risk Consequences of using (or not using) recommended siting, design, and construction practices Geographic variations in coastal hazards occur, both along and relative (perpendicular) to the coastline. Hazards affecting one region of the country may not affect another. Hazards such as wave loads, which affect construction close to the shoreline, usually have a lesser or no effect farther inland. For example, Figure 7-2 shows how building damage caused by Hurricane Eloise in 1975 was greatest at the shoreline but diminished rapidly in the inland direction. The figure represents data from only one storm but shows the trend of a typical storm surge event on coastlines (i.e., damage decreases significantly as wave height decreases). The level of damage and distance landward are dictated by the severity of the storm and geographic location. Through Flood Insurance Studies (FISs) and Flood Insurance Rate Maps (FIRMs), FEMA provides detailed coastal flood hazard information (see Section 3.5). However, these products reflect only flood hazards and do not include a consideration of a number of other hazards that affect coastal areas. Other Federal agencies and some states and communities have completed additional coastal hazard studies and delineations. The Residential Coastal Construction Web site (http://www.fema.gov/rebuild/mat/fema55.shtm) provides introductory information concerning more than 25 hazard zone delineations developed by or for individual communities or states (see "Web Sites for Information about Storms, Big Waves, and Water Level"). Some delineations have been incorporated into mandatory siting and/or construction requirements. When reviewing the hazard maps and delineations that are provided on the Residential Coastal Construction Web site, designers should be aware that coastal hazards are often mapped using different levels of risk or recurrence intervals. Thus, the consistent and acceptable level of risk (the level of risk judged by the designer to be appropriate for a particular building) should be considered early in the planning and design process (see Chapter 6). The hazard maps and delineations are provided as a historical reference only. The most up-to-date information can be obtained by contacting local officials. Figure 7-2. Average damage per structure (in thousands of 1975 dollars) versus distance from the Florida Coastal Construction Control Line for Bay County, FL, Hurricane Eloise (Florida, 1975) SOURCE: ADAPTED FROM SHOWS 1978 7-4 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 7.4 Losses Due to Natural Hazards in Coastal Areas It is easy for property owners to become complacent about the potential for a natural disaster to affect their properties. Hurricanes and earthquakes are generally infrequent events. A geographic area may escape a major hazard event for 20 or more years. Or, if an area has recently been affected, residents may believe the chances of a recurrence in the near future are remote. These perceptions are based on inaccurate assumptions and/or a lack of understanding of natural hazards and the risk of damage. The population and property values along the U.S. coast are both rapidly increasing. Although better warning systems have reduced the number of fatalities and injuries associated with natural disasters, increases in the number and value of structures along the coast have dramatically increased potential property losses. From 2000 through 2009, there were 13 presidentially declared disasters resulting from hurricanes and tropical systems, each causing more than $1 billion in losses. Hurricane Katrina in 2005 was the most expensive natural disaster in U.S. history, causing estimated economic losses of more than $125 billion and insured losses of $35 billion, surpassing Hurricane Andrews's $26.5 billion in losses in 1992. Other recent memorable storms are Tropical Storm Allison (2001), Hurricane Rita (2005), Hurricane Wilma (2005), Hurricane Ike (2008), and the 2004 hurricane season in which four storms (Charley, Frances, Ivan, and Jeanne) affected much of the East Coast in both coastal and inland areas. Following Hurricane Andrew, which ravaged south Florida in 1992, studies were conducted to determine whether the damage suffered was attributable more to the intensity of the storm or to the location and type of development. According to the Insurance Institute for Business and Home Safety (IBHS): NOTE According to the Mortgage Bankers Association (2006), from 1985 to 2005, hurricanes and tropical storms accounted for the major share of all catastrophic insurance losses. The percentages of property damage caused by various catastrophic events during this period were: ® 43.7 percent from hurricane/tropical storms a 23.3 percent from wind/thunderstorms ® 5.1 percent from earthquakes Approximately 94.4 percent of all catastrophic events occurring during this period were attributed to natural disasters. Conservative estimates from claim studies reveal that approximately 25 percent of Andrew -caused insurance losses (about $4 billion) were attributable to construction that failed to meet the code due to poor enforcement, as well as shoddy workmanship. At the same time, concentrations of population and of property exposed to hurricane winds in southern Florida grew many -fold (IBHS 1999). After Hurricane Andrew, codes and regulations were enacted that support stronger building practices and wind protection. IBHS conducted a study in 2004 following Hurricane Charley that found: ... homes built after the adoption of these new standards resulted in a decrease in the frequency and severity of damage to various building components. Furthermore, based on the analysis of additional living expense records, it is concluded that the new building code requirements allowed homeowners to return to their home more quickly and likely reduced the disruption of their day to day lives (IBHS 2004, p. 5). COASTAL CONSTRUCTION MANUAL 7-5 7 PRE -DESIGN CONSIDERATIONS Volume II The past several decades have not resulted in major losses along the Pacific coast or Great Lakes, but periodic reminders support the need for maintaining a vigilant approach to hazard -resistant design for coastal structures in other parts of the country. In February 2009, the Hawaiian Islands and portions of California were under a tsunami watch. This type of watch occurs periodically in sections of northern California, Oregon, Washington, and Alaska and supports the need to construct buildings on elevated foundations. Although tsunamis on the Pacific coast may be less frequent than coastal hazard events on the Atlantic coast, ignoring the threat can result in devastating losses. Hazard events on the coastlines of the Great Lakes have resulted in damage to coastal structures and losses that are consistent with nor'easters on the Atlantic coast. Surge levels and high winds can occur every year on the Great Lakes, and it is important for designers to ensure that homeowners and builders understand the nature of storms on the Great Lakes. As in other regions, storm -related losses can result in the need to live in a house during lengthy repairs or be displaced for extended periods while the house is being repaired. The loss of irreplaceable possessions or property not covered by flood or homeowners insurance policies are issues a homeowner should be warned of and are incentives to taking a more hazard -resistant design approach. Chapters 2 and 3 contain more information about the hazards and risks associated with building in coastal areas. 7.5 Initial, Long -Term, and Operational Costs Like all buildings, coastal residential buildings have initial, long-term, and operational costs. Initial costs include property evaluation, acquisition, permitting, design, and construction. Long-term costs include preventive maintenance and repair and replacement of deteriorated or damaged building components. A hazard -resistant design can result in lower long-term costs by preventing or reducing losses from natural hazard events. Operational costs include costs associated with the use of the building, such as the cost of utilities and insurance. Optimizing energy efficiency may result in a higher initial cost but save in operational costs. In general, the decision to build in any area subject to significant natural hazards —especially coastal areasincreases the initial, long-term, and operational costs of building ownership. Initial costs are higher because the natural hazards must be identified, the associated risks assessed, and the building designed and constructed to resist damage from the natural hazard forces. Long-term costs are likely to be higher because a building in a high -risk area usually requires more frequent and more extensive maintenance and repairs than a building sited elsewhere. Operational costs are often higher because of higher insurance costs and, in some instances, higher utility costs. Although these costs may seem higher, benefits such as potential reductions in insurance premiums and reduced repair time following a natural disaster may offset the higher costs. 7-6 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 7.5.1 Cost Implications of Siting Decisions The cost implications of siting decisions are as follows: The closer buildings are sited to the water, the more likely they are to be affected by flooding, wave action, erosion, scour, debris impact, overwash, and corrosion. In addition, wind speeds are typically higher along coastlines, particularly within the first several hundred feet inland. Repeated exposure to these hazards, even when buildings are designed to resist their effects, can lead to increased long- term costs for maintenance and damage repair. Erosion —especially long-term erosion —poses a serious threat to buildings near the water and on high bluffs above the floodplain. Wind -induced erosion can lower ground elevations around coastal buildings, exposing Zone V buildings to higher -than -anticipated forces, and exposing Zone A buildings to Zone V flood hazards. Maintenance and repair costs are high for buildings in erosion hazard areas, not only because of damage to the building, but also because of the need for remedial measures (e.g., building relocation or erosion protection projects, such as seawalls, revetments, and beach nourishment, where permitted). COST CONSIDERATION Designers and homeowners should recognize that erosion control measures can be expensive, both initially and over the lifetime of a building. In some instances, erosion control costs can equal or exceed the cost of the property or building being protected. CROSS REFERENCE For information on siting coastal residential buildings, see Chapter 4. Sites nearest the water are likely to be in Zone V where building foundations, access stairs, parking slabs, and other components below the building are especially vulnerable to flood, erosion, and scour effects. As a result, the potential for repeated damage and repair is greater for Zone V buildings than buildings in other zones, and the buildings have higher flood insurance rates and increased operational costs. In addition, although elevating a building can protect the superstructure from flood damage, it may make the entire building more vulnerable to earthquake and wind damage. 7.5.2 Cost Implications of Design Decisions The cost implications of design decisions are as follows For aesthetic reasons, the walls of coastal buildings often include a large number of openings for windows and doors, especially in the walls that face the water. Designs of this NOTE Over the long term, poor siting decisions are rarely overcome by building design. type lead to greater initial costs to strengthen the walls and to protect the windows and doors from wind and wind-borne debris (missiles). If adequate protection in the form of shutter systems or impact -resistant glazing is not provided, long-term costs are greater because of (1) the need to repair damage to glazing and secondary damage by the penetration of wind -driven rain and sea spray and/or (2) the need to install retrofit protection devices at a later date. COASTAL CONSTRUCTION MANUAL %-% 7 PRE -DESIGN CONSIDERATIONS Volume II As explained in Chapter 5, National Flood Insurance Program (NFIP) regulations allow buildings in Coastal A Zones to be constructed on perimeter wall (e.g., crawlspace) foundations or on earth fill. Open (pile, pier, or column) foundations are required only for Zone V buildings. Although a Coastal A Zone building on a perimeter wall foundation or fill may have a lower initial construction cost than a similar building on an open foundation, it may be subject to damaging waves, velocity flows, and/or erosion and scour over its useful life. As a result, the long-term costs for a building on a perimeter wall foundation or fill may actually be higher because of the increased potential for damage. In an effort to reduce initial construction costs, designers may select building materials that require high levels of maintenance. Unfortunately, the initial savings are often offset because (1) coastal buildings, particularly those near bodies of saltwater, are especially prone to the effects of corrosion, and (2) owners of coastal buildings frequently fail to sustain the continuing and time-consuming levels of maintenance required. The net effect is often increased building deterioration and sometimes a reduced capacity of structural and non-structural components to resist the effects of future natural hazard events. Table 7-1 provides examples of design elements and the cost considerations associated with implementing them. Although these elements may have increased costs when implementing them on a single building, developers may find that incorporating them into speculative houses with large-scale implementation can provide some savings. Table 7-1. Examples of Flood and Wind Mitigation Measures Adding 1 to 2 feet to the required elevation of the lowest floor or lowest horizontal structural member of the building Improving flashing and weather-stripping around windows and doors Reduces the potential 5.4.2 for the structure to be 6.2.1.3 damaged by waves and/ or floodwaters; reduces flood insurance premiums 11.4.1.2 Reduces water and wind infiltration into building May conflict with community building height restrictions; may require additional seismic design considerations; longer pilings may cost more Increases the number of important tasks for a contractor to monitor Elevating a building in a Coastal Zone A on an Reduces the potential open foundation or using 5.4.2 for the structure to be Breakaway walls still require only breakaway walls for 10.3.1 damaged by waves, flood openings in Zone A enclosures below the erosion, and floodwaters lowest floor 7-8 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 Table 7-1. Examples of Flood and Wind Mitigation Measures (concluded) Using asphalt roof Reduces shingle blowoff High bond strength shingles are shingles with high bond 11.5.1 during high winds slightly more expensive strength Using metal connectors or fasteners with a thicker 14.1.1 Increases useful life of Thicker galvanized or stainless galvanized coating or 14.2.6 connectors and fasteners steel coatings are more costly connectors made of stainless steel (a) Sections in this Manual COASTAL CONSTRUCTION MANUAL 7-9 PRE -DESIGN CONSIDERATIONS Volume II 7-10 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7.5.3 Benefits and Cost Implications of Siting, Design, and Construction Decisions This Manual is designed to help property owners manage some of the risk associated with constructing a residential building in a coastal area. As noted in Chapter 2, studies of the effects of natural disasters on buildings demonstrate that sound siting, design, engineering, construction, and maintenance practices are important factors in the ability of a building to survive a hazard event with little or no damage. This chapter and the remainder of Volume II provide detailed information about how to site, design, construct, and maintain a building to help manage risks. CROSS REFERENCE For more information on designing coastal residential buildings, see Chapter 9. Constructing to a model building code and complying with regulatory siting requirements provides a building with a certain level of protection against damage from natural hazards. However, compliance with minimum code and regulatory requirements does not guarantee that a building is not at risk from a natural hazard. Exceeding code and minimum regulatory requirements provides an added measure of safety but also adds to the cost of construction, which must be weighed against the benefit gained. The often minimal initial cost of mitigation measures offers long-term benefits that provide a cost savings from damage avoided over the life of the building. Incorporating mitigation measures can reduce a homeowner's insurance premiums and better protect the building, its contents, and occupants during a natural hazard event, thus decreasing potential losses. Similar to cost reductions provided by the U.S. Green Building Council LEED [Leadership in Energy and Environmental Design]) for Homes Reference Guide (USGBC 2009) and ICC 700-2008, incorporating hazard mitigation measures into a building may pay for themselves over a few years based on insurance premium savings and the improved energy efficiency that some of the techniques provide. Table 7-1 lists examples of flood and wind mitigation measures that can be taken to help a structure withstand natural hazard events. The need for and benefit of some mitigation measures are difficult to predict. For example, elevating a building above the design flood elevation (DFE) could add to the cost of the building. This additional cost must be weighed against the probability of a flood or storm surge exceeding the DFE. Figure 7-3 illustrates the comparative relationship between damage, project costs, and benefits associated with a hazard mitigation project on a present- valuel basis over the life of the project. CROSS REFERENCE Unless both questions presented in Section 4.8 of this Manual (regarding the acceptable level of residual risk at a site) can be answered affirmatively, the property owner should reconsider purchasing the property. 1 Present value is the current worth of future sums of money. For example, the present value of $100 to be received 10 years from now is about $38.55, using a discount rate equal to 10 percent interest compounded annually. COASTAL CONSTRUCTION MANUAL 7-11 7 PRE -DESIGN CONSIDERATIONS Figure 7-3. Basic benefit -cost model 7.6 Hazard Insurance Insurance should never be viewed as an alternative to damage prevention. However, despite best efforts to manage risk, structures in coastal areas are always subject to potential damage during a natural hazard event. Hazard insurance to offset potential financial exposure is an important consideration for homeowners in coastal areas. Insurance companies base hazard insurance rates on the potential for a building to be damaged by various hazards and the predicted ability of the building to withstand the hazards. Hazard insurance rates include the following considerations: Type of building Area of building footprint Type of construction Location of building Date of construction Age of the building n\ Volume II NOTE A single-family home is covered by homeowners insurance, and a multi -family building is covered by a dwelling policy. A homeowner policy is different from a dwelling policy. A homeowner policy is a multi - peril package policy that automatically includes fire and allied lines, theft, and liability coverage. For a dwelling policy, peril coverages are purchased separately. In addition to Federal and private flood insurance, this chapter focuses on homeowners insurance. 7-12 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 Existence and effectiveness of a fire department and fire hydrants (or other dependable, year-round sources of water) Effectiveness of the building code and local building department at the time of construction Although designers and builders may not be able to control the rates and availability of insurance, they should understand the implications of siting and construction decisions on insurance costs and should make homeowners aware of the risk and potential expense associated with owning a house in a high -hazard area. Insurance considerations can and do affect the decisions about the placement and height of coastal buildings and the materials used in their construction. Input from an insurance industry representative during the design process, rather than after the completion of the building, can positively influence important decisions in addition to potentially saving homeowners money on insurance premiums. Standard homeowners insurance policies cover multiple perils, including fire, lightning, hail, explosion, riot, smoke, vandalism, theft, volcanic eruption, falling objects, weight of snow, and freezing. Wind is usually (but not always) covered, and an endorsement can often be added for earthquake coverage. Homeowners insurance also includes liability coverage. A separate policy is normally required for flooding. 7.6.1 Flood Insurance As described in Chapter 5, flood insurance is offered through the NFIP (see Section 6.2.2.1) in communities that participate in the program (e.g., incorporated cities, towns, villages; unincorporated areas of counties, parishes, and federally recognized Indian tribal governments). This flood insurance is required as a condition of receiving federally backed, regulated, or insured financial assistance for the acquisition of buildings in Special Flood Hazard Areas (SFHAs). This includes almost all mortgages secured by property in an SFHA. NFIP flood insurance is not available in NOTE Standard homeowners insurance policies do not normally cover damage from flood or earth movement (e.g., earthquakes, mudslides). communities that do not participate in the NFIP. Most coastal communities participate in the program because they recognize the risk of flood hazard events and the need for flood insurance. The following sections summarize how coastal buildings are rated for flood insurance and how premiums are established. 7.6.1.1 Rating Factors The insurance rate is a factor that is used to determine the amount to be charged for a certain amount of insurance coverage, called the premium. Premiums are discussed in Section 7.6.1.3. The following seven rating factors are used for flood insurance coverage for buildings (not including contents): Building occupancy Building type Flood insurance zone NOTE NFIP regulations define basement as any area of a building with the floor subgrade (i.e., below ground level) on all sides. COASTAL CONSTRUCTION MANUAL 7-13 7 PRE -DESIGN CONSIDERATIONS Volume II Date of construction CROSS REFERENCE Elevation of lowest floor or bottom or the lowest horizontal structural member of the lowest floor For additional information about enclosures, the use Enclosures below the lowest floor of space below elevated buildings, and flood Location of utilities and service equipment insurance, see Chapter 5. Building Occupancy The NFIP bases rates for flood insurance in part on four types of building occupancy: Single-family Two- to four -family Other residential Non-residential Only slight differences exist among the rates for the three types of residential buildings. Building Type The NFIP bases rates for flood insurance in part on the following building -type factors: Number of floors (one floor or multiple floors) Presence of a basement First floor elevation (whether the building is elevated and/or whether there is an enclosure below the lowest elevated floor) Manufactured home affixed to a permanent foundation NFIP flood insurance is generally more expensive for buildings with basements and for buildings with enclosures below BFE. Flood Insurance Zone The NFIP bases rates for flood insurance in part on flood insurance zones. The zones are grouped as follows for rating purposes: Zone V (V, VE, and Vl V30). The zone closest to the water, subject to "coastal high hazard flooding" (i.e., flooding with wave heights greater than 3 feet). Flood insurance is most expensive in Zone V because of the severity of the hazard. However, the zone is often not very wide. Zones Vl V30 were used on FIRMs until 1986. FIRMs published since then show Zone VE. 7-14 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 Zone A (A, AE, AR, AO, and Al—A30). Coastal flood hazard areas where the wave heights are less than 3 feet. Zones AI—A30 were used on FIRMS until 1986. FIRMS published since then show Zone AE. Zones B, C, and X. The zones outside the 100-year floodplain or SFHA. Flood insurance is least expensive in these zones and generally not required by mortgage lenders. Zone B and Zone C were used on FIRMS until 1986. FIRMS published since then show Zone X. #J NOTE Because Zones B, C, and X designate areas outside the SFHA, construction in these zones is not subject to NFIP floodplain regulations. Homeowners in these areas, however, can purchase Preferred Risk Policies of flood insurance. The rates in these areas are significantly lower than those in Zone V and Zone A. FIRMS show areas designated as being in the Coastal Barrier Resource System (CBRS) or "otherwise protected areas." These areas (known as "CBRA zones") are identified in the Coastal Barrier Resources Act (CBRA) and amendments. Flood insurance is available for buildings in these zones only if the buildings were walled and roofed before the CBRA designation date shown in the FIRM legend and only if the community participates in the NFIP. Date of Construction In communities participating in the NFIP, buildings constructed on or before the date of the first FIRM for that community or on or before December 31, 1974, whichever is later, have flood insurance rates that are "grandfathered" or "subsidized." These buildings are referred to as pre -FIRM. They are charged a flat rate based on building occupancy, building type, and flood insurance zone. n\ CROSS REFERENCE For more information about the CBRA and CBRS, see Chapter 5. NOTE Flood insurance is available through the NFIP for the following types of buildings: single-family, 2- to 4-family, other residential, and non- residential buildings. Condominium policies are also available. Designers may wish to consult knowledgeable insurance agents and the Flood Insurance Manual (FEMA 2011) for policy details and exclusions that affect building design and use. Additional information is available in FEMA FIA-2, Answers to Questions about the National The rates for buildings constructed after the Flood Insurance Program (2004). date of the first FIRM (post -FIRM buildings) are based on building occupancy, building type, flood insurance zone, and two additional factors: (1) elevation of the top of the lowest floor (in Zone A) or bottom of the lowest horizontal structural member of the lowest floor (in Zone V), and (2) enclosed areas below the lowest floor in an elevated building. If a pre -FIRM building is substantially improved (i.e., the value of the improvement exceeds 50 percent of the market value of the building before the improvement was made), it is rated as a post -FIRM building. If a pre -FIRM building is substantially damaged for any reason (i.e., the true cost of repairing the building to its pre -damaged condition exceeds 50 percent of the value of the building before it was damaged), it is also rated as a post -FIRM building regardless of the amount of repairs actually undertaken. The local building COASTAL CONSTRUCTION MANUAL 7-15 7 PRE -DESIGN CONSIDERATIONS Volume II official or floodplain administrator, not the insurance agent, determines whether a building is substantially improved or substantially damaged. If a building is determined to be substantially improved or substantially damaged, the entire structure must be brought into compliance with the current FIRM requirements. An additional insurance rate table is applied to buildings constructed in Zone V on or after October 1, 1981. The table differentiates between buildings with an obstruction below the elevated lowest floor and those without such an obstruction. Elevation of Lowest Floor or Bottom or Lowest Horizontal Structural Member of the Lowest Floor In Zone A, the rating for post -FIRM buildings is based on the elevation of the lowest floor in relation to the BFE. In Zone V, the rating for post -FIRM buildings is based on the elevation WARNING of the bottom of the lowest floor's lowest horizontal structural member in relation to the BFE. Flood insurance rates are lower Differences exist between what for buildings elevated above the BFE. Rates are significantly is permitted under floodplain management regulations and higher for buildings rated at 1 foot or more below the BFE. what is covered by NFIP flood insurance. Some building design Ductwork or electrical, plumbing, or mechanical components considerations should be guided under the lowest floor must either be designed to prevent water by floodplain management infiltration or elevated above the BFE. Additional elevation of requirements and by knowledge the lowest floor may be required. of the design's impact on flood insurance policy premiums. In Zone A, a building on a crawlspace must have openings Although allowable, some designs that meet NFIP requirements will in the crawlspace walls that allow for the unimpeded flow of result in higher premiums. floodwaters more than 1-foot deep. If the crawlspace walls do not have enough properly sized openings, the crawlspace is considered an enclosed floor, and the building may be rated as having its lowest floor at the elevation of the grade inside the crawlspace. Similarly, if furnaces and other equipment serving the building are below the BFE, the insurance agent must submit more information on the structure to the NFIP underwriting department before the policy's premium can be determined. Enclosures Below the Lowest Floor In Zone V, buildings built on or after October 31, 1981, are rated in one of three ways: 1. A building is rated as "free of obstruction" if there is no enclosure below the lowest floor other than insect screening or open wood latticework. "Open" means that at least 50 percent of the lattice construction is open. 2. A building is subject to a more expensive "with obstruction" rate if service equipment or utilities are located below the lowest floor or if breakaway walls enclose an area of less than 300 square feet below the lowest floor. 3. If the area below the lowest floor has more than 300 square feet enclosed by breakaway walls, has non -breakaway walls, or is finished, the floor of the enclosed area is the building's lowest floor and 7-16 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 the insurance agent must submit more information on the structure to the NFIP before the policy's premium can be determined. Although the NFIP allows enclosures below the lowest floor, enclosures affect the flood insurance premiums. The addition of a floor system above the ground, but below the lowest floor of the living space, can result in additional impacts to flood insurance premiums. 7.6.1.2 Coverage The flood insurance that is available under the NFIP is called a Standard Flood Insurance Policy (SFIP). See FEMA F-122, National Flood Insurance Program Dwelling Form: Standard Flood Insurance Policy (FEMA 2009a) for more information about NFIP coverage. �J NOTE The amount of building and contents coverage should be based on replacement value, not market value. Replacement value To be insurable under the NFIP, a building must be walled is the actual cost of rebuilding and roofed with two or more rigid exterior walls and must the building or replacing the be more than 50 percent above grade. Examples of structures contents. This may be higher or lower than market value. that are not insurable because they do not meet this definition are gazebos, pavilions, docks, campers, underground storage tanks, swimming pools, fences, retaining walls, seawalls, bulkheads, septic tanks, and tents. Buildings constructed entirely over water or seaward of mean high tide after October 1, 1982, are not eligible for flood insurance coverage. Certain parts of boathouses located partially over water (e.g., ceiling, roof over the area where boats are floated) are not eligible for coverage. Coverage does not include contents. Contents of insurable walled and roofed buildings can be insured under separate coverage within the same policy. Finishing materials and contents in basements or in enclosures below the lowest elevated floor in post -FIRM buildings are not covered with some exceptions. Certain building components and contents in areas below the elevated floors of elevated buildings are covered. Coverage can even include some items prohibited by FEMA/local floodplain management regulations if the NFIP deems the items essential to the habitability of the building. Designers and building owners should not confuse insurability with proper design and construction. Moreover, significant financial penalties (e.g., increased flood insurance rates, increased uninsured losses) may result from improper design or use of enclosed areas below the BFE. With the above caveats in mind, buildings insured under the NFIP include coverage (up to specified policy limits) for the following items below the BFE: Minimum -code -required utility connections, electrical outlets, switches, and circuit breaker boxes Footings, foundation, posts, pilings, piers, or other foundation walls and anchorage system(s) as required for the support of the building Drywall for walls and ceilings and nonflammable insulation (in basements only) Stairways and staircases attached to the building that are not separated from the building by an elevated walkway COASTAL CONSTRUCTION MANUAL 7-17 7 PRE -DESIGN CONSIDERATIONS Volume II Elevators, dumbwaiters, and relevant equipment, except for such relevant equipment installed below the BFE on or after October 1, 1987 Building and personal property itemsnecessary for the habitability of the building —connected to a power source and installed in their functioning location as long as building and personal property coverage has been purchased. Examples of building and personal property items are air conditioners, cisterns, fuel tanks, furnaces, hot water heaters, solar energy equipment, well water tanks and pumps, sump pumps, and clothes washers and dryers. Debris removal for debris that is generated during a flood An SFIP does not provide coverage for the following building components and contents in areas below the elevated floors of elevated residential buildings: Breakaway walls and enclosures that do not provide support to the building Drywall for walls and ceilings Non-structural slabs beneath an elevated building Walks, decks, driveways, and patios outside the perimeter of the exterior walls of the building Underground structures and equipment, including wells, septic tanks, and septic systems Equipment, machinery, appliances, and fixtures not deemed necessary for the habitability of the building Fences, retaining walls, seawalls, and revetments Indoor and outdoor swimming pools Structures over water, including piers, docks, and boat houses Personal property Land and landscaping 7.6.1.3 Premiums Premiums are based on the seven rating factors discussed in Section 7.6.1.1, plus the following: An expense constant A Federal policy fee The cost of Increased Cost of Compliance coverage The amount of deductible the insured chooses If a community elects to exceed the minimum NFIP requirements, it may apply for a classification under the NFIP Community Rating System (CRS). Based on its floodplain management program, the community 7-18 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 could receive a CRS classification that provides up to a 45 percent premium discount for property owners within the community. At the time of this publication, nearly 1,250 communities were participating in the CRS, representing more than 69 percent of all flood insurance policies. For more information on the CRS, see Section 5.2.4. Tables 7-2, 7-3, and 7-4 list sample NFIP premiums for a post -FIRM, one-story, single-family residence without a basement located in various flood zones. For buildings in Zone V, premiums are somewhat higher for structures with breakaway obstructions, and premiums are dramatically higher for structures with obstructions (e.g., service equipment, utilities, non -breakaway walls) below the lowest floor. Reductions in flood insurance premiums can quickly offset the increased costs associated with building above the BFE. For buildings in Zone A, premiums are higher when proper flood openings are not provided in enclosed areas or when service equipment or utilities are located below the BFE. Table 7-2. Sample NFIP Flood Insurance Premiums for Buildings in Zone A; $250,000 Building/$100,000 Contents Coverage 0 0% $ 1,622 $ 0 1 foot 45 % $ 897 $ 725 2 feet 61 % $ 638 $ 984 3 feet 66% $ 548 $ 1,074 4 feet 67% $ 530 $ 1,092 Rates as of May 2011 per the National Flood Insurance Program Flood Insurance Manual (FEMA 2011) for a Zone V structure free of obstruction. Rates include building ($250,000), contents ($100,000), and associated fees, including increased cost of compliance. Table 7-3. Sample NFIP Flood Insurance Premiums for Buildings in Zone V Free of Obstruction Below the Lowest Floor; $250,000 Building/$100,000 Contents Coverage 0 0% $7,821 $0 1 foot 33%' $ 5,256 $ 2,55 2 feet 55% $ 3,511 $ 4,310 3 feet 65%' $ 2,764 $ 5,057 4 feet 71 % $ 2,286 $ 5,535 Rates as of May 2011 per the National Flood Insurance Program Flood Insurance Manual (FEMA 2011) for a Zone V structure free of obstruction. Rates include building ($250,000), contents ($100,000), and associated fees, including increased cost of compliance; premium to be determined by NFIP underwriting. COASTAL CONSTRUCTION MANUAL 7-19 7 PRE -DESIGN CONSIDERATIONS Volume II Table 7-4. Sample NFIP Flood Insurance Premiums for Buildings in Zone V with Obstruction Below the Lowest Floor; $250,000 Building/$100,000 Contents Coverage 0 0% $ 10,071 $ 0 2 feet 40% $ 6,056 $ 4,015 4 feet 54% $ 4,591 $ 5,480 Rates as of May 2011 per the National Flood Insurance Program Flood Insurance Manual (FEMA 2011) for a Zone V structure free of obstruction. Rates include building ($250,000), contents ($100,000), and associated fees, including increased cost of compliance; premium to be determined by NFIP underwriting. 7.6.1.4 Designing to Achieve Lower Flood Insurance Premiums Tables 7-2, 7-3, and 7-4 demonstrate that considerable savings can be achieved on flood insurance premiums by elevating a building above the BFE and by constructing it to be free of obstruction. Other siting, design and construction decisions can also lower premiums. Designers should refer to FEMNs V Zone Risk Factor Rating Form to estimate flood insurance premium discounts and as a planning tool to use with building owners. The form is in Chapter 5 of the Flood Insurance Manual (FEMA 2011), available at bttp:'// %vw.f ciiia.�rovfbtisiiiesslf'iifip§'iiiaiiiial.slitiii. Discount points, which translate into reduced premiums, are awarded for: Lowest floor elevation Siting and environmental considerations Building support systems and design details Obstruction -free and enclosure construction considerations In addition to lowest floor elevation and free -of -obstruction discounts illustrated in Tables 7-2 and 7-3, flood insurance premium discounts also can be obtained for: Distance from shoreline to building Presence of large dune seaward of the building Presence of certified erosion control device or ongoing beach nourishment project Foundation design based on eroded grade elevation and local scour Foundation design based on this Manual and ASCE 7-10 loads and load combinations Minimizing foundation bracing 7-20 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 Spacing of piles/columns/piers Size and depth of piles and pier footings Superior connections between piles/columns/piers and girders Some poor practices reduce discount points. Negative discount points, which result in higher flood insurance premiums, are given for: Shallow pile embedment Certain methods of pile installation Small -diameter piles or columns Non -bolted connections between piles/columns/piers and girders Over -notching of wood piles Small pier footings Presence of elevators, equipment, ductwork and obstructions below the BFE Presence of solid breakaway walls Presence of finished breakaway walls Table 10 (V Zone Risk Relativities) in the Flood Insurance Manual (FEMA 2011) provides an indication of how building discount points translate into flood premium discounts. Designers and owners should review this table and consult with a knowledgeable flood insurance agent regarding the flood insurance premium implications of using or avoiding certain design construction practices 7.6.2 Wind Insurance Wind insurance coverage is generally part of a homeowners insurance policy. At the time this Manual was published, underwriting associations (or "pools") provided last resort insurance to homeowners in coastal areas who could not obtain coverage from private companies. The following seven states had beach and windstorm insurance plans at the time this Manual was released: Alabama, Florida, Louisiana, Mississippi, North Carolina, South Carolina, and Texas. Georgia and New York provide this kind of coverage for windstorm and hail in certain coastal communities through other property pools. In addition, New Jersey operates the Windstorm Market Assistance Program (Wind -MAP) to help residents in coastal communities find homeowners insurance on the voluntary market. When Wind -MAP does not identify an insurance carrier for a homeowner, the New Jersey Insurance Underwriting Association, known as the FAIR Plan, may provide a policy for windstorm, hail, fire, and other perils but does not cover liability. Many insurance companies encourage their policyholders to retrofit their homes to resist wind -related damage, and some companies have established discount programs to reduce premiums, and other types of financial incentives, to reflect the risk reduction for homes that have been properly retrofitted. Some State insurance departments also have put in place insurance discount programs for properly retrofitted homes. The IBHS FORTIFIED for Existing Homes Program has been designed with the support of IBHS COASTAL CONSTRUCTION MANUAL 7-21 7 PRE -DESIGN CONSIDERATIONS Volume II member insurance companies, although each individual company makes its own decisions about how it is implemented. Wind is only one part of the rating system for multi -peril insurance policies such as a homeowners insurance policy. Most companies rely on the Homeowner's Multistate General Rules and State -specific exceptions Manual of the Insurance Services Office (ISO) as the benchmark for developing their own manuals. ISO stresses that the rules in the manual are advisory only and that each company decides what to use and charge. The ISO publishes a homeowner's manual in every state except Hawaii, North Carolina, and Washington (where State -mandated insurance bureaus operate). The seven basic factors in rating a homeowners insurance policy are: Form (determines type of coverage) Age of the structure Territory Fire protection class Building code effectiveness Construction type Protective devices The last five factors are discussed below. Premiums can also vary because of factors such as amount of coverage and deductible, but these additional factors are not related to building construction. Some companies, however, adjust their higher optional deductible credit according to construction type, giving more credit to more fire-resistant concrete and masonry buildings. 7.6.2.1 Territory Wind coverage credit varies by territory. An entire state may be one territory, but some states, such as Florida, are divided into county and sub -county territories. In Florida, the Intracoastal Waterway is often used as the boundary line. 7.6.2.2 Fire Protection Class ISO publishes a public protection classification for each municipality or fire district based on an analysis of the local fire department, water system, and fire alarm system. This classification does not affect wind coverage but is an important part of the rate. 7.6.2.3 Building Code Effectiveness Grading Schedule The adoption and enforcement of building codes by local jurisdictions are routinely assessed through the Building Code Effectiveness Grading Schedule (BCEGS) program, developed by the ISO. Participation in BCEGS is voluntary and may be declined by local governments if they do not wish to have their local 7-22 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 building codes evaluated. The results of BCEGS assessments are routinely provided to ISO's member private insurance companies, which in turn may offer rating credits for new buildings constructed in communities with strong BCEGS classifications. Conceptually, communities with well -enforced, up-to-date codes should experience fewer disaster -related losses and as a result, should have lower insurance rates. In conducting the assessment, ISO collects information related to personnel qualification and continuing education, as well as number of inspections performed per day. This type of information combined with local building codes is used to determine a grade for the jurisdiction. The grades range from 1 to 10, with a BCEGS grade of 1 representing exemplary commitment to building code enforcement, and a grade of 10 indicating less than minimum recognized protection. Most participating communities fall in the 3 to 5 grade range. 7.6.2.4 Construction Type To simplify insurance underwriting procedures, buildings are identified as being in only one of four categories: Frame: exterior walls of wood or other combustible construction, including stucco and aluminum siding Masonry veneer: exterior walls of combustible material, veneered with brick or stone Masonry: exterior walls of masonry materials; floor and roof of combustible materials Superior: non-combustible, masonry non-combustible, or fire resistive Masonry veneer and masonry are often difficult to differentiate and are therefore often given the same rating. Not many single-family homes qualify for the superior category, which results in a 15 percent credit off rates for the masonry categories. A home in the superior category may also qualify for a wind credit because some insurers believe that buildings with walls, floors, and roofs made of concrete products offer good resistance to windstorms and Category 1 hurricanes. Therefore, a fire -resistive home may get a wind -resistive credit. ISO's dwelling insurance program allows companies to collect data from the owner, the local building department, or their own inspectors to determine whether a house can be classified as wind -resistive or semi -wind -resistive for premium credit purposes. 7.6.2.5 Protective Devices Protective devices are not considered basic factors but items that may deserve some credits. This approach is more common for fire and theft coverage than for wind. Fire and theft coverage credits sprinklers and fire and/or burglar alarms tied to the local fire or police stations. ISO's rules do not address wind -protective devices except in Florida. In Florida, a premium credit is given if exterior walls and roof openings (not including roof ridge and soffit vents) are fully protected with storm shutters of any style and material that are designed and properly installed to meet the latest ASCE 7-10 engineering standard. This standard has been adopted by Dade County. Shutters must be able to withstand impact from wind-borne debris in accordance COASTAL CONSTRUCTION MANUAL 7-23 7 PRE -DESIGN CONSIDERATIONS Volume II with the standards set by the municipality, or if there are no local standards, by Dade County. The rules also provide specifications for alternatives to storm shutters, such as windstorm protective glazing material. 7.6.3 Earthquake Insurance Earthquake insurance is an addition to a regular homeowners insurance policy. Earthquake insurance carries a very high deductible —usually 10 or 15 percent of the value of the house. In most states, ISO has developed advisory earthquake loss costs based on a seismic model used to estimate potential damage to individual properties in the event of an earthquake. The model is based on seismic data, soil types, damage information from previous earthquakes, and structural analysis of various types of buildings. Based on this model, postal Zip codes have been assigned to rating bands and loss costs developed for each band. The number of bands varies within each state and, at times, within a county. In California, the California Earthquake Authority (CEA), a State -chartered insurance company, writes most earthquake policies for homeowners. These policies cover the dwelling and its contents and are subject to a 15-percent deductible. CEA rates are also based on a seismic model used to estimate potential damage to individual properties in the event of an earthquake. 7.7 Sustainable Design Considerations Sustainability concepts are increasingly being incorporated into residential building design and construction. The voluntary green building rating systems of the past decade are being replaced with adoption by local and State jurisdictions of mandatory minimum levels of compliance with rating systems such as the U.S. Green Building Council LEED for Homes Reference Guide (USGBC 2009) or consensus -based standards such as ICC 700-2008. These programs and standards use a system in which credits are accumulated as points assigned to favorable green building attributes pertaining to lot design, resource efficiency, energy efficiency, water efficiency, and indoor environmental quality. Although green building programs are implemented as above -minimum building code practices, many aspects of green construction and its impact on structural performance and durability are not readily apparent upon initial consideration. Green building programs such as National Association of Home Builders (NAHB) Green, EarthAdvantage, and other State and local programs may incorporate LEED for Homes, ICC 700-2008, EnergyStar and other rating systems or product certifications as part of their offerings. For example, a homeowner may decide to add a rooftop solar panel system after the home is built. Depending on its configuration, this system could act as a "sail' in high winds, adding significant uplift loads to the roof and possibly triggering localized structural failure. To maintain expected structural performance in a high -wind event, these additional loads not only must be accommodated by the roof framing, but the complete load path for these additional loads must be traced and connections or framing enhanced as needed. Examples of other green attributes that may require additional design consideration for resistance to natural hazards are large roof overhangs for shading (due to the potential for increased wind loads), vegetative green roofs (due to the presence of added weight and moisture to sustain the roof), and optimized or advanced framing systems that reduce overall material usage and construction waste (due to larger spacing between framing members and smaller header and framing member sizes). 7-24 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 It is important to verify that the design wind speed for an area is not in excess of the recommended maximum wind speeds for these systems. Building for resilience should not work against other green practices by unreasonably increasing the material resources needed to construct the building. However, buildings constructed to survive natural hazards reduce the need to be rebuilt and thus provide a more sustainable design approach. When new green building attributes introduce new technology or new building materials into the building design, new interactions may affect the building's structural integrity and durability. Examples of interactions between green building attributes and resistance to natural hazards (e.g., resilience of the building) are described in FEMA P-798, Natural Hazard Sustainability of Residential Construction (FEMA 2010c). When implementing green attributes into a design, the designer should consider that building for resilience is possibly the most important green building practice. A green building fails to provide benefits associated with green building practices if it is more susceptible to heavy damage from natural hazard events that result in lost building function and increased cost of repair. 7.8 Inspection Considerations After the completion of building permits and construction plans, good inspection and enforcement procedures are crucial. For coastal construction, building inspectors, code officers, designers, and floodplain managers must understand the flood -resistant design and construction requirements for which they need to check. The earlier a deviation is found, the easier it is to take corrective action working with the homeowner and builder. A plan review and inspection checklist tailored to flood -related requirements should be used. Some of the inspections that can be performed to meet compliance directives with the local community's flood -resistant provisions are listed below. For a community that does not have a DFE, a BFE is applicable. Stake -out or site inspection to verify the location of a building; distances from the flood source or body of water can also be checked Fill inspection to check compaction and final elevation when fills are allowed in SFHAs Footing or foundation inspection to check for flood -opening specifics for closed foundations, lowest floor inspection for slab -on -grade buildings, and embedment depth and pile plumbness for pile - supported structures Lowest floor inspection (floodplain inspection) per Section 109.3.3 of 2012 IBC and Section R109.1.3 of 2012 IRC. This is also a good time to verify that the mechanical and electrical utilities are above the BFE or DFE for additional protection. Final inspection points for flood -prone buildings can include: Enclosures below elevated buildings for placement of flood vents and construction of breakaway walls, where applicable Use of enclosures for consistency with the use in the permit Placement of exterior fill, where permitted, according to plans and specifications COASTAL CONSTRUCTION MANUAL 7-25 7 PRE -DESIGN CONSIDERATIONS Volume II Materials below the DFE for flood -resistance; see NFIP Technical Bulletin 2, Flood Damage -Resistant Materials Requirements (FEMA 2008) Building utilities to determine whether they have been elevated or, when instructions are provided, installed to resist flood damage Existence of as -built documentation of elevations If a plan review and inspection checklist have been used, verification that have been signed off and placed in the permit file with all other inspection documentation More information regarding inspections is available in FEMA P-762, Local Officials Guide for Coastal Construction (FEMA 2009b). 7.9 References ASCE (American Society of Civil Engineers). 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. ASCE. Flood Resistant Design and Construction. ASCE Standard ASCE 24. FEMA (Federal Emergency Management Agency). 2004. Answers to Questions about the National Flood Insurance Program. FEMA FIA-2. FEMA. 2008. Flood Damage -Resistant Materials Requirements. Technical Bulletin 2. FEMA. 2009a. National Flood Insurance Program Dwelling Form: Standard Flood Insurance Policy. FEMA F-122. FEMA. 2009b. Local Officials Guide for Coastal Construction. FEMA P-762. FEMA. 2010c. Natural Hazard Sustainability for Residential Construction. FEMA P-798. FEMA. 2011. Flood Insurance Manual. Available at Accessed May 2011. IBHS (Insurance Institute for Business and Home Safety). 1999. Coastal Exposure and Community Protection: Hurricane Andrew's Legacy. Tampa. IBHS and Insurance Research Council. 2004. The Benefits of Modern Wind Resistant Building Codes on Hurricane Claim Frequency and Severity — A Summary Report. ICC (International Code Council). 2008. National Green Building Standard. ICC 700-2008. Country Club Hills, IL: ICC. ICC. 2011a. International Building Code (2012 IBC). Country Club Hills, IL: ICC. ICC. 2011b. International Residential Code for One -and Two -Family Dwellings (2012 IRC). Country Club Hills, IL: ICC. 7-26 COASTAL CONSTRUCTION MANUAL Volume II PRE -DESIGN CONSIDERATIONS 7 Mortgage Bankers Association. 2006. Natural Disaster Catastrophic Insurance The Commercial Real Estate Finance Perspective. Washington, D.C. Shows, E.W. 1978. "Florida's Setback Line —An Effort to Regulate Beachfront Development." Coastal Zone Management journal 4 (1,2): 151-164. USGBC (U.S. Green Building Council). 2009. LEED for Homes Reference Guide. COASTAL CONSTRUCTION MANUAL 7-27 i P"I Dermining SitSite-Specificfiic Loads This chapter provides guidance on determining site -specific loads from high winds, flooding, and seismic events. The loads determined in accordance with this guidance are applied to the design of building elements described in Chapters 9 through 15. The guidance is intended to illustrate important concepts and best practices in accordance with building codes and standards and does not represent an exhaustive collection of load calculation methods. Examples of problems are provided to illustrate the application of design load provisions of ASCE 7-10. For more detailed guidance, see the applicable building codes or standards. Figure 8-1 shows the process of determining site -specific loads for three natural hazards (flood, wind, and seismic events). The process includes identifying the applicable building codes and standards for the selected site, identifying building characteristics that affect loads, and determining factored design loads using applicable load combinations. Model building codes and standards may not provide CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/ mat/fema55.shtm). NOTE All coastal residential buildings must be designed and constructed to prevent flotation, collapse, and lateral movement due to the effects of wind and water loads acting simultaneously. COASTAL CONSTRUCTION MANUAL 8-1 DETERMINING SITE -SPECIFIC LOADS Volume II load determination and design guidance for the hazards that are listed in the figure. In such instances, supplemental guidance should be sought. The loads and load combinations used in this Manual are required by ASCE 7-10 unless otherwise noted. Although the design concepts that are presented in this Manual are applicable to both Allowable Stress Design (ASD) and Load and Resistance Factor Design (LRFD), all calculations, analyses, and load combinations are based on ASD. Extension of the design concepts presented in this Manual to the LRFD format can be achieved by modifying the calculations to use strength -level loads and resistances. 8-2 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS 8.1 Dead Loads Dead load is defined in ASCE 7-10 as "... the weight of all materials of construction incorporated into the building including, but not limited to, walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items, and fixed service equipment including the weight of cranes." The sum of the dead loads of all the individual elements equals the unoccupied weight of a building. The total weight of a building is usually determined by multiplying the unit weight of the various building materials —expressed in pounds per unit area —by the surface area of the materials. Unit weights of building elements, such as exterior walls, floors and roofs, are commonly used to simplify the calculation of building weight. Minimum design dead loads are contained in ASCE 7-10, Commentary. Additional information about material weights can be found in Architectural Graphic Standards (The American Institute of Architects 2007) and other similar texts. Determining the dead load is important for several reasons: The dead load determines in part the required size of the foundation (e.g., footing width, pile embedment depth, number of piles). Dead load counterbalances uplift forces from buoyancy when materials are below the stillwater depth (see Section 85.7) and from wind (see Example 8.9). Dead load counterbalances wind and earthquake overturning moments. Dead load changes the response of a building to impacts from floodborne debris and seismic forces. Prescriptive design in the following code references and other code references is dependent on the dead load of the building. For example, wind uplift strap capacity, joist spans, and length of wall bracing required to resist seismic forces are dependent on dead load assumptions used to tabulate the prescriptive requirements in the following examples of codes and prescriptive standards: 2012 IRC, International Residential Code for One -and Two -Family Dwellings (ICC 2011b) 2012 IBC, International Building Code (ICC 2011a) ICC 600-2008, Standard for Residential Construction in High -Wind Regions (ICC 2008) WFCM-12, Wood Frame Construction Manual for One- and Two -Family Dwellings (AF&PA 2012) AISI S230-07, Standard for Cold -Jo rmed Steel Framing prescriptive Method for One- and Two family Dwellings (AISI 2007) 8.2 Live Loads Live loads are defined in ASCE 7-10 as "... loads produced by the use and occupancy of the building ... and do not include construction or environmental loads such as wind load, snow load, rain load, earthquake load, flood load, or dead load." Live loads are usually taken as a uniform load spread across the surface being designed. For residential one- and two-family buildings, the uniformly distributed live load for habitable areas (except sleeping and attic areas) in ASCE 7-10 is 40 pounds/square foot. For balconies and decks on COASTAL CONSTRUCTION MANUAL 8-3 DETERMINING SITE -SPECIFIC LOADS one- and two-family buildings, live load is 1.5 times the live load of the occupancy served but not to exceed 100 pounds/ square foot. This requirement typically translates to a live load of 60 pounds/ square foot for a deck or balcony accessed from a living room or den, or a live load of 45 pounds/square foot for a deck or balcony accessed from a bedroom. ASCE 7-10 contains no requirements for supporting a concentrated load in a residential building. Volume II 8.3 Concept of Tributary or Effective Area and Application of Loads to a Building The tributary area of an element is the area of the floor, wall, roof, or other surface that is supported by that element. The tributary area is generally a rectangle formed by one- half the distance to the adjacent element in each applicable direction. The tributary area concept is used to distribute loads to various building elements. Figure 8-2 illustrates tributary areas for roof loads, lateral wall loads, and column or pile loads. The tributary area is a factor in calculating wind pressure coefficients, as described in Examples 8.7 and 8.8. 8-4 COASTAL CONSTRUCTION MANUAL Volume II 8.4 Snow Loads DETERMINING SITE -SPECIFIC LOADS Snow loads are applied as a vertical load on the roof or other exposed surfaces such as porches or decks. Ground snow loads are normally specified by the local building code or building official. In the absence of local snow load information, ASCE 7-10 contains recommended snow loads shown on a map of the United States. When the flat roof snow load exceeds 30 pounds/square foot, a portion of the weight of snow is added to the building weight when the seismic force is determined. 8.5 Flood Loads Floodwaters can exert a variety of load types on building elements. Both hydrostatic and depth -limited breaking wave loads depend on flood depth. Flood loads that must be considered in design include: Hydrostatic load — buoyancy (flotation) effects, lateral loads from standing water, slowly moving water, and nonbreaking waves Breaking wave load Hydrodynamic load — from rapidly moving water, including broken waves Debris impact load — from waterborne objects NOTE ® Flood load calculation procedures cited in this Manual are conservative, given the uncertain conditions of a severe coastal event. ® Background information and procedures for calculating coastal flood loads are presented in a number of publications, including ASCE 7-10 and the Coastal Engineering Manual (USACE 2008). The effects of flood loads on buildings can be exacerbated by storm -induced erosion and localized scour and by long-term erosion, all of which can lower the ground surface around foundation elements and cause the loss of load -bearing capacity and loss of resistance to lateral and uplift loads. As discussed in Section 8.5.3, the lower the ground surface elevation, the deeper the water, and because the wave theory used in this Manual is based on depth -limited waves, deeper water creates larger waves and thus greater loads. 8.5.1 Design Flood In this Manual, "design flood" refers to the locally adopted regulatory flood. If a community regulates to minimum NFIP requirements, the design flood is identical to the base flood (the 1-percent-annual-chance flood or 100-year flood). If a community has chosen to exceed minimum NFIP building elevation requirements, the design flood can exceed the base flood. The design flood is always equal to or greater than the base flood. TERMINOLOGY: FREEBOARD Freeboard is additional height incorporated into the DFE to account for uncertainties in determining flood elevations and to provide a greater level of flood protection. Freeboard may be required by State or local regulations or be desired by a property owner. COASTAL CONSTRUCTION MANUAL 8-5 DETERMINING SITE -SPECIFIC LOADS Volume II 8.5.2 Design Flood Elevation Many communities have chosen to exceed minimum NFIP building elevation requirements, usually by requiring freeboard above the base flood elevation (BFE) but sometimes by regulating to a more severe flood than the base flood. In this Manual, "design flood elevation" (DFE) refers to the locally adopted regulatory flood elevation. In ASCE 24-05, the DFE is defined as the "elevation of the design flood, including wave height, relative to the datum specified on the community's flood hazard map." The design flood is the "greater of the following two flood events: (1) the base flood, affecting those areas identified as SFHAs on the community's FIRM or (2) the flood corresponding to the area designated as a flood hazard area on a community's flood hazard map or otherwise legally designated." The DFE is often taken as the BFE plus any freeboard required by a community, even if the community has not adopted a design flood more severe than the 100-year flood. Coastal floods can and do exceed BFEs shown on FIRMs and minimum required DFEs established by local and State governments. When there are differences between the minimum required DFE and the recommended elevation based on consideration of other sources, the designer, in consultation with the owner, must decide whether elevating above the DFE provides benefits relative to the added costs of elevating higher than the minimum requirement. For example, substantially higher elevations require more stairs to access the main floor and may require revised designs to meet the community's height restriction. Benefits include reduced flood damage, reduced flood insurance premiums, and the ability to reoccupy homes faster than owners of homes constructed at the minimum allowable elevation. In both Hurricanes Katrina and Ike, high water marks after the storms indicated that if the building elevations had been set to the storm surge elevation, the buildings may have survived. See FEMA 549, Hurricane Katrina in the Gulf Coast (FEMA 2006), and FEMA P-757, Hurricane Ike in Texas and Louisiana (FEMA 2009), for more information. In addition to considering the DFE per community regulations, designers should consider the following before deciding on an appropriate lowest floor elevation: The 500-year flood elevation as specified in the Flood Insurance Study (FIS) or similar study. The 500-year flood elevation (including wave effects) represents a larger but less frequent event than the typical basis for the DFE (e.g., the 100-year event). In order to compare the DFE to the 500-year flood elevation, the designer must obtain the 500-year wave crest elevation from the FIS or convert the 500- year stillwater level to a wave crest elevation if the latter is not included in the FIS report. The elevation of the expected maximum storm surge as specified by hurricane evacuation maps. Storm surge evacuation maps provide a maximum storm surge elevation for various hurricane categories. Depending on location, maps may include all hurricane categories (1 to 5), or elevations for selected storm categories only. Most storm surge evacuation maps are prepared by the U.S. Army Corps of Engineers (USACE) and are usually available from the USACE District Office or State/local emergency management agencies. Storm surge elevations are stillwater levels and do not include wave heights, so the designer must convert storm surge elevations to wave crest elevations. When storm surge evacuation maps are based on landmark boundaries (e.g., roads or other boundaries of convenience) rather than storm surge depths, the designer needs to obtain the surge elevations for a building site from the evacuation study (if available). The topographic map of the region may also provide 8-6 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS information about the storm surge depths because the physical boundary elevation should establish the most landward extent of the storm surge. Historical information and advisory flood elevations. Historical information showing flood levels and flood conditions during past flood events, if available, is an important consideration for comparison to the DFE. For areas subject to a recent coastal flood event, advisory flood elevations may be available based on the most recent flooding information unique to the site. Community FIRMs do not account for the effects of long-term erosion, subsidence, or sea level rise, all of which could be considered when establishing lowest floor elevations in excess of the DFE. Erosion can increase future flood hazards by removing dunes and lowering ground levels (allowing larger waves to reach a building site). Sea level rise can increase future flood hazards by allowing smaller and more frequently occurring storms to inundate coastal areas and by increasing storm surge elevations. Section 3.6 discusses the process a designer could follow to determine whether a FIRM represents flood hazards associated with the site under present-day and future -based flood conditions. This section provides more information on translating erosion and sea level rise data into d5 (design flood depth) calculations. Figure 8-3 illustrates a procedure that designers can follow to determine ds under a variety of future conditions. In essence, designers should determine the lowest expected ground elevation at the base of a building during its life and the highest expected stillwater elevation at the building during its life. Figure 8-3. Flowchart for estimating maximum likely design stillwater flood depth at the site COASTAL CONSTRUCTION MANUAL 8-7 DETERMINING SITE -SPECIFIC LOADS Volume II The lowest expected ground elevation is determined by considering subsidence, long-term erosion, and erosion during the base flood. Subsidence effects can be estimated by lowering all existing ground elevations at the site by the product of the subsidence rate and the building lifetime. For example, if subsidence occurs at a rate of 0.005 foot/year and the building lifetime is 50 years, the profile should be lowered 0.25 foot. Figure 8-4 illustrates a simple way to estimate long-term effects on ground elevations at the building. Translate the beach and dune portion of the profile landward by an amount equal to the product of the long-term erosion rate and the building lifetime. If the erosion rate is 3 feet/year and the building lifetime is 50 years, shift the profile back 150 feet. Figure 8-4 also shows the next step in the process, which is to assess dune erosion (see Section 3.5.1) to determine whether the dune will be removed during a base flood event. The lowest expected grade will be evident once the subsidence, long-term erosion, and dune erosion calculations are made. The stillwater level is calculated by adding the expected sea level rise element to the base flood stillwater elevation. For example, if the FIS states the 100-year stillwater elevation is 12.2 feet NAVD, and if sea level is rising at 0.01 foot/year, and if the building lifetime is 50 years, the future conditions stillwater level will be 12.7 feet NAVD (12.2 + K50)(0.01T. The design stillwater flood depth, ds, is then calculated by subtracting the future conditions eroded grade elevation from the future conditions stillwater elevation. Figure 8-4. Erosion's effects on ground elevation 8-8 COASTAL CONSTRUCTION MANUAL Volume II 8.5.3 Design Stillwater Flood Depth In a general sense, flood depth can refer to two different depths (see Figure 8-5): Stillwater flood depth. The vertical distance between the eroded ground elevation and the stillwater elevation associated with the design flood. This depth is referred to as the design stillwater flood depth (d). DETERMINING SITE -SPECIFIC LOADS U NOTE The design stillwater flood depth (d,) (including wave setup; see Section 8.5.4) should be used for calculating wave heights and flood loads. Design flood protection depth. The vertical distance between the eroded ground elevation and the DFE. This depth is referred to as the design flood protection depth (d) but is not used extensively in this Manual. This Manual emphasizes the use of the DFE as the minimum elevation to which flood - resistant design and construction efforts should be directed. Determining the maximum design stillwater flood depth over the life of a building is the most important flood load calculation. Nearly every other coastal flood load parameter or calculation (e.g., hydrostatic load, design flood velocity, hydrodynamic load, design wave height, DFE, debris impact load, local scour depth) depends directly or indirectly on the design stillwater flood depth. COASTAL CONSTRUCTION MANUAL 8-9 DETERMINING SITE -SPECIFIC LOADS Volume II In this Manual, the design stillwater flood depth (ds) is defined as the difference between the design stillwater flood elevation (E,,,) and the lowest eroded ground surface elevation (GS) adjacent to the building (see Equation 8.1) where wave setup is included in the stillwater flood elevation. Figure 8-5 illustrates the relationships among the various flood -� parameters that determine or are affected by flood depth. Note that in Figure 8-5 and Equation 8.1, GS is not the lowest existing pre- CROSS REFERENCE flood ground surface; it is the lowest ground surface that will result For a discussion of localized from long-term erosion and the amount of erosion expected to occur scour, see Section 8.5.10. during a design flood, excluding local scour effects. The process for determining GS is described in Section 3.6.4. Values for E,,, are not shown on FEMA FIRMS, but they are given in the FISs, which are produced in conjunction with the FIRM for communities. FISs are usually available from community officials and NFIP State Coordinating Agencies. Some states have made FISs available on their Web sites. Many FISs are also available on the FEMA Web site for free or are available for download for a small fee. For more information, go to http://www.msc.fema.gov. Design stillwater flood depth (d) is determined using Equation A in Example 8.1 for scenarios in which a non-100-year frequency -based DFE is specified by the Authority Having Jurisdiction (AHJ). Freeboard tied to the 100-year flood should not be used to increase ds since load factors in ASCE 7 were developed for the 100-year nominal flood load. Example 8.1 demonstrates the calculation of the design stillwater flood depth for five scenarios. All solutions to example problems are in bold text in this Manual. 8-10 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-11 DETERMINING SITE -SPECIFIC LOADS Volume II 8-12 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-13 DETERMINING SITE -SPECIFIC LOADS Volume II 4.6 4.6 7.1 7.5 8-14 COASTAL CONSTRUCTION MANUAL Volume II 8.5.4 Wave Setup Contribution to Flood Depth Pre-1989 FIS reports and FIRMS do not usually include the effects of wave setup (dus), but some post-1989 FISs and FIRMS do. Because the calculation of design wave heights and flood loads depends on an accurate determination of the total stillwater flood depth, designers should review the effective FIS carefully, using the following procedure: Check the hydrologic analyses section of the FIS for mention of wave setup. Note the magnitude of the wave setup. Check the stillwater elevation table of the FIS for footnotes regarding wave setup. If wave setup is included in the listed BFEs but not in the 100-year stillwater elevation, add wave setup before calculating the design stillwater flood depth, the design wave height, the design flood velocity, flood loads, and localized scour. If wave setup is already included in the 100-year stillwater elevation, use the 100-year stillwater elevation to determine the design stillwater flood depth and other parameters. Wave setup should not be included in the 100-year stillwater elevation when calculating primary frontal dune erosion. 8.5.5 Design Breaking Wave Height DETERMINING SITE -SPECIFIC LOADS #J NOTE Flood loads are applied to structures as follows: ® Lateral hydrostatic loads - at two-thirds depth point of stillwater elevation ® Breaking wave loads - at stillwater elevation ® Hydrodynamic loads - at mid -depth point of stillwater elevation ® Debris impact loads - at stillwater elevation TERMINOLOGY: WAVE SETUP Wave setup is an increase in the stillwater surface near the shoreline due to the presence of breaking waves. Wave setup typically adds 1.5 to 2.5 feet to the 100-year stillwater flood elevation and should be discussed in the FIS. The design breaking wave height (Hb) at a coastal building site is one of the most important design parameters. Unless detailed analysis shows that natural or manmade obstructions will protect the site during a design event, wave heights at a site should be calculated as the heights of depth -limited breaking waves, which are equivalent to 0.78 times the design stillwater flood depth (see Figure 8-5). Note that 70 percent of the breaking wave height lies above the stillwater elevation. In some situations, such as steep ground slopes immediately seaward of a building, the breaking wave height can exceed 0.78 times the stillwater flood depth. In such instances, designers may wish to increase the breaking wave height used for design, with an upper limit for the breaking wave height equal to the stillwater flood depth. 8.5.6 Design Flood Velocity Estimating design flood velocities (V) in coastal flood hazard areas is subject to considerable uncertainty. There is little reliable historical information concerning the velocity of floodwaters during coastal flood events. The direction and velocity of floodwaters can vary significantly throughout a coastal flood event. Floodwaters can approach a site from one direction during the beginning of a flood event and then shift WARNING This Manual does not provide guidance for estimating flood velocities during tsunamis. The issue is highly complex and site - specific. Designers should look for model results from tsunami inundation or evacuation studies. COASTAL CONSTRUCTION MANUAL 8-15 DETERMINING SITE -SPECIFIC LOADS Volume II to another direction (or several directions). Floodwaters can inundate low-lying coastal sites from both the front (e.g., ocean) and back (e.g., bay, sound, river). In a similar manner, flow velocities can vary from close to zero to high velocities during a single flood event. For these reasons, flood velocities should be estimated conservatively by assuming floodwaters can approach from the most critical direction relative to the site and by assuming flow velocities can be high (see Equation 8.2). c'' For design purposes, flood velocities in coastal areas should be assumed to lie between V = (gds)0-5 (the expected upper bound) and V = d It (the expected lower bound). It is recommended that designers consider the following factors before deciding whether to use the upper- or lower -bound flood velocity for design: Flood zone Topography and slope Distance from the source of flooding Proximity to other buildings or obstructions The upper bound should be taken as the design flood velocity if the building site is near the flood source, in Zone V, in Zone AO adjacent to Zone V, in Zone A subject to velocity flow and wave action, on steeply sloping terrain, or adjacent to other large buildings or obstructions that will confine or redirect floodwaters and increase local flood velocities. The lower bound is a more appropriate design flood velocity if the site is distant from the flood source, in Zone A, on flat or gently sloping terrain, or unaffected by other buildings or obstructions. Figure 8-6 shows the velocity versus design stillwater flood depth relationship for non -tsunami, upper- and lower -bound velocities. Equation 8.2 shows the equations for the lower -bound and upper -bound velocity conditions. 8-16 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Figure 8-6. Velocity versus design stillwater flood depth 8.5.7 Hydrostatic Loads Hydrostatic loads occur whenever floodwaters come into contact with a foundation, building, or building element. Hydrostatic loads can act laterally or vertically. Lateral hydrostatic forces are generally not sufficient to cause deflection or displacement of a building or building element unless there is a substantial difference in water elevation on opposite sides of the building or component. This is why the NFIP requires that openings be provided in vertical walls that form enclosures below the BFE for buildings constructed in Zone A (see Section 5.2.3.2). Likewise, vertical hydrostatic forces (buoyancy or flotation) are not generally a concern for properly constructed and elevated coastal buildings founded on adequate foundations. However, buoyant forces can have a significant effect on inadequately elevated buildings on shallow foundations. Such buildings are vulnerable to uplift from flood and wind forces because the weight of a foundation or building element is much less when submerged than when not submerged. For example, one cubic foot of a footing constructed of normal weight concrete weighs approximately 150 pounds. But when submerged, each cubic foot of concrete displaces a cubic foot of saltwater, which weighs about 64 pounds/cubic foot. Thus, the foundation's submerged weight is only 86 pounds if submerged in saltwater (150 pounds/cubic foot — 64 pounds/cubic foot = 86 pounds/cubic foot), or 88 pounds if submerged in fresh water (150 pounds/cubic foot — 62 pounds/ cubic foot = 88 pounds/cubic foot). A submerged footing contributes approximately 40 percent less uplift resistance during flood conditions. Section 3.2.2 of ASCE 7-10 states that the full hydrostatic pressure of water must be applied to floors and foundations when applicable. Sections 2.3.3 and 2.4.2 of ASCE 7-10 require factored flood loads to be considered in the load combinations that model uplift and overturning design limit states. For ASD, flood loads are increased by a factor of 1.5 in Zone V and Coastal A Zones (and 0.75 in coastal flood zones with base flood wave heights less than 1.5 feet, and in non -coastal flood zones). These load factors are applied to COASTAL CONSTRUCTION MANUAL 8-17 DETERMINING SITE -SPECIFIC LOADS Volume II account for uncertainty in establishing design flood intensity. As indicated in Equations 8-3 and 8-4 (per Figure 8-7), the design stillwater flood depth should be used when calculating hydrostatic loads. Any buoyant force (Fbuoy) on an object must be resisted by the weight of the object and any other opposing force (e.g., anchorage forces) resisting flotation. The contents of underground storage tanks and the live load on floors should not be counted on to resist buoyant forces because the tanks may be empty or the building may be vacant when the flood occurs. Buoyant or flotation forces on a building can be of concern if the actual stillwater flood depth exceeds the design stillwater flood depth. Buoyant forces are also of concern for empty or partially empty aboveground tanks, underground tanks, and swimming pools. Lateral hydrostatic loads are given by Equation 8.3 and illustrated in Figure 8-7. Note that fta (in Equation 8.3) is equivalent to the area of the pressure triangle and acts at a point equal to 2/3 ds below the water surface (see Figure 8-7). Figure 8-7 is presented here solely to illustrate the application of lateral hydrostatic force. In communities participating in the NFIP, local floodplain ordinances or laws require that buildings in Zone V be elevated above the BFE on an open foundation and that the foundation walls of buildings in Zone A be equipped with openings that allow floodwater to enter so that internal and external hydrostatic pressures will equalize (see Section 5.2) and not damage the structure. Vertical hydrostatic forces are given by Equation 8.4 and are illustrated by Figure 8-8. c'' 8-18 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Figure 8-7. Lateral flood force on a vertical component c'' COASTAL CONSTRUCTION MANUAL 8-19 DETERMINING SITE -SPECIFIC LOADS 8.5.8 Wave Loads Calculating wave loads requires the designer to estimate expected wave heights, which, for the purposes of this Manual, are limited by water depths at the site of interest. These data can be estimated using a variety of models. FEMA uses its Wave Height Analysis for Flood Insurance Studies (WHAFIS) model to estimate wave heights and wave crest elevations, and results from this model can be used directly by designers to calculate wave loads. Wave forces can be separated into four categories: Volume II CROSS REFERENCE For additional guidance in calculating wave loads, see ASCE 7-10. From nonbreaking waves — can usually be computed as hydrostatic forces against walls and hydrodynamic forces against piles From breaking waves — short duration but large magnitude From broken waves — similar to hydrodynamic forces caused by flowing or surging water 8-20 COASTAL CONSTRUCTION MANUAL Volume II Uplift — often caused by wave run-up, deflection, or peaking against the underside of horizontal surfaces The forces from breaking waves are the highest and produce the most severe loads. It is therefore strongly recommended that the breaking wave load be used as the design wave load. The following three breaking wave loading conditions are of interest in residential design: DETERMINING SITE -SPECIFIC LOADS CROSS REFERENCE For more information about FEMNs WHAFIS model, see http://www.fema.gov/plan/ Waves breaking on small -diameter vertical elements below the DFE (e.g., piles, columns in the foundation of a building in Zone V) Waves breaking against walls below the DFE (e.g., solid foundation walls in Zone A, breakaway walls in Zone V) Wave slam, where just the top of a wave strikes a vertical wall 8.5.8.1 Breaking Wave Loads on Vertical Piles The breaking wave load on a pile can be assumed to act at the stillwater elevation and is calculated using Equation 8.5. Wave loads produced by breaking waves are greater than those produced by nonbreaking or broken waves. Example 8.3 shows the difference between the loads imposed on a vertical pile by nonbreaking waves and by breaking waves. COASTAL CONSTRUCTION MANUAL 8-21 DETERMINING SITE -SPECIFIC LOADS 8.5.8.2 Breaking Wave Loads on Vertical Walls Breaking wave loads on vertical walls are best calculated according to the procedure described in Criteria for Evaluating Coastal Flood -Protection Structures (Walton et al. 1989). The procedure is suitable for use in wave conditions typical during coastal flood and storm events. The relationship for breaking wave load per unit length of wall is shown in Equation 8.6. Volume II #j NOTE Equation 8.6 includes the hydrostatic component calculated using Equation 8.3. If Equation 8.6 is used, lateral hydrostatic force from Equation 8.3 should not be added to avoid double counting. The procedure assumes that the vertical wall causes a reflected or standing wave to form against the seaward side of the wall and that the crest of the wave reaches a height of 1.2 d, above the stillwater elevation. The resulting dynamic, static, and total pressure distributions against the wall and resulting loads are as shown in Figure 8-9. 8-22 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Table 8-1. Value of Dynamic Pressure Coefficient (Cp) as a Function of Probability of Exceedance Buildings and other structures that represent a low hazard to human life or 1.6 property in the event of failure 0.5 3.2 Buildings and other structures, the failure of which could pose a substantial 0.002 risk to human life Figure 8-9. Breaking wave pressure distribution against a vertical wall COASTAL CONSTRUCTION MANUAL 8-23 DETERMINING SITE -SPECIFIC LOADS Volume II #j NOTE: BREAKAWAY WALLS When designing breakaway versus solid foundation walls using Equation 8.6, the designer should use a Cp of 1.0 rather than the Cp of 1.6 shown in Table 8-1. For more information on breakaway walls, see Section 9.3. WARNING The likelihood of damage or loss can be reduced by installing louvered panels in solid walls or creating flood openings in breakaway walls for small flood depths, so that the panels do not break away under minor (nuisance) flood conditions. 8-24 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Figure 8-11. Water depth versus wave height, and water depth versus breaking wave force against, a vertical wall COASTAL CONSTRUCTION MANUAL 8-25 DETERMINING SITE -SPECIFIC LOADS Volume II 8-26 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-27 DETERMINING SITE -SPECIFIC LOADS 8.5.9 Hydrodynamic Loads Volume II As shown in Figure 8-13, water flowing around a building (or a structural element or other object) imposes loads on the building. In the figure, note that the lowest floor of the building is above the flood level and the loads imposed by flowing water affect only the foundation walls. However, open foundation systems, unlike that shown in Figure 8-13, can greatly reduce hydrodynamic loading. Hydrodynamic loads, which are a function of flow velocity and structural geometry, include frontal impact on the upstream face, drag along the sides, and suction on the downstream side. One of the most difficult steps in quantifying loads imposed by moving water is determining the expected flood velocity (see Section 8.5.6 for guidance on design flood velocities). In this Manual, the velocity of floodwater is assumed to be constant (i.e., steady-state flow). Hydrodynamic loads can be calculated using Equation 8.8. Elevating above the DFE provides additional protection from hydrodynamic loads for elevated enclosed areas. The drag coefficient used in Equation 8.8 is taken from the Shore Protection Manual, Volume 2 (USACE 1984). Additional guidance is provided in Section 5.4.3 of ASCE 7-10 and in FEMA 259, Engineering Principles and Practices for Retrofitting Floodprone Residential Buildings (FEMA 2001). The drag coefficient is a function of the shape of the object around which flow is directed. When an object is something other than a round, square, or rectangular pile, the coefficient is determined by one of the following ratios (see Table 8-2): 1. The ratio of the width of the object (w) to the height of the object (h) if the object is completely immersed in water 2. The ratio of the width of the object (w) to the stillwater flood depth of the water (d) if the object is not fully immersed Figure 8-13. Hydrodynamic loads on a building Negative pressure (suction) on downstream side Flood level Foundation wall t F rontal ir�Pac e 0 e Drag effect on sides Direction of flow NOTE d design stillwater flood depth w width of building perpendicular to the direction of flow 8-28 COASTAL CONSTRUCTION MANUAL Volume II Flow around a building or building element also creates flow -perpendicular forces (lift forces). When a building element is rigid, lift forces can be assumed to be small. When the element is not rigid, lift forces can be greater than drag forces. The equation for lift force is the same as that for hydrodynamic force except that the drag coefficient (Q) is replaced with the lift coefficient (Cl). In this Manual, the foundations of coastal residential buildings are considered rigid, and hydrodynamic lift forces can therefore be ignored. Equation 8.8 provides the total force against a building of a given surface area, A. Dividing the total force by either length or width yields a force per linear unit; dividing by surface area, A, yields a force per unit area. Example 8.3 shows the difference between the loads imposed on a vertical pile by nonbreaking and breaking waves. As noted in Section 8.5.8, nonbreaking wave forces on piles can be calculated as hydrodynamic forces. DETERMINING SITE -SPECIFIC LOADS Table 8-2. Drag Coefficients for Ratios of Width to Depth (w/ds) and Width to Height (w/h) 13-20 1.3 21-32 1.4 33-40 1.5 81-120 1.8 NOTE Lift coefficients (C) are provided in Introduction to Fluid Mechanics (Fox and McDonald 1985) and in many other fluid mechanics textbooks. COASTAL CONSTRUCTION MANUAL 8-29 DETERMINING SITE -SPECIFIC LOADS Volume II 8-30 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS 8.5.10 Debris Impact Loads Debris impact loads are imposed on a building by objects carried by moving water. The magnitude of these loads is very difficult to predict, but some reasonable allowance must be made for them. The loads are influenced by where the building is located in the potential debris stream, specifically if it is: Immediately adjacent to or downstream from another building Downstream from large floatable objects (e.g., exposed or minimally covered storage tanks) Among closely spaced buildings A familiar equation for calculating debris loads is given in ASCE 7-10, Commentary. This equation has been simplified into Equation 8.9 using Cs,,, the values of which are based on assumptions appropriate for the typical coastal buildings that are covered in this Manual. The parameters in Equation 8.9 are discussed below. See Chapter C5 of ASCE 7-10 for a more detailed discussion of the parameters. Equation 8.9 contains the following uncertainties, each of which must be quantified before the effect of debris loading can be calculated: Size, shape, and weight (LY) of the waterborne object Design flood velocity (V) Velocity of the waterborne object compared to the flood velocity Duration of the impact (At) (assumed to be equal to 0.03 seconds in the case of residential buildings is incorporated in CS, which is explained in more detail below) Portion of the building to be struck COASTAL CONSTRUCTION MANUAL 8-31 DETERMINING SITE -SPECIFIC LOADS Volume II Designers should consider locally adopted guidance because it may be based on more recent information than ASCE 7-10 or on information specific to the local hazards. Local guidance considerations may include the following: Size, shape, and weight of waterborne debris. The size, shape, and weight of waterborne debris may vary according to region. For example, the coasts of Washington, Oregon, and other areas may be subject to very large debris in the form of whole trees and logs along the shoreline. The southeastern coast of the United States may be more subject to debris impact from dune crossovers and destroyed buildings than other areas. In the absence of information about the nature of potential debris, a weight of 1,000 pounds is recommended as the value of W. Objects with this weight could include portions of damaged buildings, utility poles, portions of previously embedded piles, and empty storage tanks. Debris velocity. As noted in Section 8.5.6, flood velocity can be approximated within the range given by Equation 8.2. For calculating debris loads, the velocity of the waterborne object is assumed to be the same as the flood velocity. Although this assumption may be accurate for small objects, it may overstate debris velocities for large objects that drag on the bottom or that strike nearby structures. Portion of the building to be struck. The object is assumed to be at or near the water surface level when it strikes the building and is therefore assumed to strike the building at the stillwater elevation. Depth coefficient. The depth coefficient (CD) accounts for reduced debris velocity as water depth decreases. For buildings in Zone A with stillwater flood depths greater than 5 feet or for buildings in Zone V, the depth coefficient = 1.0. For other conditions, the depth coefficient varies, as shown in Table 8-3. 8-32 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Table 8-3. Depth Coefficient (CD) by Flood Hazard Zone and Water Depth Floodway(a) or Zone V 1.0 Zone A, stillwater flood depth = 4 ft 0.75 Zone A, stillwater flood depth < 1 ft 0.00 (a) Per ASCE 24-05, a "floodway" is a "channel and that portion of the floodplain reserved to convey the base flood without cumulatively increasing the water surface elevation more than a designated height." Blockage coefficient. The blockage coefficient (CB) is used to account for the reduction in debris velocity expected to occur because of the screening provided by trees and other structures upstream from the structure or building on which the impact load is being calculated. The blockage coefficient varies, as shown in Table 8-4. Table 8-4. Values of Blockage Coefficient CB No upstream screening, flow path wider than 30 ft 1.0 Moderate upstream screening, flow path 10-ft wide 0.2 Building structure coefficient. The building structure coefficient, Cftr, is derived from Equation C5-3, Chapter C5, ASCE 7-10. Coefficient values for C, , (0.2, 0.4, and 0.8 as defined above for Equation 8.9) were generated by selecting input values recommended in ASCE 7-10, Chapter C5, with appropriate assumptions made to model typical coastal residential structures. The derived building structure coefficient formula with inputs is defined as follows: _ 3.14CICoRmaa Cs,,. 2gAt where: CI = importance coefficient = 1.0 CO = orientation coefficient = 0.80 At = duration of impact = 0.03 sec g = gravitational constant (32.2 ft/sec2) Rm = maximum response ratio assuming approximate natural period, T, of building types as follows: for timber pile and masonry column, T= 0.75 sec; for concrete pile or concrete or steel moment resisting frames, T= 0.35 sec; and for reinforced concrete foundation walls, T = 0.2 sec. The ratio of impact duration (0.03 sec) to approximate natural period (T) is entered into Table C5-4 of ASCE 7-10 to yield the R,n,, value. COASTAL CONSTRUCTION MANUAL 8-33 DETERMINING SITE -SPECIFIC LOADS 8.5.11 Localized Scour Volume II Waves and currents during coastal flood conditions create turbulence around foundation elements, causing localized scour around those elements. Determining potential scour is critical in designing coastal foundations to ensure that failure does not occur as a result of the loss in either bearing capacity or anchoring resistance around the posts, piles, piers, columns, footings, or walls. Localized scour determinations will require knowledge of the flood conditions, soil characteristics, and foundation type. At some locations, soil at or below the ground surface can be resistant to localized scour, and the scour depths calculated as described below would be excessive. When the designer believes the soil at a site may be scour -resistant, the assistance of a geotechnical engineer should be sought before calculated scour depths are reduced. Localized scour around vertical piles. Generally, localized scour calculation methods in coastal areas are based largely on laboratory tests and empirical evidence gathered after storms. The evidence suggests that the localized scour depth around a single pile or column or other thin vertical members is equal to approximately 1.0 to 1.5 times the pile diameter. In this Manual, a ratio of 2.0 is recommended (see Equation 8.10), consistent with the rule of thumb given in the Coastal Engineering Manual (USACE 2008). Figure 8-14 illustrates localized scour at a pile, with and without a scour -resistant terminating stratum. Figure 8-14. Scour at single vertical foundation member, with and without underlying scour -resistant stratum Flood elevation Pile Eroded ground surface d Direction of flow Sm with terminating stratum S,,,ax without Terminating; stratum of terminating stratum non-erodable soil or bedrock NOTE cl. design stillwater flood depth n diameter of pile S,,,ax localized maximum scour depth 8-34 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS EQUATION 8.10. LOCALIZED SCOUR AROUND A SINGLE VERTICAL PILE Sma, =I2.Oa (Eq. 8.10) where: S,nax = maximumlocalized scour depth (ft) a = diameter of a round foundation element or the maximum diagonal cross-section dimension for a rectangular element Observations after some hurricanes have shown cases in which localized scour around foundations far exceeded twice the diameter of any individual foundation pile. This was probably a result of flow and waves interacting with the group of foundation piles. In some cases, scour depressions were observed or reported to be 5 to 10 feet deep (see Figure 8-15). This phenomenon has been observed at foundations with or without slabs on grade but appears to be aggravated by the presence of the slabs. Figure 8-15. Deep scour around foundation piles, Hurricane Ike (Bolivar Peninsula, TX, 2008) Some research on the interaction of waves and currents on pile groups suggests that the interaction is highly complex and depends on flow characteristics (depth, velocity, and direction), wave conditions (wave height, period, and direction), structural characteristics (pile diameter and spacing) and soil characteristics (Sumer et al. 2001). Conceptually, the resulting scour at a pile group can be represented as shown in Figure 8-16. In this Manual, the total scour depth under a pile group is estimated to be 3 times the single pile scour depth, plus an allowance for the presence of a slab or grade beam, as shown in Equation 8.11. The factor of 3 is consistent with data reported in the literature and post -hurricane observations. COASTAL CONSTRUCTION MANUAL 8-35 DETERMINING SITE -SPECIFIC LOADS Volume II Figure 8-16. Scour around a group of foundation piles SOURCE: ADAPTED FROM SUMER ET AL. 2001 One difficulty for designers is determining whether local soils and coastal flood conditions will result in pile group scour according to Equation 8.11. Observations after Hurricanes Rita and Ike suggest that such scour is widespread along the Gulf of Mexico shoreline in eastern Texas and southwestern Louisiana, and observations after Hurricanes Opal and Ivan suggest that it occurs occasionally along the Gulf of Mexico shoreline in Alabama and Florida. Deep foundation scour has also been observed occasionally on North Carolina barrier islands (Hurricane Fran) and American Samoa (September 2009 tsunami). These observations suggest that some geographic areas are more susceptible than others, but deep foundation scour can occur at any location where there is a confluence of critical soil, flow, and wave conditions. Although these critical conditions cannot be identified precisely, designers should (1) be aware of the phenomenon, (2) investigate historical records for evidence of deep foundation scour around pile groups, and (3) design for such scour when the building site is low-lying, the soil type is predominantly silty, and the site is within several hundred feet of a shoreline. Localized scour around vertical walls and enclosures. Localized scour around vertical walls and enclosed areas (e.g., typical Zone A construction) can be greater than that around single vertical piles, 8-36 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS but it usually occurs at a corner or along one or two edges of the building (as opposed to under the entire building). See Figure 8-16. Scour depths around vertical walls and enclosed areas should be calculated in accordance with Equation 8.12, which is derived from information in Coastal Engineering Manual (USACE 2006). The equation is based on physical model tests conducted on large -diameter vertical piles exposed to waves and currents ("large" means round and square objects with diameters/side lengths corresponding to several tens of feet in the real world, which is comparable to the coastal residential buildings considered in this Manual). Equation 8.12, like Equation 8.11, has no explicit consideration of soil type, so designers must consider whether soils are highly erodible and plan accordingly. 8.5.12 Flood Load Combinations Designers should be aware that not all of the flood loads described in Section 8.5 act at certain locations or against certain building types. Table 8-5 provides guidance for calculating appropriate flood loads in Zone V and Coastal A Zones (flood load combinations for the portion of Zone A landward of the Limit of Moderate Wave Action [LiMWA] are shown for comparison). Table 8-5. Selection of Flood Loads for Fa in ASCE 7-10 Load Combinations for Global Forces Pile or open foundation in Zone V or Coastal A Zone Solid (perimeter wall) foundation Greater of Fbrhy or Fdyn (on front row of piles only) Fdyn (on all other piles) + F, (on one pile only) Greater of Fbrhw or Fdyn + F, (in one corner) As discussed in Section 8.5.7, hydrostatic loads are included only when standing water will exert lateral or vertical loads on the building; these situations are usually limited to lateral forces being exerted on solid walls or buoyancy forces being exerted on floors and do not dominate in the Zone V or Coastal A Zone environment. Section 8.5.7 includes a discussion about how to include these hydrostatic flood loads in the ASCE 7-10 load combinations. COASTAL CONSTRUCTION MANUAL 8-37 DETERMINING SITE -SPECIFIC LOADS Volume II The guidance in ASCE 7-10, Sections 2.3 and 2.4 (Strength Design and Allowable Stress Design, respectively) also indicates which load combinations the flood load should be applied to. In the portion of Zone A landward of the LiMWA, the flood load Fa could either be hydrostatic or hydrodynamic loads. Both of these loads could be lateral loads; only hydrostatic will be a vertical load (buoyancy). When designing for global forces that will create overturning, sliding or uplift reactions, the designer should use Fa as the flood load that creates the most restrictive condition. In sliding and overturning, Fa should be determined by the type of expected flooding. Hydrostatic forces govern if the flooding is primarily standing water possibly saturating the ground surrounding a foundation; hydrodynamic forces govern if the flooding is primarily from moving water. When designing a building element such as a foundation, the designer should use Fa as the greatest of the flood forces that affect that element (F,,, or Fd j + Fj (impact loads on that element acting at the stillwater level). The combination of these loads must be used to develop the required resistance that must be provided by the building element. The designer should assume that breaking waves will affect foundation elements in both Zone V and Zone A. In determining total flood forces acting on the foundation at any given point during a flood event, it is generally unrealistic to assume that impact loads occur on all piles at the same time as breaking wave loads. Therefore, it is recommended that the load be calculated as a single wave impact load acting in combination with other sources of flood loads. For the design of foundations in Zone V or Coastal A Zone, load combination cases considered should include breaking wave loads alone, hydrodynamic loads alone, and the greater of hydrodynamic loads and breaking wave loads acting in combination with debris impact loads. The value of flood load, Fa, used in ASCE 7-10 load combinations, should be based on the greater of Fbrk or Fdy,,, as applicable for global forces (see Table 8-5) or Fj + (Fbrk or FdYj, as applicable for an individual building element such as a pile. Example 8-4 is a summary of the information regarding flood loads and the effects of flooding on an example building. 8-38 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-39 DETERMINING SITE -SPECIFIC LOADS Volume II 8-40 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-41 DETERMINING SITE -SPECIFIC LOADS Volume II 8-42 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS The following worksheets will facilitate flood load computations. COASTAL CONSTRUCTION MANUAL 8-43 DETERMINING SITE -SPECIFIC LOADS Volume II Worksheet 1. Flood Load Computation Non -Tsunami Coastal A Zones (Solid Foundation) Constants yu, = specific weight of water = 62.4 lb/ft3 for fresh water and 64.0 lb/ft3 for saltwater p = mass density of fluid) = 1.94 slugs/ft3 for fresh water and 1.99 slugs/ft3 for saltwater g = gravitational constant = 32.2 ft/seC Variables ds = design stillwater flood depth (ft) = Vol = volume of floodwater displaced (ft3) _ V = velocity (fps) = Cdb = breaking wave drag coefficient = Hb = breaking wave height (ft) _ Cp = dynamic pressure coefficient = Cf = slam coefficient = Cd = drag coefficient = w = width of element hit by water (ft) _ h = vertical distance (ft) wave crest extends above bottom of member = A = area of structure face (ft2) _ W = weight of object (lb) _ CD = depth coefficient = CB = blockage coefficient = Cstr = building structure coefficient = a = diameter of round foundation element = L = horizontal length alongside building exposed to waves (ft) Summary of Loads Ffta = Fbuoy = Fbrkw = Ff = Fdyn = Fi _ S." = STOT = 8-44 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Worksheet 1. Flood Load Computation Non -Tsunami Coastal A Zones (Solid Foundation) (concluded) COASTAL CONSTRUCTION MANUAL 8-45 DETERMINING SITE -SPECIFIC LOADS Volume II Worksheet 2. Flood Load Computation Non-Tsunamic Zone V and Coastal A Zone (Open Foundation) 8-46 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Worksheet 2. Flood Load Computation Non-Tsunamic Zone V and Coastal A Zone (Open Foundation) (concluded) 8.6 Tsunami Loads In general, tsunami loads on residential buildings may be calculated in the same fashion as other flood loads; the physical processes are the same, but the scale of the flood loads is substantially different in that the wavelengths and runup elevations of tsunamis are much greater than those of waves caused by tropical and extratropical cyclones (see Section 3.2). If the tsunami acts as a rapidly rising tide, most of the damage is the result of buoyant and hydrostatic forces (see Tsunami Engineering [Camfield 1980]). When the tsunami forms a bore -like wave, the effect is a surge of water to the shore and the expected flood velocities are substantially higher than in non -tsunami conditions. The tsunami velocities are very high and if realized at the greater water depths, would cause substantial damage to buildings in the path of the tsunami. Additional guidance on designing for tsunami forces including flow velocity, buoyant forces, hydrostatic forces, debris impact, and impulsive forces is provided in FEMA P646, Guidelines for Design of Structures for Vertical Evacuation from Tsunami (FEMA 2008b). For debris impact loads under tsunami conditions, see Section 6.5.6 of FEMA P646, which recommends an alternative to Equation 8.6 in this Manual for calculating tsunami debris impact loads. 8.7 Wind Loads ASCE 7-10 is the state-of-the-art wind load design standard. It contains a discussion of the effects of wind pressure on a variety of building types and building elements. Design for wind loads is essentially the same whether the winds are due to hurricanes, thunderstorms, or tornadoes. Important factors that affect wind load design pressures include: Location of the building site on wind speed maps COASTAL CONSTRUCTION MANUAL 8-47 DETERMINING SITE -SPECIFIC LOADS Volume II Topographic effects (hills and escarpments), which create a wind speedup effect Building risk category (one- and two-family dwellings are assigned to Risk Category II; accessory structures may be assigned to Risk Category I) (see Section 6.2.1.1) Building height and shape Building enclosure category: enclosed, partially enclosed or open Terrain conditions, which determine building exposure category #j NOTE The effects of wind on buildings can be summarized as follows: Basic mapped wind speeds Windward walls and windward surfaces of steep -sloped in ASCE 7-10 for Category II roofs are acted on by inward -acting, or positive pressures. structures (residential buildings) See Figure 8-17. are higher than those in ASCE 7-05 because they represent Leeward walls and leeward surfaces of steep -sloped roofs ultimate wind speeds or strength - and both windward and leeward surfaces of low -sloped p based design wind speeds. Load factors for wind in ASCE 7-10 are roofs are acted on by outward -acting, or negative pressures. also different from those in ASCE See Figure 8-17. 7-05. In ASCE 7-10, the wind load factor in the load combinations Air flow separates at sharp edges and at locations where the for LRFD strength design (LRFD) building geometry changes. is 1.0 (but ASCE 7-05 provides a load factor of 1.6), and the Localized suction, or negative, pressures at eaves, ridges, ASD wind load factor in the load and the corners of roofs and walls are caused by turbulence combinations for allowable stress design (ASD) for wind is 0.6 (but and flow separation. These pressures affect loads on ASCE 7-05 provides a load factor components and cladding (C&C) and elements of the of 1.0). main wind force resisting system (MWFRS). The phenomena of localized high pressures occurring at locations where the building geometry changes is accounted for by the various pressure coefficients in the equations for both MWFRS and C&C. Internal pressures must be included in the determination of net wind pressures and are additive to (or subtractive from) the external pressures. Openings and the natural porosity of building elements contribute to internal Figure 8-17. Effect of wind on an enclosed building and a building with an opening 8-48 COASTAL CONSTRUCTION MANUAL Volume II pressure. the magnitude of internal pressures depends on whether the building is enclosed, partially enclosed, or open, as defined in ASCE 7-10. Figure 8-17 shows the effect of wind on an enclosed and partially enclosed building. In wind-borne debris regions (as defined in ASCE 7-10), in order for a building to be considered enclosed for design purposes, glazing must either be impact -resistant or protected with shutters or other devices that are impact -resistant. This requirement also applies to glazing in doors. Methods of protecting glazed openings are described in ASCE 7-10 and in Chapter 11 of this Manual. 8.7.1 Determining Wind Loads In this Manual, design wind pressures for MWFRS are based on the results of the envelope procedure for low-rise buildings. A low-rise building is defined in ASCE 7-10. The envelope procedure in ASCE 7-10 is only one of several for determining MWFRS pressures in ASCE 7-10, but it is the procedure most commonly used for designing low-rise residential buildings. The envelope procedure for low-rise buildings is applicable for enclosed and partially enclosed buildings with a mean roof height (h) of less than or equal to 60 feet and where mean roof height (h) does not exceed the smallest horizontal building dimension. Figure 8-18 depicts the distribution of external wall and roof pressures and internal pressures from wind. The figure also shows the mean roof height, which is defined in ASCE 7-10 DETERMINING SITE -SPECIFIC LOADS TERMINOLOGY: HURRICANE -PRONE REGIONS In the United States and its territories, hurricane -prone areas are defined by ASCE 7-10 as (1) the U.S. Atlantic Ocean and Gulf of Mexico Coasts where the basic wind speed for Risk Category II buildings is greater than 115 mph and (2) Hawaii, Puerto Rico, Guam, the Virgin Islands, and American Samoa. 44 FORMULA The following formula converts ASCE 7-05 wind speeds to ASCE 7-10 Risk Category II wind speeds. ASCE 7-10 = (ASCE 7-05)( 1.6) For conversion from ASCE 7-10 to ASCE 7-05, use: ASCE 7-10 ASCE 7-05 = 1.6 Figure 8-18. Distribution of roof, wall, and internal pressures on one-story, pile -supported building COASTAL CONSTRUCTION MANUAL 8-49 DETERMINING SITE -SPECIFIC LOADS as "the average of the roof eave height and the height to the highest point on the roof surface ..." Mean roof height is not the same as building height, which is the distance from the ground to the highest point. For calculating both MWFRS and C&C pressures, velocity pressures (q) should be calculated in accordance with Equation 8.13. Velocity pressure varies depending on many factors including mapped wind speed at the site, height of the structure, local topographic effects, and surrounding terrain that affects the exposure coefficient. Volume II #j NOTE ASCE 7-10 Commentary states that where a single component, such as a roof truss, comprises an assemblage of structural elements, the elements of that component should be analyzed for loads based on C&C coefficients, and the single component should be analyzed for loads as part of the MWFRS. The design wind pressure is calculated from the combination of external and internal pressures acting on a building element. This combination of pressures for both MWFRS and C&C loads in accordance with provisions of ASCE 7-10 is represented by Equation 8.14. 8-50 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Figure 8-19 depicts how net suction pressures can vary across different portions of the building. Central portions of the walls represent the location of the least suction, while wall corners, the roof ridge, and the roof perimeter areas have potential for suction pressures that are 1.3, 1.4, and 2 times the central wall areas, respectively. Wall areas and roof areas that experience the largest suction pressures are shown as edge zones in Figure 8-19. The variation of pressures for different portions of the building is based on an enclosed structure (e.g., GCp1 _ +/- 0.18) and use of external pressure coefficients of the low-rise building provisions. Approximate maximum increases in negative pressures used on location = 1.0x 10, <$<_ 90' $= Roof slope Edge zone not less than 6 feet Edge Z IN Figure 8-19. Variation of maximum negative MWFRS pressures based on envelope procedures for low-rise buildings To simplify design for wind, as well as establish consistency in the application of the wind design provisions of ASCE 7-10, several consensus standards with prescriptive designs tabulate maximum wind loads for the design of specific building elements based on wind pressures (both MWFRS and C&C are often referred to as "prescriptive" standards because they prescribe or tabulate load requirements for pressures) in accordance with ASCE 7-10. These standards, which are referenced in the 2012 IRC, are specific building applications based on factors such as wind speed, exposure, and height above grade. Examples of prescriptive standards for wind design that are referenced in the 2012 IRC are: ICC 600-2008, Standard for Residential Construction in High -Wind Regions (ICC 2008) ANSI/AF&PA, Wood Frame Construction Manual (WFCM) (AF&PA 2012) ANSI/AISI-S230, Standard for Cold -Formed Steel Framing -Prescriptive Method for One and Two Family Dwellings (AISI 2007) Tabulated wind load requirements in these standards often use conservative assumptions for sizing members and connections. Therefore, load requirements are often more conservative than those developed by direct application of ASCE 7-10 pressures when design loads can be calculated for each element's unique characteristics. COASTAL CONSTRUCTION MANUAL 8-51 DETERMINING SITE -SPECIFIC LOADS Volume II 8.7.2 Main Wind Force Resisting System The MWFRS consists of the foundation; floor supports (e.g., joists, beams); columns; roof rafters or trusses; and bracing, walls, and diaphragms that assist in transferring loads. ASCE 7-10 defines the MWFRS as 11 ... an assemblage of structural elements assigned to provide support and stability for the overall structure. The system generally receives wind load from more than one surface." Individual MWFRS elements of shear walls and roof diaphragms (studs and cords) may also act as components and should also be analyzed under the loading requirements of C&C. For a typical building configuration with a gable roof, the wind direction is perpendicular to the roof ridge for two cases and parallel to the ridge in the other two cases. A complete analysis of the MWFRS includes determining windward and leeward wall pressures, side wall pressures, and windward and leeward roof pressures for wind coming from each of four principal directions. Figure 8-18 depicts pressures acting on the building structure for wind in one direction only. The effect of the combination of pressures on the resulting member and connection forces is of primary interest to the designer. As a result, for each direction of wind loading, structural calculations are required to determine the maximum design forces for members and connections of the building structure. Prescriptive standards can be used to simplify the calculation of MWFRS design loads. Examples of prescriptive MWFRS design load tables derived from the application of ASCE 7-10 wind load provisions are included in this Manual for the purpose of illustration, as follows: Roof uplift connector loads (see Table 8-6). The application of ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.5. Equation 8.13 for velocity pressure and Equation 8.14 for determining design wind pressure are used to arrive at the design uplift connector load. The roof uplift connection size is based on moment balance of forces acting on both the windward and leeward side of the roof. The uplift load is used to size individual connectors and also provides the distributed wind uplift load acting at the buildings perimeter walls. Note that while wind speeds are based on 700-year Mean Recurrence Interval, the resulting uplift loads are based on ASD design. Diaphragm loads due to wind acting perpendicular to the ridge (see Table 8-7). Application of the ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.6. The diaphragm load is based on wind pressures simultaneously acting on both the windward and leeward side of the building. The diaphragm load is used to size the diaphragm for resistance to wind and is also used for estimating total lateral forces for a given wind direction based on combining diaphragm loads for the roof and wall(s) as applicable. Total lateral forces from wind for a given direction can be used for preliminary sizing of the foundation and for determining shear wall capacity requirements. The example loads in Table 8-6 and Table 8-7, which are based on ASCE 7-10 envelope procedures for low- rise buildings, are used in Examples 8.7 and 8.8 to illustrate their application in the wind design of select load path elements. Tables 8-6 and 8-7 and Examples 8.5 and 8.6 are derived from wind load procedures in the WFCM (AF&PA 2012). Tables 8-6 and 8-7 are not intended to replace requirements of the building code or applicable reference standards for the actual design of a building to resist wind. 8-52 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Table 8-6. Roof Uplift Connector Loads (Based on ASD Design) at Building Edge Zones, plf (33-ft mean roof height, Exposure C) 24 189 215 241 298 358 424 494 568 647 32 237 269 303 374 451 534 622 716 816 40 285 324 364 450 544 643 750 864 985 48 333 379 426 527 636 753 879 1,012 1,154 (a) 700-Year wind speed, 3-sec gust. (b) Uplift connector loads are based on 33-ft mean roof height, Exposure C, roof dead load of 10 psf, and roof overhang length of 2 ft (see Example 8.5). Uplift (c) Uplift connector loads are tabulated in pounds per linear ft of wall. Individual connector loads FRoof nnector can be calculated for various spacing of connectors (e.g., for spacing of connectors at 2 ft o.c., the individual connector load would be 2 ft times the tabulated value). (d) Tabulated uplift connector loads are conservatively based on a 20-degree roof slope. Span-4T Reduced uplift forces may be calculated for greater roof slopes. Table 8-7. Lateral Diaphragm Load from Wind Perpendicular to Ridge, plf (33-ft mean roof height, Exposure C) 24 138 151 164 192 223 256 291 329 369 32 161 176 191 224 260 299 340 384 430 40 186 203 221 259 301 345 393 443 497 48 210 230 250 294 341 391 445 503 563 Floor diaphragm load (plf) Any 154 168 183 214 249 286 325 367 411 Legend (a) 700-Year wind speed, 3-sec gust. Tributary area for roof (b) Lateral diaphragm loads are based on 33-ft mean roof height, Exposure C, and wall diaphram height of 8 ft (see Example 8.6). Tabulated roof diaphragm loads are for a 7:12 roof Tributary area for floor slope. Larger loads can be calculated for steeper roof slopes and smaller loads can diaphram be calculated for shallower roof slopes. (c) Total shear load equals the tabulated unit lateral load by the building length perpendicular to the wind direction. U��LUU�u� Same figure as Example 8.6, Illustration A COASTAL CONSTRUCTION MANUAL 8-53 DETERMINING SITE -SPECIFIC LOADS Volume II 8-54 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-55 DETERMINING SITE -SPECIFIC LOADS Volume II 8-56 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-57 DETERMINING SITE -SPECIFIC LOADS Volume II 8-58 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-59 DETERMINING SITE -SPECIFIC LOADS Volume II 8-60 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS 8.7.3 Components and Cladding ASCE 7-10 defines components and cladding (C&C) as "... elements of the building envelope that do not qualify as part of the MWFRS." These elements include roof sheathing, roof coverings, exterior siding, windows, doors, soffits, fascia, and chimneys. The design and installation of the roof sheathing attachment may be the most critical consideration because the attachment location for the sheathing is where the uplift load path begins (load path is described more fully in Chapter 9 of this Manual). C&C pressures are determined for various "zones" of the building. ASCE 7-10 includes illustrations of those zones for both roofs and walls. Illustrations for gable, monoslope, and hip roof shapes are presented. The pressure coefficients vary according to roof pitch (from 0 degrees to 45 degrees) and effective wind area (defined in ASCE 7-10). C&C loads act on all elements exposed to wind. These elements and their attachments must be designed to resist these forces to prevent failure that could lead to breach of the building envelope and create sources of flying debris. Examples of building elements and their connections subject to C&C loads include the following: Exterior siding Roof sheathing Roof framing Wall sheathing Wall framing (e.g., studs, headers) Wall framing connections (e.g., stud -to -plate, header -to -stud) Roof coverings Soffits and overhangs Windows and window frames Skylights Doors and door frames, including garage doors Wind-borne debris protection systems Any attachments to the building (e.g., antennas, chimneys, roof and ridge vents, roof turbines) Furthermore, individual MWFRS elements of shear walls and roof diaphragms (studs and chords) may also act as components and should also be analyzed under the loading requirements of C&C. Figure 8-20 shows the locations of varying localized pressures on wall and roof surfaces. The magnitude of roof uplift and wall suction pressures is based on the most conservative wind pressures in each location for given roof types and slopes in accordance with Figure 30.4 of ASCE 7-10. As noted previously, prescriptive COASTAL CONSTRUCTION MANUAL 8-61 DETERMINING SITE -SPECIFIC LOADS Volume II NOTE Edge zone dimension, A, is measured as the horizontal projection on the building roof and walls. A = the smaller of 10 percent of the least horizontal dimension of the building (i.e. either L or W) or 40 percent of the mean roof height (MRH), but not less than either 4 percent of the least horizontal dimension or 3 feet. L = length W = width Figure 8-20. Components and cladding wind pressures standards can be used to simplify the calculation of C&C design loads. Examples of prescriptive C&C design load tables for purposes of illustration are included in this Manual as follows: Roof and wall suction pressures (see Table 8-8). Application of ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.7. Suction pressures are used to size connections between sheathing and framing and to size the sheathing material itself for wind induced bending. In ASCE 7-10, there is no adjustment for effective wind areas less than 10 square feet; therefore, sheathing suction loads are based on an effective wind area of 10 square feet. Lateral connector loads from wind and building end zones (see Table 8-9). Application of ASCE 7-10 provisions and typical assumptions used to derive the tabulated load values are addressed in Example 8.8. Lateral connector loads from wind are used to size the connection from wall stud -to -plate, wall plate -to -floor, and wall plate -to -roof connections to ensure that higher C&C loads acting over smaller wall areas can be adequately resisted and transferred into the roof or floor diaphragm. In ASCE 7-10, the effective wind area for a member is calculated as the span length times an effective width of not less than one-third the span length. For example, the effective area for analysis is calculated as h213 where h represents the span (or height) of the wall stud. 8-62 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Example load tables and example problems are derived from more wind load procedures provided in the WFCM-2012 load Tables 8-8 and 8-9 are not intended to replace requirements of the building code or reference standard for the actual design of C&C attachments for a building. Table 8-8. Roof and Wall Sheathing Suction Loads (based on ASD design), psf (33-ft mean roof height, Exposure C) Zone 1 18.6 20.4 22.2 26.0 30.2 34.7 39.4 44.5 44.9 Zone 2 31.3 34.2 37.2 43.7 50.7 58.2 66.2 74.7 83.8 Zone 2 Overhang 34.8 38.0 41.4 48.5 56.3 64.6 73.5 83.0 93.1 Zone 3 47.1 51.5 56.0 65.8 76.3 87.5 99.6 112.4 126.1 Zone 3 Overhang 58.5 63.9 69.6 81.6 94.7 108.7 123.7 139.6 156.5 Wall, suction pressure(b)(c) (psf) Zone 4 20.2 22.1 24.1 28.2 32.8 37.6 42.8 48.3 54.1 Zone 5 25.0 27.3 29.7 34.9 40.4 46.4 52.8 59.6 66.8 (a) 700-year wind speed, 3-sec gust. (b) Roof and wall sheathing suction loads are based on 33-ft mean roof height and Exposure C (see Example 8.7). (c) Loads based on minimum effective area of 10 ft2 Table 8-9. Lateral Connector Loads from Wind at Building End Zones (Based on ASD Design), plf (33-ft mean roof height, Exposure C) 8 92 101 110 129 150 172 196 221 248 10 110 120 131 154 179 205 233 263 295 12 127 139 151 177 206 236 269 303 340 14 143 156 170 200 231 266 302 341 383 16 158 173 188 221 256 294 335 378 423 (a) 700-Year wind speed, 3-sec gust. (b) Lateral connector loads are based on 33-ft mean roof height and Exposure C (see Example 8.8). (c) Lateral connector loads are tabulated in pounds per linear ft of wall. Individual connector loads can be ,� calculated for various spacing of connectors (e.g., for spacing of connectors at 2 ft o.c., the individual connector load would be 2 ft times the tabulated value). 1L(d) Loads based on minimum area of (wall height)213 COASTAL CONSTRUCTION MANUAL 8-63 DETERMINING SITE -SPECIFIC LOADS Volume II 8-64 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-65 DETERMINING SITE -SPECIFIC LOADS Volume II 8-66 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS 8.8 Tornado Loads Tornadoes have wind speeds that vary based on the magnitude of the event; more severe tornadoes have wind speeds that are significantly greater than the minimum design wind speeds required by the building code. Designing an entire building to resist tornado -force winds of EF3 or greater based on the Enhanced Fujita tornado damage scale (in EF2 tornadoes, large trees are snapped or uprooted) may be beyond the realm WARNING Safe rooms should be located outside known flood -prone areas, including the 500-year floodplain, and away from any potential large debris sources. See Figure 5-2 of FEMA 320 for more direction regarding recommended siting for a safe room. COASTAL CONSTRUCTION MANUAL 8-67 DETERMINING SITE -SPECIFIC LOADS Volume II of practicality and cost-effectiveness, but this does not mean that solutions that provide life -safety protection cannot be achieved while maintaining cost-effectiveness. A more practical approach is to construct an interior room or space that is "hardened" to resist not only tornado -force winds but also the impact of wind-borne missiles. FEMA guidance on safe rooms can be found in FEMA 320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business (FEMA 2008c), which provides prescriptive design solutions for safe rooms of up to 14 feet x 14 feet. These solutions can be incorporated into a structure or constructed as a nearby stand-alone safe room to provide occupants with a place of near -absolute protection. The designs in FEMA 320 are based on wind pressure calculations that are described in FEMA 361, Design and Construction Guidance for Community Safe Rooms (FEMA 2008a). FEMA 361 focuses on larger community safe rooms, but the process of design and many of the variables are the same for smaller residential safe rooms. An additional reference, ANSI/ICC 500-2008 complements the information in FEMA 320 and FEMA 361 and is referenced in the 2012 IBC and 2012 IRC. Safe rooms can be designed to resist both tornado and hurricane hazards, and though many residents of coastal areas are more concerned with hurricanes, tornadoes can be as prevalent in coastal areas as they are in inland areas such as Oklahoma, Kansas, and Missouri. Constructing to minimum requirements of the building code does not include the protection of life -safety or property of occupants from a direct hit of large tornado events. Safe rooms are not recommended in flood hazard areas. 8.9 Seismic Loads This Manual uses the seismic provisions of ASCE 7-10 to illustrate a method for calculating the seismic base shear. To simplify design, the effect of dynamic seismic ground motion accelerations can be considered an equivalent static lateral force applied to the building. The magnitude of dynamic motion, and therefore the magnitude of the equivalent static design force, depends on the building characteristics, and the spectral response acceleration parameter at the specific site location. The structural configuration in Figure 8-21 is called an "inverted pendulum" or "cantilevered column" system. This configuration occurs in elevated pile -supported buildings where almost all of the weight is at the top of the piles. For a timber frame cantilever column system, ASCE 7-10 assigns a response modification factor (R) equal to 1.5 (e.g., R = 1.5). For wood frame, wood structural panel shear walls, ASCE 7-10 assigns an R factor equal to 6.5. The R factor of 1.5 can be conservatively used to determine shear for the design of all elements and connections of the structure. An R factor of 1.5 is not permitted for use in Seismic Design Categories E and F per ASCE 7-10. ASCE 7-10 contains procedures for the seismic design of structures with different structural systems stacked vertically within a single structure. Rules for vertical combinations can be applied to enable the base of the structure to be designed for shear forces associated with R=1.5 and the upper wood frame, wood structural panel shear wall structure to be designed for reduced shear forces associated with R=6.5. ASCE 7-10 also provides R factors for cantilever column systems using steel and concrete columns. A small reduction in shear forces for steel piles or concrete columns could be obtained by using what ASCE 7-10 calls a "steel special cantilever column system" or a "special reinforced concrete moment frame," both of which have an R = 2.5. However, these systems call for additional calculations, connection design, and 8-68 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Figure 8-21. Effect of seismic forces on supporting piles COASTAL CONSTRUCTION MANUAL 8-69 DETERMINING SITE -SPECIFIC LOADS Volume II The calculated seismic force at each story must be distributed into the building frame. The horizontal shear forces and related overturning moments are taken into the foundation through a load path of horizontal floor and roof diaphragms, shear walls, and their connections to supporting structural elements. A complete seismic analysis includes evaluating the structure for vertical and plan irregularities, designing elements and their connections in accordance with special seismic detailing, and considering structural system drift criteria. Example 8.9 illustrates the use of basic seismic calculations. 8-70 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-71 DETERMINING SITE -SPECIFIC LOADS Volume II 8-72 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS 8.10 Load Combinations It is possible for more than one type of natural hazard to occur at the same time. Floods can occur at the same time as a high -wind event, which happens during most hurricanes. Heavy rain, high winds, and flooding conditions can occur simultaneously. ASCE 7-10 addresses the various load combination possibilities. The following symbols are used in the definitions of the load combinations: D = dead load L = live load E = earthquake load F = load due to fluids with well-defined pressures and maximum heights (e.g., fluid load in tank) Fa = flood load H = loads due to weight and lateral pressures of soil and water in soil Ly, = roof live load COASTAL CONSTRUCTION MANUAL 8-73 DETERMINING SITE -SPECIFIC LOADS Volume II S = snow load R = rain load T = self -straining force W = wind load Loads combined using the ASD method are considered to act in the following combinations for buildings in Zone V and Coastal A Zone (Section 2.4.1 of ASCE 7-10), whichever produces the most unfavorable effect on the building or building element: Combination No. 1: D Combination No. 2: D + L Combination No. 3: D + (Lr or S or R) Combination No. 4: D + 0.75L + 0.75(Lr or S or R) Combination No. 5: D + (0.6 Wor 0.7E) Combination No. 6a: D + 0.75L + 0.75(0.6W) + 0.75(Lr or S or R) Combination No. 6b: D + 0.75L + 0.750.70 + 0.75S Combination No. 7: 0.6D + 0.6W Combination No. 8: 0.6D + 0.7E When a structure is located in a flood zone, the following load combinations should be considered in addition to the basic combinations in Section 2.4.1 of ASCE 7-10: In Zone V or Coastal A Zone, 1.5Fa should be added to load combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6 In the portion of Zone A landward of the LiMWA, 0.75Fa should be added to combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6. The ASCE 7-10 Commentary states "Wind and earthquake loads need not be assumed to act simultaneously. However, the most unfavorable effects of each should be considered in design, where appropriate." The designer is cautioned that F is intended for fluid loads in tanks, not hydrostatic loads. Fa should be used for all flood loads, including hydrostatic loads, and should include the various components of flood loads as recommended in Section 8.5.11 in this chapter. It is important to note that wind and seismic loads acting on a building produce effects in both the vertical and horizontal directions. The load combinations discussed in this section must be evaluated carefully, with consideration given to whether a component of the wind or seismic load acts in the same vertical or horizontal direction as other loads in the combination. In some cases, gravity loads (dead and live loads) may counteract the effect of the wind or seismic load, either vertically or horizontally. Building elements submerged in water have a reduced effective weight due to buoyancy. Example 8.10 illustrates the use of load combinations for determining design loads. 8-74 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-75 DETERMINING SITE -SPECIFIC LOADS Volume II 8-76 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-77 DETERMINING SITE -SPECIFIC LOADS Volume II 8-78 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS COASTAL CONSTRUCTION MANUAL 8-79 DETERMINING SITE -SPECIFIC LOADS Volume II The following worksheet can be used to facilitate load combination computations. Worksheet 3. Load Combination Computation 8-80 COASTAL CONSTRUCTION MANUAL Volume II DETERMINING SITE -SPECIFIC LOADS Worksheet 3. Load Combination Computation (concluded) D + 0.75L + 0.75(Ly, or S or R) = D + (0.6 W or 0.7E) _ D + 0.75L + 0.75(0.6W) + 0.75(Ly, or S or R) = D + 0.75L + 0.75(0.7E) + 0.75S = 0.6D + 0.6 W = 0.6D + 0.7E = When a structure is located in a flood zone, the following load combinations should be considered in addition to the basic combinations: In Zone V or Coastal A Zone, 1.5F, should be added to load combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6. In the portion of Zone A landward of the LiMWA, 0.75F, should be added to load combinations Nos. 5, 6, and 7, and E should be set equal to zero in Nos. 5 and 6. 8.11 References AF&PA (American Forest & Paper Association). 2012. Wood Frame Construction Manual for One- and Two -Family Dwellings. WFCM-12. AISI (American Institute of Steel Institute). 2007. Standard for Cold formed Steel Framing prescriptive Method for One- and Two-family Dwellings. AISI S230-07. AISC (American Institute of Steel Construction) / ICC (International Code Council). 2008. Standard for the Design and Construction of Storm Shelters. ANSI/ICC 500-2008. The American Institute of Architects. 2007. Architectural Graphic Standards. A. Pressman, ed. Hoboken, NJ: John Wiley & Sons, Inc. ASCE (American Society of Civil Engineers). 1995. Wave Forces on Inclined and Vertical Wall Surfaces. ASCE. 2005a. Flood Resistant Design and Construction. ASCE Standard ASCE 24-05. ASCE. 2005b. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-05. ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. COASTAL CONSTRUCTION MANUAL 8-81 DETERMINING SITE -SPECIFIC LOADS Volume II AWC (American Wood Council). 2009. Prescriptive Residential Wood Deck Construction Guide. AWC DCA6. Bea, R.G., T. Xu, J. Stear, and R. Ramos. 1999. "Wave Forces on Decks of Offshore Platforms." journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 125, No. 3, pp. 136-144. Camfield, F.E. 1980. Tsunami Engineering. Vicksburg, MS: Coastal Engineering Research Center. FEMA (Federal Emergency Management Agency). 2001. Engineering Principles and Practices for Retrofitting Floodprone Residential Buildings. FEMA 259. FEMA. 2006. Hurricane Katrina in the Gulf Coast. FEMA 549. FEMA. 2008a. Design and Construction Guidance for Community Safe Rooms. FEMA 361. FEMA. 2008b. Guidelines for Design of Structures for Vertical Evacuation from Tsunamis. FEMA P646. FEMA. 2008c. Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business. FEMA 320. FEMA. 2009. Hurricane Ike in Texas and Louisiana. FEMA P-757. Fox, R.W. and A.T. McDonald. 1985. Introduction to Fluid Mechanics. New York: John Wiley & Sons, Inc. ICC (International Code Council). 2008. Standard for Residential Construction in High -Wind Regions. ICC 600-2008. ICC. 2011a. International Building Code. 2012 IBC. ICC: Country Club Hills, IL. ICC. 2011b. International Residential Code for One -and Two -Family Dwellings. 2012 IRC. ICC: Country Club Hills, IL. McConnell, K., W. Allsop, and 1. Cruickshank. 2004. Piers, jetties and Related Structures Exposed to Waves: Guidelines for Hydraulic Loadings. London: Thomas Telford Publishing Sumer, B.M., R.J.S. Whitehouse, and A. Torum. 2001. "Scour around Coastal Structures: A Summary of Recent Research." Coastal Engineering, Vol. 44, Issue 2, pp. 153-190. USACE (U.S. Army Corps of Engineers). 1984. Shore Protection Manual, Volume 2. USACE. 2006. Coastal Engineering Manual. USACE. 2008. Coastal Engineering Manual. Walton, T.L. Jr., J.P. Ahrens, C.L. Truitt, and R.G. Dean. 1989. Criteria for Evaluating Coastal Flood - Protection Structures. Coastal Engineering Research Center Technical Report 89-15. U.S. Army Corps of Engineers Waterways Experiment Station. 8-82 COASTAL CONSTRUCTION MANUAL i r"I igning the Building This chapter provides guidance on design considerations for buildings in coastal environments. The topics discussed in this chapter are developing a load path through elements of the building structure, considerations for selecting building materials, requirements for breakaway walls, and considerations for designing appurtenances. Examples of problems for the development of the load path for specific building elements are provided, as well as guidance on requirements for breakaway walls, selection of building materials, and appurtenances. 9.1 Continuous Load Path CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/ mat/fema55.shtm). In hazard -resistant construction, the ability of the elements of a building, from the roof to the foundation, to carry or resist loads is critical. Loads include lateral and uplift loads. A critical aspect of hazard -resistant construction is the capability of a building or structure to carry and resist all loads —including lateral and uplift loads —from the roof, walls, and other elements to the foundation and into the ground. The term "continuous load path" refers to the structural condition required to resist loads acting on a building. A load path can be thought of as a chain running through the building. A building may contain hundreds of continuous load paths. The continuous load path starts at the point or surface where loads are applied, moves through the building, continues through the foundation, and terminates where the loads are transferred to the soils that support the building. Because all applied loads must be transferred to the foundation, the load path must connect to the foundation. To be effective, each link in the load path chain must be strong enough to transfer loads without breaking. COASTAL CONSTRUCTION MANUAL 9-1 DESIGNING THE BUILDING Volume II Buildings that lack strong and continuous load paths may fail when exposed to forces from coastal hazards, thus causing a breach in the building envelope or the collapse of the building. The ability of a building to resist these forces depends largely on whether the building's construction provides a continuous load path and materials that are appropriate for the harsh coastal environment. The history of storm damage is replete with instances of failures in load paths. Figures 9-1 through 9-5 show instances of load path failure. Figure 9-1. Load path failure at gable end, Hurricane Andrew (Dade County, FL, 1992) Figure 9-2. Load path failure in connection between home and its foundation, Hurricane Fran (North Carolina, 1996) 9-2 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Figure 9-3. Roof framing damage and loss due to load path failure at top of wall/roof structure connection, Hurricane Charley (Punta Gorda, FL, 2004) Figure 9-4. Load path failure in connections between roof decking and roof framing, Hurricane Charley (Punta Gorda, FL, 2004) Most load path failures have been observed to occur at connections as= opposed to the failure of an individual structural member (e.g. roof CROSS REFERENCE rafter or wall stud). Improvements in codes, design, and materials over For a discussion of building the past decade have resulted in improved performance of structural envelope issues, see systems. As the structural systems perform better, other issues related Chapter 11 of this Manual. to load path —such as building envelope issuesbecome apparent. COASTAL CONSTRUCTION MANUAL 9-3 DESIGNING THE BUILDING Volume II Figure 9-5. Newer home damaged from internal pressurization and inadequate connections, Hurricane Katrina (Pass Christian, MS, 2005) Load path guidance in this chapter is focused primarily on elements of the building structure, excluding foundation elements. Foundation elements are addressed in Chapter 10. Examples are provided primarily to illustrate how the load path resists wind uplift forces, but a complete building design includes a consideration of numerous other forces on the load path, including those from gravity loads and lateral loads. The examples illustrate important concepts and best practices in accordance with building codes and standards but do not represent an exhaustive collection of load calculation methods. See the applicable building code, standard, or design manual for more detailed guidance. Figure 9-6 shows a load path for wind uplift beginning with the connection of roof sheathing to roof framing and ending with the resistance of the pile to wind uplift. Links #1 through #8 in the figure show connections that have been observed during investigations after high -wind events to be vulnerable to localized failure. However, the load path does not end with the resistance of the pile to wind uplift. The end of transfer through the load path occurs when the loads from the building are transferred into the soil (see Chapter 10 for information about the interaction of foundations and soils). Adequately sizing and detailing every link is important for overall performance because even a small localized failure can lead to a progressive failure of the building structure. The links shown in Figure 9-6 are discussed in more detail in Sections 9.1.1 through 9.1.8. For additional illustration of the concept of load path, see Fact Sheet 4.1, Load Paths, in FEMA P-499 (FEMA 2010b). 9.1.1 Roof Sheathing to Framing Connection (Link #1) Link #1 is the nailed connection of the roof sheathing to the roof framing (see Figures 9-6 and 9-7). Design considerations include ensuring the connection has adequate strength to resist both the withdrawal of the nail shank from the roof framing and the sheathing's pulling over the head of the fastener (also referred to as "head pull -through"). Because of the potential for head pull -through and the required minimum nailing for diaphragm shear capacity, fastener spacing is typically not increased even where shank withdrawal strength 9-4 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING COASTAL CONSTRUCTION MANUAL 9-5 DESIGNING THE BUILDING Figure 9-7. Connection of the roof sheathing to the roof framing (Link #1) Volume II is significantly greater than that provided by a smooth shank nail. Additional strength can be added by using ring shank nails, also called deformed shank nails. The grooves and ridges along the shank act as wedges, giving the nail more withdrawal strength than a typical smooth shank nail. Fastener attachment requirements for roof sheathing to roof framing are available in building codes and design standards and are presented in terms of nailing schedules dependent on nail diameter and length, framing spacing, specific gravity of framing lumber, and wind speed. Common assumptions for calculating nailing schedules to resist wind uplift are provided in Example 9.1. Minimum roof sheathing attachment prescribed in building codes and reference prescriptive standards is 6 inches o.c. at panel edges and 12 inches o.c. in the field of the panel. 9-6 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING COASTAL CONSTRUCTION MANUAL 9-7 DESIGNING THE BUILDING Volume II 9.1.2 Roof Framing to Exterior Wall (Link #2) Link #2 is the connection between the roof framing member (truss or rafter) and the top of the wall below (see Figures 9-6 and 9-8) for resistance to wind uplift. Metal connectors are typically used where uplift forces are large. A variety of metal connectors are available for attaching roof framing to the wall. Manufacturers' literature should be consulted for proper use of the connector and allowable capacities for resistance to uplift. Prescriptive solutions for the connection of the roof framing to the wall top plates are available in building codes and wind design standards. One method of sizing the connection between the roof framing and the exterior wall is provided in Example 9.2. Figure 9-8. Connection of roof framing to exterior wall (Link #2) 9-8 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING COASTAL CONSTRUCTION MANUAL 9-9 DESIGNING THE BUILDING Volume II Figure 9-9 shows truss -to -wood wall connections made with metal connectors. Figure 9-10 shows a rafter -to - masonry wall connector that is embedded into the concrete -filled or grouted masonry cell. Figure 9-9. Connection of truss to wood -frame wall 9.1.3 Wall Top Plate to Wall Studs (Link #3) Link #3 is the connection between the wall top plates and the wall stud over the window header (see Figures 9-6 and 9-11). The connection provides resistance to the same uplift force as used for the roof framing to the exterior connection minus the weight of the top plates. An option for maintaining the uplift load path is the use of metal connectors between the top plates and wall studs or wood structural panel sheathing (see Figure 9-12). The uplift load path can be made with wood structural panel wall sheathing, particularly when the uplift and shear forces in the wall are not very high. Guidance on using wood structural panel wall sheathing for resisting wind uplift is provided in ANSI/AF&PA SDPWS-08. The lateral load path (e.g., out -of -plane wall loads) is maintained by stud -to -top plate nailing. 9-10 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Figure 9-10. Roof truss -to -masonry wall connectors embedded into concrete -filled or grouted masonry cell (left-hand side image has a top plate installed while the right-hand side does not) COASTAL CONSTRUCTION MANUAL 9-11 DESIGNING THE BUILDING Volume II Figure 9-12. Wall top plate -to -wall stud metal connector 9.1.4 Wall Sheathing to Window Header (Link #4) Link #4 is the connection between the wood structural panel wall sheathing and the window header (see Figures 9-6 and 9-13). The connection maintains the uplift load path from the wall top plates for the same force as determined for the roof connection to the wall minus additional dead load from the wall. Options for maintaining the uplift load path include using metal connectors between the wall studs and header or wood structural panel sheathing (see Figures 9-13 and 9-14). The uplift load path is frequently made with wood structural panel wall sheathing, particularly when the uplift and shear forces in the wall are not very high. Additional design considerations include the resistance of the window header to bending from gravity loads, wind uplift, and out -of -plane bending loads from wind. In masonry construction, a masonry or concrete bond beam, or a pre -cast concrete or masonry header, is often used over the window opening. Design considerations for this beam include resistance to bending in both the plane of the wall and normal to the wall. Resistance to bending is accomplished by placing reinforcing steel in the bond beam. Reinforcing steel must be placed in the bond beam in order for the beam to adequately resist bending stresses. The design of these members is beyond the scope of this Manual; therefore, the prescriptive methods presented in ICC 600-2008, or concrete and masonry references should be used. 9.1.5 Window Header to Exterior Wall (Link #5) Link #5 is the connection from the window header to the adjacent wall framing (see Figures 9-6 and 9-14). Link #5 provides resistance to wind uplift and often consists of a metal strap or end -nailing the stud to the header. The total uplift force is based on the uplift forces tributary to the header. Maintaining the load path for the out -of -plane forces at this location includes consideration of both the positive (inward) and the negative (outward) pressures from wind. This load path is commonly developed by the stud -to -header nailing. One method of sizing the connection between the window header and the exterior wall is provided in Example 9.3. 9-12 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Wall stud Structural sheathing I I _ 1• _`�I •, _ ,I I Window ------I I� header - Link #4 I ; Jack studs Wall stud Figure 9-13. Connection of wall sheathing to window header (Link #4) Figure 9-14. Connection of window header to exterior wall (Link #5) COASTAL CONSTRUCTION MANUAL 9-13 DESIGNING THE BUILDING Volume II 9-14 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9.1.6 Wall to Floor Framing (Link #6) Link #6 is the connection of the wall framing to the floor framing (see Figures 9-6 and 9-15) for resistance to wind uplift. This connection often includes use of metal connectors between the wall studs and the band joist or wood structural panel sheathing. In addition to uplift, connections between wall and floor framing can be used to maintain the load path for out -of -plane wall forces from positive and negative wind pressures and forces in the plane of the wall from shear. One method of sizing the wind uplift and lateral connections between the wall framing and the floor framing is provided in Example 9.4. Figure 9-15. Connection of wall to floor framing (Link #6) COASTAL CONSTRUCTION MANUAL 9-15 DESIGNING THE BUILDING Volume II 9-16 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9.1.7 Floor Framing to Support Beam (Link #7) Link #7 is the connection between the floor framing and the floor support beam (see Figures 9-6, 9-16, 9-17, and 9-18). The connection transfers the uplift forces that are calculated in Example 9.4. Options for maintaining the uplift load path for wind uplift include using metal connectors (see Figures 9-16 and 9-17) between the floor joist and the band joist or wood blocking (see Figure 9-18). Connections are also necessary to maintain a load path for lateral and shear forces from the floor and wall framing into the support beam. One method of sizing the wind uplift connections between the floor framing and support beam is provided in Example 9.5. Figure 9-16. Connection of floor framing to support beam (Link #7) (band joist nailing to the floor joist is adequate to resist uplift forces) 0 Figure 9-17. Metal joist -to -beam connector COASTAL CONSTRUCTION MANUAL 9-17 DESIGNING THE BUILDING Volume II 9-18 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Figure 9-18. Connection of floor support beam to foundation (Link #8) COASTAL CONSTRUCTION MANUAL 9-19 DESIGNING THE BUILDING Volume II Figure 9-19. Diaphragm stiffening and corner pile bracing to reduce pile cap rotation 2x floor joist material or sheathing screwed 16 inches on center into bottoms of joists (typical) I�>I Floor T joists T) N R m U A Floor support beam Q Band joist E0. 9.33 feet 2x joist #12 3-inch-long galvanized or 2x joist material stainless steel screws, 3 per joist or sheathing per board (typical) Section A -A 9-20 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9.2 Other Load Path Considerations Several additional design considerations must be investigated in order for a design to be complete. The details of these investigations are left to the designer, but they are mentioned here to more thoroughly cover the subject of continuous load paths and to point out that many possible paths require investigation. Using the example of the building shown in Example 9.3, Illustration A, the following load paths should also be investigated: Load paths for shear transfer between shear walls and diaphragms including uplift due to shear wall overturning Gable wall support for lateral wind loads Uplift of the front porch roof Uplift of the main roof section that spans the width of the building Other factors that influence the building design and its performance are: Connection choices Building eccentricities Framing system Roofshape 9.2.1 Uplift Due to Shear Wall Overturning The shear wall that contains Link #6 includes connections designed to resist overturning forces from wind acting perpendicular to the ridge (see Example 9.7, Illustration A). Calculation of the overturning induced uplift and compressive forces are given in Example 9.7. COASTAL CONSTRUCTION MANUAL 9-21 DESIGNING THE BUILDING Volume II 9-22 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Because of the magnitude of overturning induced uplift and compression forces, it is desirable to align shear wall ends with piles to provide direct vertical support and to minimize offset of the tension or compression load path from the axis of the pile. Where shear wall end posts are aligned with piles below, detailing that allows connection of the shear wall end post holddown directly to the pile is desirable to minimize forces transferred through other members such as the support beams. Where direct transfer of overturning induced uplift and compression forces into the pile is not possible, minimizing the offset distance reduces bending stresses in the primary support beam (see Figure 9-20). For the holddown connection shown in Figure 9-20, the manufacturers' listed allowable load will be reduced because the bolted connection to the wood beam is loaded perpendicular to grain rather than parallel to grain. COASTAL CONSTRUCTION MANUAL 9-23 DESIGNING THE BUILDING Figure 9-20. Shear wall holddown connector with bracket attached to a wood beam Volume II 9.2.2 Gable Wall Support There are many cases of failures of gable -end frames during high -wind events. The primary failure modes in gable -end frames are as follows: A gable wall that is not braced into the structure collapses, and the roof framing falls over (see Figure 9-21) An unsupported rake outrigger used for overhangs is lifted off by the wind and takes the roof sheathing with it The bottom chord of the truss is pulled outward, twisting the truss and causing an inward collapse The need for and type of bracing at gable -end frames depend on the method used to construct the gable end. Recommendations for installing rafter outriggers at overhangs for resistance to wind loads are provided in the Wood Frame Construction Manual (American Wood Council, 2001). In addition to using the gable -end truss bracing shown in Figure 9-22, installing permanent lateral bracing on all roof truss systems is recommended. Gable -end trusses and conventionally framed gable -end walls should be designed, constructed, and sheathed as individual components to withstand the pressures associated with the established basic wind speed. 9.2.3 Connection Choices Alternatives for joining building elements include: Mechanical connectors such as those available from a variety of manufacturers Fasteners such as nails, screws, bolts, and reinforcing steel -0 CROSS REFERENCE For recommendations on corrosion -resistant connectors, see Table 1 in NFIP Technical Bulletin 8, Corrosion Protection for Metal Connectors in Coastal Areas (FEMA 1996). 9-24 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Figure 9-21. Gable -end failure, Hurricane Andrew (Dade County, FL, 1992) Connectors such as wood blocks Alternative materials such as adhesives and strapping Most commercially available mechanical connectors recognized in product evaluation reports are fabricated metal devices formed into shapes designed to fit snugly around elements such as studs, rafters, and wall plates. To provide their rated load, these devices must be attached as specified by the manufacturer. Mechanical connectors are typically provided with various levels of corrosion resistance such as levels of hot -dip galvanizing and stainless steel. Hot -dip galvanizing may be applied before or after fabrication. Thicker galvanized coatings can consist of 1 to 2 ounces of zinc per square foot. Thicker coatings provide greater protection against corrosion. Welded steel products generally have a hot -dip galvanized zinc coating or are painted for corrosion protection. Stainless steel (A304 and A316) connectors also provide corrosion resistance. Because exposed metal fasteners (even when galvanized) can corrode in coastal areas within a few years of installation, stainless steel is recommended where rapid corrosion is expected. According to FEMA NFIP Technical Bulletin 8-96, the amount of salt spray in the air is greatest near breaking waves and declines with increasing distance away from the shoreline. The decline may be rapid in the first 300 to 3,000 feet. FEMA P-499 recommends using stainless steel within 3,000 feet of the coast (including sounds and back bays). Metal connectors must be used in accordance with the manufacturer's installation instructions in order for the product to provide the desired strength rating and to ensure that the product is suitable for a particular application. Particular attention should be given to the following information in the installation instructions: Preservative treatments used for wood framing Level of corrosion protection Wood species or lumber type used in framing (e.g., sawn lumber, pre -fabricated wood I -joists, laminated veneer lumber) COASTAL CONSTRUCTION MANUAL 9-25 DESIGNING THE BUILDING Volume II Figure 9-22. Gable -end bracing detail; nailing schedule, strap specification, brace spacing, and overhang limits should be adapted for the applicable basic wind speed 9-26 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Rated capacity of connector for all modes of failure (e.g., shear, uplift, gravity loading) Level of corrosion protection for nails, bolts, and/or screws Nail, bolt, and/or screw size and type required to achieve rated loads 9.2.4 Building Eccentricities The L-shaped building configuration produces stress concentrations in the re-entrant corner of the building structure. Additionally, differences between the center of rotation and the center of mass produce torsional forces that must be transferred by the diaphragms and accounted for in the design of shear walls. Provisions for torsional response are different for wind and seismic hazards. Design methods to account for building eccentricities is beyond the scope of this Manual; therefore, the user is referred to building code requirements and provisions of ASCE 7-10 and applicable material design standards. 9.2.5 Framing System Methods used for maintaining a load path throughout the structure depend on the framing system or structural system that makes up the building structure. Specifics related to platform framing, concrete/ masonry construction, and moment -resistant framing are provided below. 9.2.5.1 Platform Framing Across the United States, platform framing is by far the most common method of framing a wood -stud or steel -stud residential building. In the platform framing method, a floor assembly consisting of beams, joists, and a subfloor creates a "platform" that supports the exterior and interior walls. The walls are normally laid out and framed flat on top of the floor, tilted up into place, and attached at the bottom to the floor through the wall bottom plate. The walls are attached at the top to the next -level floor framing or in a one-story building to the roof framing. Figure 9-23 is an example of platform framing in a two-story building. This method is commonly used on all types of foundation systems, including walls, piles, piers, and columns consisting of wood, masonry, and concrete materials. Less common framing methods in wood -frame construction are balloon framing in which wall studs are continuous from the foundation to the roof and post -and -beam framing in which a structure of beams and columns is constructed first, including the floors and roof, and then walls are built inside the beam and column structure. 9.2.5.2 Concrete/Masonry Masonry exterior walls are normally constructed to full height (similar to wood balloon framing), and then wood floors and the roof are framed into the masonry. Fully or partially reinforced and grouted masonry is required in high -wind and seismic hazard areas. Floor framing is normally supported by a ledger board fastened to a bond beam in the masonry, and the roof is anchored to a bond beam at the top of the wall. Connections can be via a top plate as shown in Figure 9-24 or direct embedded truss anchors in the bond beam as shown in �J NOTE Masonry frames typically require continuous footings. However, continuous footings are not allowed in Zone V or Coastal A Zones and are not recommended in Zone A. COASTAL CONSTRUCTION MANUAL 9-27 DESIGNING THE BUILDING Volume II Figure 9-23. Example of two-story platform framing on a pile -and -beam foundation Figure 9-6. Options for end walls are hip roofs, continuous masonry gables, and braced gable frames. Details and design tables for all of the above can be found in ICC 600-2008. Figure 9-24 is an example of masonry wall construction in a two-story building. 9.2.5.3 Moment -Resisting Frames Over the past few decades, an increasing number of moment -resisting frames have been built and installed in coastal homes (Hamilton 1997).The need for this special design is a result of more buildings in coastal high hazard areas being constructed with large glazed areas on exterior walls, with large open interior areas, and with heights of two to three stories. Figure 9-25 shows a typical steel moment frame. Large glazed areas pose challenges to the designer because they create: Large openings in shear walls Large deflection in shear walls Difficulties in distributing the shear load to the foundation 9-28 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Figure 9-24. Two-story masonry wall with wood floor and roof framing COASTAL CONSTRUCTION MANUAL 9-29 DESIGNING THE BUILDING Volume II A moment -resisting frame usually resists shear by taking the lateral load into the top of the frame thus creating a moment at the base of the frame. The design professional must design a moment connection at the base between the steel frame and the wood, masonry, or concrete foundation. In residential construction, moment frames are frequently tubular steel. Tubular steel shapes that are close to the size of nominal framing lumber can be selected. This approach alleviates the need for special, time- consuming methods required to make the steel frame compatible with wood; however, frames made with tubular steel are more difficult to build than frames made with "H" or "WF" flange shapes because all connections in the frame are welded. There are a number of pre -manufactured moment frame products on the market now that have been designed for a variety of lateral forces to fit a variety of wall lengths and heights. 9.2.6 Roof Shape Roof shape, both the structural aspect and the covering, plays a significant role in roof performance. Compared to other types of roofs, hip roofs generally perform better in high winds because they have fewer sharp corners and fewer distinctive building geometry changes. Steeply pitched roofs usually perform better than flat roofs. Figures 9-26 and 9-27 show two types of roofs in areas of approximately similar terrain that experienced the winds of Hurricane Marilyn. The gable roof in Figure 9-26 failed, while the hip roof in Figure 9-27 survived the same storm with little to no damage. Whether the roof is a gabled roof or hip roof, proper design and construction are necessary for successful performance in high -wind events. 9.3 Breakaway Wall Enclosures In Zone V and Coastal A Zones, breaking waves are almost certain to occur simultaneously with peak flood conditions. As breaking waves pass an open piling or column foundation, the foundation experiences cyclic fluid impact and drag forces. The flow peaks at the wave crest, just as the wave breaks. Although the flow creates drag on the foundation, most of the flow under the building is undisturbed. This makes open foundations somewhat resistant to wave actions and pile and column foundations a manageable design. When a breaking wave hits a solid wall, the effect is quite different. When the crest of a breaking wave strikes a vertical surface, a pocket of air is trapped and compressed by the wave. As the air pocket compresses, it exerts a high-pressure burst on the vertical surface, focused at the stillwater level. The pressures can be extreme. For example, a 5-foot wave height can produce a peak force of 4,500 pounds/square foot, roughly 100 times the force caused by a 170-mph wind. These extremely high loads make designing solid foundation walls for small buildings impractical in areas subject to the effects of breaking waves. Prudent design dictates elevating buildings on an open foundation above potential breaking waves. In fact, the 2012 IBC and the 2012 IRC require that new, substantially damaged, and substantially improved buildings in Zone V be elevated above the BFE on an open foundation (e.g., pile, post, column, pier). The 2012 IBC and 2012 IRC prohibit obstructions below elevated buildings but allow enclosures below the BFE as long as they are constructed with insect screening, lattice, or walls designed and constructed to fail under the loads imposed by floodwaters (termed "breakaway walls"). Because such enclosures fail under flood forces, they do not transfer additional significant loads to the foundation. Regulatory requirements and design criteria concerning enclosures and breakaway walls below elevated buildings in Zone V are discussed in FEMA NFIP Technical Bulletin 9 (FEMA 2008a). Additional guidance is contained in Fact 9-30 COASTAL CONSTRUCTION MANUAL Volume II I DESIGNING THE BUILDING '17 Figure 9-26. Gable -end failure caused by high winds, Hurricane Marilyn (U.S. Virgin Islands, 1995) Figure 9-27. Hip roof that survived high winds with little to no damage, Hurricane Marilyn (U.S. Virgin Islands, 1995) COASTAL CONSTRUCTION MANUAL 9-31 DESIGNING THE BUILDING Volume II Sheet No. 8.1, Enclosures and Breakaway Walls in FEMA P-499. Breakaway walls may be of wood- or metal - frame or masonry construction. Figure 9-28 shows how a failure begins in a wood -frame breakaway wall. Note the failure of the connection between the bottom plate of the wall and the floor of the enclosed area. Figure 9-29 shows a situation in which utility components placed on and through a breakaway wall prevented it from breaking away cleanly. To increase the likelihood of collapse as intended, it is recommended that the vertical framing members (such as 2x4s) on which the screen or lattice work is mounted be spaced at least 2 feet apart. Either metal or synthetic screening is acceptable. Wood and plastic lattice is available in 4-foot x 8-foot sheets. The material used to fabricate the lattice should be no thicker than 1/2 inch, and the finished sheet should have an opening ratio of at least 40 percent. Figure 9-30 shows lattice used to enclose an area below an elevated building. Figure 9-28. Typical failure mode of breakaway wall beneath an elevated building — failure of the connection between the bottom plate of the wall and the floor of the enclosed area, Hurricane Hugo (South Carolina, 1989) Figure 9-29. Breakaway wall panel prevented from breaking away cleanly by utility penetrations, Hurricane Opal (Florida, 1995) -kN 1 LWOW" it a l k _ _.E. 9-32 COASTAL CONSTRUCTION MANUAL Volume II 9.4 Building Materials DESIGNING THE BUILDING Figure 9-30. Lattice beneath an elevated house in Zone V The choice of materials is influenced by many considerations, including whether the materials will be used above or below the DFE. Below the DFE, design considerations include the risk of inundation by seawater, and the forces to be considered include those from wave action, water velocity, and waterborne debris impact. Materials intermittently wetted by floodwater below the BFE are subject to corrosion and decay. Above the DFE, building materials also face significant environmental effects. The average wind velocity increases with height above ground. Wind -driven saltwater spray can cause corrosion and moisture intrusion. The evaporation of saltwater leaves crystalline salt that retains water and is corrosive. Each type of commonly used material (wood, concrete, steel, and masonry) has both characteristics that can be advantageous and that can require special consideration when the materials are used in the coastal environment (see Table 9-1). A coastal residential structure usually has a combination of these materials. Table 9-1. General Guidance for Selection of Materials rr... Steel • Generally available and commonly used • With proper design, can generally be used in most structural applications • Variety of products available • Can be treated to resist decay • Some species are naturally decay -resistant • Used for forces that are larger than wood can resist • Can span long distances • Can be coated to resist corrosion • Easily over -cut, over -notched, and over -nailed • Requires special treatment and continued maintenance to resist decay and damage from termites and marine borers • Requires protection to resist weathering • Subject to warping and deterioration • Not corrosion -resistant • Heavy and not easily handled and fabricated by carpenters • May require special connections such as welding COASTAL CONSTRUCTION MANUAL 9-33 DESIGNING THE BUILDING Table 9-1. General Guidance for Selection of Materials (concluded) • Resistant to corrosion if reinforcing is properly protected Reinforced • Good material for compressive loads Concrete • Can be formed into a variety of shapes • Pre -stressed members have high load capacity • Resistant to corrosion if reinforcing is Masonry properly protected • Good material for compressive loads • Commonly used in residential construction 9.4.1 Materials Below the DFE Volume II • Saltwater infiltration into concrete cracks causes reinforcing steel corrosion • Pre -stressed members require special handling • Water intrusion and freeze -thaw cause deterioration and spalling • Not good for beams and girders • Water infiltration into cracks causes reinforcing steel corrosion • Requires reinforcement to resist loads in coastal areas .d,4 The use of flood -resistant materials below the BFE is discussed NOTE in FEMA NFIP Technical Bulletin 2 (FEMA 2008b). According to the bulletin, "All construction below the lowest Although NFIP regulations, 2012 floor is susceptible to flooding and must consist of flood- IBC, and 2012 IRC specify that resistant materials. Uses of enclosed areas below the lowest flood -resistant materials be used floor in a residential building are limited to parking, access, below the BFE, in this Manual, and limited storage —areas that can withstand inundation by flood -resistant materials belowthe DFE are recommended. floodwater without sustaining significant structural damage." The 2012 IBC and 2012 IRC require that all new construction and substantial improvements in the SFHA be constructed with materials that are resistant to flood damage. Compliance with these requirements in coastal areas means that the only building elements below the BFE are: Foundations — treated wood; concrete or steel piles; <' concrete or masonry piers; or concrete, masonry, or treated CROSS REFERENCE wood walls For NFIP compliance provisions Breakaway walls as described in the 2012 IBC and the 2012 IRC, see Chapter 5 of Enclosures used for parking, building access, or storage this Manual. below elevated buildings Garages in enclosures under elevated buildings or attached to buildings CROSS REFERENCE Access stairs Material choices for these elements are limited to materials that meet the requirements provided in FEMA NFIP Technical Bulletin 2. Even for materials meeting those requirements, characteristics of various materials can be advantageous or may require special consideration when the materials are used for For examples of flood insurance premiums for buildings in which the lowest floor is above the BFE and in which there is an enclosure below the BFE, see Table 7-2 in Chapter 7. 9-34 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING different building elements. Additional information about material selection for various locations and uses in a building is included in "Material Durability in Coastal Environments," available on the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/mat/fema55.shtm). 9.4.2 Materials Above the DFE Long-term durability, architectural, and structural considerations are normally the most important factors in material selection. Material that will be used in a coastal environment will be subjected to weathering, corrosion, termite damage, and decay from water infiltration, in addition to the stresses induced by loads from natural hazard events. These influences are among the considerations for selecting appropriate materials. "Material Durability in Coastal Environments" contains additional information about a variety of wood products and the considerations that are important in their selection and use. 9.4.3 Material Combinations Materials are frequently combined in the construction of a single residence. The most common combinations are as follows: Masonry or concrete lower structure with wood on upper level Wood piles supporting concrete pile caps and columns that support a wood superstructure Steel framing with wood sheathing For the design professional working with of coastal buildings, important design considerations when combining materials include: 1. The compatibility of metals is a design consideration because dissimilar metals that are in contact with each other may corrode in the presence of salt and moisture. "Material Durability in Coastal Environments" addresses a possible problem when galvanized fasteners and hardware are in contact with certain types of treated wood. 2. Connecting the materials together is crucial. Proper embedment of connectors (if into concrete or masonry) and proper placement of connectors are necessary for continuity of the vertical or horizontal load path. Altering a connector location after it has been cast into concrete or grout is a difficult and expensive task. 3. Combining different types of material in the same building adds to construction complexity and necessitates additional skills to construct the project. Figure 9-31 shows a coastal house being constructed with preservative -treated wood piles that support a welded steel frame, resulting in metal coming into direct contact with treated wood. 4. Material properties, such as stiffness of one material relative to another, affect movement or deflection of one material relative to the other. COASTAL CONSTRUCTION MANUAL 9-35 DESIGNING THE BUILDING Volume II Figure 9-31. House being constructed with a steel frame on wood piles 9.4.4 Fire Safety Considerations Designing and constructing townhouses and low-rise multi -family coastal buildings to withstand natural hazards and meet the building code requirements for adequate fire separation presents some challenges. Although fire separation provisions of the 2012 IBC and 2012 IRC differ, they both require that the common walls between living units be constructed of materials that provide a minimum fire resistance rating. The intent is for units to be constructed so that if a fire occurs in one unit, the structural frame of that unit would collapse within itself and not affect either the structure or the fire resistance of adjacent units. For townhouse -like units, the common framing method is to use the front and rear walls for the exterior load -bearing walls so that firewalls can be placed between the units. Beams that are parallel to the front and rear exterior walls are typically used to provide support for these walls as well as the floor framing. Figure 9-32 illustrates a framing system for a series of townhouses in which floor beams are perpendicular to the primary direction of flood forces. Design issues include the following: 5. The floor support beams are parallel to the shore and perpendicular to the expected flow and may therefore create an obstruction during a greater -than -design flood event. 6. The fire separation between townhouse units limits options for structural connections between units, making the transfer of lateral loads to the foundation more difficult to achieve. 7. The exposed undersides of buildings elevated on an open foundation (e.g., pile, pier, post, column) must be protected with a fire -rated material. Typically, this is accomplished with use of fire-resistant gypsum board; however, gypsum board is not a flood -damage -resistant material. An alternative approach is to use other materials such as cement -fiber board (with appropriate fire rating), which has a greater resistance to damage from floodwaters, and fire retardant treated wood. Other alternative materials or methods of protection that are flood -damage -resistant may be required in order to meet the competing demands of flood- and fire -resistance. 9-36 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Figure 9-32. Townhouse framing system The requirement for separation of the foundation elements between townhouse units makes structural rigidity in the direction parallel to the shore more difficult to achieve. If the houses in Figure 9-32 were in a seismic hazard area, the designer could decide to place diagonal bracing parallel to the shore (i.e., perpendicular to the primary flood flow direction) or use more closely spaced and larger piles. Diagonal bracing would provide rigidity but would also create an obstruction below the DFE. The design professional should consult FEMA NFIP Technical Bulletin 5 (FEMA 2008c) for information about the types of construction that constitute an obstruction. One solution to some of the issues illustrated by Figure 9-32 would be to use two parallel independent walls to provide the required fire separation between units. Each wall could be attached to the framing system of the unit on one side of the separation and supported by a beam running perpendicular to the shore and bearing on the open foundation of that unit. 9.4.5 Corrosion Modern construction techniques often rely heavily on metal fasteners and connectors to resist the forces of various coastal hazards. To be successful, these products must have lifetimes that are comparable to those of the other materials used for construction. Near saltwater coastlines, corrosion has been found to drastically shorten the lifetime of standard fasteners and connectors. Corrosion is one of the most underestimated hazards affecting the overall strength and lifetime of coastal buildings. To be successful, hazard -resistant buildings must match the corrosion exposure of each element with the proper corrosion -resistant material. COASTAL CONSTRUCTION MANUAL 9-37 DESIGNING THE BUILDING 9.5 Appurtenances The NFIP regulations define "appurtenant structure" as "a structure which is on the same parcel of property as the principal structure to be insured and the use of which is incidental to the use of the principal structure" (44 CFR § 59.1). In this Manual, "appurtenant structure" means any other building or constructed element on the same property as the primary building, such as decks, covered porches, access to elevated buildings, pools, and hot tubs. 9.5.1 Decks and Covered Porches Attached to Buildings Volume II CROSS REFERENCE For additional information about the types of building elements that are allowed below the BFE and for respective site development issues, see FEMA NFIP Technical Bulletin 5. Many decks and other exterior attached structures have failed during hurricanes. For decks and other structures without roofs, the primary cause of failure has been inadequate support: the pilings have either not been embedded deep enough to prevent failure or have been too small to carry the large forces from natural hazards. The following are recommendations for designing decks and other exterior attached structures: If a deck is structurally attached to a structure, the bottom of the lowest horizontal supporting member of the deck must be at or above the BFE. Deck supports that extend below the BFE (e.g., pilings, bracing) must comply with Zone V design and construction requirements. The structure must be designed to accommodate any increased loads resulting from the attached deck. Some attached decks are located above the BFE but rely on support elements that extend below the BFE. These supports must comply with Zone V design and construction requirements. If a deck or patio (not counting its supports) lies in whole or in part below the BFE, it must be structurally independent from the structure and its foundation system. If the deck surface is constructed at floor level, the deck surface/floor level joint provides a point of entry for wind -driven rain. This problem can be eliminated by lowering the deck surface below the floor level. If deck dimensions can be accommodated with cantilevering from the building, this eliminates the need for piles altogether and should be considered when the deck dimensions can be accommodated with this structural technique. Caution must be exercised with this method to keep water out of the house framing. Chapter 11 discusses construction techniques for flashing cantilever decks that minimize water penetration into the WARNING house. Decks should not cantilever Exposure to the coastal environment is severe for decks over bulkheads or retaining p walls where waves can run up and other exterior appurtenant structures. Wood must be the vertical wall and under the preservative -treated or naturally decay resistant, and fasteners deck. must be corrosion resistant. 9-38 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9.5.1.1 Handrails To minimize the effects of wind pressure, flood forces, and wave impacts, deck handrails should be open and have slender vertical or horizontal members spaced in accordance with the locally adopted building code. Many deck designs include solid panels (some made of impact -resistant glazing) between the top of the deck handrail and the deck. These solid panels must be able to resist the design wind and flood loads (below the DFE) or they will become debris. 9.5.1.2 Stairways Many coastal homes have stairways leading to ground level. During flooding, flood forces often move the stairs and frequently separate them from the point of attachment. When this occurs, the stairs become debris and can cause damage to nearby houses and other buildings. Recommendations for stairs that descend below the BFE include the following: To the extent permitted by code, use open -riser stairs to let floodwater through the stair stringers and anchor the stringers to a permanent foundation by using, for example, piles driven to a depth sufficient to prevent failure from scour. Extend the bottom of the stair carriages several feet below grade to account for possible scour. Stairs constructed in this fashion are more likely to remain in place during a coastal hazard event and therefore more likely to be usable for access after the event. In addition, by decreasing the likelihood of damage, this approach reduces the likelihood of the stairs becoming debris. 9.5.2 Access to Elevated Buildings The first floor of buildings in the SFHA is elevated from a few feet to many feet above the exterior grade in order to protect the building and its contents from flood damage. Buildings in Zone A may be only a few feet above grade; buildings in Zone V may be 8 feet to more than 12 feet above grade. Access to these elevated buildings must be provided by one or more of the following: Stairs Ramps Elevator Stairs must be constructed in accordance with the local building code so that the run and rise of the stairs conform to the requirements. The 2012 IBC and 2012 IRC require a minimum run of 11 inches per stair tread and a maximum rise of 7 inches per tread. An 8-foot elevation difference requires 11 treads or almost 12 feet of horizontal space for the stairs. Local codes also have requirements concerning other stair characteristics, such as stair width and handrail height. Ramps that comply with regulations for access by persons with disabilities must have a maximum slope of 1:12 with a maximum rise of 30 inches and a maximum run of 30 feet without a level landing. The landing length must be a minimum of 60 inches. As a result, access ramps are generally not practical for buildings elevated more than a few feet above grade and then only when adequate space is available. COASTAL CONSTRUCTION MANUAL 9-39 DESIGNING THE BUILDING Elevators are being installed in many one- to four -family residential structures and provide an easy way to gain access to elevated floors of a building (including the first floor). There must be an elevator entrance on the lowest floor; therefore, in flood hazard areas, some of the elevator equipment may be below the BFE. FEMNs NFIP Technical Bulletin 4 (FEMA 2010a) provides guidance on how to install elevators so that damage to elevator elements is minimized during a flood. 9.5.3 Pools and Hot Tubs Volume II CROSS REFERENCE For more information about elevator installation in buildings located in SFHAs, see FEMA NFIP Technical Bulletin 4. Many homes at or near the coast have a swimming pool or hot tub as an accessory. Some of the pools are fiberglass and are installed on a pile -supported structural frame. Others are in -ground concrete pools. The design professional should consider the following when a pool is to be installed at a coastal home: Only an in -ground pool may be constructed beneath an elevated Zone V building. In addition, the top of the pool and the accompanying deck NOTE or walkway must be flush with the existing grade, and the area below the lowest floor of the building Check with local floodplain management must remain unenclosed. officials for information about regulations governing the disturbance of primary Enclosures around pools beneath elevated frontal dunes. Such regulations can affect various types of coastal construction, buildings constitute recreational use and are including the installation of appurtenant therefore not allowed, even if constructed to structures such as swimming pools. breakaway standards. Lattice and insect screening are allowed because they do not create an enclosure under a community's NFIP-compliant floodplain management ordinance or law. NOTE A pool adjacent to an elevated Zone V building The construction of pools below or may be either constructed at grade or elevated. adjacent to buildings in coastal high Elevated pools must be constructed on an open hazard areas must meet the requirements foundation and the bottom of the lowest horizontal presented in FEMA NFIP Technical structural member must be at or above the DFE so Bulletin 5. In general, pools must be that the pool will not act as an obstruction. (1) elevated above the BFE on an open foundation or (2) constructed in the The designer must assure community officials that ground in such a way as to minimize the effects of scour and the potential for the a pool beneath or adjacent to an elevated Zone creation of debris. V building will not be subject to breaking up or floating out of the ground during a coastal flood and will therefore not increase the potential for damage to the foundations and elevated portions of any nearby buildings. If an in -ground pool is constructed in an area that can be inundated by floodwaters, the elevation of the pool must account for the potential buoyancy of the pool. If a buoyancy check is necessary, it should be made with the pool empty. In addition, the design professional must design and site the pool so that any increased wave or debris impact forces will not affect any nearby buildings. 9-40 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING Pools and hot tubs have water pumps, piping, heaters, filters, and other equipment that is expensive and that can be damaged by floodwaters and sediment. All such equipment should be placed above the DFE where practical. Equipment required for fueling the heater, such as electric meters or gas tanks, should be placed above the DFE. It may also be necessary to anchor the gas tank to prevent a buoyancy failure. If buried, tanks must not be susceptible to erosion and scour and thus failure of the anchoring system. The design intent for concrete pools includes the following: Elevation of an in -ground pool should be such that scour will not permit the pool to fail from either normal internal loads of the filled pool or from exterior loads imposed by the flood forces. The pool should be located as far landward as possible and should be oriented in such a way that flood forces are minimized. One way to minimize flood forces includes placing the pool with the narrowest dimension facing the direction of flow, orienting the pool so there is little to no angle of attack from floodwater, and installing a pool with rounded instead of square corners. All of these design choices reduce the amount of scour around the pool and improve the chances the pool will survive a storm. These concepts are illustrated in Figure 9-33. A concrete pool deck should be frangible so that flood forces create concrete fragments that help reduce scour. The concrete deck should be installed with no reinforcing and should have contraction joints placed at 4-foot squares to "encourage" failure. See Figure 9-34 for details on constructing a frangible concrete pad. Pools should not be installed on fill in or near Zone V. Otherwise, a pool failure may result from scour of the fill material. For concrete pools, buoyancy failure is also possible when floodwaters cover the pool. In addition, flood flows can scour the soil surrounding a buried pool and tear the pool from its anchors. When this happens, the pieces of the pool become large waterborne debris. Frangible concrete deck y House Rounded corners -Z Narrowest dimension Porch 0° angle of attack Flood flow Figure 9-33. Recommendations for orientation of in -ground pools COASTAL CONSTRUCTION MANUAL 9-41 DESIGNING THE BUILDING Figure 9-34. Recommended contraction joint layout for frangible slab -on - grade below elevated building Contraction joint Detail section through slab Volume II Isolation joint -+ ~;'-'column Note: Install expansion and isolation joints as appropriate in accordance with standard practice or as required by state and local codes. 9-42 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING 9.6 References AF&PA (American Forest & Paper Association ). 2008. Special Design Provisions for Wind and Seismic. ANSI/AF&PA SDPWS-08. AF&PA. 2012. Wood Frame Construction Manual for One- and Two -Family Dwellings. Washington, DC. ASCE (American Society of Civil Engineers). 2010. Minimum Design Loads for Buildings and Other Structures, ASCE Standard ASCE 7-10. AWC (American Wood Council). 2001. Wood Frame Construction Manual. AWC. 2006. National Design Specification for Wood Construction (NDS). FEMA (Federal Emergency Management Agency). 1996. Corrosion Protection ofMetal Connectors in Coastal Areas for Structures Located in Special Flood Hazard Areas. NFIP Technical Bulletin 8-96. FEMA. 2008a. Design and Construction Guidance for Breakaway Walls Below Elevated Coastal Buildings, FEMA NFIP Technical Bulletin 9. FEMA. 2008b. Flood Damage -Resistant Materials Requirements, FEMA NFIP Technical Bulletin 2. FEMA. 2008c. Free of Obstruction Requirements for Buildings Located in Coastal High Hazard Areas. NFIP Technical Bulletin 5. FEMA. 2009. Local Officials Guide for Coastal Construction. FEMA 762. FEMA. 2010a. Elevator Installation for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program. NFIP Technical Bulletin 4. FEMA. 2010b. Home Builder's Guide to Coastal Construction Technical Fact Sheets. FEMA P-499. Hamilton, P. 1997. "Installing a Steel Moment Frame." journal ofLight Construction. March. ICC (International Code Council). 2008. Standard for Residential Construction in High -Wind Regions. ICC 600-2008. ICC: Country Club Hills, IL. ICC. 2011a. International Building Code. 2012 IBC. ICC: Country Club Hills, IL. ICC. 2011b. International Residential Code for One -and Two -Family Dwellings. 2012 IRC. ICC: Country Club Hills, IL. WPPC (Wood Products Promotion Council). 1996. Guide to Wood Construction in High WindAreas. COASTAL CONSTRUCTION MANUAL 9-43 i i•I I g the Foundation This chapter provides guidance on designing foundations, including selecting appropriate materials, in coastal areas. It provides general guidance on designing foundations in a coastal environment and is not intended to provide complete guidance on designing foundations in every coastal area. Design professionals should consult other guidance documents, codes, and standards as needed. Design considerations for foundations in coastal environments are in many ways similar to those in inland areas. Like all CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/ mat/fema55.shtm). foundations, coastal foundations must support gravity loads, resist uplift and lateral loads, and maintain lateral and vertical load path continuity from the elevated building to the soils below. Foundations in coastal areas are different in that they must generally resist higher winds, function in a corrosive environment, and withstand the environmental aspects that are unique to coastal areas: storm surges, rapidly moving floodwaters, wave action, and scour and erosion. These aspects can make coastal flooding more damaging than inland flooding. Like many design processes, foundation design is an iterative process. First, the loads on the elevated structure are determined (see Chapter 9). Then a preliminary foundation design is considered, flood loads on the preliminary design are determined, and foundation style is chosen and the respective elements are sized to resist those loads. With information on foundation size, the design professional can accurately determine flood loads on the foundation and can, through iteration, develop an efficient final design. Because flood loads depend greatly on the foundation design criteria, the discussion of foundation design begins there. The appropriate styles of foundation are then discussed and how the styles can be selected to reduce vulnerability to natural hazards. COASTAL CONSTRUCTION MANUAL 10-1 10 DESIGNING THE FOUNDATION The distinction between code requirements and bestpractices is described throughout the chapter. 10.1 Foundation Design Criteria Volume II Foundations should be designed in accordance with the latest edition of the 2012 IBC or the 2012 IRC and must address any locally adopted building ordinances. Designers will find that other resources will likely be needed in addition to the building codes in order to properly design a coastal foundation. These resources are listed at the end of this chapter. Properly designed and constructed foundations are expected to: Support the elevated building and resist all loads expected to be imposed on the building and its foundation during a design flood, wind, or seismic event In SFHAs, prevent flotation, collapse, and lateral movement of the building Function after being exposed to scour and erosion In addition, the foundation must be constructed with flood -resistant materials below the BFE. See Technical Bulletin 2, Flood Damage -Resistant Materials Requirements (FEMA 2008a), and Fact Sheet 1.7, Coastal Buildin,eMaterials, in FEMA P-499 (FEMA 2011). Some coastal areas mapped as Zone A are referred to as "Coastal A Zones." Following Hurricane Katrina (2005), Coastal A Zones have also been referred to as areas with a Limit of Moderate Wave Action (LiMWA). Buildings in Coastal A Zones may be subjected to damaging waves and erosion and, when constructed to minimum NFIP requirements for Zone A, may sustain major damage or be destroyed during the base flood. Therefore, in this Manual, foundations for buildings in Coastal A Zones are strongly recommended to be designed and constructed with foundations that resist the damaging effects of waves. 10.2 Foundation Styles TERMINOLOGY: LiMWA AND COASTAL A ZONE Limit of Moderate Wave Action (LiMWA) is an advisory line indicating the limit of the 1.5- foot wave height during the base flood. FEMA requires new flood studies in coastal areas to delineate the LiMWA. In this Manual, foundations are described as open or closed and shallow or deep. The open and closed descriptions refer to the above -grade portion of the foundation. The shallow and deep descriptions refer to the below -grade portion. Foundations can be open and deep, open and shallow, or closed and shallow. Foundations can also be closed and deep, but these foundations are relatively rare and generally found only in areas where (1) soils near the surface are relatively weak (700 pounds/square foot bearing capacity or less), (2) soils near the surface contain expansive clays (also called shrink/swell soils) that shrink when dry and swell when wet, or (3) other soil conditions exist that necessitate foundations that extend into deep soil strata to provide sufficient strength to resist gravity and lateral loads. Open, closed, deep, and shallow foundations are described in the following subsections. 10-2 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 10.2.1 Open Foundations An open foundation allows water to pass through the foundation of an elevated building, reducing the lateral flood loads the foundation must resist. Examples of open foundations are pile, pier, and column foundations. An open foundation is designed and constructed to minimize the amount of vertical surface area that is exposed to damaging flood forces. Open foundations have the added benefit of being less susceptible than closed foundations to damage from flood -borne debris because debris is less likely to be trapped. Open foundations are required in Zone V and recommended in Coastal A Zone. Table 10-1 shows the recommended practices in Coastal A Zone and Zone V. Table 10-1. Foundation Styles in Coastal Areas Open/deep Acceptable Acceptable Acceptable Closed/shallow Not permitted Not recommended Acceptable LiMWA = Limit of Moderate Wave Action (a) Shallow foundations in Coastal A Zone are acceptable only if the maximum predicted depth of scour and erosion can be accurately predicted and foundations can be constructed to extend below that depth. 10.2.2 Closed Foundations A closed foundation is typically constructed using continuous perimeter foundation walls. Examples of closed foundations are crawlspace foundations and stem wall foundations,l which are usually filled with compacted soil. Slab -on -grade foundations are also considered closed. A closed foundation does not allow water to pass easily through the foundation elements below an elevated building. Thus, these types of foundations obstruct floodwater flows and present a large surface area upon which waves and flood forces act. Closed foundations are prohibited in Zone V and are not recommended in Coastal A Zones. If perimeter walls enclose space below the DFE, they must be equipped with openings that allow floodwaters to flow in and out of the area enclosed by the walls (see Figure 2-19). The entry and exit of floodwater equalizes the water pressure on both sides of the wall and reduces the likelihood that the wall will fail. See Fact Sheet No. 3.5, Foundation Walls, in FEMA P-499, Home Builder's Guide to Coastal Construction Technical Fact Sheet Series (FEMA 2010). Closed foundations also create much larger obstructions to moving floodwaters than open foundations, which significantly increases localized scour. Scour, with and without generalized erosion, can remove soils that support a building and can undermine the foundation and its footings. Once undermined, shallow footings readily fail (see Figure 10-1). 1 Stem wall foundations (in some areas, referred to as chain wall foundations) are similar to crawlspace foundations where the area enclosed by the perimeter walls are filled with compacted soil. Most stem wall foundations use a concrete slab -on -grade for the first floor. The NFIP requires flood vents in crawlspace foundations but not in stem wall foundations (see Section 6.1.1.1 and Section 7.6.1.1.5). COASTAL CONSTRUCTION MANUAL 10-3 10 DESIGNING THE FOUNDATION Volume II Figure 10-1. Closed foundation failure due to erosion and scour undermining; photograph on right shows a close-up view of the foundation failure and damaged house wall, Hurricane Dennis (Navarre Beach, FL, 2005) 10.2.3 Deep Foundations Buildings constructed on deep foundations are supported by soils that are not near grade. Deep foundations include driven timber, concrete or steel piles, and caissons. Deep foundations are much more resistant to the effects of localized scour and generalized erosion than shallow foundations. Because of that, deep foundations are required in Zone V where scour and erosion effects can be extreme. Open/deep foundations are recommended in Coastal A Zones and in some riverine areas where scour and erosion can undermine foundations. 10.2.4 Shallow Foundations Buildings constructed on shallow foundations are supported by soils that are relatively close to the ground surface. Shallow foundations include perimeter strip footings, monolithic slabs, discrete pad footings, and some mat foundations. Because of their proximity to grade, shallow foundations are vulnerable to damage from scour and erosion, and because of that, they are not allowed in Zone V and are not recommended in Coastal A Zones unless they extend below the maximum predicted scour and erosion depth. In colder regions, foundations are typically designed to extend below the frost depth, which can exceed several feet below grade. Extending the foundation below the frost depth is done to prevent the foundation from heaving when water in the soils freeze and to provide adequate protection from scour and erosion. However, scour and erosion depths still need to be investigated to ensure that the foundation is not vulnerable to undermining. 10.3 Foundation Design Requirements and Recommendations Foundations in coastal areas must elevate the home to satisfy NFIP criteria. NFIP criteria vary for Zone V and Zone A. In Zone V, the NFIP requires that the building be elevated so that the bottom of the lowest 10-4 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 horizontal structural member is elevated to the BFE. In Zone A, the NFIP requires that the home be constructed such that the top of the lowest floor is elevated to the BFE. In addition to elevation, the NFIP contains other requirements regarding foundations. Because of the increased flood, wave, flood -borne debris, and erosion hazards in Zone V, the NFIP requires homes to be elevated on open/deep foundations that are designed to withstand flood forces, wind forces, and forces for flood -borne debris impact. They must also resist scour and erosion. 10.3.1 Foundation Style Selection Many foundation designs can be used to elevate buildings to the DFE. Table 10-1 shows which foundation styles are acceptable, not recommended, or not permitted in Zone V, Coastal A Zone, and Zone A. Additional information concerning foundation performance can be found in Fact Sheet 3.1, Foundations in Coastal Areas, in FEMA P-499. A best practices approach in the design and construction of coastal foundations is warranted because of the extreme environmental conditions in coastal areas, the vulnerability of shallow foundations to scour and erosion, the fact that the flood loads on open foundations are much lower than those on closed foundations, and foundation failures typically result in extensive damage to or total destruction of the elevated building. Structural fill can also be used to elevate and support stem wall, crawlspace, solid wall, slab -on -grade, pier, and column foundations in areas not subject to damaging wave action, erosion, and scour. The NFIP precludes the use of structural fill in Zone V. For more information, see FEMA Technical Bulletin 5, Free -of -Obstruction Requirements (FEMA 2008b). 10.3.2 Site Considerations The selected foundation design should be based on the characteristics of the building site. A site characteristic study should include the following: Design flood conditions. Determine which flood zone the site is located in —Zone V, Coastal A Zone, or Zone A. Flood zones have different hazards and design and construction requirements. Site elevation. The site elevation and DFE determine how far the foundation needs to extend above grade. Long- and short-term erosion. Erosion patterns (along with scour) dictate whether a deep foundation is required. Erosion depth affects not only foundation design but also flood loads by virtue of its effect on design stillwater depth (see Section 8.5). Site soils. A soils investigation report determines the soils that exist on the site and whether certain styles of foundations are acceptable. 10.3.3 Soils Data Accurate soils data are extremely important in the design of flood -resistant foundations in coastal areas. Although many smaller or less complex commercial buildings and most homes in non -coastal areas are COASTAL CONSTRUCTION MANUAL 10-5 10 DESIGNING THE FOUNDATION Volume II designed without the benefit of specific soils data, all buildings in coastal sites, particularly those in Zone V, should have a thorough investigation of the soils at the construction site. Soils data are available in numerous publications and from onsite soils tests. 10.3.3.1 Sources of Published Soils Data Numerous sources of soil information are available. Section 12.2 of the Timber Pile Design and Construction Manual (Collin 2002) lists the following: Topographic maps from the U.S. Geologic Survey (USGS) Topographic maps from the Army Map Service Topographic maps from the U.S. Coast and Geodetic Survey Topographic information from the USACE for some rivers and adjacent shores and for the Great Lakes and their connecting waterways Nautical and aeronautical charts from the Hydrographic Office of the Department of the Navy Geologic information from State and local governmental agencies, the Association of Engineering Geologists, the Geological Society of America, the Geo-Institute of the American Society of Civil Engineers, and local universities Soil survey maps from the Soil Conservation Service of the U.S. Department of Agriculture 10.3.3.2 Soils Data from Site Investigations Site investigations for soils include surface and subsurface investigations. Surface investigations can identify evidence of landslides, areas affected by erosion or scour, and accessibility for equipment needed for subsurface testing and for equipment needed in construction. Surface investigations can also help identify the suitability or unsuitability of particular foundation styles based on the past performance of existing structures. However, caution should be used when basing the selection of a foundation style solely on the performance of existing structures because the structures may not have experienced a design event. The 2012 IBC requires that geotechnical investigations be conducted by Registered Design Professionals. Section 1803.2 allows building officials to waive geotechnical investigations where satisfactory data are available from adjacent areas and demonstrate that investigations are not required. The 2012 IRC requires building officials to determine whether soils tests are needed where "quantifiable data created by accepted soil science methodologies indicate expansive, compressible, shifting or other questionable soil characteristics are likely to be present." Because of the hazards in coastal areas, a best practices approach is to follow the 2012 IBC requirements. Subsurface exploration provides invaluable data on soils at and below grade. The data are both qualitative (e.g., soil classification) and quantitative (e.g., bearing capacity). Although some aspects of subsurface exploration are discussed here, subsurface exploration is too complicated and site -dependent to be covered fully in one document. Consulting with geotechnical engineers familiar with the site is strongly recommended. 10-6 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Subsurface exploration typically consists of boring or creating test pits, soils sampling, and laboratory tests. The Timber Pile Design and Construction Manual (Collin 2002) recommends a minimum of one boring per structure, a minimum of one boring for every 1,000 square feet of building footprint, and a minimum of two borings for structures that are more than 100 feet wide. Areas with varying soil structure and profile dictate more than the minimum number of borings. Again, local geotechnical engineers should be consulted. The following five types of data from subsurface exploration are discussed in the subsections below: soil classification, bearing capacity, compressive strength, angle of internal friction, and subgrade modulus. Soil Classification Soil classification qualifies the types of soils present along the boring depth. ASTM D2487-10 is a consensus standard for soil classification. Soil classification is based on whether soils are cohesive (silts and clays) or non - cohesive (composed of granular soils particles). The degree of cohesiveness affects foundation design. Coupled with other tests such as the plasticity/Atterburg Limits soil classification can identify unsuitable or potentially problematic soils. Table 10-2 contains the soil classifications from ASTM D2487-10. ASTM D2488-09a is a simplified standard for soil classification that may be used when directed by a design professional. Bearing Capacity Bearing capacity is a measure of the ability of soil to support gravity loads without soil failure or excessive settlement. Bearing capacity is generally measured in pounds/square foot and occasionally in tons/square foot. Soil bearing capacity typically ranges from 1,000 pounds/square foot (relatively weak soils) to more than 10,000 pounds/square foot (bedrock). Bearing capacity has a direct effect on the design of shallow foundations. Soils with lower bearing capacities require proportionately larger foundations to effectively distribute gravity loads to the supporting soils. For deep foundations, like piles, bearing capacity has less effect on the ability of the foundation to support gravity loads because most of the resistance to gravity loads is developed by shear forces along the pile. Presumptive allowable load bearing values of soils are provided in the 2012 IBC and the 2012 IRC. Frequently, designs are initially prepared based on presumed bearing capacities. The builder's responsibility is to verify that the actual site conditions agree with the presumed bearing capacities. As a best practices approach, the actual soil bearing capacity should be determined to allow the building design to properly account for soil capacities and characteristics. Compressive Strength Compressive strength is typically determined by Standard Penetration Tests. Compressive strength controls the design of shallow foundations via bearing capacity and deep foundations via the soil's resistance to lateral loads. Compressive strength is also considered when determining the capacity of piles to resist vertical loads. Compressive strength is determined by advancing a probe, 2 inches in diameter, into the bottom of the boring by dropping a 140-pound slide hammer a height of 30 inches. The number of drops, or blows, required to advance the probe 6 inches is recorded. Blow counts are then correlated to soil properties. COASTAL CONSTRUCTION MANUAL 10-7 10 DESIGNING THE FOUNDATION Table 10-2. ASTM D2487-10 Soil Classifications Volume II Well -graded gravels Classification D60 and gravel -sand on basis of C u Ci0 than 4 mixtures, little or no percentage of greater GW fines fines: lD3o�� • Less than 5% Cz = l �Dio� (D60 pass No. 200 1 \J sieve: GW, between 1 and 3 GP, SW, SPNot Poorly graded meeting both criteria for GW GP gravels and gravel- • More than sand mixtures, little 12% pass or no fines No. 200 sieve: GM, Silty gravels, gravel- GC, SM, SC Atterberg limits Atterberg limits sand -silt mixtures . 5% to 12% plot below plotting in GM pass No. "A" line or hatched area 200 sieve: plasticity index are borderline borderline less than 4 classifications Clayey gravels, classification Atterberg limits requiring use of dual gravel -sand -clay requiring dual plot above symbols. GC mixtures symbols "A" line or plasticity index less than 7 Well -graded sands and gravelly sands, little or no fines SW Poorly graded sands SP and gravelly sands, little or no fines Silty sands, sand -silt mixtures SM Clayey sands, sand - clay mixtures Sc C — D60 u Ci0 greater than 6 (D30)h Cz `D10 ) ( D60 between 1 and 3 Not meeting both criteria for SW Atterberg limits Atterberg limits plot below plotting in "A" line or hatched area plasticity index are borderline less than 4 classifications Atterberg requiring use of dual limits plot symbols. above "A" line or plasticity index greater than 7 10-8 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Table 10-2. ASTM D2487-10 Soil Classifications (concluded) Inorganic silts, very fine sands, rock flout, silty or clayey fine sands Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays Organic silts and organic silty clays of low plasticity Inorganic silts, micaceous or diatomaceous fine sands or silts, elastic silts Inorganic clays of CH high plasticity, fat clays Organic clays of OH medium to high plasticity Peat, muck, and PT other highly organic soils Adapted, with permission, from ASTM D2487-10 Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. The complete standard is available at ASTM International, http://www.astm.org. Angle of Internal Friction/Soil Friction Angle The angle of internal friction is a measure of the soil's ability to resist shear forces without failure. Internal friction depends on soil grain size, grain size distribution, and mineralogy. The angle of internal friction is used in the design of shallow and deep foundations. It is also used to determine the sliding resistance developed between the bottom of a footing and the foundation at the adjacent soil strata via Equation 10.1. The following factors should be considered. The normal force includes only the weight of the building (dead load). Live loads should not be considered. Also, ASD load factors in ASCE 7-10 allow only 60 percent of the dead load of a structure to be considered when resisting sliding forces. Foundation materials exert less normal force on a foundation when submerged, so the submerged weight of all foundation materials below the design stillwater depth should be used. Editions of the IBC contain presumptive coefficients of friction for various soil types (for example, coefficients of friction are contained in Table 1806.2 in the 2009 IBC). Those coefficients can be used in Equation 10.1 by substituting them for the term "tan ((p)." COASTAL CONSTRUCTION MANUAL 10-9 10 DESIGNING THE FOUNDATION Volume II Subgrade Modulus nh The subgrade modulus (nh) is used primarily in the design of pile foundations. It, along with the pile properties, determines the depth below grade of the point of fixity (point of zero movement and rotation) of a pile under lateral loading. The inflection point is critical in determining whether piles are strong enough to resist bending moments caused by lateral loads on the foundation and the elevated building. The point of fixity is deep for soft soils (low subgrade modulus) and stiff piles and shallow for stiff soils (high subgrade modulus) and flexible piles. Subgrade moduli range from 6 to 150 pounds/cubic inch for soft clays to 800 to 1,400 pounds/cubic inch for dense sandy gravel. See Section 10.5.3 for more information on subgrade modulus. 10.4 Design Process The following are the major steps in foundation analysis and design. Determine the flood zone that the building site is in. For a site that spans more than one flood zone (e.g., Zone V and Coastal A Zone, Coastal A Zone and Zone A), design the foundation for the most severe zone (see Chapter 3). Determine the design flood elevation and design stillwater elevation (see Chapter 8). Determine the projected long- and short-term erosion (see Chapter 8). Determine the site elevation and determine design stillwater depths (see Chapter 8). Determine flood loads including breaking wave loads, hydrodynamic loads, flood -borne debris loads, and hydrostatic loads. Buoyancy reduces the weight of all submerged materials, so hydrostatic loads need to be considered on all foundations (see Chapter 8). Obtain adequate soils data for the site (see Section 10.3.3). Determine maximum scour and erosion depths (see Chapter 8). Select foundation type (open/deep, open/shallow, closed/deep, or closed/shallow). Use open/deep foundations in Zone V and Coastal A Zone. Use open/shallow foundations in Coastal A Zone only when scour and erosion depths can be accurately predicted and when the foundation can extend beneath the erosion depths. See Sections 10.2 and 10.3.1. Determine the basic wind speed, exposure, and wind pressures (see Chapter 8). Determine live and dead loads and calculate all design loads on the elevated building and on the foundation elements (see Chapter 8). 10-10 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION Determine forces and moments at the top of the foundation elements for all load cases specified in ASCE 7-10. Use load combinations specified in Section 2.3 for strength -based designs or Section 2.4 for stress -based designs. Apply forces and moments to the foundation. Design the foundation to resist all design loads and load combinations when exposed to maximum predicted scour and erosion. 10.5 Pile Foundations Pile foundations are widely used in coastal environments and offer several benefits. Pile foundations are deep and, when properly imbedded, offer resistance to scour and erosion. Piles are often constructed of treated timber, concrete, or steel although other materials are also used. Treated timber piles are readily available and because they are wood, they can be cut, sawn, and drilled with standard construction tools used for wood framing. ASTM D25-99 contains specifications on round timber piles including quality requirements, straightness, lengths and sizes (circumferences and diameters) as well as limitations on checks, shakes, and knots. The National Design Specification for Wood Construction (ANSI/ AF&PA 2005) contains design values for timber piles that meet ASTM D25-99 specifications. Pre -cast (and typically pre -stressed) concrete piles are not readily available in some areas but offer several benefits over treated timber piles. Generally, they can be fabricated in longer lengths than timber piles. For the same cross section, they are stronger than timber piles and are not vulnerable to rot or wood -destroying insects. The strength of concrete piles can allow them to be used without grade beams. Foundations without grade beams are less vulnerable to scour than foundations that rely on grade beams (See Section 10.5.6). Steel piles are generally not used in residential construction but are common in commercial construction. Field connections are relatively straightforward, and since steel can be field drilled and welded, steel -to -wood and steel -to -concrete connections can be readily constructed. ASTM A36/A36M-08 contains specifications for mild (36 kip/square inch) steels in cast or rolled shapes. ASTM standards for other shapes and steels include: For steel pipe, ASTM A53/A53M-10, Standard Specification for Pipe, Steel, Black and Hot -Dipped, Zinc -Coated, Welded and Seamless (ASTM 2010c) For structural steel tubing, ASTM A500-10, Standard Specification for Cold -Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes (ASTM 2010b); and ASTM A501-07, Standard Specification for Hot -Formed Welded and Seamless Carbon Steel Structural Tubing (ASTM 2007) For welded and seamless steel pipe piles, ASTM 252-10, Standard Specification for Welded and Seamless Steel Pipe Piles (ASTM 2010d) Fiber -reinforced polymer (FRP) piles are becoming more commonplace in transportation and marine infrastructure but are rarely used in residential applications. However, the usage of FRP piles in residential applications is expected to increase. New construction materials can offer many benefits such as sustainability, durability, and longevity but like any new construction material, the appropriateness of FRP piles should be thoroughly investigated before being used in new applications. Although FRP is not discussed in the COASTAL CONSTRUCTION MANUAL 10-11 10 DESIGNING THE FOUNDATION Volume II publication, Technical Fact Sheet 1.8, Non -Traditional Building Materials and Systems, in FEMA P-499 provides guidance on using new materials and new systems in coastal environments. Table 10-3 is a summary of the advantages and special considerations for three of the more common pile materials. Table 10-3. Advantages and Special Considerations of Three Types of Pile Materials • Comparatively low initial cost • Difficult to splice • Readily available in most areas • Subject to eventual decay when in soil • Easy to cut, saw and drill or intermittently submerged in water Wood • Permanently submerged piles resistant to decay • Vulnerable to damage from driving • Relatively easy to drive in soft soil (splitting) • Suitable for friction and end bearing pile • Comparatively low compressive load • Relatively low allowable bending stress • Available in longer lengths than wood piles • High initial cost • Corrosion resistant • Not available in all areas • Can be driven through some types of hard • Difficult to make field adjustments for material connections Concrete • Suitable for friction and end -bearing piles • Because of higher weight, require • Reinforced piles have high bending strength special consideration in high seismic • High bending strength allows taller or more areas heavily loaded pile foundations to be constructed without grade beams • High resistance to bending • Vulnerable to corrosion • Easy to splice • May be permanently deformed if struck • Available in many lengths, sections, and sizes by heavy object Steel • Can be driven through hard subsurface material • High initial cost • Suitable for friction and end -bearing piles • Some difficulty with attaching wood • High bending strength, which allows taller or framing more heavily loaded pile foundations to be constructed without grade beams The critical aspects of pile foundations include the pile material and size and pile embedment depth. Pile foundations with inadequate embedment do not have the structural capacity to resist sliding and overturning (see Figure 10-2). Inadequate embedment and improperly sized piles greatly increase the probability for structural collapse. However, when properly sized, installed, and braced with adequate embedment into the soil (with consideration for erosion and scour effects), a building's pile foundation performance allows the building to remain standing and intact following a design flood event (see Figure 10-3). 10.5.1 Compression Capacity of Piles — Resistance to Gravity Loads The compression capacity of piles determines their ability to resist gravity loads from the elevated structure they support. One source that provides an equation for the compression capacity of piles is the Foundation andEarth Structures, Design Manual 7.2 (USDN 1986). The manual contains Equation 10.2 for determining 10-12 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Figure 10-2. Near collapse due to insufficient pile embedment, Hurricane Katrina (Dauphin Island, AL, 2005) Figure 10-3. Surviving pile foundation, Hurricane Katrina (Dauphin Island, AL, 2005) the compression capacity of a single pile when placed in granular (non -cohesive) soils. Design Manual 7.2 also contains methods of determining compression capacity of a pile placed in cohesive soils. The resistance of the pile is the sum of the capacity that results from end bearing and friction. The capacity from end bearing is the first term in Equation 10.2; the capacity from friction is given in the second term. Equation 10.2 gives the ultimate compression capacity of a pile. The allowable capacity (Qd11o,,) used in ASD depends on a Factor of Safety applied to the ultimate capacity. For ASD, Design Manual 7.2 recommends a Factor of Safety of 3.0; thus, Qallow = Qu,tl3. COASTAL CONSTRUCTION MANUAL 10-13 10 DESIGNING THE FOUNDATION Volume II Table 10-4. Bearing Capacity Factors (Nq ) 26 28 30 31 32 33 34 35 36 37 38 39 40 10 15 21 24 29 35 42 50 62 77 86 120 145 5 8 10 12 14 17 21 25 30 38 43 60 72 Nq = bearing capacity factor rp = angle of internal friction (a) Limit (p to 28' if jetting is used (b) When a bailer or grab bucket is used below the groundwater table, calculate end bearing based on cp not exceeding 28 degrees. For piers larger than 24 inches in diameter, settlement rather than bearing capacity usually controls the design. For estimating settlement, take 50% of the settlement for an equivalent footing resting on the surface of comparable granular soils. Table 10-5. Earth Pressure Coefficients 0.5 — 1.0 0.3 — 0.5 1.0-1.5 0.6-1.0 1.5 — 2.0 1.0 — 1.3 0.4 — 0.9 0.3 — 0.6 0.7 0.4 KHc-= earth pressure compression coefficient KHT= earth pressure tension coefficient 10-14 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 1 Table 10-6. Friction Angle Between Soil and Pile (6) Timber 3/a sp Concrete 3/4� Steel 20 degrees T = angle of internal friction 10.5.2 Tension Capacity of Piles The tension capacity of piles determines their ability to resist uplift and overturning loads on the elevated structure. One source that provides pile capacity in tension load is the Design Manual 7.2, which is also a reference on compression capacity. Equation 10.3 determines the tension capacity in a single pile. The Design Manual 7.2 provides tables to identify bearing capacity factors (Nq), earth pressure coefficients (KHC and KHT), and friction angle between pile and soil (6) based on pile type and the angle of internal friction (gyp) of the soil. Example 10.1 illustrates compression and tension capacity calculations for a single pile not affected by scour or erosion. Table 10-7 contains example calculations using Equations 10.2 and 10.3 for the allowable compression (gravity loading) and tension (uplift) capacities of wood piles for varying embedments, pile diameters, and installation methods. The table also illustrates the effect of scour around the pile on the allowable compression and tension loads. Scour (and erosion) reduces pile embedment and therefore pile capacity. For this table, a scour depth of twice the pile diameter (2d) with no generalized erosion is considered. COASTAL CONSTRUCTION MANUAL 10-15 10 DESIGNING THE FOUNDATION Volume II 10-16 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 The purpose of Table 10-7 is to illustrate the effects of varying diameters, depths of embedment, and installation methods on allowable capacities. See Section 10.5.4 for information of installation methods. Example calculations used to determine the values in Table 10-7 are used in Example 10.1. The values in Table 10-7 are not intended to be used for design purposes. COASTAL CONSTRUCTION MANUAL 10-17 10 DESIGNING THE FOUNDATION Volume II Table 10-7. Allowable Compression and Tension of Wood Piles Based on Varying Diameters, Embedments, and Installation Methods Driven 11,698 9,406 3,804 2,857 Jetted 7,894 6,548 1,902 1,429 Augered 6,990 5,545 2,536 1,905 Driven 18,416 15,560 6,763 5,478 Jetted 11,652 10,081 3,382 2,739 Augered 11,292 9,453 4,509 3,652 Driven 9,004 7,482 3,170 2,505 Jetted 5,834 4,977 1,585 1,252 Augered 5,470 4,497 2,114 1,670 d= diameter D = depth of embedment 10.5.3 Lateral Capacity of Piles The lateral capacity of piles is dictated by the piles and the pile/soil interface. The ability of the pile to resist lateral loads depends on the pile size and material, the soil properties, and on presence or absence of pile bracing. One of the critical aspects of pile design is the distance between the lateral load application point and the point of fixity of the pile. That distance constitutes a moment arm and governs how much bending moment develops when a pile is exposed to lateral loads. For a foundation to perform adequately, that moment must be resisted by the pile without pile failure. Equation 10.4 determines the distance between the point where the lateral load is applied and the point of fixity for an unbraced pile. Note that in Equation 10.4, "d" is the depth below grade of the point of fixity, not the diameter of the pile. Also, see Figure 10-4 for the deflected shape of a laterally loaded pile. Table 10-8 lists recommended values for nh, modulus of subgrade reaction, for a variety of soils (Bowles 1996). For wood pilings, the depths to points of fixity range from approximately 1 foot in stiff soils to approximately 5 feet in soft soils. The ability of site soils to resist lateral loads is a function of the soil characteristics, their location on the site, and their compressive strength. Chapter 7 of the Timber Pile Design and Construction Manual (Collin 2002) contains methods of determining the lateral resistance of timber piles for both fixed pile head conditions (i.e., piles used with grade beams or pile caps) and free pile head conditions (i.e., piles free to rotate at their top). The manual also contains methods of approximating lateral capacity and predicting pile capacity when detailed soils data are known. 10-18 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Figure 10-4. Deflected pile shape for an unbraced pile COASTAL CONSTRUCTION MANUAL 10-19 10 DESIGNING THE FOUNDATION Volume II 10.5.4 Pile Installation Methods for installing piles include driving, augering, and jetting. A combination of methods may also be used. For example, piles may be placed in augered holes and then driven to their final depth. Combining installation methods can increase the achievable embedment depth. With increased depths, a pile's resistance to lateral and vertical loads can be increased, and its vulnerability to scour and erosion will be reduced. Driving involves hitting the top of the pile with a pile driver or hammer until the pile reaches the desired depth or it is driven to refusal. Piles can be driven with vibratory hammers. Vibratory hammers generate vertical oscillating movements that reduce the soil stress against the pile and which makes the piles easier to drive. Ultimate load resistance is achieved by a combination of end bearing of the pile and frictional resistance between the pile and the soil. A record of the blow counts from the pile driver can be used with a number of empirical equations to determine capacity. Augering involves placing the pile into a pre -drilled hole typically made with an auger. The augured hole can be the full diameter of the pile or a smaller diameter than the pile. Pre -drilling is completed to a predetermined depth, which often is adjusted for the soils found on the site. After placing the pile into the pre -drilled hole, the pile is then driven to its final desired depth or until it reaches refusal. Jetting is similar to augering but instead of using a soils auger, jetting involves using a jet of water (or air) to remove soils beneath and around the pile. Like augering, jetting is used in conjunction with pile driving. Both augering and jetting remove natural, undisturbed soil along the side of the pile. Load resistance for both of these methods is achieved by a combination of end bearing and frictional resistance, although the frictional resistance is much less than that provided by driven piles. Figure 10-5 illustrates the three pile installation methods. Table 10-9 lists advantages and special considerations for each method. Figure 10-5. Pier installation methods 10-20 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Table 10-9. Advantages and Special Considerations of Pile Installation Methods • Well -suited for friction piles Driving • Common construction practice • Pile capacity can be determined empirically • Economical • Minimal driving vibration to adjacent structures Augering • Well -suited for end bearing • Visual inspection of some soil stratum possible • Convenient for low headroom situations • Easier to maintain column lines • Minimal driving vibration to adjacent structures Jetting . Well -suited for end bearing piles • Easier to maintain column lines KHc-= earth pressure compression coefficient KHT= earth pressure tension coefficient • Requires subsurface investigation • May be difficult to reach terminating soil strata if piles are only driven • Difficult to maintain plumb during driving and thus maintain column lines • Requires subsurface investigation • Not suitable for highly compressed material • Disturbs soil adjacent to pile, thus reducing earth pressure coefficients KHcandKHr.to 40 percent of that driven for piles • Capacity must be determined by engineering judgment or load test • Requires subsurface investigation • Disturbs soil adjacent to pile, thus reducing earth pressure coefficients KHcandKHr.to 40 percent of that driven for piles • Capacity must be determined by engineering judgment or load test 10.5.5 Scour and Erosion Effects on Pile Foundations Coastal homes are often exposed to scour and erosion, and because moving floodwaters cause both scour and erosion, it is rare for an event to produce one and not the other. As Figure 10-6 illustrates, scour and erosion have a cumulative effect on pile foundations. They both reduce piling embedment. Figure 10-6. Scour and erosion effects on piling embedment COASTAL CONSTRUCTION MANUAL 10-21 10 DESIGNING THE FOUNDATION Volume II A properly designed pile foundation must include a consideration of the effects of scour and erosion on the foundation system. Scour washes away soils around the piling, reducing pile embedment, and increases stresses within the pile when the pile is loaded. The reduced embedment can cause the foundation to fail at the pile/soil interface. The increased stresses can cause the pile itself to fracture and fail. Erosion is even more damaging. In addition to reducing pile embedment depths and increasing stresses on piles, erosion increases the flood forces the foundation must resist by increasing the stillwater depth at the foundation that the flood produces. Pile foundations that are adequate to resist flood and wind forces without being undermined by scour and erosion can fail when exposed to even minor amounts of scour and erosion. An example analysis of the effects of scour and erosion on a foundation is provided in Erosion, Scour, and Foundation Design (FEMA 2009a), published as part of Hurricane Ike Recovery Advisories and available at http://www.fema.gov/library/viewRecord.do?id=3539. The structure in the example is a two-story house with 10-foot story heights and a 32-foot by 32-foot foundation. The house is away from the shoreline and elevated 8 feet above grade on 25 square timber piles spaced 8 feet apart. Soils are medium dense sands. The house is subjected to a design wind event with a 130-mph (3-second gust) wind speed and a 4-foot stillwater depth above the uneroded grade, with storm surge and broken waves passing under the elevated building. Lateral wind and flood loads were calculated in accordance with ASCE 7-05. Although the wind loads in ASCE 7-10 vary from ASCE 7-05 somewhat, the results of the analyses do not change significantly. Piles were analyzed under lateral wind and flood loads only; dead, live, and wind uplift loads were neglected. If the neglected loads are included, deeper pile embedment and possibly larger piles than the results of the analysis indicated may be needed. Three timber pile sizes (8-inch square, 10-inch square, and 12-inch square) were evaluated using pre -storm embedment depths of 10 feet, 15 feet, and 20 feet and five erosion and scour conditions (erosion = 0 or 1 foot; scour = 2.0 times the pile diameter to 4.0 times the pile diameter). The results of the analysis are shown in Table 10-10. A shaded cell indicates that the combination of pile size, pre -storm embedment, and erosion/scour does not provide the bending resistance and/or embedment required to resist lateral loads. The reason for foundation failure is indicated in each shaded cell ("P" for failure due to bending and overstress within the pile and "E" for an embedment failure from the pile/soil interaction). "OK" indicates that the bending and foundation embedment criteria are both satisfied by the particular pile size/pile embedment/erosion-scour combination. The key points from the example analysis are as follows: Scour and erosion can cause pile foundations to fail and must be considered when designing pile foundations. Failures can result from either overloading the pile itself or from overloading at the pile/soil interface. Increasing a pile's embedment depth does not offset a pile with a cross section that is too small or pile material that is too weak. Increasing a pile's cross section (or its material strength) does not compensate for inadequate pile embedment. 10-22 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Table 10-10. Example Analysis of the Effects of Scour and Erosion on a Foundation Erosion = 0, Scour = 0 Erosion = 1 foot, Scour = 2.Oa Erosion = 1 foot, Scour = 2.5a Erosion = 1 foot, Scour = 3.Oa Erosion = 1 foot, Scour = 4.Oa Erosion = 0, Scour = 0 Erosion = 1 foot, Scour = 2.Oa Erosion = 1 foot, Scour = 2.5a Erosion = 1 foot, Scour = 3.Oa Erosion = 1 foot, Scour = 4.Oa Erosion = O, Scour = 0 Erosion = 1 foot, Scour = 2.Oa Erosion = 1 foot, Scour = 2.5a Erosion = 1 foot, Scour = 3.Oa Erosion = 1 foot, Scour = 4.Oa No OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK OK Two-story house supported on square timber piles and located away from the shoreline, storm surge and broken waves passing under the building, 130-mph wind zone, soil = medium dense sand. a = pile diameter E = foundation fails to meet embedment requirements OK = bending and foundation embedment criteria are both satisfied by the particular pile size/pile embedment/erosion-scour combination P = foundation fails to meet bending 10.5.6 Grade Beams for Pile Foundations Piles can be used with or without grade beams or pile caps. Grade beams create resistance to rotation (also called "fixity") at the top of the piles and provide a method to accommodate misalignment in piling placement. When used with grade beams, the piles and foundation elements above the grade beams work together to elevate the structure, provide vertical and lateral support for the elevated home, and transfer loads imposed on the elevated home and the foundation to the ground below. Pile and grade beam foundations should be designed and constructed so that the grade beams act only to provide fixity to the foundation system and not to support the lowest elevated floor. If grade beams support the lowest elevated floor of the home, they become the lowest horizontal structural member and significantly higher flood insurance premiums would result. Grade beams must also be designed to span between adjacent piles, and the piles must be capable of resisting both the weight of the grade beams when undermined by erosion and scour and the loads imposed on them by forces acting on the structure. COASTAL CONSTRUCTION MANUAL 10-23 10 DESIGNING THE FOUNDATION Volume II Pile foundations with grade beams must be constructed with adequate strength to resist all lateral and vertical loads. Failures during Hurricane Katrina often resulted from inadequate connections between the columns and footings or grade beams below (see Figure 10-7). If grade beams are used with wood piles, the potential for rot must be considered when designing the connection between the grade beam and the pile. The connection must not encourage water retention. The maximum bending moment in the piles occurs at the grade beams, and decay caused by water retention at critical points in the piles could induce failure under high -wind or flood forces. While offering some advantages, grade beams can become exposed by moving floodwaters if they are not placed deeply enough. Once exposed, the grade beams create large horizontal obstructions in the flood path that significantly increase scour. Extensive scour was observed after Hurricane Ike in 2008 around scores of homes constructed with grade beams (see Figure 10-8). Although not possible for all piling materials, foundations should be constructed without grade beams whenever possible. For treated timber piles, this can limit elevations to approximately 8 feet above grade. The actual limit depends greatly on flood forces, number of piles, availability of piles long enough to be driven to the required depth and extend above grade enough to adequately elevate the home, and wind speed and geometry of the elevated structure. For steel and concrete piles, foundations without grade beams are practical in many instances, even for taller foundations. Without grade beams to account for pile placement, additional attention is needed for piling alignment, and soils test are needed for design because pile performance depends on the soils present, and presumptive piling capacities may not adequately predict pile performance. Figure 10-7. Column connection failure, Hurricane Katrina (Belle Fontaine Point, Jackson County, MS, 2005) 10-24 COASTAL CONSTRUCTION MANUAL Volume II Figure 10-8. Scour around grade beam, Hurricane Ike (Galveston Island, TX, 2008) 10.6 Open/Deep Foundations DESIGNING THE FOUNDATION 11 In this section, some of the more common types of open/deep foundation styles are discussed. Treated timber pile foundations are discussed in Section 10.6.1, and other types of open/deep pile foundations are discussed in Section 10.6.2. 10.6.1 Treated Timber Pile Foundations In many coastal areas, treated timber piles are the most common type of an open/deep style foundation. Timber piles are the first choice of many builders because they are relatively inexpensive, readily available, and relatively easy to install. The driven timber pile system (see Figure 10-9) is suitable for moderate elevations. Home elevations greater than 10 feet may not be practical because of pile length availability, the pile strength required to resist lateral forces (particularly when considering erosion and scour), and the pile embedment required to resist lateral loads after being undermined by scour and erosion. When used without grade beams, timber piles typically extend from the pile tip to the lowest floor of the elevated structure. With timber piles and wood floor framing, the connection of the elevated structure to the piling is essentially a pinned connection because moment resisting connections in wood framing are difficult to achieve. Pinned connections do not provide fixity and require stronger piles to resist the same loads as piles that benefit from moment resisting connections at their tops. Improved performance can be achieved if the piles extend beyond the lowest floor to the roof (or an upper floor level). Doing so provides resistance to rotation where the pile passes through the first floor. This not only reduces stresses within the piles but also increases the stiffness of the pile foundation and reduces movement under lateral forces. Extending piles in this fashion improves survivability of the building. The timber pile system is vulnerable to flood -borne debris. During a hurricane event, individual piles can be damaged or destroyed by large, floating debris. Two ways of reducing this vulnerability are (1) using piles with diameters that are larger than those called for in the foundation design and (2) using more piles and continuous beams that can redistribute loads around a damaged pile. Using more piles and continuous beams increases structural redundancy and can improve building performance. COASTAL CONSTRUCTION MANUAL 10-25 10 DESIGNING THE FOUNDATION Volume II 10-26 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Although connections play an integral role in the design of structures, they are typically regarded as the weakest link. Guidance for typical wood -pile to wood -girder connections can be found in Fact Sheet 3.3, Wood Pile to Beam Connections, in FEMA P-499. 10.6.1.2 Pile Bracing When timber piles with a sufficiently large cross section are not available, timber piles may require bracing to resist lateral loads. Bracing increases the lateral stiffness of a pile foundation system so that less sway is felt under normal service loads. Bracing also lowers the location where lateral forces are applied to individual piles and reduces bending stresses in the pile. When bracing is used, the forces from moving floodwaters and from flood -borne debris that impacts the braces should be considered. J NOTE Fact Sheet 3.2, Pile Installation, in FEMA P-499 recommends that pile bracing be used only for reducing the structure's sway and vibration for comfort. In other words, bracing should be used to address serviceability issues and not strength issues. The foundation design should consider the piles as being unbraced as the condition that may occur when floating debris removes or damages the bracing. If the pile foundation is not able to provide the desired strength performance without bracing, the designer should consider increasing the pile size. Diagonal Bracing Bracing is typically provided by diagonal bracing or knee bracing. Diagonal bracing is more effective from a structural standpoint, but because diagonal bracing extends lower into floodwaters, it is more likely to be damaged by flood -borne debris. It can also trap flood -borne debris, and trapped flood -borne debris increases flood forces on the foundation. Knee bracing does not extend as deeply into floodwaters as cross bracing and is less likely to be affected by flood -borne debris but is less effective at reducing stresses in the pile and also typically requires much stronger connections to achieve similar structural performance as full-length cross bracing. Diagonal bracing often consists of dimensional lumber that is nailed or bolted to the wood piles. Steel rod bracing and wire rope (cable) bracing can also be used. Steel rod bracing and cable bracing have the benefit of being able to use tensioning devices, such as turnbuckles, which allow the tension of the bracing to be maintained. Cable bracing has an additional benefit in that the cables can be wrapped around pilings without having to rely on bolted connections, and wrapped connections can transfer greater loads than bolted connections. Figure 10-10 shows an example of diagonal bracing using dimensional lumber. Diagonal braces tend to be slender, and slender braces are vulnerable to compression buckling. Most bracing is therefore considered tension -only bracing. Because wind and flood loads can act in opposite directions, tension -only bracing must be installed in pairs. One set of braces resists loads from one direction, and the second set resists loads from the opposite direction. Figure 10-11 shows how tension -only bracing pairs resist lateral loads on a home. The placement of the lower bolted connection of the diagonal brace to the pile requires some judgment. If the connection is too far above grade, the pile length below the connection is not braced and the overall foundation system is less strong and stiff. COASTAL CONSTRUCTION MANUAL 10-27 10 DESIGNING THE FOUNDATION Volume II Figure 10-10. Diagonal bracing using dimensional lumber Figure 10-11. Diagonal bracing schematic 10-28 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 COASTAL CONSTRUCTION MANUAL 10-29 10 DESIGNING THE FOUNDATION Volume II For timber piles, if the connection is too close to grade, the bolt hole #J is more likely to be flooded and subject to decay or termite infestation, NOTE which can weaken the pile at a vulnerable location. All bolt holes should be treated with preservative after drilling and prior to bolt placement. Bolt holes in timber piles should be field -treated (see Chapter 11). Knee Bracing Knee braces involve installing short diagonal braces between the upper portions of the pilings and the floor system of the elevated structure (see Figure 10-12). The braces increase the stiffness of an elevated pile foundation and can contribute to resisting lateral forces. Although knee braces do not stiffen a foundation as much as diagonal bracing, they offer some advantages over diagonal braces. For example, knee braces present less obstruction to waves and debris, are shorter and less prone to compression buckling than diagonal braces, and may be designed for both tension and compression loads. The entire load path into and through the knee brace must be designed. The connections at each end of each knee brace must have sufficient capacity to handle both tension and compression and to resist axial loads in the brace. The brace itself must have sufficient cross -sectional area to resist compression and tensile loads. Figure 10-12. Knee bracing 10-30 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 The feasibility of knee bracing is often governed by the ability to construct strong connections in the braces that connect the wood piles to the elevated structure. 10.6.1.3 Timber Pile Treatment Although timber piles are chemically treated to resist rot and damage from insects, they can be vulnerable to wood -destroying organisms such as fungi and insects if the piles are subject to both wetted and dry conditions. If the piles are constantly submerged, fungal growth and insect colonies cannot be sustained; if only periodically submerged, conditions exist that are sufficient to sustain wood -destroying organisms. Local design professionals familiar with the performance of driven, treated timber piles can help quantify the risk. Grade beams can be constructed at greater depths or alternative pile materials can be selected if damage from wood -destroying organisms is a major concern. Cutting, drilling, and notching treated timber piles disturb portions of the piles that have been treated for rot and insect damage. Because pressure -preservative -treated piles, timbers, and lumber are used for many purposes in coastal construction, the interior, untreated parts of the wood can be exposed to possible decay and infestation. Although treatments applied in the field are much less effective than factory treatments, the potential for decay can be minimized with field treatments. AWPA M4-06 describes field treatment procedures and field cutting restrictions for poles, piles, and sawn lumber. Field application of preservatives should be done in accordance with the instructions on the label, but if instructions are not provided, dip soaking for at least 3 minutes is considered effective. When dip soaking for 3 minutes is impractical, treatment can be accomplished by thoroughly brushing or spraying the exposed area. The preservative is absorbed better at the end of a member or end grains than on the sides or side grains. To safeguard against decay in bored holes, the preservative should be poured into the holes. If the hole passes through a check (such as a shrinkage crack caused by drying), the hole should be brushed; otherwise, the preservative will run into the check instead of saturating the hole. Copper naphthenate is the most widely used preservative for field treatment. Its color (deep green) may be objectionable aesthetically, but the wood can be painted with alkyd paints after extended drying. Zinc naphthenate is a clear alternative to copper naphthenate but is not as effective in preventing insect infestation and should not be painted with latex paints. Tributyltin oxide is available but should not be used in or near marine environments because the leachates are toxic to aquatic organisms. Sodium borate is also available, but it does not readily penetrate dry wood and rapidly leaches out when water is present. Sodium borate is therefore not recommended. Waterborne arsenicals, pentachlorophenol, and creosote are unacceptable for field applications. 10.6.2 Other Open/Deep Pile Foundation Styles Several other styles of pile foundations, in addition to treated timber piles, are used although their use often varies geographically depending on the availability of materials and trained contractors. FEMA P-550 contains foundation designs that use deep, driven steel and treated timber piles and grade beams that support a system of concrete columns. The second edition of FEMA P-550 (FEMA 2006) added a new design for treated timber piles that incorporates elevated reinforced beams constructed on the concrete columns. In the new design, the elevated beams work with the columns and grade beams to create reinforced concrete portal frames that assist in resisting lateral loads. The elevated beams also create a suitable platform COASTAL CONSTRUCTION MANUAL 10-31 10 DESIGNING THE FOUNDATION Volume II that can support a home designed to a prescriptive standard such as Wood Framed Construction Manual for One- and Two -Family Dwellings (AF&PA 2012) or ICC 600-2008. Figure 10-13 shows one of the deep pile foundation systems that uses treated timber piles and grade beams. The steel pipe pile and grade beam foundation system contained in FEMA P-550 is similar but requires fewer piles because the higher presumptive strength of the steel piles compared to the timber piles. Figure 10-14 shows the foundation system added in the Second Edition of FEMA P-550 (FEMA 2009b), which incorporates an elevated concrete beam. Figure 10-13. Section view of a steel pipe pile with concrete column and grade beam foundation type DEVELOPED FROM FEMA P-550, CASE B 10-32 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION Figure 10-14. Section view of a foundation constructed with reinforced concrete beams and columns to create portal frames SOURCE: ADAPTED FROM FEMA P-550, SECOND EDITION, CASE H COASTAL CONSTRUCTION MANUAL 10-33 10 DESIGNING THE FOUNDATION Volume II 10.7 Open/Shallow Foundations Open/shallow foundations are recommended for areas that are exposed to moving floodwaters and moderate wave actions but are not exposed to scour and erosion, which can undermine shallow footings. Open/shallow foundations are recommended for some riverine areas where an open foundation style is desirable and for buildings in Coastal A Zone where scour and erosion is limited. In Coastal A Zones where the predicted scour and erosion depths extend below the achievable depth of shallow footings and in Coastal A Zone where scour and erosion potential is unknown or cannot be accurately predicted, open/deep foundations should be installed. FEMA P-550 contains designs for open shallow foundations. The foundations are resistant to moving floodwaters and wave action, but because they are founded on shallow soils, they can be vulnerable to scour and erosion. Figure 10-15. Profile of an open/ shallow foundation SOURCE: ADAPTED FROM FEMA P-550. CASE D 10-34 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 The FEMA P-550 designs make use of a rigid mat to resist lateral forces and overturning moment. Frictional resistance between the grade beams and the supporting soils resist lateral loads. The weight of the foundation and the elevated structure resist uplift forces. Because the foundation lacks the uplift resistance provided by piles, foundation elements often need to be relatively large to provide sufficient dead load to resist uplift, particularly when they are submerged. Grade beams need to be continuous because, as is shown in Section 10.9, discrete foundations that have sufficient capacity to resist lateral and uplift forces without overturning are difficult to design. FEMA P-550 contains two types of open/shallow foundations. The foundation type shown in Figure 10-15 uses a matrix of grade beams and concrete columns to elevate the building. The grade beam shown in Figure 10-15 should not be used as structural support for a concrete slab that is below an elevated building in Zone V. If the grade beam is used to support the slab, the slab will be considered the lowest floor of the building, which will lead to the insurance ramifications described in Section 10.6.2. When used to support wood framing, the columns of open/shallow foundations are typically designed as cantilevered beam/columns subjected to lateral forces, gravity forces and uplift forces from the elevated structure and flood forces on the foundation columns. Because of the inherent difficulty of creating moment connections with wood framing, the connections between the top of the columns and the bottom of the elevated structure are typically considered pinned. Maximum shear and moment occurs at the bottom of the columns, and proper reinforcement and detailing is needed in these areas. Also, because there are typically construction joints between the tops of the grade beams and the bases of the columns where salt -laden water can seep into the joints, special detailing is needed to prevent corrosion. Designing an open/shallow foundation that uses concrete columns and elevated concrete beams can create a frame action that increases the foundation's ability to resist lateral loads. This design accomplishes two things. First, the frame action reduces the size of the columns and in turn reduces flood loads on them, and second, when properly designed, the elevated beams act like the tops of a perimeter foundation wall. Homes constructed to one of the designs contained in prescriptive codes can be attached to the elevated concrete beams with minimal custom design. Unlike deep, driven -pile foundations, both types of open/shallow foundations can be undermined by erosion and scour. Neither foundation type should be used where erosion or scour is anticipated to expose the grade beam. 10.8 Closed/Shallow Foundations Closed/shallow foundations are similar to the foundations that are used in non -coastal areas where flood forces are limited to slowly rising floods with no wave action and only limited flood velocities. In those areas, conventional foundation designs, many of which are included for residential construction in prescriptive codes and standards such as the 2012 IRC and ICC 600-2008, may be used. However, these codes and standards do not take into account forces from moving floodwaters and short breaking waves that can exist inland of Coastal A Zones. Therefore, caution should be used when using prescribed foundation designs in areas exposed to moving floodwaters and breaking waves. FEMA P-550 contains two foundation designs for closed/shallow foundations: a stem wall foundation and a crawlspace foundation. Crawlspace foundation walls in SFHAs must be equipped with flood vents COASTAL CONSTRUCTION MANUAL 10-35 10 DESIGNING THE FOUNDATION Volume II to equalize hydrostatic pressures on either side of the wall. See FEMA Technical Bulletin 1, Openings in Foundation Walls and Walls of Enclosures (FEMA 2008c). However, the flood vents do not significantly reduce hydrodynamic loads or breaking wave loads, and even with flood vents, flood forces in Coastal A Zones can damage or destroy these foundation styles. Both closed/shallow foundations contained in FEMA P-550 are similar to foundations found in prescriptive codes but contain the additional reinforcement requirement to resist moving floodwaters and short (approximately 1.5-foot) breaking waves. Figure 10-16 shows the stem wall foundation design in FEMA P-550. Figure 10-16. Stem wall foundation design SOURCE: ADAPTED FROM FEMA P-550, CASE F 10-36 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Figure 10-17. Performance comparison of pier foundations: piers on discrete footings (foreground) failed by rotating and overturning while piers on more substantial footings (in this case a concrete mat) survived Hurricane Katrina (Pass Christian, MS, 2005) only when wind and flood loads are relatively low. Piers placed on continuous concrete grade beams or concrete footings provide much greater resistance to lateral loads and are much less prone to failure. Footings and grade beams must be reinforced to resist the moment forces that develop at the base of the piers from the lateral loads on the foundation and the elevated home. Like other open/shallow foundations, pier foundations are appropriate only where there is limited potential for erosion or scour. The maximum estimated depth for long- and short-term erosion and localized scour should not extend below the bottom of the footing or grade beam. In addition, adequate resistance to lateral loads is often difficult to achieve for common pier sizes on continuous footings. Even for relatively small lateral loads, larger piers designed as shear walls are often necessary to provide adequate resistance. The following section provides an analysis of a pier foundation on discrete concrete footings. The analysis shows that discrete pier footings that must resist lateral loads are typically not practical. 10.9.1 Pier Foundation Design Examples The following three examples discuss pier foundation design. Example 10.3 provides an analysis of the pier footing under gravity loads only (see Figure 10-18) and the footing size required to ensure that the allowable soil bearing pressure is not exceeded. Example 10.4 provides a consideration of uplift forces that many footings (see Figure 10-19) must resist to prevent failure during a design wind event. The analysis in Example 10.4 assumes that other foundation elements are in place to resist the lateral loads that must accompany uplift forces. Example 10.5 adds lateral loads to the pier and footing (see Figure 10-20) to model buildings that lack continuous foundation walls or other lateral load resisting features. The lateral loads can result from wind, seismic or moving floodwaters. COASTAL CONSTRUCTION MANUAL 10-37 Volume II DESIGNING THE FOUNDATION 11 Figure 10-17. Performance comparison of pier foundations: piers on discrete footings (foreground) failed by rotating and overturning while piers on more substantial footings (in this case a concrete mat) survived Hurricane Katrina (Pass Christian, MS, 2005) only when wind and flood loads are relatively low. Piers placed on continuous concrete grade beams or concrete footings provide much greater resistance to lateral loads and are much less prone to failure. Footings and grade beams must be reinforced to resist the moment forces that develop at the base of the piers from the lateral loads on the foundation and the elevated home. Like other open/shallow foundations, pier foundations are appropriate only where there is limited potential for erosion or scour. The maximum estimated depth for long- and short-term erosion and localized scour should not extend below the bottom of the footing or grade beam. In addition, adequate resistance to lateral loads is often difficult to achieve for common pier sizes on continuous footings. Even for relatively small lateral loads, larger piers designed as shear walls are often necessary to provide adequate resistance. The following section provides an analysis of a pier foundation on discrete concrete footings. The analysis shows that discrete pier footings that must resist lateral loads are typically not practical. 10.9.1 Pier Foundation Design Examples The following three examples discuss pier foundation design. Example 10.3 provides an analysis of the pier footing under gravity loads only (see Figure 10-18) and the footing size required to ensure that the allowable soil bearing pressure is not exceeded. Example 10.4 provides a consideration of uplift forces that many footings (see Figure 10-19) must resist to prevent failure during a design wind event. The analysis in Example 10.4 assumes that other foundation elements are in place to resist the lateral loads that must accompany uplift forces. Example 10.5 adds lateral loads to the pier and footing (see Figure 10-20) to model buildings that lack continuous foundation walls or other lateral load resisting features. The lateral loads can result from wind, seismic or moving floodwaters. COASTAL CONSTRUCTION MANUAL 10-37 10 DESIGNING THE FOUNDATION Volume II Figure 10-18. Pier foundation and spread footing under gravity loading 10-38 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 Figure 10-20. Pier foundation and spread footing exposed to uplift and lateral forces COASTAL CONSTRUCTION MANUAL 10-39 10 DESIGNING THE FOUNDATION Volume II 10-40 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 COASTAL CONSTRUCTION MANUAL 10-41 10 DESIGNING THE FOUNDATION Volume II 10-42 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 At some value of lateral load or eccentricity, the compressive stresses on one side of the footing go to zero. Because there are no tensile connections between the footing and the supporting soils, the footing becomes unstable at that point and can fail by rotation. Failure can also occur when the bearing strength on the other side of the footing is exceeded. Equation 10.6 relates soil bearing pressure to axial load, lateral load, and footing dimension. For a given axial load, lateral load, and footing dimension, the equation can be used to solve for the maximum and minimum soil bearing pressures, q on each edge of the footing. The maximum can be compared to the allowable soil bearing pressure to determine whether the soils will be overstressed. The minimum stress determines whether instability occurs. Both maximum and minimum stresses are used to determine footing size. Alternatively, for a given allowable soil bearing pressure, axial load, and lateral load, the equation can be solved for the minimum footing size. COASTAL CONSTRUCTION MANUAL 10-43 10 DESIGNING THE FOUNDATION Volume II 10-44 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION 11 10.9.2 Pier Foundation Summary These analyses indicate that piers with discrete footings are practical to construct when they are required to resist gravity loads only but are not practical when they must resist uplift forces or lateral loads. Although prescriptive designs for pier foundations are available in some codes and standards, users of the codes and standards should ensure that the designs take into account all of the loads the foundations must resist. Prescriptive designs should only be used to resist lateral and uplift loads after they have been confirmed to be adequate. Constructing piers on continuous footings makes pier foundations much more resistant to coastal hazards, but prescriptive designs for piers on continuous footings are not present in widely adopted codes such as the IRC and IBC. Until prescriptive designs using piers are developed, these styles of foundations should be engineered. Continuous footings are discussed in Section 11.1.5 of FEMA 549, Hurricane Katrina in the Gulf Coast (FEMA 2006), and continuous footing designs that can be used for the basis of engineered foundations are contained in FEMA P-550. COASTAL CONSTRUCTION MANUAL 10-45 10 DESIGNING THE FOUNDATION Volume II 10.10 References ACI (American Concrete Institute). 2008. Building Code Requirements for Structural Concrete and Commentary, ACI 318-08. ACI ASCE (American Society of Civil Engineer / TMS (The Masonry Society). 2008. Building Code Requirements and Specifications for Masonry Structures and Related Commentaries, ACI 530-08. AF&PA (American Forest & Paper Association). 2012. Wood Frame Construction Manual for One- and Two -Family Dwellings. Washington, D.C. ANSI (American National Standards Institute) / AF&PA. 2005. National Design Specification for Wood Construction. ASTM (American Society for Testing and Materials). 2005. Standard Specification for Round Timber Piles, ASTM D25-99. ASTM. 2007. Standard Specification for Hot -Formed Welded and Seamless Carbon Steel Structural Tubing. ASTM A501-07. ASTM. 2008. Standard Specification for Carbon Structural Steel. ASTM A36/A36M-08. ASTM. 2009. Standard Practice for Description and Identification of Soils (Visual -Manual Procedure). ASTM D2488-09a. ASTM. 2010a. Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). ASTM D2487-10. ASTM. 2010b. Standard Specification for Cold -Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes. ASTM A500-10. ASTM. 2010c. Standard Specification for Pipe, Steel, Black and Hot -Dipped, Zinc -Coated, Welded and Seamless. ASTM A53/A53M-10. ASTM. 2010d. Standard Specification for Welded and Seamless Steel Pipe Piles. ASTM 252-10. ASCE (American Society of Civil Engineers). 2010 Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. AWPA (American Wood Protection Association). 2006. Standard for the Care of Preservative -Treated Wood Products, AWPA M4-06. Bowles, J.E. 1996. Foundation Analysis and Design, 5th Ed. New York: McGraw-Hill. Collin, J.G. 2002. Timber Pile Design and Construction Manual. The Timber Piling Council of the American Wood Preservers Institute. FEMA (Federal Emergency Management Agency). 2006. Recommended Residential Construction for the Gulf Coast. FEMA P-550. FEMA. 2008a. Flood Damage -Resistant Materials Requirements. Technical Bulletin 2. 10-46 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE FOUNDATION J FEMA. 2008b. Free -of -Obstruction Requirements. Technical Bulletin 5. FEMA. 2008c. Openings in Foundation Walls and Walls of Enclosures. Technical Bulletin 1. FEMA. 2009a. Erosion, Scour, and Foundation Design. Available at http://www.fema.gov/library/ viewRecord.do?id=3539. Accessed on June 12, 2011. FEMA. 2009b. Recommended Residential Construction for Coastal Areas: Building on Strong and Safe Foundations. FEMA P-550, Second Edition. FEMA. 2010. Home Builder's Guide to Coastal Construction Technical Fact Sheet Series, FEMA P-499. ICC (International Code Council). 2008. Standard for Residential Construction in High -Wind Regions, ICC 600-2008. ICC: Country Club Hills, IL. ICC. 2011a. International Building Code. 2012 IBC. ICC: Country Club Hills, IL. ICC. 2011b. International Residential Code for One and Two Family Residences. 2012 IRC. ICC: Country Club Hills, IL. TMS (The Masonry Society). 2007. Masonry Designers' Guide, Fifth Edition, MDG-5. USDN (U.S. Department of the Navy). 1982. Foundation and Earth Structures, Design Manual 7.2. COASTAL CONSTRUCTION MANUAL 10-47 I i•I esi iming the Building Envelope This chapter provides guidance on the design of the building envelope in the coastal environment.) The building envelope comprises exterior doors, windows, skylights, exterior wall coverings, soffits, roof systems, and attic vents. In buildings elevated on open foundations, the floor is also considered a part of the envelope. High wind is the predominant natural hazard in the coastal environment that can cause damage to the building envelope. Other natural hazards also exist in some localities. These CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/rebuild/ mat/fema55.shtm). may include wind -driven rain, salt -laden air, seismic events, hail, and wildfire. The vulnerabilities of the building envelope to these hazards are discussed in this chapter, and recommendations on mitigating them are provided. Good structural system performance is critical to avoiding injury and minimizing damage to a building and its contents during natural hazard events but does not ensure occupant or building protection. Good 1 The guidance in this chapter is based on a literature review and field investigations of a large number of houses that were struck by hurricanes, tornadoes, or straight-line winds. Some of the houses were exposed to extremely high wind speeds while others experienced moderately high wind speeds. Notable investigations include Hurricane Hugo (South Carolina, 1989) (McDonald and Smith, 1990); Hurricane Andrew (Florida, 1992) (FEMA FIA 22; Smith, 1994); Hurricane Iniki (Hawaii, 1992) (FEMA FIA 23); Hurricane Marilyn (U.S. Virgin Islands, 1995) (FEMA unpublished); Typhoon Paka (Guam, 1997) (FEMA-1193-DR-GU); Hurricane Georges (Puerto Rico, 1998) (FEMA 339); Hurricane Charley (Florida, 2004) (FEMA 488); Hurricane Ivan (Alabama and Florida, 2004) (FEMA 489); Hurricane Katrina (Louisiana and Mississippi, 2005) (FEMA 549); and Hurricane Ike (Texas, 2008) (FEMA P-757). COASTAL CONSTRUCTION MANUAL 11-1 11 DESIGNING THE BUILDING ENVELOPE Volume II performance of the building envelope is also necessary. Good building envelope performance is critical for buildings exposed to high winds and wildfire. Good performance depends on good design, materials, installation, maintenance, and repair. A significant shortcoming in any of these five elements could jeopardize the performance of the building. Good design, however, is the key element to achieving good performance. Good design can compensate to some extent for inadequacies in the other elements, but the other elements frequently cannot compensate for inadequacies in design. The predominant cause of damage to buildings and their contents during high -wind events has been shown to be breaching of the building envelope, as shown in Figure 11-1, and subsequent water infiltration. Breaching includes catastrophic failure (e.g., loss of the roof covering or windows) and is often followed by wind -driven water infiltration through small openings at doors, windows, and walls. The loss of roof and wall coverings and soffits on the house in Figure 11-1 resulted in significant interior water damage. Recommendations for avoiding breaching are provided in this chapter. For buildings that are in a Special Wind Region (see Figure 3-7) or in an area where the basic (design) wind speed is greater than 115 mph,2 it is particularly important to consider the building envelope design and construction recommendations in this chapter in order to avoid wind and wind -driven water damage. In wind-borne debris regions (as defined in ASCE 7), building envelope elements from damaged buildings are often the predominant source of wind-borne debris. The wall shown in Figure 11-2 has numerous wind- borne debris scars. Asphalt shingles from nearby residences were the primary source of debris. Following the design and construction recommendations in this chapter will minimize the generation of wind-borne debris from residences. Figure 11-1. Good structural system performance but the loss of shingles, underlayment, siding, housewrap, and soffits resulted in significant interior water damage. Estimated wind speed: 125 mph.3 Hurricane Katrina (Louisiana, 2005) Pip %E left 2 The 115-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05, or an earlier version is used, the equivalent wind speed trigger is 90 mph. 3 The estimated wind speeds given in this chapter are for a 3-second gust at a 33-foot elevation for Exposure C (as defined in ASCE 7).Most of the buildings for which estimated speeds are given in this chapter are located in Exposure B, and some are in Exposure D. For buildings in Exposure B, the actual wind speed is less than the wind speed for Exposure C conditions. For example, a 130-mph Exposure C speed is equivalent to 110 mph in Exposure B. 11-2 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Building integrity in earthquakes is partly dependent on the performance of the building envelope. Residential building envelopes have historically performed well during seismic events because most envelope elements are relatively lightweight. Exceptions have been inadequately attached heavy elements such as roof tile. This chapter provides recommendations for envelope elements that are susceptible to damage in earthquakes. A building's susceptibility to wildfire depends largely on the presence of nearby vegetation and the characteristics of the building envelope, as illustrated in Figure 11-3. See FEMA P-737, Home Builder's Guide to Construction in Wildfire Zones (FEMA 2008), for guidance on materials and construction techniques to reduce risks associated with wildfire. Figure 11-2. Numerous wind-borne debris scars on the wall of this house and several missing asphalt shingles. Estimated wind speed: 140 to 150 mph. Hurricane Charley (Florida, 2004) Figure 11-3. House that survived a wildfire due in part to fire-resistant walls and roof while surrounding houses were destroyed SOURCE: DECRA ROOFING SYSTEMS, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 11-3 11 DESIGNING THE BUILDING ENVELOPE Volume II This chapter does not address basic design issues or the general good practices that are applicable to residential design. Rather, the chapter builds on the basics by addressing the special design and construction considerations of the building envelope for buildings that are susceptible to natural hazards in the coastal environment. Flooding effects on the building envelope are not addressed because of the assumption that the envelope will not be inundated by floodwater, but envelope resistance to wind -driven rain is addressed. The recommended measures for protection against wind -driven rain should also be adequate to protect against wave spray. 11.1 Floors in Elevated Buildings Sheathing is commonly applied to the underside of the bottom floor framing of a building that is elevated on an open foundation. The sheathing provides the following protection: (1) it protects insulation between joists or trusses from wave spray, (2) it helps minimize corrosion of framing connectors and fasteners, and (3) it protects the floor framing from being knocked out of alignment by flood -borne debris passing under the building. A variety of sheathing materials have been used to sheath the framing, including cement -fiber panels, gypsum board, metal panels, plywood, and vinyl siding. Damage investigations have revealed that plywood offers the most reliable performance in high winds. However, as shown in Figure 11-4, even though plywood has been used, a sufficient number of fasteners are needed to avoid blow -off. Since ASCE 7 does not provide guidance for load determination, professional judgment in specifying the attachment schedule is needed. As a conservative approach, loads can be calculated by using the C&C coefficients for a roof with the slope of 7 degrees or less. However, the roof corner load is likely overly conservative for the underside of elevated floors. Applying the perimeter load to the corner area is likely sufficiently conservative. To achieve good long-term performance, exterior grade plywood attached with stainless steel or hot -dip galvanized nails or screws is recommended (see the corroded nails in Figure 11-4). 11.2 Exterior Doors This section addresses exterior personnel doors and garage doors. The most common problems are entrance of wind- CROSS REFERENCE driven rain and breakage of glass vision panels and sliding glass doors by wind-borne debris. Blow -off of personnel doors is For information regarding garage uncommon but as shown in Figure 11-5, it can occur. Personnel doors in breakaway walls, see door blow -off is typically caused by inadequate attachment of Fact Sheet 8.1, Enclosures and the door frame to the wall. Garage door failure via negative Breakaway Walls, in FEMA P-499, Home Builder's Guide to Coastal (suction) or positive pressure was common before doors with Construction Technical Fact high -wind resistance became available (see Figure 11-6). Sheet Series (FEMA 2010b). Garage door failure is typically caused by the use of door and track assemblies that have insufficient wind resistance or by inadequate attachment of the tracks to nailers or to the wall. Failures such as those shown in Figures 11-5 and 11-6 can result in a substantial increase in internal pressure and can allow entrance of a significant amount of wind -driven rain. 11-4 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-4. Plywood panels on the underside of a house that blew away because of excessive nail spacing. Note the corroded nails (inset). Estimated wind speed: 105 to 115 mph. Hurricane Ivan (Alabama, 2004) Figure 11-5. Sliding glass doors pulled out of their tracks by wind suction. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) COASTAL CONSTRUCTION MANUAL 11-5 11 DESIGNING THE BUILDING ENVELOPE Figure 11-6. Garage door blown from its track as a result of positive pressure. Note the damage to the adhesive -set tiles (left arrow; see Section 11.5.4.1). This house was equipped with roll -up shutters (right arrow; see Section 11.3.1.2). Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) 11.2.1 High Winds Exterior door assemblies (i.e., door, hardware, frame, and frame attachment to the wall) should be designed to resist high winds ®r and wind -driven rain. 11.2.1.1 Loads and Resistance The IBC and IRC require door assemblies to have sufficient strength to resist the positive and negative design wind pressure. Personnel doors are normally specified to comply with AAMA/WDMA/CSA 101/I.S.2/A440, which references ASTM E330 for wind load testing. However, where the basic wind speed is greater than 150 mph,4 it is recommended that design professionals specify that personnel doors comply with wind load testing in accordance with ASTM E1233. ASTM E1233 is the recommended test method in high -wind areas because it is a cyclic test method, whereas ASTM E330 is a static test. The cyclical test method is more representative of loading conditions in high -wind areas than ASTM E330. Design professionals should also specify the attachment of the door frame to the wall (e.g., type, size, spacing, edge distance of frame fasteners). It is recommended that design professionals specify that garage doors comply with wind load testing in accordance with ANSI/ DASMA 108. For garage doors attached to wood nailers, design professionals should also specify the attachment of the nailer to the wall. Volume II CROSS REFERENCE For design guidance on the attachment of door frames, see AAMA TI R-A-14. For a methodology to confirm an anchorage system provides load resistance with an appropriate safety factor to meet project requirements, see AAMA 2501. Both documents are available for purchase from the American Architectural Manufacturers Association (http://aamanet.org). J_ CROSS REFERENCE For design guidance on the attachment of garage door frames, see Technical Data Sheet #161, Connecting Garage Door Jambs to Building Framing (DASMA 2010). Available at http://www.dasma.com/ PubTechData.asp. 4 The 150-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 120 mph. 11-6 COASTAL CONSTRUCTION MANUAL Volume II 11.2.1.2 Wind -Borne Debris DESIGNING THE BUILDING ENVELOPE 1. If a solid door is hit with wind-borne debris, the debris may penetrate the door, but in most cases, the debris opening will not be large enough to result in significant water infiltration or in a substantial increase in internal pressure. Therefore, in wind-borne debris regions, except for glazed vision panels and glass doors, ASCE 7, IBC, and IRC do not require doors to resist wind-borne debris. However, the 2007 FBC requires all exterior doors in the High -Velocity Hurricane Zone (as defined in the FBC) to be tested for wind-borne debris resistance. It is possible for wind-borne debris to cause door latch or hinge failure, resulting in the door being pushed open, an increase in internal pressure, and potentially the entrance of a significant amount ofwind-driven rain. As a conservative measure in wind - CROSS REFERENCE For more information about wind-borne debris and glazing in borne debris regions, solid personnel door assemblies could be doors, see Section 11.3.1.2. specified that resist the test missile load specified in ASTM E1996. Test Missile C is applicable where the basic wind speed is less than 164 mph. Test Missile D is applicable where the basic wind speed is 164 mph or greater.s See Section 11.3.1.2 regarding wind-borne debris testing. If wind-borne debris -resistant garage doors are desired, the designer should specify testing in accordance with ANSI/DASMA 115. 11.2.1.3 Durability For door assemblies to achieve good wind performance, it is necessary to avoid strength degradation caused by corrosion and termites. To avoid corrosion problems with metal doors or frames, anodized aluminum or galvanized doors and frames and stainless steel frame anchors and hardware are recommended for buildings within 3,000 feet of an ocean shoreline (including sounds and back bays). Galvanized steel doors and frames should be painted for additional protection. Fiberglass doors may also be used with wood frames. In areas with severe termite problems, metal door assemblies are recommended. If concrete, masonry, or metal wall construction is used to eliminate termite problems, it is recommended that wood not be specified for blocking or nailers. If wood is specified, see "Material Durability in Coastal Environments," a resource document available on the Residential Coastal Construction Web site, for information on wood treatment methods. 11.2.1.4 Water Infiltration Heavy rain that accompanies high winds can cause significant wind -driven water infiltration. The magnitude of the problem increases with the wind speed. Leakage can occur between the door and its frame, the frame and the wall, and the threshold and the door. When wind speeds approach 150 mph, some leakage should be anticipated because of the high -wind pressures and numerous opportunities for leakage path development. 5 The 164-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 130 mph. 6 The 150-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 120 mph. COASTAL CONSTRUCTION MANUAL 11-7 11 DESIGNING THE BUILDING ENVELOPE Volume II The following elements can minimize infiltration around exterior doors: Vestibule. Adding a vestibule allows both the inner and outer doors to be equipped with weatherstripping. The vestibule can be designed with water-resistant finishes (e.g., tile), and the floor can be equipped with a drain. In addition, installing exterior threshold trench drains can be helpful (openings must be small enough to avoid trapping high -heeled shoes). Trench drains do not eliminate the problem because water can penetrate at door edges. Door swing. Out -swinging doors have weatherstripping on the interior side where it is less susceptible to degradation, which is an advantage to in -swinging doors. Some interlocking weatherstripping assemblies are available for out -swinging doors. Pan flashing. Adding flashing under the door threshold helps prevent penetration of water into the subflooring, a common place for water entry and subsequent wood decay. More information is available in Fact Sheet 6.1, Window and Door Installation, in FEMA P-499, Home Builder's Guide to Coastal Construction Technical Fact Sheet Series (FEMA 2010b). Door/wall integration. Successfully integrating the door frame and wall is a special challenge when designing and installing doors to resist wind -driven rain. More information is available in Fact Sheet 6.1 in FEMA P-499. Weatherstripping. A variety of pre -manufactured weatherstripping elements are available, including drips, door shoes and bottoms, thresholds, and jamb/ head weatherstripping. More information is available in Fact Sheet 6.1 in FEMA P-499. Figure 11-7 shows a pair of doors that successfully resisted winds that were estimated at between 140 and 160 mph. However, as shown in the inset, a gap of about 3/8 inch between the threshold and the bottom of the door allowed a significant amount of water to be blown into the house. The weatherstripping and thresholds shown in Fact Sheet 6.1 in FEMA P-499 can minimize water entry. Figure 11-7. A 3/8-inch gap between the threshold and door (illustrated by the spatula handle), which allowed wind -driven rain to enter the house. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) 11-8 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. 11.3 Windows and Sklylights This section addresses exterior windows (including door vision panels) and skylights. The most common problems in the coastal environment are entrance of wind -driven rain and glazing breakage by wind-borne debris. It is uncommon for windows to be blown -in or blown -out, but it does occur (see Figure 11-8). The type of damage shown in Figure 11-8 is typically caused by inadequate attachment of the window frame to the wall, but occasionally the glazing itself is blown out of the frame. Breakage of glazing from over - pressurization sometimes occurs with windows that were manufactured before windows with high -wind resistance became available. Strong seismic events can also damage windows although it is uncommon in residential construction. Hail can cause significant damage to skylights and occasionally cause window breakage. 11.3.1 High Winds Window and skylight assemblies (i.e., glazing, hardware for operable units, frame, and frame attachment to the wall or roof curb) should be designed to resist high winds and wind -driven rain. In wind-borne debris regions, the assemblies should also be designed to resist wind-borne debris or be equipped with shutters, as discussed below. 11.3.1.1 Loads and Resistance The IBC and IRC require that window and skylight assemblies have sufficient strength to resist the positive and negative design wind pressures. Windows and skylights are normally specified to comply with AAMA/ WDMA/CSA 101/I.S.2/A440, which references ASTM E330 for wind load testing. However, where the basic wind speed is greater than 150 mph,7 it is recommended that design professionals specify that Figure 11-8. Window frame pulled out of the wall because of inadequate window frame attachment. Hurricane Georges (Puerto Rico, 1998) 7 The 150-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 120 mph. COASTAL CONSTRUCTION MANUAL 11-9 11 DESIGNING THE BUILDING ENVELOPE Volume II windows and skylights comply with wind load testing in accordance with ASTM E1233. ASTM E1233 is the recommended test method in high -wind areas because it is a cyclic test method, whereas ASTM E330 is a static test. The cyclical test method is more representative of loading conditions in high -wind areas than ASTM E330. Design professionals should also specify the attachment of the window and skylight frames to the wall and roof curb (e.g., type, size, spacing, edge distance of frame fasteners). Curb attachment to the roof deck should also be specified. For design guidance on the attachment of frames, see AAMA TIR-A14 and AAMA 2501. 11.3.1.2 Wind -Borne Debris When wind-borne debris penetrates most materials, only a small opening results, but when debris penetrates most glazing materials, a very large opening can result. Exterior glazing that is not impact -resistant (such as annealed, heat -strengthened, or tempered glass) or not protected by shutters is extremely susceptible to breaking if struck by debris. Even small, low -momentum debris can easily break glazing that is not protected. Broken windows can allow a substantial amount of water to be blown into a building and the internal air pressure to increase greatly, both of which can damage interior partitions and ceilings. In windstorms other than hurricanes and tornadoes, the probability of a window or skylight being struck by debris is extremely low, but in hurricane -prone regions, the probability is higher. Although the debris issue was recognized decades ago, as illustrated by Figure 11-9, wind-borne debris protection was not incorporated into U.S. codes and standards until the 1990s. In order to minimize interior damage, the IBC and IRC, through ASCE 7, prescribe that exterior glazing in wind-borne debris regions be impact -resistant (i.e., laminated glass or polycarbonate) or protected with an impact -resistant covering (shutters). ASCE 7 refers to ASTM E1996 for missile (debris) loads and to ASTM E1886 for the test method to be used to demonstrate compliance with the ASTM E1996 load criteria. Regardless of whether the glazing is laminated glass, polycarbonate, or protected by shutters, glazing is required to meet the positive and negative design air pressures. Figure 11-9. Very old building with robust shutters constructed of 2x4 lumber, bolted connections, and heavy metal hinges. Hurricane Marilyn (U.S. Virgin Islands, 1995) 11-10 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Wind-borne debris also occurs in the portions of hurricane -prone regions that are inland of wind-borne debris regions, but the quantity and momentum of debris are typically lower outside the wind-borne debris region. As a conservative measure, impact -resistant glazing or shutters could be specified inland of the wind- borne debris region. If the building is located where the basic wind is 125 mph8 or greater and is within a few hundred feet of a building with an aggregate surface roof or other buildings that have limited wind resistance, it is prudent to consider impact -resistant glazing or shutters. With the advent of building codes requiring glazing protection in wind-borne debris regions, a variety of shutter designs have entered the market. Shutters typically have a lower initial cost than laminated glass. However, unless the shutter is permanently anchored to the building (e.g., accordion shutter, roll -up shutter), storage space is needed. Also, when a hurricane is forecast, the shutters need to be deployed. The difficulty of shutter deployment and demobilization on upper -level glazing can be avoided by using motorized shutters, although laminated glass may be a more economical solution. Because hurricane winds can approach from any direction, when debris protection is specified, it is important to specify that all exterior glazing be protected, including glazing that faces open water. At the house shown in Figure 11-10, all of the windows were protected with roll -up shutters except for those in the cupola. One of the cupola windows was broken. Although the window opening was relatively small, a substantial amount of interior water damage likely occurred. Figure 11-10. Unprotected cupola window that was broken. Estimated wind speed: 110 mph. Hurricane Ike f� T (Texas, 2008) - � FE •-r �L � -.� The FBC requires exterior windows and sliding glass doors to have a permanent label or marking, indicating information such as the positive and negative design pressure rating and impact -resistant rating (if applicable). Impact -resistant shutters are also required to be labeled. Figure 11-11 is an example of a permanent label on a window assembly. This label provides the positive and negative design pressure rating, test missile rating, 8 The 125-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 100 mph. COASTAL CONSTRUCTION MANUAL 11-11 11 DESIGNING THE BUILDING ENVELOPE Volume II and test standards that were used to evaluate the pressure and impact resistance. Without a label, ascertaining whether a window or shutter has sufficient strength to meet pressure and wind-borne debris loads is difficult (see Figure 11-12). It is therefore recommended that design professionals specify that windows and shutters have permanently mounted labels that contain the type of information shown in Figure 11-11. Figure 11-11. Design pressure and impact -resistance information in a permanent window label. Hurricane Ike (Texas, 2008) Figure 11-12. Roll -up shutter slats that detached from the tracks. The lack of a label makes it unclear whether the shutter was tested in accordance with a recognized method. Estimated wind speed: 110 mph. Hurricane Katrina (Louisiana, 2005) a �spd tin :ceereance wrcre AAMA 506.2000 ANSIIAAMAINVVW0A 101ti.5.2-97 PROGRAM M1S$: µ,LC5O�6rRq ON5 P AM GL 1 SERIES 77��n ainGiE nLhL Rae ng { Z. M%B4 "; i Z. W 2one. 3 — G00e: MWQ-1 CONFORMS TO: ASTM F 5W c&vam w E tee enejE t I Glazing Protection from Tile Debris Residential glazing in wind-borne debris regions is required to resist the test missile C or D, depending on the basic wind speed. However, field investigations have shown that roof tile can penetrate shutters that comply with test missile D (see Figure 11-13). Laboratory research conducted at the University of Florida indicates that test missile D compliant shutters do not provide adequate protection against tile debris (Fernandez et al. 2010). Accordingly, if tile roofs occur within 100 to 200 feet (depending on basic wind speed), it is recommended that shutters complying with test missile E be specified. CROSS REFERENCE More information, including a discussion of various types of shutters and recommendations pertaining to them, is available in Fact Sheet 6.2, Protection of Openings — Shutters and Glazing, in FEMA P-499. 11-12 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-13. Shutter punctured by roof tile. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) Jalousie Louvers In tropical climates such as Puerto Rico, some houses have metal jalousie louvers in lieu of glazed window openings (see Figure 11-14). Metal jalousies have the appearance of a debris -resistant shutter, but they typically offer little debris resistance. Neither the UBC nor IRC require openings equipped with metal jalousie louvers to be debris resistant because glazing does not occur. However, the louvers are required to meet the design wind pressure. Because the louvers are not tightly sealed, the building should be evaluated to determine whether it is enclosed or partially enclosed (which depends on the distribution and size of the jalousie windows). Jalousie louvers are susceptible to significant water infiltration during high winds. 11.3.1.3 Durability Achieving good wind performance in window assemblies requires avoiding strength degradation caused by corrosion and termites. To avoid corrosion, wood or vinyl frames are recommended for buildings within 3,000 feet of an ocean shoreline (including sounds and back bays). Stainless steel frame anchors and hardware are also recommended in these areas. In areas with severe termite problems, wood frames should either be treated or not used. If concrete, masonry, or metal wall construction is used to eliminate termite problems, it is recommended that wood not be specified for blocking or nailers. If wood is specified, see "Material Durability in Coastal Environments," a resource document available on the Residential Coastal Construction Web site, for information on wood treatment methods. COASTAL CONSTRUCTION MANUAL 11-13 11 DESIGNING THE BUILDING ENVELOPE Figure 11-14. House in Puerto Rico with metal jalousie louvers 11.3.1.4 Water Infiltration Heavy rain accompanied by high winds can cause wind -driven water infiltration. The magnitude of the problem increases with wind speed. Leakage can occur at the glazing/frame interface, the frame itself, or between the frame and wall. When the basic wind speed is greater than 150 mph,9 because of the very high design wind pressures and numerous opportunities for leakage path development, some leakage should be anticipated when the design wind speed conditions are approached. A design option that partially addresses this problem is to specify a strip of water-resistant material, such as tile, along walls that have a large amount of glazing instead of extending the carpeting to the wall. During a storm, towels can be placed along the strip to absorb water infiltration. These actions can help protect carpets from water damage. It is recommended that design professionals specify that window and skylight assemblies comply with AAMA 520. AAMA 520 has 10 performance levels. The level that is commensurate with the project location should be specified. The successful integration of windows into exterior walls to protect against water infiltration is a challenge. To the extent possible, when detailing the interface between the wall and u Volume II NOTE Laboratory research at the University of Florida indicates that windows with compression seals (i.e., awning and casement windows) are generally more resistant to wind -driven water infiltration than windows with sliding seals (i.e., hung and horizontal sliding windows) (Lopez et al. 2011). CROSS REFERENCE For guidance on window installation, see: ® FMA/AAMA 100 ® FMA/AAMA 200 9 The 150-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 120 mph. 11-14 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. the window, design professionals should rely on sealants as the secondary line of defense against water infiltration rather than making the sealant the primary protection. If a sealant joint is the first line of defense, a second line of defense should be designed to intercept and drain water that drives past the sealant joint. CROSS REFERENCE For a comparison of wind -driven rain resistance as a function of window installation in accordance with ASTM E2112 (as referenced in Fact Sheet 6.1 in FEMA P-499), When designing joints between walls and windows, the design FMA/AAMA 100, and FMA/AAMA professional should consider the shape of the sealant joint (i.e., , 200, see Salzano et al. (2010). hour -glass shape with a width -to -depth ratio of at least 2:1) and the type of sealant to be specified. The sealant joint should be designed to enable the sealant to bond on only two opposing surfaces (i.e., a backer rod or bond -breaker tape should be specified). Butyl is recommended as a sealant for concealed joints and polyurethane for exposed joints. During installation, cleanliness of the sealant substrate is important, particularly if polyurethane or silicone sealants are specified, as is the tooling of the sealant. Sealant joints can be protected with a removable stop (as illustrated in Figure 2 of Fact Sheet 6.1 of FEMA P-499). The stop protects the sealant from direct exposure to the weather and reduces the possibility of wind -driven rain penetration. Where water infiltration protection is particularly demanding and important, onsite water infiltration testing in accordance with AAMA 502 can be specified. AAMA 502 provides pass/fail criteria based on testing in accordance with either of two ASTM water infiltration test methods. ASTM El105 is the recommended test method. 11.3.2 Seismic Glass breakage due to in -plane wall deflection is unlikely, but special consideration should be given to walls with a high percentage of windows and limited shear capacity. In these cases, it is important to analyze the in -plane wall deflection to verify that it does not exceed the limits prescribed in the building code. 11.3.3 Hail A test method has not been developed for testing skylights for hail resistance, but ASTM E822 for testing hail resistance of solar collectors could be used for assessing the hail resistance of skylights. 11.4Bearing IIS, Wall Coverings,Soffits This section addresses exterior non -load -bearing walls, wall coverings, and soffits. The most common problems in the coastal environment are soffit blow -off with subsequent entrance of wind -driven rain into attics and wall covering blow -off with subsequent entrance of wind -driven rain into wall cavities. Seismic events can also damage heavy wall systems including coverings. Although hail can damage walls, significant damage is not common. COASTAL CONSTRUCTION MANUAL 11-15 11 DESIGNING THE BUILDING ENVELOPE Volume II A variety of exterior wall systems can be used in the coastal environment. The following wall coverings are commonly used over wood -frame construction: aluminum siding, brick veneer, fiber cement siding, exterior insulation finish systems (EIFS), stucco, vinyl siding, and wood siding (boards, panels, or shakes). Concrete or concrete masonry unit (CMU) wall construction can also be used, with or without a wall covering. 11.4.1 High Winds Exterior non -load -bearing walls, wall coverings, and soffits should be designed to resist high winds and wind -driven rain. The IBC and IRC require that exterior non -load -bearing walls, wall coverings, and soffits have sufficient strength to resist the positive and negative design wind pressures. 11.4.1.1 Exterior Walls NOTE ASCE 7, IBC, and IRC do not require exterior walls or soffits to resist wind-borne debris. However, the FBC requires exterior wall assemblies in the High -Velocity Hurricane Zone (as defined in the FBC) to be tested for wind-borne debris or to be deemed to comply with the wind-borne debris provisions that are stipulated in the FBC. It is recommended that the exterior face of studs be fully clad with plywood or oriented strand board (OSB) sheathing so the sheathing can withstand design wind pressures that produce both in -plane and out -of - plane loads because a house that is fully sheathed with plywood or OSB is more resistant to wind-borne debris and water infiltration if the wall cladding is lost.10 The disadvantage of not fully cladding the studs with plywood or OSB is illustrated by Figure 11-15. At this residence, OSB was installed at the corner areas to provide shear resistance, but foam insulation was used in lieu of OSB in the field of the wall. In some wall areas, the vinyl siding and foam insulation on the exterior side of the studs and the gypsum board on the interior side of the studs were blown off. Also, although required by building codes, this wall system did not have a moisture barrier between the siding and OSB/ foam sheathing. In addition to the wall covering damage, OSB roof sheathing was also blown off. Wood siding and panels (e.g., textured plywood) and stucco over CMU or concrete typically perform well during high winds. However, blow - off of stucco applied directly to concrete walls (i.e., wire mesh is not applied over the concrete) has occurred during high winds. This problem can be avoided by leaving the concrete exposed or by painting it. More blow -off problems have been experienced with vinyl siding than with NOTE Almost all wall coverings permit the passage of some water past the exterior surface of the covering, particularly when the rain is wind -driven. For this reason, most wall coverings should be considered water - shedding rather than waterproofing. A secondary line of protection with a moisture barrier is recommended to avoid moisture - related problems. Asphalt -saturated felt is the traditional moisture barrier, but housewrap is now the predominate moisture barrier. Housewrap is more resistant to air flow than asphalt -saturated felt and therefore offers improved energy performance. Fact Sheet 1.9, Moisture Barrier Systems, and Fact Sheet 5.1, Housewrap, in FEMA P-499 address key issues regarding selecting and installing moisture barriers as secondary protection in exterior walls. 10 This recommendation is based on FEMA P-757, Mitigation Assessment Team Report: Hurricane Ike in Texas and Louisiana (FEMA 2009). 11-16 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. other siding or panel materials (see Figure 11-15). Problems with aluminum and fiber cement siding have also occurred (see Figure 11-16). Siding A key to the successful performance of siding and panel systems is attachment with a sufficient number of proper fasteners (based on design loads and tested resistance) that are correctly located. Fact Sheet 5.3, Siding Installation and Connectors, in FEMA P-499 provides guidance on specifying and installing vinyl, wood siding, and fiber cement siding in high -wind regions. Brick Veneer NOTE In areas that experience frequent wind -driven rain and in areas that are susceptible to high winds, a pressure -equalized rain screen design should be considered when specifying wood or fiber cement siding. A rain screen design is accomplished by installing suitable vertical furring strips between the moisture barrier and siding material. The cavity facilitates drainage of water from the space between the moisture barrier and backside of the siding and facilitates drying of the siding and moisture barrier. For more information, see Fact Sheet 5.3, Siding Installation in High -Wind Regions, in FEMA P-499. Figure 11-15. Blown -off vinyl siding and foam sheathing; some blow -off of interior gypsum board (circle). Estimated wind speed: 130 mph. Hurricane Katrina (Mississippi, 2006) Blow -off of brick veneer has occurred often during high winds. Common failure modes include tie (anchor corrosion), tie fastener pull-out, failure of masons to embed ties into the mortar, and poor bonding between ties and mortar, and poor -quality mortar. Four of these failure modes occurred at the house shown in Figure 11-17.The lower bricks were attached to CMU and the upper bricks were attached to wood studs. In addition to the wall covering damage, roof sheathing was blown off along the eave. COASTAL CONSTRUCTION MANUAL 11-17 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-16. Blown -off fiber cement siding; broken window (arrow). Estimated wind speed: 125 mph. Hurricane Katrina (Mississippi, 2006) Figure 11-17. Four brick veneer failure modes; five corrugated ties that were not embedded in the mortar joints (inset). Hurricane Ivan (Florida, 2004) A key to the successful performance of brick veneer is attachment with a sufficient number of properly located ties and proper tie fasteners (based on design loads and tested resistance). Fact Sheet 5.4, Attachment of Brick Veneer in High -Wind Regions, in FEMA P-499 provides guidance on specifying and installing brick veneer in high -wind regions. 11-18 COASTAL CONSTRUCTION MANUAL Volume II Exterior Insulating Finishing System EIFS can be applied over steel -frame, wood -frame, concrete, or CMU construction. An EIFS assembly is composed of several types of materials, as illustrated in Figure 11-18. Some of the layers are adhered to one another, and one or more of the layers is typically mechanically attached to the wall. If mechanical fasteners are used, they need to be correctly located, of the proper type and size, and of sufficient number (based on design loads and tested resistance). Most EIFS failures are caused by an inadequate number of fasteners or an inadequate amount of adhesive. At the residence shown in Figure 11-19, the synthetic stucco was installed over molded expanded polystyrene (MEPS) insulation DESIGNING THE BUILDING ENVELOPE 1. u NOTE When a window or door assembly is installed in an EIFS wall assembly, sealant between the window or door frame and the EIFS should be applied to the EIFS base coat. After sealant application, the top coat is then applied. The top coat is somewhat porous; if sealant is applied to it, water can migrate between the top and base coats and escape past the sealant. that was adhered to gypsum board that was mechanically attached to wood studs. Essentially all of the gypsum board blew off (the boards typically pulled over the fasteners). The failure was initiated by detachment of the gypsum board or by stud blow off. Some of the gypsum board on the interior side of the studs was also blown off. Also, two windows were broken by debris. Option A Steel or wood framing EIFS may be attached by mechanical fasteners (as shown) or by adhesive (as shown in Option B). Steel or wood framing Substrate Insulation board Fasteners Reinforced mesh embedded in base coat Dat Figure 11-18. Typical EIFS assemblies Option B Concrete or masonry EIFS attached to concrete or masonry using adhesive. Mechanical fasteners may also be used. Concrete or masonry substrate Adhesive applied to insulation board Insulation board Reinforced mesh embedded in base coat ;oat COASTAL CONSTRUCTION MANUAL 11-19 11 DESIGNING THE BUILDING ENVELOPE Figure 11-19. Blown -off EIFS, resulting in extensive interior water damage; detachment of the gypsum board or stud blow off (circle); two windows broken by debris (arrow). Estimated wind speed: 105 to 115 mph. Hurricane Ivan (Florida, 2004) Volume II Several of the studs shown in Figure 11-19 were severely rotted, indicating long-term moisture intrusion behind the MEPS insulation. The residence shown in Figure 11-19 had a barrier EIFS design, rather than the newer drainable EIFS design (for another example of a barrier EIFS design, see Figure 11-21). EIFS should be designed with a drainage system that allows for dissipation of water leaks. Concrete and Concrete Masonry Unit Properly designed and constructed concrete and CMU walls are capable of providing resistance to high -wind loads and wind- borne debris. When concrete and CMU walls are exposed to sustained periods of rain and high wind, it is possible for water to be driven through these walls. While both the IBC and IRC allow concrete and CMU walls to be installed without water -resistive barriers, the design professional should consider water -penetration -resistance treatments. Breakaway Walls Breakaway walls (enclosures) are designed to fail under base flood conditions without jeopardizing the elevated building. Breakaway walls should also be designed and constructed so that when they break away, they do so without damaging the wall above the line of separation. NOTE Insulated versions of flood - opening devices can be used when enclosures are insulated. Flood openings are recommended in breakaway walls in Zone V and required in foundation walls and walls of enclosures in Zone A and Coastal A Zones. CROSS REFERENCE For information on breakaway walls, see Fact Sheet 8.1, Enclosures and Breakaway Walls, in FEMA P-499. 11-20 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. At the house shown in Figure 11-20, floodwater collapsed the breakaway wall and initiated progressive peeling of the EIFS wall covering. A suitable flashing at the top of the breakaway wall would have avoided the progressive failure. When a wall covering progressively fails above the top of a breakaway wall, wave spray and/or wind -driven water may cause interior damage. Figure 11-20. Collapse of the breakaway wall, resulting in EIFS peeling. A suitable transition detail at the top of breakaway walls avoids the type of peeling damage shown by the arrows. Estimated wind speed: 105 to 115 mph. Hurricane Ivan (Alabama, 2004) 11.4.1.2 Flashings Water infiltration at wall openings and wall transitions due to poor flashing design and/or installation is a common problem in many coastal homes (see Figure 11-21). In areas that experience frequent wind -driven rain and areas susceptible to high winds, enhanced flashing details and attention to their execution are recommended. Enhancements include flashings that have extra -long flanges, use of sealant, and use of self - adhering modified bitumen tape. When designing flashing, the design professional should recognize that wind -driven rain can be pushed vertically. The height to which water can be pushed increases with wind speed. Water can also migrate vertically and horizontally by capillary action between layers of materials (e.g., between a flashing flange and housewrap) unless there is sealant between the layers. NOTE Some housewrap manufacturers have comprehensive, illustrated installation guides that address integrating housewrap and flashings at openings. A key to successful water diversion is installing layers of building materials correctly to avoid water getting behind any one layer and leaking into the building. General guidance is offered below, design professionals should also attempt to determine the type of flashing details that have been used successfully in the area. COASTAL CONSTRUCTION MANUAL 11-21 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-21. EIFS with a barrier design: blown -off roof decking (top circle); severely rotted 0S13 due to leakage at windows (inset). Hurricane Ivan (2004) Door and Window Flashings An important aspect of flashing design and application is the integration of the door and window flashings with the moisture barrier. See the recommendations in FMA/AAMA 100, FMA/AAMA 200, and Salzano et al. (2010), as described in Section 11.3.1.4, regarding installation of doors and windows, as well as the recommendations given in Fact Sheet 5.1, Housewrap, in FEMA P-499. Applying self -adhering modified bitumen flashing tape at doors and windows is also recommended. Roof -to -Wall and Deck -to -Wall Flashing Where enhanced protection at roof -to -wall intersections is desired, step flashing with a vertical leg that is 2 to 4 inches longer than normal is recommended. For a more conservative design, in addition to the long leg, the top of the vertical flashing can be taped to the wall sheathing with 4-inch-wide self -adhering modified bitumen tape (approximately 1 inch of tape on the metal flashing and 3 inches on the sheathing). The housewrap should be extended over the flashing in the normal fashion. The housewrap should not be sealed to the flashing —if water reaches the backside of the housewrap farther up the wall, it needs to be able to drain out at the bottom of the wall. This detail and a deck -to -wall flashing detail are illustrated in Fact Sheet No. 5.2, Roof -to -Wall and Deck -to -Wall Flashing, in FEMA P-499. 11.4.1.3 Soffits Depending on the wind direction, soffits can be subjected to either positive or negative pressure. Failed soffits may provide a convenient path for wind -driven rain to enter the building, as illustrated by Figure 11-22. This house had a steep -slope roof with a ventilated attic space. The exterior CMU/stucco wall stopped just above the vinyl soffit. Wind -driven rain entered the attic space where the soffit had blown away. This example and other storm -damage research have shown that water blown into attic spaces after the loss of soffits can cause significant damage and the collapse of ceilings. Even when soffits remain in place, water can penetrate through soffit vents and cause damage (see Section 11.6). 11-22 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-22. Blown -away soffit (arrow), which allowed wind -driven rain to enter the attic. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) Loading criteria for soffits were added in ASCE 7-10. At this time, the only known test standard pertaining to soffit wind and wind -driven rain resistance is the FBC Testing Application Standard (TAS) No. 100(A)-95 (ICC 2008). Wind -pressure testing is conducted to a maximum test speed of 140 mph, and wind -driven rain testing is conducted to a maximum test speed of 110 mph. Laboratory research has shown the need for an improved test method to evaluate the wind pressure and wind -driven rain resistance of soffits. Plywood or wood soffits are generally adequately anchored to wood framing attached to the roof structure or walls. However, it has been common practice for vinyl and aluminum soffit panels to be installed in tracks that are frequently poorly connected to the walls and fascia at the edge of the roof overhang. Properly installed vinyl and aluminum soffit panels should be fastened to the building structure or to nailing strips placed at intervals specified by the manufacturer. Key elements of soffit installation are illustrated in Fact Sheet 7.5, Minimizing Water Intrusion Through Roof Vents in High -Wind Regions, in FEMA P-499. 11.4.1.4 Durability For buildings within 3,000 feet of an ocean shoreline (including sounds and back bays), stainless steel fasteners are recommended for wall and soffit systems. For other components (e.g., furring, blocking, struts, hangers), nonferrous components (such as wood), stainless steel, or steel with a minimum of G-90 hot - dipped galvanized coating are recommended. Additionally, access panels are recommended so components within soffit cavities can be inspected periodically for corrosion or wood decay. COASTAL CONSTRUCTION MANUAL 11-23 11 DESIGNING THE BUILDING ENVELOPE Volume II See "Material Durability in Coastal Environments," a resource document located on the Residential Coastal Construction Web site, for information on wood treatment if wood is specified in areas with severe termite problems. 11.4.2 Seismic Concrete and CMU walls need to be designed for the seismic load. When a heavy covering such as brick veneer or stucco is specified, the seismic design should account for the added weight of the covering. Inadequate connection of veneer material to the base substrate has been a problem in earthquakes and can result in a life -safety hazard. For more information on the seismic design of brick veneer, see Fact Sheet 5.4, Attachment of Brick Veneer in High -Wind Regions, in FEMA P-499. Some non -ductile coverings such as stucco can be cracked or spalled during seismic events. If these coverings are specified in areas prone to large ground -motion accelerations, the structure should be designed with additional stiffness to minimize damage to the wall covering. 11.5 Roof Systems This section addresses roof systems. High winds, seismic events, and hail are the natural hazards that can cause the greatest damage to roof systems in the coastal environment. When high winds damage the roof covering, water infiltration commonly occurs and can cause significant damage to the interior of the building and its contents. Water infiltration may also occur after very large hail impact. During seismic events, heavy roof coverings such as tile or slate may be dislodged and fall from the roof and present a hazard. A roof system that is not highly resistant to fire exposure can result in the destruction of the building during a wildfire. Residential buildings typically have steep -slope roofs (i.e., a slope greater than 3:12), but some have low -slope roofs. Low - slope roof systems are discussed in Section 11.5.8. NOTE When reroofing in high -wind areas, the existing roof covering should be removed rather than re-covered so that the roof deck can be checked for deterioration and adequate attachment. See Figure 11-23. Also see Chapter 14 in this Manual. NOTE Historically, damage to roof systems has been the leading A variety of products can be used for coverings on steep -slope cause m building performance problems during high winds. roofs. The following commonly used products are discussed in this section: asphalt shingles, cement -fiber shingles, liquid - applied membranes, tiles, metal panels, metal shingles, slate, and wood shingles and shakes. The liquid -applied membrane and metal panel systems are air -impermeable, and the other systems are air-permeable.11 At the residence shown in Figure 11-23, new asphalt shingles had been installed on top of old shingles. Several of the newer shingles blew off. Re-covering over old shingles causes more substrate irregularity, which can interfere with the bonding of the self -seal adhesive of the new shingles. 11 Air permeability of the roof system affects the magnitude of air pressure that is applied to the system during a wind storm. 11-24 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-23. Blow -off of several newer shingles on a roof that had been re-covered by installing new asphalt shingles on top of old shingles (newer shingles are lighter and older shingles are darker). Hurricane Charley (Florida, 2004) 11.5.1 Asphalt Shingles The discussion of asphalt shingles relates only to shingles with self -seal tabs. Mechanically interlocked shingles are not addressed because of their limited use. 11.5.1.1 High Winds The key elements to the successful wind performance of asphalt shingles are the bond strength of the self-sealing adhesive; mechanical properties of the shingle; correct installation of the shingle fasteners; and enhanced attachment along the eave, hip, ridge, and rakes. In addition to the tab lifts, the number and/or location of fasteners used to attach the shingles may influence whether shingles are blown off. Underlayment If shingles blow off, water infiltration damage can be avoided if the underlayment remains attached and is adequately sealed at penetrations. Figures 11-24 and 11-25 show houses with underlayment that was not effective in avoiding water leakage. Reliable NOTE Neither ASCE 7, IBC, or IRC require roof assemblies to resist wind-borne debris. However, the FBC requires roof assemblies located in the High -Velocity Hurricane Zone (as defined by the FBC) to be tested for wind-borne debris or be deemed to comply with the wind-borne debris provisions as stipulated in the FBC. n\ NOTE Storm damage investigations have revealed that gutters are often susceptible to blow -off. ANSI/ SPRI GD-1, Structural Design Standard for Gutter Systems Used with Low -Slope Roofs (ANSI/SPRI 2010) provides information on gutter wind and water and ice loads and includes methods for testing gutter resistance to these loads. Although the standard is intended for low -slope roofs, it should be considered when designing and specifying gutters used with steep -slope roofs. ANSI/SPRI GD-1 specifies a minimum safety factor of 1.67, but a safety factor of 2 is recommended. COASTAL CONSTRUCTION MANUAL 11-25 11 DESIGNING THE BUILDING ENVELOPE Figure 11-24. Small area of sheathing that was exposed after loss of a few shingles and some underlayment. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) Figure 11-25. Typical underlayment attachment; underlayment blow -off is common if the shingles are blown off, as shown. Estimated wind speed: 115 mph. Hurricane Katrina (Louisiana, 2005) tt. .16r Volume II secondary protection requires an enhanced underlayment design. Design enhancements include increased blow -off resistance of the underlayment, increased resistance to water infiltration (primarily at penetrations), and increased resistance to extended weather exposure. If shingles are blown off, the underlayment may be exposed for only 1 or 2 weeks before a new roof covering is installed, but many roofs damaged by hurricanes are not repaired for several weeks. If a hurricane strikes a heavily populated area, roof covering damage is typically extensive. Because of the heavy workload, large numbers of roofs may not be repaired for several months. It is not uncommon for some roofs to be left for as long as a year before they are reroofed. 11-26 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. The longer an underlayment is exposed to weather, the more durable it must be to provide adequate water infiltration protection for the residence. Fact Sheet 7.2, Roof Underlayment for Asphalt Shingle Roofs, in FEMA P-499 provides three primary options for enhancing the performance of underlayment if shingles are blown off. The options in the fact sheet are listed in order of decreasing resistance to long-term weather exposure. The fact sheet provides guidance for option selection, based on the design wind speed and population of the area. The following is a summary of the enhanced underlayment options: Enhanced Underlayment Option 1. Option 1 provides the greatest reliability for long-term exposure. This option includes a layer of self -adhering modified bitumen. Option 1 has two variations. The first variation is shown in Figure 11-26. In this variation, the self -adhering sheet is applied to the sheathing, and a layer of #15 felt is tacked over the self -adhering sheet before the shingles are installed. The purpose of the felt is to facilitate future tear -off of the shingles. This variation is recommended in southern climates (e.g., south of the border between North and South Carolina). If a house is located in moderate or cold climates or has a high interior humidity (such as from an indoor swimming pool), the second variation, shown in Figure 11-27, is recommended. U NOTE Some OSB has a factory - applied wax that interferes with the bonding of self -adhering modified bitumen. To facilitate bonding to waxed sheathing, a field -applied primer is needed. If self -adhering modified bitumen sheet or tape is applied to OSB, the OSB manufacturer should be contacted to determine whether a primer needs to be applied to the OSB. In the second variation (Figure 11-27), the sheathing joints are taped with self -adhering modified bitumen. A #30 felt is then nailed to the sheathing, and a self -adhering modified bitumen sheet is applied to the felt before the shingles are installed. The second variation costs more than the first variation because the second variation requires sheathing tape, many more felt fasteners, and heavier felt. The purpose of taping the joints Figure 11-26. Enhanced underlayment Option 1, first variation: self - adhering modified bitumen over the sheathing COASTAL CONSTRUCTION MANUAL 11-27 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-27. Enhanced underlayment Option 1, second variation: self - adhering modified bitumen over the felt 11-28 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Enhanced Underlayment Option 3. Option 3 is the typical underlayment scheme (i.e., a single layer of #15 felt tacked to the sheathing, as shown in Figure 11-25) with the added enhancement of self - adhering modified bitumen tape. This option provides limited protection against water infiltration if the shingles blow off. However, this option provides more protection than the typical underlayment scheme. Option 3 is illustrated in Fact Sheet 7.2 in FEMA P-499. Figure 11-28 shows a house that used Option 3. The self -adhering modified bitumen tape at the sheathing joints was intended to be a third line of defense against water leakage (with the shingles the first line and the felt the second line). However, as shown in the inset at Figure 11-28, the tape did not provide a watertight seal. A post -storm investigation revealed application problems with the tape. Staples (arrow, inset) were used to attach the tape because bonding problems were experienced during application. Apparently, the applicator did not realize the tape was intended to prevent water from leaking through the sheathing joints. With the tape in an unbonded and wrinkled condition, it was incapable of fulfilling its intended purpose. Self -adhering modified bitumen sheet and tape normally bond quite well to sheathing. Bonding problems are commonly attributed to dust on the sheathing, wet sheathing, or a surfacing (wax) on the sheathing that interfered with the bonding. In addition to taping the sheathing joints in the field of the roof, the hip and ridge lines should also be taped unless there is a continuous ridge vent, and the underlayment should be lapped over the hip and ridge. By doing so, leakage will be avoided if the hip or ridge shingles blow off (see Figure 11-29). See Section 11.6 for recommendations regarding leakage avoidance at ridge vents. Figure 11-28. House that used enhanced underlayment Option 3 with taped sheathing joints (arrow). The self -adhering modified bitumen tape (inset) was stapled because of bonding problems. Estimated wind speed: 110 mph. Hurricane Ike (Texas, 2008) SOURCE: IBHS, USED WITH PERMISSION COASTAL CONSTRUCTION MANUAL 11-29 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-29. Underlayment that was not lapped over the hip; water entry possible at the sheathing joint (arrow). Estimated wind speed: 130 mph. Hurricane Katrina (Mississippi, 2005) Shingle Products, Enhancement Details, and Application Shingles are available with either fiberglass or organic reinforcement. Fiberglass -reinforced shingles are commonly specified because they have greater fire resistance. Fiberglass -reinforced styrene-butadiene-styrene (SBS)-modified bitumen shingles are another option. Because of the flexibility imparted by the SBS polymers, if a tab on a modified bitumen shingle lifts, it is less likely to tear or blow off compared to traditional asphalt shingles.13 Guidance on product selection is provided in Fact Sheet 7.3, Asphalt Shingle Roofing for High - Wind Regions, in FEMA P-499. The shingle product standards referenced in Fact Sheet 7.3 specify a minimum fastener (nail) pull -through resistance. However, if the basic wind speed is greater than 115 mph,14 the Fact Sheet 7.3 recommends minimum pull -through values as a function of wind speed. If a fastener pull -through resistance is desired that is greater than the minimum value given in the product standards, the desired value needs to be specified. ASTM D7158 addresses wind resistance of asphalt shingles.ls ASTM D7158 has three classes: Class D, G, and H. Select shingles that have a class rating equal to or greater than the basic wind speed prescribed in the building code. Table 11-1 gives the allowable basic wind speed for each class, based on ASCE 7-05 and ASCE 7-10. Shingle blow -off is commonly initiated at eaves (see Figure 11-30) and rakes (see Figure 11-31). Blow -off of ridge and hip shingles, as shown in Figure 11-29, is also common. For another example of blow -off of ridge 13 Tab lifting is undesirable. However, lifting may occur for a variety of reasons. If lifting occurs, a product that is not likely to be torn or blown off is preferable to a product that is more susceptible to tearing and blowing off. 14 The 115-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05, or an earlier version is used, the equivalent wind speed trigger is 90 mph. 15 Fact Sheet 7.3 in FEMA P-499 references Underwriters Laboratories (UL) 2390. ASTM D7158 supersedes UL 2390. 11-30 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Table 11-1. Allowable Basic Wind Speed as a Function of Class D 90 mph 115 mph G 120 mph 152 mph H 150 mph 190 mph (a) Classes are based on a building sited in Exposure C. They are also based on a building sited where there is no abrupt change in topography. If the residence is in Exposure D and/or where there is an abrupt change in topography (as defined in ASCE 7), the design professional should consult the shingle manufacturer. Figure 11-30. Loss of shingles and underlayment along the eave and loss of a few hip shingles. Estimated wind speed: 115 mph. Hurricane Katrina (Louisiana, 2005) Figure 11-31. Loss of shingles and underlayment along the rake. Estimated != wind speed: 110 mph. Hurricane Ike (Texas, 2008) r r` COASTAL CONSTRUCTION MANUAL 11-31 11 DESIGNING THE BUILDING ENVELOPE Volume II and hip shingles, see Figure 11-35. Fact Sheet 7.3 in FEMA P-499 provides enhanced eave, rake, and hip/ ridge information that can be used to avoid failure in these areas. Storm damage investigations have shown that when eave damage occurs, the starter strip was typically incorrectly installed, as shown in Figure 11-32. Rather than cutting off the tabs of the starter, the starter was rotated 180 degrees (right arrow). The exposed portion of the first course of shingles (left arrow) was unbounded because the self -seal adhesive (dashed line) on the starter was not near the eave. Even when the starter is correctly installed (as shown on shingle bundle wrappers), the first course may not bond to the starter because of substrate variation. Fact Sheet 7.3 in FEMA P-499 provides information about enhanced attachment along the eave, including special recommendations regarding nailing, use of asphalt roof cement, and overhang of the shingle at the eave. Figure 11-32. Incorrect installation of the starter course (incorrectly rotated starter, right arrow, resulted in self -seal adhesive not near the eave, dashed line). Estimated wind speed: 130 mph. Hurricane Katrina (Mississippi, 2005) Storm damage investigations have shown that metal drip edges (edge flashings) with vertical flanges that are less than 2 inches typically do not initiate eave or rake damage. However, the longer the flange, the greater the potential for flange rotation and initiation of damage. If the vertical flange exceeds 2 inches, it is recommended that the drip edge be in compliance with ANSI/SPRI ES-1. As with eaves, lifting and peeling failure often initiates at rakes and propagates into the field of the roof, as shown in Figure 11-33. Rakes are susceptible to failure because of the additional load exerted on the overhanging shingles and the configuration of the self-sealing adhesive. Along the long dimension of the shingle (i.e., parallel to the eave), the tab is sealed with self-sealing adhesive that is either continuous or nearly SO. However, along the rake, the ends of the tab are only sealed at the self -seal lines, and the tabs are therefore typically sealed at about 5 inches on center. The result is that under high -wind loading, the adhesive at the rake end is stressed more than the adhesive farther down along the tab. With sufficient wind loading, the corner tab of the rake can begin to lift up and progressively peel, as illustrated in Figure 11-33. Fact Sheet 7.3 in FEMA P-499 provides information about enhanced attachment along the rake, including recommendations regarding the use of asphalt roof cement along the rake. Adding dabs of cement, as shown in the Fact Sheet 7.3 in FEMA P-499 and Figure 11-33, distributes the uplift load across the ends of the rake shingles to the cement and self -seal adhesive, thus minimizing the possibility of tab uplift and progressive peeling failure. 11-32 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. COASTAL CONSTRUCTION MANUAL 11-33 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-34. A bleeder strip (double - arrow) that was used at a rake blow -off; lack of contact between the tab of the overlying shingle and the bleeder's self -seal adhesive (upper arrow). Estimated wind speed: 125 mph. Hurricane Katrina (Mississippi, 2005) Figure 11-35. Inadequate sealing of the self-sealing adhesive at a hip as a result of the typical hip installation procedure. Estimated wind speed: 105 mph. Hurricane Katrina (Mississippi, 2005) Four fasteners per shingle are normally used where the basic wind speed is less than 115 mph.16 Where the basic wind speed is greater than 115 mph, six fasteners per shingle are recommended. Fact Sheet 7.3 in FEMA P-499 provides additional guidance on shingle fasteners. Storm damage investigations have shown that significant fastener mislocation is common on damaged roofs. When nails are too high above the nail line, they can miss the underlying shingle headlap or have inadequate edge distance, as illustrated 16 The 115-mph basic wind speed is based on ASCE 7-10, Risk Category II buildings. If ASCE 7-05 or an earlier version is used, the equivalent wind speed trigger is 90 mph. 11-34 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. in Figure 11-36. When laminated shingles are used, high nailing may miss the overlap of the laminated shingles; if the overlap is missed, the nail pull -through resistance is reduced (see Figure 11-37). High nailing may also influence the integrity of the self -seal adhesive bond by allowing excessive deformation (ballooning) in the vicinity of the adhesive. The number of nails (i.e., four versus six) and their location likely play little role in wind performance as long at the shingles remain bonded. However, if they are unbounded prior to a storm, or debonded during a storm, the number and location of the nails and the shingles' nail pull -through resistance likely play an important role in the magnitude of progressive damage. Figure 11-36. Proper and improper location of shingle fasteners (nails). When properly located, the nail engages the underlying shingle in the headlap area (center nail). When too high, the nail misses the underlying shingle (left nail) or is too close to the edge of the underlying shingle (right nail) COASTAL CONSTRUCTION MANUAL 11-35 11 DESIGNING THE BUILDING ENVELOPE Volume II Shingles manufactured with a wide nailing zone provide roofing mechanics with much greater opportunity to apply fasteners in the appropriate locations. Shingle damage is also sometimes caused by installing shingles via the raking method. With this method, shingles are installed from eave to ridge in bands about 6 feet wide. Where the bands join one another, at every other course, a shingle from the previous row needs to be lifted up to install the end nail of the new band shingle. Sometimes installers do not install the end nail, and when that happens, the shingles are vulnerable to unzipping at the band lines, as shown in Figure 11-38. Raking is not recommended by the National Roofing Contractors Association or the Asphalt Roofing Manufacturers Association. Figure 11-38. Shingles that unzipped at the band lines because the raking method was used to install them. Estimated wind speed: 135 mph. Hurricane Katrina (Mississippi, 2005) 11.5.1.2 Hail Underwriters Laboratories (UL) 2218 is a method of assessing simulated hail resistance of roofing systems. The test yields four ratings (Classes 1 to 4). Systems rated Class 4 have the greatest impact resistance. Asphalt shingles are available in all four classes. It is recommended that asphalt shingle systems on buildings in areas vulnerable to hail be specified to pass UL 2218 with a class rating that is commensurate with the hail load. Hail resistance of asphalt shingles depends partly on the condition of the shingles when they are exposed to hail. Shingle condition is likely to decline with roof age. 11.5.2 Fiber -Cement Shingles Fiber -cement roofing products are manufactured to simulate the appearance of slate, tile, wood shingles, or wood shakes. The properties of various fiber -cement products vary because of differences in material composition and manufacturing processes. 11-36 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. 11.5.2.1 High Winds Because of the limited market share of fiber -cement shingles in areas where research has been conducted after high -wind events, few data are available on the wind performance of these products. Methods to calculate uplift loads and evaluate load resistance for fiber -cement products have not been incorporated into the IBC or IRC. Depending on the size and shape of the fiber -cement product, the uplift coefficient that is used for tile in the IBC may or may not be applicable to fiber -cement. If the fiber -cement manufacturer has determined that the tile coefficient is applicable to the product, Fact Sheet 7.4, Tile Roofing for High -Wind Areas, in FEMA P-499 is applicable for uplift loads and resistance. If the tile coefficient is not applicable, demonstrating compliance with ASCE 7 will be problematic with fiber -cement until suitable coefficient(s) have been developed. Stainless steel straps, fasteners, and clips are recommended for roofs located within 3,000 feet of an ocean shoreline (including sounds and back bays). For underlayment recommendations, refer to the recommendation at the end of Section 11.5.4.1. 11.5.2.2 Seismic Fiber -cement products are relatively heavy and, unless they are adequately attached, they can be dislodged during strong seismic events and fall from the roof. At press time, manufacturers had not conducted research or developed design guidance for use of these products in areas prone to large ground -motion accelerations. The guidance provided in Section 11.5.4.2 is recommended until guidance is developed for cement -fiber products. 11.5.2.3 Hail It is recommended that fiber -cement shingle systems on buildings in areas vulnerable to hail be specified to pass UL 2218 at a class rating that is commensurate with the hail load. If products with the desired class are not available, another type of product should be considered. 11.5.3 Liquid -Applied Membranes Liquid -applied membranes are not common on the U.S. mainland but are common in Guam, the U.S. Virgin Islands, Puerto Rico, and American Samoa. 11.5.3.1 High Winds Investigations following hurricanes and typhoons have revealed that liquid -applied membranes installed over concrete and plywood decks have provided excellent protection from high winds if the deck remains attached to the building. This conclusion is based on performance during Hurricanes Marilyn and Georges. This type of roof covering over these deck types has high -wind -resistance reliability. Unprotected concrete roof decks can eventually experience problems with corrosion of the slab reinforcement, based on performance observed after Hurricane Marilyn. All concrete roof decks are recommended to be covered with some type of roof covering. COASTAL CONSTRUCTION MANUAL 11-37 11 DESIGNING THE BUILDING ENVELOPE Volume II 11.5.3.2 Hail It is recommended that liquid -applied membrane systems on buildings in areas vulnerable to hail be specified to pass UL 2218 or Factory Mutual Global testing with a class rating that is commensurate with the hail load. 11.5.4 Tiles Clay and extruded concrete tiles are available in a variety of profiles and attachment methods. 11.5.4.1 High Winds During storm damage investigations, a variety of tile profiles (e.g., S-tile and flat) of both clay and concrete tile roofs have been observed. No significant wind performance differences were attributed to tile profile or material (i.e., clay or concrete). Figure 11-39 illustrates the type of damage that has often occurred during moderately high winds. Blow - off of hip, ridge, or eave tiles is caused by inadequate attachment. Damage to field tiles is typically caused by wind-borne debris (which is often tile debris from the eaves and hips/ridges). Many tile roofs occur over waterproof (rather than water -shedding) underlayment. Waterproof underlayments have typically been well - attached and therefore have not normally blown off after tile blow -off. Hence, many residences with tile roofs have experienced significant tile damage, but little, if any water infiltration from the roof Figure 11-40 shows an atypical underlayment blow -off, which resulted in substantial water leakage into the house. The four methods of attaching tile are wire -tied, mortar -set, mechanical attachment, and foam -adhesive (adhesive -set). Wire -tied systems are not commonly used in high -wind regions of the continental United States. On the roof shown in Figure 11-41, wire -tied tiles were installed over a concrete deck. Nose hooks occurred at the nose. In addition, a bead of adhesive occurred between the tiles at the headlap. Tiles at the first three perimeter rows were also attached with wind clips. The clips prevented the perimeter tiles from lifting. However, at the field of the roof, the tiles were repeatedly lifted and slammed against deck, which caused the tiles to break and blow away. Damage investigations have revealed that mortar -set systems often provide limited wind resistance (Figure 11-42).17 As a result of widespread poor performance of mortar -set systems during Hurricane Andrew (1992), adhesive -set systems were developed. Hurricane Charley (2004) offered the first opportunity to evaluate the field performance of this new attachment method during very high winds (see Figures 11-43 and 11-44). Figure 11-43 shows a house with adhesive -set tile. There were significant installation problems with the foam paddies, including insufficient contact area between the patty and the tile. As can be seen in Figure 11-43, most of the foam failed to make contact with the tile. Some of the foam also debonded from the mineral surface cap sheet underlayment (see Figure 11-44). Figure 11-45 shows tiles that were mechanically attached with screws. At the blow -off area, some of the screws remained in the deck, while others were pulled out. The ridge tiles were set in mortar. 17 Fact Sheet 7.4, Tile Roofing for High -Wind Areas, in FEMA 499 recommends that mechanical or adhesively attached methods be used in lieu of the mortar -set method. 11-38 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-39. Blow -off of eave and hip tiles and some broken tiles in the field of the roof. Hurricane Ivan (Alabama, 2004) Figure 11-40. Large area of blown - off underlayment on a mortar -set tile roof. The atypical loss of waterproofing tile underlayment resulted in substantial water leakage into the house. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) Figure 11-41. Blow -off of wire -tied tiles installed over a concrete deck. Typhoon Paka (Guam, 1997) COASTAL CONSTRUCTION MANUAL 11-39 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-42. Extensive blow -off of mortar -set tiles. Hurricane Charley (Florida, 2004) Figure 11-43. Blown -off adhesive -set tile. Note the very small contact area of the foam at the tile heads (left side of the tiles) and very small contact at the nose (circles). Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) Damage investigations have revealed that blow off of hip and ridge failures are common (see Figures 11-39, 11-45, and 11-46). Some of the failed hip/ridge tiles were attached with mortar (see Figure 11-45), while others were mortared and mechanically attached to a ridge board. At the roof shown in Figure 11-46, the hip tiles were set in mortar and attached to a ridge board with a single nail near the head of the hip tile. Because of the brittle nature of tile, tile is often damaged by wind-borne debris, including tile from nearby buildings or tile from the same building (see Figure 11-47). At houses on the coast, fasteners and clips that are used to attach tiles are susceptible to corrosion unless they are stainless steel. Figure 11-48 shows a 6-year-old tile roof on a house very close to the ocean that failed because the heads of the screws attaching the tile had corroded off. Stainless steel straps, fasteners, and clips are recommended for roofs within 3,000 feet of an ocean shoreline (including sounds and back bays). 11-40 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-44. Adhesive that debonded from the cap sheet Figure 11-45. Blow -off of mechanically attached tiles. Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) COASTAL CONSTRUCTION MANUAL 11-41 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-46. Blow -off of hip tiles that were nailed to a ridge board and set in mortar. Hurricane Ivan (Florida, 2004) Figure 11-47. Damage to field tiles caused by tiles from another area of the roof, including a hip tile (circle). Estimated wind speed: 140 to 160 mph. Hurricane Charley (Florida, 2004) The house in Figure 11-48 had a lightning protection system (LPS), and the LPS conductors were placed under the ridge tile. Conductors are not susceptible to wind damage if they are placed under the tile and the air terminals (lightning rods) are extended through the ridge. 11-42 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-48. The fastener heads on this mechanically attached tile roof had corroded; air terminals (lightning rods) in a lightning protection system (circle). Hurricane Ivan (Alabama, 2004) To avoid the type of problems shown in Figures 11-39 through 11-48, see the guidance and recommendations regarding attachment and quality control in Fact Sheet 7.4, Tile Roofing for High-WindAreas, in FEMA P-499. Fact Sheet 7.4 references the Third Edition of the Concrete and Clay Roof Tile Installation Manual (FRSA/ TRI 2001) but, as of press time, the Fourth Edition is current and therefore recommended (FRSA/TRI 2005). The Manual includes underlayment recommendations. 11.5.4.2 Seismic Tiles are relatively heavy, and unless they are adequately attached, they can be dislodged during strong seismic events and fall away from the roof. Manufacturers have conducted laboratory research on seismic resistance of tiles, but design guidance for these products in areas prone to large ground -motion accelerations has not been developed. As shown in Figures 11-49, 11-50, and 11-51, tiles can be dislodged if they are not adequately secured. In seismic areas where short period acceleration, Ss, exceeds 0.5g, the following are recommended: If tiles are laid on battens, supplemental mechanical attachment is recommended. When tiles are only loose laid on battens, they can be shaken off, as shown in Figure 11-49 where most of the tiles on the roof were nailed to batten strips. However, in one area, several tiles were not nailed. Because of the lack of nails, the tiles were shaken off the battens. Tiles nailed only at the head may or may not perform well. If they are attached with a smooth -shank nail into a thin plywood or OSB sheathing, pullout can occur. Figure 11-50 shows tiles that were nailed to thin wood sheathing. During the earthquake, the nose of the tiles bounced and pulled out the nails. Specifying ring -shank or screw -shank nails or screws is recommended, but even with these types of fasteners, the nose of the tile can bounce, causing enlargement of the nail hole by repeated pounding. To overcome this problem, wind clips near the nose of the tile or a bead of adhesive between the tiles at the headlap should be specified. COASTAL CONSTRUCTION MANUAL 11-43 11 DESIGNING THE BUILDING ENVELOPE Figure 11-49. Area of the roof where tiles were not nailed to batten strips. Northridge Earthquake (California, 1994) Figure 11-50. Tiles that were nailed to thin wood sheathing. Northridge Earthquake (California, 1994) .00� t 171 - r 96 Volume II Tiles that are attached by only one fastener experience eccentric loading. This problem can be overcome by specifying wind clips near the nose of the tile or a bead of adhesive between the tiles at the headlap. Two-piece barrel (i.e., mission) tiles attached with straw nails can slide downslope a few inches because of deformation of the long straw nail. This problem can be overcome by specifying a wire -tied system or proprietary fasteners that are not susceptible to downslope deformation. When tiles are cut to fit near hips and valleys, the portion of the tile with the nail hole(s) is often cut away. Figure 11-51 shows a tile that slipped out from under the hip tiles. The tile that slipped was trimmed to fit at the hip. The trimming eliminated the nail holes, and no other attachment was provided. The friction fit was inadequate to resist the seismic forces. Tiles must have supplemental securing to avoid displacement of these loose tiles. 11-44 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-51. Tile that slipped out from under the hip tiles. Northridge Earthquake (California, 1994) Securing rake, hip, and ridge tiles with mortar is ineffective. If mortar is specified, it should be augmented with mechanical attachment. Rake trim tiles fastened just near the head of the tile often slip over the fastener head because the nail hole is enlarged by repeated pounding. Additional restraint is needed for the trim pieces. Also, the design of some rake trim pieces makes them more inherently resistant to displacement than other rake trim designs. Stainless steel straps, fasteners, and clips are recommended for roofs within 3,000 feet of an ocean shoreline (including sounds and back bays). 11.5.4.3 Hail Tile manufacturers assert that UL 2218 is not a good test method to assess non -ductile products such as tiles. A proprietary alternative test method is available to assess non -ductile products, but as of press time, it had not been recognized as a consensus test method. 11.5.5 Metal Panels and Metal Shingles A variety of metal panel and shingle systems are available. Fact Sheet 7.6, Metal Roof Systems in High -Wind Regions, in FEMA P-499 discusses metal roofing options. Some of the products simulate the appearance of tiles or wood shakes. 11.5.5.1 High Winds Damage investigations have revealed that some metal roofing systems have sufficient strength to resist extremely high winds, while other systems have blown off during winds that were well below the design speeds given in ASCE 7. Design and construction guidance is given in Fact Sheet 7.6 in FEMA P-499. Figure 11-52 illustrates the importance of load path. The metal roof panels were screwed to wood nailers that were attached to the roof deck. The panels were well attached to the nailers. However, one of the nailers was inadequately attached. This nailer lifted and caused a progressive lifting and peeling of the metal panels. Note the cantilevered condenser platform (arrow), a good practice, and the broken window (circle). COASTAL CONSTRUCTION MANUAL 11-45 11 DESIGNING THE BUILDING ENVELOPE Volume II Figure 11-52. Blow -off of one of the nailers (dashed line on roof) caused panels to progressively fail; cantilevered condenser platform (arrow); broken window (circle). Estimated wind speed: 130 mph. Hurricane Katrina (Louisiana, 2005) 11.5.5.2 Hail Several metal panel and shingle systems have passed UL 2218. Although metal systems have passed Class 4 (the class with the greatest impact resistance), they often are severely dented by the testing. Although they may still be effective in inhibiting water entry, the dents can be aesthetically objectionable. The appearance of the system is not included in the UL 2218 evaluation criteria. 11.5.6 Slate Some fiber -cement and tile products are marketed as "slate," but slate is a natural material. Quality slate offers very long life. However, long -life fasteners and underlayment are necessary to achieve roof system longevity. 11.5.6.1 High Winds Because of limited market share of slate in areas where research has been conducted after high -wind events, few data are available on its wind performance. However, as shown in Figure 11-53, wind damage can occur. Methods to calculate uplift loads and evaluate load resistance for slate have not been incorporated into the IBC or IRC. Manufacturers have not conducted research to determine a suitable pressure coefficient. Demonstrating slate's compliance with ASCE 7 will be problematic until a coefficient has been developed. A consensus test method for uplift resistance has not been developed for slate. In extreme high -wind areas, mechanical attachment near the nose of the slate should be specified in perimeter and corner zones and perhaps in the field. Because this prescriptive attachment suggestion is based on limited information, the uplift resistance that it provides is unknown. 11-46 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Figure 11-53. Damaged slate roof with nails that typically pulled out of the deck. Some of the slate broke and small portions remained nailed to the deck. Estimated wind speed: 130 mph. Hurricane Katrina (Mississippi, 2005) Stainless steel straps, fasteners, and clips are recommended for roofs within 3,000 feet of an ocean shoreline (including sounds and back bays). For underlayment recommendations, refer to the recommendation at the end of Section 11.5.4.1. 11.5.6.2 Seismic Slate is relatively heavy and unless adequately attached, it can be dislodged during strong seismic events and fall away from the roof. Manufacturers have not conducted research or developed design guidance for use of slate in areas prone to large ground -motion accelerations. The guidance provided for tiles in Section 11.5.4.2 is recommended until guidance has been developed for slate. 11.5.6.3 Hail See Section 11.5.4.3. 11.5.7 Wood Shingles and Shakes 11.5.7.1 High Winds Research conducted after high -wind events has shown that wood shingles and shakes can perform very well during high winds if they are not deteriorated and have been attached in accordance with standard attachment recommendations. Methods to calculate uplift loads and evaluate load resistance for wood shingles and shakes have not been incorporated into the IBC or IRC. Manufacturers have not conducted research to determine suitable pressure coefficients. Demonstrating compliance with ASCE 7 will be problematic with wood shingles and shakes COASTAL CONSTRUCTION MANUAL 11-47 11 DESIGNING THE BUILDING ENVELOPE Volume II until such coefficients have been developed. A consensus test method for uplift resistance has not been developed for wood shingles or shakes. For enhanced durability, preservative -treated wood is recommended for shingle or shake roofs on coastal buildings. Stainless steel fasteners are recommended for roofs within 3,000 feet of an ocean shoreline (including sounds and back bays). See Figure 11-54 for an example of shingle loss due to corrosion of the nails. Figure 11-54. Loss of wood shingles due to fastener corrosion. Hurricane Bertha (North Carolina, 1996) 11.5.7.2 Hail At press time, no wood -shingle assembly had passed UL 2218, but heavy shakes had passed Class 4 (the class with the greatest impact resistance) and medium shakes had passed Class 3. The hail resistance of wood shingles and shakes depends partly on their condition when affected by hail. Resistance is likely to decline with roof age. 11.5.8 Low -Slope Roof Systems Roof coverings on low -slope roofs need to be waterproof membranes rather than the water -shedding coverings that are used on steep -slope roofs. Although most of the low -slope membranes can be used on dead -level substrates, it is always preferable (and required by the IBC and IRC) to install them on substrates that have some slope (e.g., 1/4 inch in 12 inches [2 percent]). The most commonly used coverings on low -slope roofs are built-up, modified bitumen, and single -ply systems. Liquid -applied membranes (see Section 11.5.3), structural metal panels (see Section 11.5.5), and sprayed polyurethane foam may also be used on low -slope roofs. Information on low -slope roof systems is available in The NRCA Roofing Manual (NRCA 2011). Low -slope roofing makes up a very small percentage of the residential roofing market. However, when low - slope systems are used on residences, the principles that apply to commercial roofing also apply to residential 11-48 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. work. The natural hazards presenting the greatest challenges to low -sloped roofs in the coastal environment are high winds (see Section 11.5.8.1), earthquakes (see Section 11.5.8.2), and hail (see Section 11.5.8.3). 11.5.8.1 High Winds Roof membrane blow -off is typically caused by lifting and peeling of metal edge flashings (gravel stops) or copings, which serve to clamp down the membrane at the roof edge. In hurricane -prone regions, roof membranes are also often punctured by wind-borne debris. Following the criteria prescribed in the IBC will typically result in roof systems that possess adequate wind uplift resistance if properly installed. IBC references ANSI/SPRI ES-1 for edge flashings and copings. ANSI/SPRI ES-1 does not specify a minimum safety factor. Accordingly, a safety factor of 2.0 is recommended for residences. PJ NOTE The 2009 edition of the IBC prohibits the use of aggregate roof surfacing in hurricane -prone regions. A roof system that is compliant with IBC (and the FBC) is susceptible to interior leakage if the roof membrane is punctured by wind-borne debris. If a roof system is desired that will avoid interior leakage if struck by debris, refer to the recommendations in FEMA P-424, Design Guide for Improving School Safety in Earthquakes, Floods and High Winds (FEMA 2010a). Section 6.3.3.7 also provides other recommendations for enhancing wind performance. 11.5.8.2 Seismic If a ballasted roof system is specified, its weight should be considered during seismic load analysis of the structure. Also, a parapet should extend above the top of the ballast to restrain the ballast from falling over the roof edge during a seismic event. 11.5.8.3 Hail It is recommended that a system that has passed the Factory Mutual Research Corporation's severe hail test be specified. Enhanced hail protection can be provided by a heavyweight concrete -paver -ballasted roof system. If the pavers are installed over a single -ply membrane, it is recommended that a layer of extruded polystyrene intended for protected membrane roof systems be specified over the membrane to provide protection if the pavers break. Alternatively, a stone protection mat intended for use with aggregate -ballasted systems can be specified. 11.6 Attic Vents High winds can drive large amounts of water through attic ventilation openings, which can lead to collapse of ceilings. Fact Sheet 7.5, Minimizing Water Intrusion Through Roof Vents in High -Wind Regions, in FEMA P-499 provides design and application guidance to minimize water intrusion through new and existing attic ventilation systems. Fact Sheet 7.5 also contains a discussion of unventilated attics. COASTAL CONSTRUCTION MANUAL 11-49 11 DESIGNING THE BUILDING ENVELOPE Volume II Continuous ridge vent installations, used primarily on roofs with asphalt shingles, have typically not addressed the issue of maintaining structural integrity of the roof sheathing. When the roof sheathing is used as a structural diaphragm, as it is in high -wind and seismic hazard areas, the structural integrity of the roof can be compromised by the continuous vent. Roof sheathing is normally intended to act as a diaphragm. The purpose of the diaphragm is to resist lateral forces. To properly function, the diaphragm must have the capability of transferring the load at its boundaries from one side of the roof to the other; it normally does this through the ridge board. The continuity, or load transfer assuming a blocked roof diaphragm, is accomplished with nails. This approach is illustrated by Figure 11-55. The problem with the continuous ridge vent installation is the need to develop openings through the diaphragm to allow air to flow from the attic space up to and through the ridge vent. For existing buildings not equipped with ridge vents, cutting slots or holes in the sheathing is required. If a saw is used to cut off 1 to 2 inches along either side of the ridge, the integrity of the diaphragm is affected. This method of providing roof ventilation should not be used without taking steps to ensure proper load transfer. The two methods of providing the proper ventilation while maintaining the continuity of the blocked roof diaphragm are as follows: NOTE When cutting a slot in a deck for a ridge vent, it is important to set the depth of the saw blade so that it only slightly projects below the bottom of the sheathing. Otherwise, as shown in Fact Sheet 7.5, the integrity of the trusses can be affected. 1. Drill 2- to 3-inch-diameter holes in the sheathing between each truss or rafter approximately 1 1/2 inches down from the ridge. The holes should be equally spaced and should remove no more than one- half of the total amount of sheathing area between the rafters. For example, if the rafters are spaced 24 inches o.c. and 2-inch-diameter holes are drilled, they should be spaced at 6 inches o.c., which will allow about 12 square inches of vent area per linear foot when the holes are placed along either side of the ridge. This concept is illustrated in Figure 11-56. Figure 11-55. Method for maintaining a continuous load path at the roof ridge by nailing roof sheathing Nails from sheathing to ridge board i NOTE: If roof sheathing is cut and removed ' - -i to achieve an air slot, continuity and :r - diaphragm action are affected. --''- �� "- �i ' i �Z Roof sheathing 11-50 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1. Sheathing vent holes on each side of ridge board O =0 �Z Roof Sheathing Joist or truss 2. Install two ridge boards separated by an air space of at least 3 inches, with solid blocking between the ridge boards at each rafter or truss. Stop the sheathing at the ridge board and fully nail the sheathing as required. The ridge vent must be wide enough to cover the 3-inch gap between the ridge boards. The ridge board and blocking must be nailed to resist the calculated shear force. For new construction, the designer should detail the ridge vent installation with the proper consideration for the load transfer requirement. Where high -diaphragm loads may occur, a design professional should be consulted regarding the amount of sheathing that can be removed or other methods of providing ventilation while still transferring lateral loads. The need to meet these requirements may become a significant problem in large or complex residential buildings where numerous ventilation openings are required. In these instances, ridge vents may need to be augmented with other ventilating devices (e.g., off -ridge vents or gable end vents). Many ridge vent products are not very wide. When these products are used, it may be difficult to provide sufficiently large openings through the sheathing and maintain diaphragm integrity if holes are drilled through the sheathing. Manufacturers' literature often illustrates large openings at the ridge with little or no consideration for the transfer of lateral loads. U Figure 11-56. Holes drilled in roof sheathing for ventilation and roof diaphragm action is maintained (sheathing nails not shown) NOTE When continuous ridge vents are used, it is not possible to continue the underlayment across the ridge. Hence, if wind -driven rain is able to drive through the vent or if the ridge vent blows off, water will leak into the house. It is likely that the ridge vent test standard referenced in Fact Sheet 7.5 in FEMA P-499 is inadequate. One option is to avoid vent water infiltration issues by designing an unventilated attic (where appropriate, as discussed in Fact Sheet 7.5). The other option is to specify a vent that has passed the referenced test method and attach the vent with closely spaced screws (with spacing a function of the design wind speed). COASTAL CONSTRUCTION MANUAL 11-51 11 DESIGNING THE BUILDING ENVELOPE Volume II 11.7 Additional Environmental Considerations In addition to water intrusion and possible resulting decay, sun (heat and ultraviolet [UV] radiation) and wind -driven rain must also be considered in selecting materials to be used in coastal buildings. The coastal environment is extremely harsh, and materials should be selected that not only provide protection from the harsh elements but also require minimal maintenance. 11.7.1 Sun Buildings at or near the coast are typically exposed to extremes of sun, which produces high heat and UV radiation. This exposure has the following effects: The sun bleaches out many colors Heat and UV shorten the life of many organic materials Heat dries out lubricants such as those contained in door and window operating mechanisms To overcome these problems: Use materials that are heat/UV-resistant Shield heat/UV susceptible materials with other materials Perform periodic maintenance and repair (refer to Chapter 14) 11.7.2 Wind -Driven Rain Wind -driven rain is primarily a problem for the building envelope. High winds can carry water droplets into the smallest openings and up, into, and behind flashings, vents, and drip edges. When buildings are constructed to provide what is considered to be complete protection from the effects of natural hazards, any small "hole" in the building envelope becomes an area of weakness into which sufficiently high wind can drive a large amount of rain. 11.8 References AAMA (American Architectural Manufacturers Association). 2008. Standard/Specification for Windows, Doors, and Unit Skylights. AAMA/WDMA/CSA 101/I.S.2/A440-08. AAMA. 2008. Voluntary Specification for Field Testing of Newly Installed Fenestration Products. AAMA 502-08. AAMA. 2009. Voluntary Specification for Rating the Severe Wind -Driven Rain Resistance of Windows, Doors, and Unit Skylights. AAMA 520-09. AAMA. Fenestration Anchorage Guidelines. AAMA TIR-A14. 11-52 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1.1 AAMA. Voluntary Guideline for Engineering Analysis of Window and Sliding Glass Door Anchorage Systems. AAMA 2501. ANSI/SPRI (American National Standards Institute / Single -Ply Roofing Industry). 2003. Wind Design Standard for Edge Systems Used with Low Slope Roofing Systems. ANSI/SPRI ES-1. ANSI/SPRI. 2010. Structural Design Standard for Gutter Systems Used with Low -Slope Roofs. ANSI/SPRI GD-1. ASCE (American Society of Civil Engineers). 2005. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-05. ASCE. 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. ASTM. Standard Practice for Determining Resistance of Solar Collector Covers to Hail by Impact with Propelled Ice Balls. ASTM E822. ASTM. Standard Specification for Performance ofExterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes. ASTM E1996. ASTM. Standard Test Method for Field Determination of Water Penetration oflnstalled Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. ASTM E1105. ASTM. Standard Test Method for Performance ofExterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials. ASTM E1886. ASTM. Standard Test Method for Structural Performance ofExterior Windows, Doors, Skylights, and Curtain Walls by Uniform Static Air Pressure Difference. ASTM E330. ASTM. Standard Test Method for Structural Performance ofExterior Windows, Doors, Skylights, and Curtain Walls by Cyclic Air Pressure Differential. ASTM E1233. ASTM. Standard Test Method for Wind Resistance ofAsphalt Shingles (Uplift Force/Uplift Resistance Method). ASTM D7158. DASMA (Door & Access Systems Manufacturers Association International). 2005. Standard Method for Testing Sectional Garage Doors and Rolling Doors: Determination of Structural Performance Under Missile Impact and Cyclic Wind Pressure. ANSI/DASMA 115. Available at http://www.dasma.com. Accessed January 2011. DASMA. 2005. Standard Method For Testing Sectional Garage Doors and Rolling Doors: Determination of Structural Performance Under Uniform Static Air Pressure Difference. ANSI/DASMA 108. Available at http://www.dasma.com. Accessed January 2011. DASMA. 2010. Connecting Garage Doorjambs to Building Framing. Technical Data Sheet #161. Available at http://www.dasma.com/PubTechData. asp. Accessed January 2011. FEMA (Federal Emergency Management Agency). 1992. Building Performance: Hurricane Andrew in Florida — Observations, Recommendations, and Technical Guidance. FEMA FIA 22. COASTAL CONSTRUCTION MANUAL 11-53 11 DESIGNING THE BUILDING ENVELOPE Volume II FEMA. 1993. Building Performance: Hurricane Iniki in Hawaii - Observations, Recommendations, and Technical Guidance. FEMA FIA 23. FEMA. 1998. Typhoon Paka: Observations and Recommendations on Building Performance and Electrical Power Distribution System, Guam, U.S.A. FEMA-1 193 -DR-GU. FEMA. 1999. Building Performance Assessment Team (BPAT) Report - Hurricane Georges in Puerto Rico, Observations, Recommendations, and Technical Guidance. FEMA 339. FEMA. 2005a. Mitigation Assessment Team Report: Hurricane Charley in Florida. FEMA 488. FEMA. 2005b. Hurricane Ivan in Alabama and Florida: Observations, Recommendations and Technical Guidance. FEMA 489. FEMA. 2006. Hurricane Katrina in the Gulf Coast. FEMA 549. FEMA. 2008. Home Builder's Guide to Construction in Wildfire Zones. FEMA P-737. FEMA. 2009. Hurricane Ike in Texas and Louisiana. FEMA P-757. FEMA. 2010a. Design Guide for Improving School Safety in Earthquakes, Floods and High Winds. FEMA P-424. FEMA. 2010b. Home Builder's Guide to Coastal Construction Technical Fact Sheet Series. FEMA P-499. Fernandez, G., F. Masters, and K. Gurley. 2010. "Performance of Hurricane Shutters under Impact by Roof Tiles," Engineering Structures Vol. 32, Issue 10, pp. 3384-3393. FMA/AAMA (Fenestration Manufacturers Association/American Architectural Manufacturers Association). 2007. Standard Practice for the Installation of Windows with Flanges or Mounting Fins in Wood Frame Construction. FMA/AAMA 100-07. FMA/AAMA. 2009. Standard Practice for the Installation of Windows with Frontal Flanges for Surface Barrier Masonry Construction for Extreme Wind/Water Conditions. FMA/AAMA 200-09. FRSA/TRI (Florida Roofing, Sheet Metal and Air Conditioning Contractors Association, Inc./The Roofing Institute). 2001. Concrete and Clay Roof Tile Installation Manual. Third Edition. FRSA/TRI.2005. Concrete and Clay Roof Tile Installation Manual. Fourth Edition. ICC (International Code Council). 2008. 2007Florida Building Code: Building. ICC. 2009a. International Building Code (2009 IBC). Country Club Hills, IL: ICC. ICC. 2009b. International Residential Code (2009 IRC). Country Club Hills, IL: ICC. ICBO (International Council of Building Officials). Uniform Building Code. Lopez, C., F.J. Masters, and S. Bolton. 2011. "Water Penetration Resistance of Residential Window and Wall Systems Subjected to Steady and Unsteady Wind Loading," Building and Environment 46, Issue 7, pp. 1329-1342. 11-54 COASTAL CONSTRUCTION MANUAL Volume II DESIGNING THE BUILDING ENVELOPE 1.1 McDonald, J.R. and T.L. Smith. 1990. Performance of Roofing Systems in Hurricane Hugo. Institute for Disaster Research, Texas Tech University. NRCA (National Roofing Contractors Association). 2011. The NRCA Roofing Manual. Salzano, C.T., F.J. Masters, and J.D. Katsaros. 2010. "Water Penetration Resistance of Residential Window Installation Options for Hurricane -prone Areas," Building and Environment 45, Issue 6, pp. 1373-1388. Smith, T.L. 1994. "Causes of Roof Covering Damage and Failure Modes: Insights Provided by Hurricane Andrew," Proceedings of the Hurricanes of 1992, ASCE. COASTAL CONSTRUCTION MANUAL 11-55 i r"I t�g Mechanical Equipment and Utilities This chapter provides guidance on design considerations for elevators, exterior -mounted and interior mechanical equipment, and utilities (electric, telephone, and cable TV systems and water and wastewater systems). Protecting mechanical equipment and utilities is a key component of successful building performance during and after a disaster event. 12.1 Elevators CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www.fema.gov/ rebui Id/mat/fema55.shtm). Elevators are being installed with increasing frequency in elevated, single-family homes in coastal areas. The elevators are generally smaller than elevators in non-residential buildings but are large enough to provide handicap accessibility and accommodate small household furniture and equipment. Small (low-rise) residential elevators that are added as part of a post -construction retrofit are usually installed in a shaft independent of an outside wall. Residential elevators designed as part of new construction can be installed in a shaft in the interior of the structure. In either case, the elevator shaft must have a landing, which is usually at the ground level, and a cab platform near the top. The bottom or pit of an elevator with a landing at the lower level is almost always below the BFE. COASTAL CONSTRUCTION MANUAL 12-1 12 INSTALLING MECHANICAL EQUIPMENT AND UTILITIES Volume II Appendix H in NFIP Technical Bulletin 4, Elevator Installation for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program (FEMA 2010a), discusses the installation of elevator systems and equipment in the floodplain. As explained in the bulletin, elevator shafts and enclosures that extend below the BFE in coastal areas must be designed to resist hydrostatic, hydrodynamic, and wave forces as well as erosion and scour, but are not required to include hydrostatic openings or breakaway walls. In addition, elevator accessory equipment should be installed above the BFE, replaced with flood damage - resistant elements, or treated with flood damage -resistant paint or coatings to minimize flood damage. For safety reasons, commercial and large (high-rise) elevators are designed with "fire recall" circuitry that sends the elevator to a designated floor during a fire so emergency services personnel can use the elevators. However, during flooding, this feature may expose the cab directly to floodwaters. Therefore, for elevators in coastal buildings, the elevator must be equipped with a float switch that sends the elevator cab to a level above the BFE. In addition, the design professional must ensure that the elevator stops at a level above the BFE when the power is lost. This can be accomplished by installing an emergency generator or a battery descent feature that is integrated into the float switch, as described in NFIP Technical Bulletin 4. Finally, although elevators and elevator equipment are permitted for building access and may be covered by flood insurance, their presence, location, and size can affect flood insurance premiums. For buildings in Zone V, the NFIP considers an elevator enclosure a building enclosure or an obstruction, which may be subject to an insurance rate loading depending on: Square footage of the enclosure Value of the elevator equipment Location of the elevator equipment in relation to the BFE 12.2 Exterior -Mounted Mechanical Equipment Exterior -mounted mechanical equipment can include exhaust fans, vent hoods, air conditioning units, duct work, pool motors, and well pumps. High winds, flooding, and seismic events are the natural hazards that can cause the greatest damage to exterior -mounted mechanical equipment. 12.2.1 High Winds Equipment is typically damaged because it is not anchored or the anchorage is inadequate. Damage may also be caused by inadequate equipment strength or corrosion. Relatively light exhaust fans and vent hoods are commonly blown away during high winds. Air conditioning condensers, which are heavier than fans and vent hoods, can also be blown off of buildings. Considering the small size of most exhaust fans, vent hoods, and air-conditioning units used on residential buildings, the following prescriptive attachment recommendations should be sufficient for most residences: For curb -mounted units, #14 screws with gasketed washers For curbs with sides smaller than 12 inches, one screw at each side of the curb 12-2 COASTAL CONSTRUCTION MANUAL Volume II INSTALLING MECHANICAL EQUIPMENT AND UTILITIES 11 For curbs between 12 and 24 inches, two screws per side For curbs between 24 and 36 inches, three screws per side For buildings within 3,000 feet of the ocean, stainless steel screws For units that have flanges attached directly to the roof, #14 pan -head screws, a minimum of two screws per side, and a maximum spacing of 12 inches o.c. Air conditioning condenser units, 1/2-inch bolts at the four corners of base of each unit If the equipment is more than 30 inches above the curb, the attachment design should be based on calculated wind loads. ASCE 7-10 contains provisions for determining the horizontal and lateral force and the vertical uplift force on rooftop equipment for buildings with a mean roof height less than or equal to 60 feet. The lateral force is based on the vertical area of the equipment as projected on a vertical plane normal to the direction of the wind. The uplift force is based on the horizontal area of the equipment as projected on a horizontal plane above the equipment and parallel to the direction of the wind. Until equipment manufacturers produce more wind -resistant equipment, job -site strengthening of vent hoods is recommended. One approach is to use 1/8-inch-diameter stainless steel cables. Two or four cables are recommended, depending on design wind conditions. Alternatively, additional heavy straps can be screwed to the hood and curb. To avoid corrosion problems in equipment within 3,000 feet of the ocean shoreline (including sounds and backbays), nonferrous metal, such as aluminum, stainless steel, or steel with minimum G-90 hot -dip galvanized coating, is recommended for the equipment, equipment stands, and equipment anchors. Stainless steel fasteners are also recommended. See Section 11.6 for guidance regarding attic vents. 12.2.2 Flooding Flood damage to mechanical equipment is typically caused by the failure to elevate equipment sufficiently, as shown in Figure 12-1. Figure 12-2 shows proper elevation of an air-conditioning condenser in a flood - prone area. Exterior -mounted mechanical equipment in one- to four -family buildings is normally limited to the following: CROSS REFERENCE Air-conditioning condensers Ductwork (air supply and return) Exhaust fans Pool filter motors Submersible well pumps Floodwaters can separate mechanical equipment from the supports and sever the connection to mechanical or electric For additional information, see FEMA 348, Protecting Building Utilities From Flood Damage — Principles and Practices for the Design and Construction of Flood -Resistant Building Utility Systems (FEMA 1999), and Fact Sheet 8.3, Homebuilder's Guide to Coastal Construction, in FEMA P-499 (FEMA 2010b). COASTAL CONSTRUCTION MANUAL 12-3 12 INSTALLING MECHANICAL EQUIPMENT AND UTILITIES Figure 12-1. Condenser damaged as a result of insufficient elevation, Hurricane Georges (U.S. Gulf Coast, 1998) Figure 12-2. Proper elevation of an air-conditioning condenser in a floodprone area; additional anchorage is recommended h� ` �---- - till►. �r q"M Volume II 12-4 COASTAL CONSTRUCTION MANUAL Volume II INSTALLING MECHANICAL EQUIPMENT AND UTILITIES 11 systems. Mechanical equipment can also be damaged or destroyed when inundated by floodwaters, especially saltwater. Although a short period of inundation may not destroy some types of mechanical equipment, any inundation of electric equipment causes, at a minimum, significant damage to wiring and other elements. Minimizing flood damage to mechanical equipment requires elevating it above the DFE. Because of the uncertainty of wave heights and the probability of wave run-up, the designer should consider additional elevation above the DFE for this equipment. NOTE Although the 2012 IBC and 2012 IRC specify that flood damage - resistant materials be used below the BFE, in this Manual, flood damage -resistant materials are recommended below the DFE. In Zone V, mechanical equipment must be installed either on a cantilevered platform supported by the first floor framing system or on an open foundation. A cantilevered platform is recommended. However, if the platform is not cantilevered, it is strongly recommended that the size of the elements, depth, and structural integrity of the open foundation that is used to support mechanical equipment be the same as the primary building foundation. Although smaller diameter piles could be used because the platform load is minimal, the smaller piles are more susceptible to being broken by floodborne debris, as shown in Figure 12-3. In Zone A, mechanical equipment must be elevated to the DFE on open or closed foundations or otherwise protected from floodwaters entering or accumulating in the equipment elements. For buildings constructed over crawlspaces, the ductwork of some heating, ventilation, and air-conditioning systems are routed through the crawlspace. The ductwork must be installed above the DFE or be made watertight in order to minimize flood damage. Many ductwork systems today are constructed with insulated board, which is destroyed by flood inundation. Figure 12-3. Small piles supporting a platform broken by floodborne debris COASTAL CONSTRUCTION MANUAL 12-5 12 INSTALLING MECHANICAL EQUIPMENT AND UTILITIES Volume II 12.2.3 Seismic Events Residential mechanical equipment is normally fairly light. Therefore, with some care in the design of the attachment of the equipment for resistance to shear and overturning forces, these units should perform well during seismic events. Because air-conditioning units that are mounted on elevated platforms experience higher accelerations than ground -mounted units, extra attention should be given to attaching these units in areas that are prone to large ground accelerations. 12.3 Interior Mechanical Equipment Interior mechanical equipment includes but is not limited to furnaces, boilers, water heaters, and distribution ductwork. High winds normally do not affect interior mechanical equipment. Floodwaters, however, can cause significant damage to furnaces, boilers, water heaters, and distribution ductwork. Floodwaters can extinguish gas -powered flames, short circuit the equipment's electric system, and inundate equipment and ductwork with sediment. The following methods of reducing flood damage to interior equipment are recommended: Elevate the equipment and the ductwork above the DFE by hanging the equipment from the existing first floor or placing it in the attic or another location above the DFE. In areas other than Zone V (where enclosure of utilities below the BFE is not recommended), build a waterproof enclosure around the equipment, allowing access for maintenance and replacement of equipment parts. 12.4 Electric Utility, Telephone, and Cable TV Systems Electric utilities serving residential buildings in coastal areas are frequently placed in harsh and corrosive environments. Such environments increase maintenance and shorten the lifespan of the equipment. Common electric elements of utilities in residential buildings that might be exposed to severe wind or flood events, which increase maintenance and shorten the lifespan further, are electric meters, electric service laterals and service drops from the utility company, electric panelboards, electric feeders, branch circuit wiring, receptacles, lights, security system wiring and equipment, and telephone and cable television wiring and equipment. The primary method of protecting elements from flooding is to elevate them above the DFE, but elevation is not always possible. Floodplain management requirements and other code requirements sometimes conflict. One conflict that is difficult to fully resolve is the location of the electric meter. Figure 12-4 shows a bank of meters and electric feeds that failed during Hurricane Opal. Utility companies typically require electric meters to be mounted where they can be easily read for billing purposes; meters are usually centered approximately 5 feet above grade. They are normally required by utility regulations to be no higher than eye level. However, this height is often below the DFE for coastal homes, and the placement therefore conflicts with floodplain management requirements that meters be installed above the DFE. Since meter sockets typically extend 12 inches below the center of the meter, design floods 12-6 COASTAL CONSTRUCTION MANUAL Volume II INSTALLING MECHANICAL EQUIPMENT AND UTILITIES 11 Figure 12-4. Electric service meters and feeders that were destroyed by floodwaters during Hurricane Opal (1995) that produce 4 feet of flooding can cause water to enter the meter socket and disrupt the electric service. When a meter is below the flood level, electric service can be exposed to floodborne debris, wave action, and flood forces. Figure 12-5 shows an electric meter that is easily accessible by the utility company but is above the DFE. Since many utility companies no longer manually read meters, there may be flexibility in meter socket mounting, preferably above the design flood. The use of automatic meter reading ("smart meters") by electric utility companies is increasing. The designer should consult the utility to determine whether smart meters can be placed higher than meters that must be read manually. Similar situations often exist with other electrical devices. For example, switches for controlling access and egress lighting and security sensors occasionally need to be placed below the DFE. The following methods are recommended when necessary to reduce the potential for damage to electric wiring and equipment and to facilitate recovery from a flood event: Wiring methods. Use conduit instead of cable. Placing insulated conductors in conduits allows flood - damaged wiring to be removed and replaced. The conduit, after being cleaned and dried, can typically be reused. In saltwater environments, non-metallic conduits should be used. Routing and installation. Install main electric feeders on piles or other vertical structural elements to help protect them from floating debris forces. Since flood damage is often more extensive on the seaward side of a building, routing feeders on the landward side of the structural elements of the building can further reduce the potential for damage. Do not install wiring or devices on breakaway walls. Figure 12-5 is an illustration of recommended installation techniques for electric lines, plumbing, and other utility elements. Design approach. Install the minimum number of electric devices below the DFE that will provide compliance with the electric code. Feed the branch circuit devices from wiring above the DFE to minimize the risk of flood inundation. COASTAL CONSTRUCTION MANUAL 12-7 12 INSTALLING MECHANICAL EQUIPMENT AND UTILITIES Volume II 12-8 COASTAL CONSTRUCTION MANUAL Volume II INSTALLING MECHANICAL EQUIPMENT AND UTILITIES 11 12.4.1 Emergency Power*�Mw) Because a severe wind event often interrupts electric service, designers and homeowners need to make a decision about the need for backup power. Emergency power can be provided by permanently installed onsite generators or by temporary generators brought to the site after the event. For permanently installed units, the following is recommended: Locate the generator above the DFE. Figure 12-6. Damage caused by dropped overhead service, Hurricane Marilyn (U.S. Virgin Islands, 1995) CROSS REFERENCE For guidance on determining the proper size of an emergency generator, see Section VI-D of FEMA 259, Engineering Principles and Practices for Retrofitting Flood Prone Residential Buildings (FEMA 2001). If located on the exterior of the building, place the unit to prevent engine exhaust fumes from being drawn into doors, windows, or any air intake louvers into the building. If located on the inside of the building, provide ventilation for combustion air and cooling air and provision for adequately discharging exhaust fumes. Locate the fuel source above the DFE and store an amount of fuel adequate for the length of time the generator is expected to operate. Install the generator where its noise and vibration will cause the least disruption. Determine the expected load (e.g., heat, refrigeration, lights, sump pumps, sewer ejector pumps). Non -fuel -fired heating systems and most cooling systems require large generators. Capacity considerations may limit the generator to providing only freeze protection and localized cooling. Install manual or automatic transfer switches that prevent backfeeding power from the generator into the utility's distribution system. Backfeeding power from generators into the utility's distribution system COASTAL CONSTRUCTION MANUAL 12-9 12 INSTALLING MECHANICAL EQUIPMENT AND UTILITIES can kill or injure workers attempting to repair damaged electrical lines. Provide an "emergency load" subpanel to supply critical circuits. Do not rely on extension cords. Supply the emergency panel from the load side of a manual or automatic transfer switch. Volume II WARNING Do not "backfeed" emergency power through the service panel. Utility workers can be killed! Determine whether operation of the generator will be manual or automatic. Manual operation is simpler and less expensive. However, a manual transfer switch requires human intervention. Owners should not avoid or delay evacuation to tend to an emergency power source. Size the generator, transfer switches, and interconnecting wiring for the expected load. The generator should be large enough to operate all continuous loads and have ample reserve capacity to start the largest motor load while maintaining adequate frequency and voltage control and maintaining power quality. 12-10 COASTAL CONSTRUCTION MANUAL Volume II INSTALLING MECHANICAL EQUIPMENT AND UTILITIES 11 12.5.2 Septic Systems WARNING Leach fields and septic tanks, and the pipes that connect them, are highly susceptible to erosion and scour, particularly in In some areas, high Coastal A Zone and Zone V with velocity flow risks. The best groundwater levels may preclude the installation of way to protect leach fields and other onsite sewage management septic tanks below the level of elements is to locate them outside the floodplain. expected erosion and scour. If septic systems cannot be located outside the floodplain, the design of septic systems for protection from severe events must include a consideration of the following, at a minimum: If the septic tank is dislodged from its position in the ground, the piping will be disconnected, releasing sewage into floodwaters. Also, the tank could damage the nearest structure. Therefore, bury the system below the expected depth of erosion and scour, if possible, and ensure the tank is anchored to prevent a buoyancy failure. The sewage riser lines and septic tank risers must be protected from water and debris flow damage; risers should be on the landward side of a pile or other vertical structural member or inside an enclosure designed to withstand the forces from the event (see Figure 12-5). If leach fields, pipes, and tanks cannot be located outside the floodplain, one possible way to protect them is to bury them below the expected scour depth. However, many local health codes or ordinances restrict or even prohibit the placement of septic elements in the floodplain. In these cases, alternate sewage management systems must be used. Because leach fields rely on soil to absorb moisture, saturated soil conditions can render leach fields inoperable. This problem and its potential mitigating measures depend on complex geotechnical considerations. Therefore, a geotechnical engineer and/or a qualified sewer designer should be consulted for the design and installation of leach fields. 12.5.3 Sanitary Systems To protect sanitary systems from a severe event, the design must include a consideration of the following, at a minimum: Sanitary riser lines must be protected from water and debris flow damage; risers should be on the landward side of a pile or other vertical structural member or inside an enclosure designed to withstand the forces from the event (see Figure 12-5). When the line breaks at the connection of the building line and main sewer line, raw sewage can flow back out of the line, contaminating the soil near the building. A check valve in the line may help prevent this problem. COASTAL CONSTRUCTION MANUAL 12-11 12 INSTALLING MECHANICAL EQUIPMENT AND UTILITIES Volume II 12.5.4 Municipal Water Connections If water risers are severed during a coastal event, damage to the water supply system can include waste from flooded sewer or septic systems intruding into the water system, sediment filling some portion of the pipes, and breaks in the pipes at multiple locations. Protecting municipal water connections is accomplished primarily by protecting the water riser that enters the building from damage by debris. See Section 12.5.1 for more information. 12.5.5 Fire Sprinkler Systems Protecting the fire sprinkler system is similar to protecting the other systems discussed in Section 12.5. The primary issue is to locate the sprinkler riser such that the location provides shielding from damage. In addition, there must be consideration to the location of shutoff valves and other elements so that if an unprotected portion of the fire water supply line is damaged, the damage is not unnecessarily added to the damage caused by the natural hazard event. 12.6 References ASCE (American Society of Civil Engineers). 2010. Minimum Design Loads for Buildings and Other Structures. ASCE Standard ASCE 7-10. FEMA (Federal Emergency Management Agency). 1999. Principles and Practices for Flood -Resistant Building Utilities. FEMA P-348. FEMA. 2001. Engineering Principles and Practices for Retrofitting Flood Prone Residential Buildings. FEMA 259. FEMA. 2010a. Elevator Installation for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program. FEMA NFIP Technical Bulletin 4. FEMA. 2010b. Homebuilder's Guide to Coastal Construction. FEMA P-499. FEMA. 2010c. National Flood Insurance Program Flood Insurance Manual. ICC (International Code Council). 2011a. International Building Code. 2012 IBC. Country Club Hills, IL: ICC. ICC. 2011b. International Residential Code for One -and Two -Family Dwellings. 2012 IRC. Country Club Hills, IL: ICC. 12-12 COASTAL CONSTRUCTION MANUAL i r"I onst;tr cting the Building This chapter provides guidance on constructing residential buildings in coastal areas, which presents challenges that are usually not present in more inland locations (risk of high winds and coastal flooding and a corrosive environment) and other challenges such as the need to elevate the building. Considerations related to these challenges include the need to: Perform more detailed inspections of connection details than those performed in noncoastal areas to ensure the details can withstand the CROSS additional hazards found in coastal areas REFERENCE Include with the survey staking the building within property line For resources that setbacks and at or above the design flood elevation (DFE) (see augment the guidance Section 4.5 for additional coastal survey regulatory requirements) and other informationin this Manual, see the Ensure that all elements of the building will be able to withstand the Residential Coastal Construction Web site forces associated with high winds, coastal flooding, or other hazards (http://www.fema.gov/ required of the design rebuild/mat/fema55. shtm). Ensure that the building envelope is constructed to minimize and withstand the intrusion of air and moisture during high -wind events (see Section 11.3.1.4) Provide durable exterior construction that can withstand a moist and sometimes salt -laden environment Protect utilities, which may include placing them at or above the DFE COASTAL CONSTRUCTION MANUAL 13-1 13 CONSTRUCTING THE BUILDING Volume II Constructing coastal residential buildings on elevated pile foundations present the following additional challenges: The difficulty of constructing a driven pile foundation to accepted construction plan tolerances The difficulty of constructing a building on an elevated post -and -beam foundation, which is more difficult than building on a continuous wall foundation This chapter discusses the construction aspects of the above challenges and other aspects of the coastal construction process, including the construction items that are likely to require the most attention from the builder in order for the design intent to be achieved. Although much of the discussion in this chapter is related to constructing the building to meet the architect's and engineer's design intent for existing and future conditions (such as erosion and sea -level rise), durability of the building elements is also important. Wood decay, termite infestation, metal corrosion, and concrete and masonry deterioration can weaken a building significantly, making it hazardous to occupy under any conditions and more likely to fail in a severe natural hazard event. Builders may find that the permitting and inspection procedures in coastal areas are more involved than those in inland areas. Not only must all Federal, State, and local Coastal Zone Management and other regulatory requirements be met, the design plans and specifications may need to be sealed by a design professional. Building permit submittals must often include detailed drawings and other types of information for all elements of the wind -resisting load path, including sheathing material, sheathing nailing, strap and tiedown descriptions, bolted connections, and pile description and placement. The placement of utilities at or above the DFE, breakaway walls, and flood equalization openings must be clearly shown. Site inspections are likely to focus on the approved plans, and building officials may be less tolerant of deviations from these approved construction documents than those in noncoastal areas. Inspection points are also discussed. 13.1 Foundation Construction Constructing a foundation in a coastal environment includes designing the layout, selecting the foundation type, selecting the foundation material with consideration for durability, and installing the foundation. Although pile foundations are the most common foundation type in Zone V and should be used in Coastal A Zones, shallow foundations, both masonry and concrete, may be acceptable elsewhere. Whether masonry, concrete, wood, or steel, all coastal foundation materials must be designed and installed to withstand the likelihood of high winds, moisture, and salt -laden air. See Chapter 10 for guidance on the design of coastal foundations. 13.1.1 Layout Surveying and staking must be done accurately in order to establish the building setback locations, the DFE, and the house plan and support locations. Figure 13-1 is a site layout with pile locations, batter boards, and setbacks and is intended to show the constraints a builder may face when laying out a pile -supported structure on a narrow coastal lot. There may be conflicts between what the contractor would like to do to prepare the site and what the environmental controls dictate can be done on the site. For example, leveling the site, especially altering dunes, and removing existing vegetation may be restricted. Furthermore, these 13-2 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 Figure 13-1. Site layout restrictions may limit access by pile drivers and other heavy equipment. Similarly, masonry and concrete foundations may require concrete pumping because of limited access to the traditional concrete mix truck and chute. In an elevated building with a pile foundation, the layout of the horizontal girders and beams should anticipate the fact that the final plan locations of the tops of the piles will likely not be precise. Irregularities in the piles and soil often prevent the piles from being driven perfectly plumb. The use of thick shims or overnotching for alignment at bolted pile -girder connections may have a significant adverse effect on the connection capacity and should be avoided. Figure 13-2 shows the typical process of pile notching; the use of a chain saw for this process can lead to inaccuracies at this early stage of construction. Figure 13-3 shows a wood pile that is overnotched. Figure 13-4 shows a pile that has been properly notched to support the floor girder and cut so plenty of wood remains at the top of the pile. COASTAL CONSTRUCTION MANUAL 13-3 13 CONSTRUCTING THE BUILDING Volume II Figure 13-2. Typical pile notching process SOURCE: PATTY MCDANIEL, USED WITH PERMISSION Trr�; 411 .k OR Figure 13-3. Improper overnotched wood pile SOURCE: PATTY MCDANIEL, USED WITH PERMISSION 13-4 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 Figure 13-4. Properly notched pile; outer member of this three - member beam supported by the through -bolt rather than the beam seat A rule of thumb regarding notching is to notch no more than 50 percent of the pile cross section, but in no case should notching be in excess of that specified by the design professional. Section 13.2 presents information concerning the reinforcement of overnotched and misaligned piles. The primary floor girders spanning between pile or foundation supports should be oriented parallel to the primary flow of potential floodwater and wave action if possible. This orientation (normally at right angles to the shoreline) allows the lowest horizontal structural member perpendicular to flow to be the floor joists. Thus, in an extreme flood, the girders are not likely be subjected to the full force of the floodwater and debris along their more exposed surfaces. The entire structure is built on the first floor, and it is therefore imperative that the first floor be level and square. The "squaring" process normally involves taking diagonal measurements across the outer corners and shifting either or both sides until the diagonal measurements are the same, at which point the building is square. An alternative is to take the measurements of a "3-4-5" triangle and shift the floor framing until the "3-4-5" triangular measurement is achieved. 13.1.2 Pile Foundations Pile foundations are the most common foundation type in Zone V coastal buildings and should also be used in Coastal A Zones where scour and erosion conditions along with potentially destructive wave forces make it inadvisable to construct buildings on shallow foundations. In many coastal areas, the most common type of pile foundation is the elevated wood pile foundation in which the tops of the piles extend above grade to about the level of the DFE (see Figure 13-5). COASTAL CONSTRUCTION MANUAL 13-5 13 CONSTRUCTING THE BUILDING Figure 13-5. Typical wood pile foundation Volume II Horizontal framing girders connected to the tops of the piles form a platform on which the house is built. Appendix B of ICC 600-2008 contains some girder designs for use with foundations discussed in FEMA P-550, Recommended Residential Construction for the Gulf Coast (FEMA 2006). In addition, the 2012 IRC contains prescriptive designs of girder and header spans. Furthermore, Fact Sheet 3.2, Pile Installation, in FEMA P-499 (FEMA 2011) presents basic information about pile design and installation, including pile types, sizes and lengths, layout, installation methods, bracing, and capacities. For more information on pile - to -beam connections, see Fact Sheet 3.3, Wood Pile -to -Beam Connections, in FEMA P-499, which presents basic construction guidance for various construction methods. The discussion in this section is focused on the construction of an elevated wood pile foundation. Precautions should be taken in handling and storing pressure -preservative -treated round or square wood piles. They should not be dragged along the ground or dropped. They should be stored well -supported on skids so that there is air space beneath the piles and the piles are not in standing water. Additional direction and precautions for pile handling, storage, and construction are found in Section 10.5 of this Manual and AWPA Standard M4-91. The effectiveness of pile foundations and the pile load capacity is related directly to the method of installation. The best method is to use a pile driver, which uses leads to hold the pile in position while a single- or double-acting diesel- or air -powered hammer drives the pile into the ground. Pile driving is often used with auguring to increase pile embedment. Augurs are used to drill the first several feet into the soil, and the piles are then driven to refusal. Auguring has the added benefit of improving pile alignment. WARNING The amount of long-term and storm -induced erosion expected to occur at the site (see Section 3.5 in Volume I of this Manual) must be determined before any assumptions about soils are made or analyses of the soils are conducted. Only the soils that will remain after erosion can be relied on to support the foundation members. 13-6 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING J The pile driver method is cost-effective in a development when a number of houses are constructed at one time but may be expensive for a single building. The drop hammer method is a lower cost alternative and is considered a type of pile driving, as discussed in Section 10.5.4. A drop hammer consists of a heavy weight that is raised by a cable attached to a power -driven winch and then dropped onto the end of the pile. A less desirable but frequently used method of inserting piles into sandy soil is "jetting." Jetting involves forcing a high-pressure stream of water through a pipe advanced along the side of the pile. The water blows a hole in the sand into which the pile is continuously pushed or dropped until the required depth is reached. Unfortunately, jetting loosens the soil around the pile and the soil below the tip, resulting in a lower load capacity. CROSS REFERENCE See Section 10.5.4 for a discussion of pile capacities for various installation methods. Holes for piles may be excavated by an auger if the soil is sufficiently clayey or silty. In addition, some sands may contain enough clay or silt to permit augering. This method can be used by itself or in conjunction with pile driving. If the hole is full-sized, the pile is dropped in and the void backfilled. Alternatively, an undersized hole can be excavated and a pile driven into it. When the soil conditions are appropriate, the hole stays open long enough to drop or drive in a pile. In general, piles dropped or driven into augered holes may not have as much capacity as those driven without augering. If precast concrete piles or steel piles are used, only a regular pile driver with leads and a single- or double- acting hammer should be used. For any pile driving, the building jurisdiction or the engineer -of -record will probably require that a driving log be kept for each pile. The log will show the number of inches per blow as the driving progressesa factor used in determining the pile capacity, as shown in Equation 13-1. As noted in Section 10.3, the two primary determinants of pile capacity are the depth of embedment in the soil and the soil properties. Piles must be able to resist vertical loads (both uplift and gravity) and lateral loads. Sections 8.5 and 8.10 contain guidance on determining pile loads. It is common practice to estimate the ultimate vertical load bearing capacity of a single pile on the basis of the driving resistance. Several equations are available for making such estimates. However, the results are not always reliable and may over -predict or under -predict the capacity, so the equations should be used with caution. One method of testing the recommended capacity based on an equation is to load test at least one pile at each location of known soil variation. The designer should also keep in mind that constructing a pile foundation appropriately for the loads it must resist in the coastal environment may drastically reduce future costs by helping to avoid premature failure. Many factors in addition to vertical and lateral loads must be taken into account in the coastal environment. For example, erosion and scour can add stress on the foundation members and change the capacity to which the piles should be designed. The complex and costly repairs to the home shown in Figure 10-2 could have been avoided if all forces and the reduced pile capacity resulting from erosion and scour had been considered in the pile foundation design. Equation 13.1 can be used to determine pile capacity for drop hammer pile drivers. Equations for other pile driver configurations are provided in U.S. Department of the Navy Design Manual 7.2, Foundation and Earth Structures Design (USDN 1982). COASTAL CONSTRUCTION MANUAL 13-7 13 CONSTRUCTING THE BUILDING Volume II Lateral and uplift load capacity of piles varies greatly with the soils present at the site. Pile foundation designs should be based on actual soil borings at the site (see Section 10.3.3.2). Variation in the final locations of the pile tops can complicate subsequent construction of floor beams and bracing. The problem is worsened by piles with considerable warp, non -uniform soil conditions, and material buried below the surface of the ground such as logs, gravel bars, and abandoned foundations. Builders should inquire about subsurface conditions at the site of a proposed building before committing to the type of pile or the installation method (see Section 10.3.3). A thorough investigation of site conditions can help prevent costly installation errors. The soils investigation should determine the following: Type of foundations that have been installed in the area in the past Type of soil that might be expected (based on past soil borings and soil surveys) Whether the proposed site has been used for any other purpose and if so, the likelihood of buried materials present on the site Scour and erosion both reduce pile capacities and erosion can increase flood loads on a pile. Scour and erosion must be considered in a properly designed pile foundation. Additional guidance on the effects of scour and erosion on piles is provided in Section 8.5.11 and Section 10.5.5. 13.1.3 Masonry Foundation Construction The combination of high winds and moist and sometimes salt - laden air can have a damaging effect on masonry construction by forcing moisture into the smallest cracks or openings in the masonry joints. The entry of moisture into reinforced masonry construction can lead to corrosion of the reinforcement and subsequent cracking and spalling if proper protection of the reinforcement is not provided, as required by TMS 402/ACI 530/ ASCE 5 and TMS 602/ACI 530.1/ASCE 6. Moisture resistance WARNING Open masonry foundations in earthquake hazard areas require special reinforcement detailing and pier proportions to meet the requirement for increased ductility. 13-8 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 is highly influenced by the quality of the materials and the quality of the masonry construction at the site. Masonry material selection is discussed in Section 9.4 of this Manual. The quality of masonry construction depends on many considerations. Masonry units and packaged mortar and grout materials should be stored off the ground and covered. Mortar and grouts must be carefully batched and mixed. As the masonry units are placed, head and bed joints must be well mortared and tooled. The 2012 IRC provides grouting requirements. Masonry work in progress must be well protected. Moisture penetration or retention must be carefully controlled where masonry construction adjoins other materials. As in any construction of the building envelope in the coastal environment, flashing at masonry must be continuous, durable, and of sufficient height and extent to impede the penetration of expected wind - driven precipitation. For more information on moisture barrier systems, see Fact Sheet 1.9, Moisture Barrier Systems, in FEMA P-499. Because most residential buildings with masonry foundations have other materials (e.g., wood, concrete, steel, vinyl) attached to the foundation, allowance must be made for NOTE shrinkage of materials as they dry out and for differential movement between the materials. Expansion and contraction joints must be Tooled concave joints and placed so that the materials can move easily against each other. V-joints provide the best moisture resistance. Masonry is used for piers, columns, and foundation walls. As explained in Section 10.2.1, the National Flood Insurance Program (NFIP) regulations require open foundations (e.g., piles, piers, posts, columns) for buildings constructed in Zone V. Buildings in Zone A may be constructed on any foundation system. However, because of the history of observed damage in Coastal A Zone and the magnitude of the flood and wind forces that can occur in these areas, this Manual recommends that only open foundation systems be constructed in Coastal A Zones. Figure 13-6 shows an open masonry foundation with only two rows of piers. It is unlikely that this foundation system could resist the overturning caused by the forces described in Chapter 8 and shown in Example 8-10. Fact Sheet 3.4, Reinforced Masonry Pier Construction, in FEMA P-499 provides recommendations on pier construction best practices. Fact Sheet 4.2, Masonry Details, in FEMA P-499 provides details on masonry wall -to -foundation connections. Reinforced masonry has much more strength and ductility than unreinforced masonry for resisting large wind, water, and earthquake forces. This Manual recommends that permanent masonry foundation construction in and near coastal flood hazard areas (both Zone A and Zone V) be fully or partially reinforced and grouted solid regardless of the purpose of the construction and the design loads. Grout should be in conformance with the requirements of the 2012 IBC. Knockouts should be placed at the bottom of fully grouted cells to ensure that the grout completely fills the cells from top to bottom. Knockouts are required only for walls (or piers) exceeding 5 feet in height. #J NOTE For CMUs, shrinkage cracking can be minimized by using Type I In areas not subject to moisture -controlled units and keeping them dry in transit and on earthquake hazards, the job. Usually, for optimum crack control, Type S mortar should breakaway walls below be used for below -grade applications and Type N mortar for above- elevated buildings may be constructed using grade applications. The 2012 IBC specifies grout proportions by unreinforced and ungrouted volume for masonry construction. masonry. COASTAL CONSTRUCTION MANUAL 13-9 13 CONSTRUCTING THE BUILDING Volume II Figure 13-6. Open masonry foundation 13.1.4 Concrete Foundation Construction Concrete foundation or superstructure elements in coastal construction almost always require steel reinforcement. Figure 13-7 shows a concrete foundation, and Figure 13-8 shows a house being constructed with concrete. Completed cast -in -place exterior concrete elements should generally provide 1-1/2 inches or more of concrete cover over the reinforcing bars. Minimum cover values vary according to bar size and exposure to earth or weather per ACI 318-08. This thickness of concrete cover serves to protect the reinforcing bars from corrosion, as does an epoxy coating. The bars are also protected by the natural alkalinity of the concrete. However, if saltwater penetrates the concrete cover and reaches the reinforcing steel, the concrete alkalinity will be reduced by the salt chloride and the steel can corrode if it is not otherwise protected. As the corrosion forms, it expands and cracks the concrete, allowing the additional entry of water and further corrosion. Eventually, the corrosion of the reinforcement and the cracking of the concrete weaken the concrete structural element, making it less able to resist loads caused by natural hazards. During placement, concrete normally requires vibration to eliminate air pockets and voids in the finished surface. The vibration must be sufficient to eliminate the air without separating the concrete or water from the mix. 13-10 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 Figure 13-7. Concrete foundation Figure 13-8. Concrete house r WW^ r ! '3. To ensure durability and long life in coastal, saltwater -affected locations, it is especially important to carefully carry out concrete construction in a fashion that promotes durability. "Material Durability in Coastal Environments," available on the Residential Coastal Construction Web site (http://www.fema.gov/ rebuild/mat/fema55.html) describes the 2012 IBC requirements for more durable concrete mixes with lower water -cement ratios and higher compressive strengths (5,000 pounds/square inch) to be used in a saltwater environment. The 2012 IBC also requires that additional cover thickness be provided. Proper placement, consolidation, and curing are also essential for durable concrete. The concrete mix water -cement ratio required by 2012 IBC or by the design should not be exceeded by the addition of water at the site. It is likely that concrete will have to be pumped at many sites because of access limitations or elevation differences between the top of the forms and the concrete mix truck chute. Pumping concrete requires some COASTAL CONSTRUCTION MANUAL 13-11 13 CONSTRUCTING THE BUILDING minor changes in the mix so that the concrete flows smoothly through the pump and hoses. Plasticizers should be used to make the mix pumpable; water should not be used to improve the flow of the mix. Concrete suitable for pumping must generally have a slump of at least 2 inches and a maximum aggregate size of 33 to 40 percent of the pump pipeline diameter. Pumping also increases the temperature of the concrete, thus changing the curing time and characteristics of the concrete depending on the outdoor temperature. Volume II #J NOTE ACI 318-08 specifies minimum amounts of concrete cover for various construction applications. Per the Exception to 1904.3 in the 2012 IBC, concrete mixtures for any R occupancies need only comply with the freeze/thaw requirements (as traditionally tabulated in the 2012 IBC and 2012 IRC), not the permeability and corrosion requirements of ACI 318-08. Freeze protection may be needed, particularly for columns and slabs, if pouring is done in cold temperatures. Concrete placed in cold weather takes longer to cure, and the uncured concrete may freeze, which adversely affects its final strength. Methods of preventing concrete from freezing during curing include: Heating adjacent soil before pouring on -grade concrete Warming the mix ingredients before batching Warming the concrete with heaters after pouring (avoid overheating) Placing insulating blankets over and around the forms after pouring Selecting a cement mix that will shorten curing time Like masonry, concrete is used for piers, columns, and walls; the recommendation in Section 13.1.3 regarding open foundations in Coastal A Zones also applies to concrete foundations. In addition, because the environmental impact of salt -laden air and moisture make the damage potential significant for concrete, this Manual recommends that all concrete construction in and near coastal flood hazard areas (both Zone V and Zone A) be constructed with the more durable 5,000-pounds/square inch minimum compressive strength concrete regardless of the purpose of the construction and the design loads. 13.1.5 Wood Foundation Construction All of the wood used in the foundation piles, girders, beams, and braces must be preservative -treated wood or, when allowed, naturally decay -resistant wood. Section 9.4 discusses materials selection for these wood elements. Piles must be treated with waterborne arsenicals, creosote, or both. Girders and braces may be treated with waterborne arsenicals, pentachlorophenol, or creosote. Certain precautions apply to working with any of these treated wood products, and additional precautions apply for pentachlorophenol- and creosote -treated wood (see Section 13.1.5.1). Additional information is available in Consumer Information Sheets where the products are sold. Wood foundations are being constructed in some parts of the country as part of a basement or crawlspace. These foundation elements have walls constructed with pressure -preservative -treated plywood and footings constructed with wide pressure- preservative -treated wood boards such as 2x10s or 2xl2s. Because the NFIP regulations allow continuous foundation walls (with the required openings) in Coastal A Zones, continuous 13-12 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 wood foundations might seem to be acceptable in these areas. However, because of the potential forces from waves less than 2 feet high (as discussed in Section 10.8), a wood foundation supported on a wood footing is not recommended in Coastal A Zones. When working with treated wood, the following health and safety precautions should be taken: Avoid frequent or prolonged inhalation of the sawdust. When sawing and boring, wear goggles and a dust mask. Use only treated wood that is visibly clean and free of surface residue should be used for patios, decks, and walkways. Before eating or drinking, wash all exposed skin areas thoroughly. If preservatives or sawdust accumulate on clothes, wash the clothes (separately from other household clothing) before wearing them again. Dispose of the cuttings by ordinary trash collection or burial. The cuttings should not be burned in open fires or in stoves, fireplaces, or residential boilers because toxic chemicals may be produced as part of the smoke and ashes. The cuttings may be burned only in commercial or industrial incinerators or boilers in accordance with Federal and State regulations. Avoid frequent or prolonged skin contact with pentachlorophenol or creosote -treated wood; when handling it, wear long-sleeved shirts and long pants and use gloves impervious to the chemicals (e.g., vinyl -coated gloves). Do not use pentachlorophenol-pressure-treated wood in residential interiors except for laminated beams or for building elements that are in ground contact and are subject to decay or insect infestation and where two coats of an appropriate sealer are applied. Sealers may be applied at the installation site. Urethane, shellac, latex epoxy enamel, and varnish are acceptable sealers. Do not use creosote -treated wood in residential interiors. Coal tar pitch and coal tar pitch emulsion are effective sealers for outdoor creosote -treated wood -block flooring. Urethane, epoxy, and shellac are acceptable sealers for all creosote -treated wood. 13.1.6 Foundation Material Durability Ideally, all of the pile -and -beam foundation framing of a coastal building is protected from rain by the overhead structure, even though all of the exposed materials should be resistant to decay and corrosion. In practice, the overhead structure includes both enclosed spaces (such as the main house) and outside decks. The spaces between the floor boards on an outside deck allow water to pass through and fall on the framing below. A worst case for potential rain and moisture penetration exists when less permeable decks collect water and channel it to fall as a stream onto the framing below. In addition, wind -driven rain and ocean spray penetrates into many small spaces, and protection of the wood in these spaces is therefore important to long-term durability of the structure. The durability of the exposed wood frame can be improved by detailing it to shed water during wetting and to dry readily afterward. Decay occurs in wetted locations where the moisture content of the exposed, COASTAL CONSTRUCTION MANUAL 13-13 13 CONSTRUCTING THE BUILDING Volume II untreated interior core of treated wood elements remains above the fiber saturation point —about 30 percent. The moisture content of seasoned, surface -dry 2x lumber (S-DRY) is less than or equal to 19 percent content when it arrives at the job site, but the moisture content is quickly reduced as the wood dries in the finished building. The moisture content of the large members (i.e., greater than 3 times) is much higher than 19 percent when they arrive at the job site, and the moisture content takes months to drop below 19 percent. The potential for deterioration is greatest at end grain surfaces. Water is most easily absorbed along the grain, allowing it to penetrate deep into the member where it does not readily dry. Figure 13-9 illustrates deterioration in the end of a post installed on a concrete base. This is a typical place for wood deterioration to occur. Even when the end grain is more exposed to drying, the absorptive nature of the end grain creates an exaggerated shrink/swell cycling, resulting in checks and splits, which in turn allow increased water penetration. Exposed pile tops present the vulnerable horizontal end grain cut to the weather. Cutting the exposed top of a pile at a slant does not prevent decay and may even channel water into checks. Water enters checks and splits in the top and side surfaces of beams and girders. It can then penetrate into the untreated core and cause decay. These checks and splits occur naturally in large sawn timbers as the wood dries and shrinks over time. They are less common in glue -laminated timbers and built-up sections. It is generally, but not universally, agreed that caulking the checks and splits is unwise because caulking is likely to promote water retention more than keep water out. The best deterrent is to try to keep the water from reaching the checks and splits. Framing construction that readily collects and retains moisture, such as pile tops, pile -beam connections, and horizontal girder and beam top surfaces, can be covered with flashing or plywood. However, there should always be an air gap between the protected wood and the flashing so that water vapor passing out of the wood is not condensed at the wood surface. For example, a close -fitting cap of sheet metal on a pile top can cause water vapor coming out of the pile top to condense and cause decay. The cap can also funnel water into the end grain penetrations of the vertical fasteners. Figure 13-9. Wood decay at the base of a post supported by concrete 13-14 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 When two flat wood surfaces are in contact in a connection, the contact surface tends to retain any water directed to it. The wider the connection's least dimension, the longer the water is retained and the higher the likelihood of decay. Treated wood in this contact surface is more resistant to decay but only at an uncut surface. The least dimension of the contact surface should be as small as possible. When the contact surfaces are for structural bearing, only as much bearing surface as needed should be provided, considering both perpendicular -to -grain and parallel -to -grain bearing design stresses. For example, deck boards on 2x joists have a smaller contact surface least dimension than deck boards on 4x joists. A beam bolted alongside an unnotched round wood pile has a small least dimension of the contact surface. Figure 13-10 illustrates the least -dimension concept. Poor durability performance has been observed in exposed sistered members. When sistered members must be used in exposed conditions, they should be of ground -contact -rated treated wood, and the top surface should be covered with a self -adhering modified bitumen ("peel and stick") flashing membrane. This material is available in rolls as narrow as 3 inches. The membranes seal around nail penetrations to keep water out. In contrast, sheet -metal flashings over sistered members, when penetrated by nails, can channel water into the space between the members. Other methods of improving exposed structural frame durability include: Using drip cuts to avoid horizontal water movement along the bottom surface of a member. Figure 13-11 shows this type of cut. Contact f surfaces Contact surfaces Connectors O Connectors Contact surfaces Contact --------- surfaces I ------- Connectors Connectors Figure 13-10. Examples of minimizing the least dimension of wood contact surfaces COASTAL CONSTRUCTION MANUAL 13-15 13 CONSTRUCTING THE BUILDING Volume II Avoiding assemblies that form "buckets" and retain water adjacent to wood. Avoiding designs that result in ledges below a vertical or sloped surface. Ledges collect water quite readily, and the resulting ponding from rain or condensation alternating with solar radiation causes shrink -swell cycling, resulting in checks that allow increased water penetration. To the extent possible, minimizing the number of vertical holes in exposed horizontal surfaces from nails, lags, and bolts. When possible, avoiding the use of stair stringers that are notched for each stair. Notching exposes the end grain, which is then covered by the stair. As a result, the stair tends to retain moisture at the notch where the bending stress is greatest at the minimum depth section. Figure 13-12 illustrates stair stringer exposure, and Figure 13-13 shows the type of deterioration that can result. Figure 13-12. Exposure of end grain in stair stringer cuts Figure 13-13. Deterioration in a notched stair stringer 13-16 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 Using the alternative stair stringer installation shown in Figure 13-14 when the stair treads are either nailed onto a cleat or the stringer is routed out so the tread fits into the routed -out area. Even these alternatives allow water retention at end grain surfaces, and these surfaces should therefore be field - treated with wood preservative. Caulking joints at wood connections to keep water out. Caulk only the top joints in the connection. Recaulk after the wood has shrunk, which can take up to a year for larger members. When structurally possible, considering using spacers or shims to separate contact surfaces. A space of about 1/16-inch discourages water retention by capillary action but can easily fill with dirt and debris. A 1/4- to 1/2-inch space is sufficient to allow water and debris to clear from the interface. This spacing has structural limitations; a bolted connection with an unsupported shim has much less shear capacity than an unspaced connection because of increased bolt bending and unfavorable bearing stress distribution in the wood. COASTAL CONSTRUCTION MANUAL 13-17 13 CONSTRUCTING THE BUILDING 13.1.8 Substitutions During construction, a builder may find that materials called for in the construction plans or specifications are not available or that the delivery time for those materials is too long and will delay the completion of the building. These conflicts require decisions about substituting one type of construction material for another. Because of the high natural hazard forces imposed on buildings near the coast and the effects of the severe year-round environment in coastal areas, substitutions should be made only after approval by a design professional and, if necessary, the local building official. 13.1.9 Foundation Inspection Points Volume II WARNING When substitutions are proposed, the design professional's approval should be obtained before the substitution is made. The ramifications of the change must be evaluated, including the effects on the building elements, constructability, and long-term durability. Code and regulatory ramifications should also be considered. If the foundation is not constructed properly, many construction details in the foundation can cause failure during a severe natural hazard event or premature failure because of deterioration caused by the harsh coastal environment. Improperly constructed foundations are frequently covered up, so any deficiency in the load - carrying or distributing capacity of one member is not easily detected until failure occurs. It is therefore very important to inspect the foundation while construction is in progress to ensure that the design is completed as intended. Table 13-1 is a list of suggested critical inspection points for the foundation. Table 13-1. Foundation and Floor Framing Inspection Points 1. Pile -to -girder connection Ensures that pile is not overnotched, that it is field -treated, and that bolts are properly installed with washers and proper end and edge distance 3. Joist blocking Ensures that the bottom of the joist is prevented from bending/buckling 5. Material storage - Ensures that the wood does not absorb too much moisture prior to protection from elements installation —exposure promotes checks and splits in wood, warp, and prior to installation separation in plywood 13.1.10 Top Foundation Issues for Builders The top foundation -related issues for builders are as follows: Piles, piers, or columns must be properly aligned. Piles, piers, or columns must be driven or placed at the proper elevation to resist failure and must extend below the expected depth of scour and erosion. 13-18 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING Foundation materials must be damage -resistant to flooding (pressure -treated wood, masonry, or concrete). The support at the top of the foundation element must be adequate to properly attach the floor framing system. Notching of a wood foundation element should not exceed the specifications in the construction documents. Breakaway walls should not be overnailed to the foundation. They are intended to fail. Utilities and other obstructions should not be installed behind these walls, and the interior faces should not be finished. For masonry or concrete foundation elements (except slabs -on -grade), the proper size of reinforcing, proper number of steel bars, and proper concrete cover over the steel should be used. Concrete must have the proper mix to meet the specialized demands of the coastal environment. Exposed steel in the foundation corrodes; corrosion should be planned for by installing hot -dipped galvanized or stainless steel. Areas of pressure -treated wood that have been cut or drilled retain water and decay; these cut areas should be treated in the field. 13.2 Structural Frame Structural framing includes framing the floors, walls, and roof and installing critical connections between each element. WARNING The connections described 13.2.1 Structural Connections in this Manual are designed to hold the building One of the most critical aspects of building in a coastal area together in a design event. is the method that is used to connect the structural members. Builders should never A substantial difference usually exists between connections underestimate the importance of installing connectors acceptable in inland construction and those required to withstand according to manufacturers' the natural hazard forces and environmental conditions in recommendations. Installing coastal areas. Construction in noncoastal, nonseismic areas must connectors properly is normally support only vertical dead and live loads and modest extremely important. wind loads. In most coastal areas, large forces are applied by wind, velocity flooding, wave impact, and floating debris. The calculated forces along the complete load path usually require that the builder provide considerable lateral and uplift capacity in and between the roof, walls, floors, girders, and piles. Consequently, builders should be sure to use the specified connectors or approved substitutes. Connectors that look alike may not have the same capacity, and a connector designed for gravity loads may have little uplift resistance. Fact Sheet 4.1, Load Path, in FEMA P-499 describes load paths and highlights important connections in a typical wind load path. The nails required for the connection hardware may not be regularly found on the job site. For example, full - diameter 8d to 20d short nails are commonly specified for specific hurricane/seismic connection hardware. COASTAL CONSTRUCTION MANUAL 13-19 13 CONSTRUCTING THE BUILDING Figure 13-15. Connector failure caused by insufficient nailing WARNING Proper nail selection and installation are critical. Builders should not substitute different nails or nailing patterns without approval from the designer. Volume II For full strength, these connections require that all of the holes in the hardware be nailed with the proper nails. In the aftermath of investigated hurricanes, failed connector straps and other hardware have often been found to have been attached with too few nails, nails of insufficient diameter, or the wrong type of nail. Figure 13-15 shows a connector that failed because of insufficient nailing. As mentioned previously, connection hardware must be corrosion -resistant. If galvanized connectors are used, additional care must be taken during nailing. installation, some of the galvanizing protection is knocked off. One way to avoid this problem is to use corrosion -resistant connectors that do not depend on a galvanized coating, such as stainless steel or wood (see Section 9.2.3). Only stainless steel nails should be used with stainless steel connectors. An alternative to hand -nailing is to use a pneumatic hammer that "shoots" nails into connector holes. All connections between members in a wood - frame building are made with nails, bolts, screws, or a similar fastener. Each fastener is installed by hand. The predominant method of installing nails When a hammer strikes the connector and nail during �J NOTE Additional information about pneumatic nail guns can be obtained from the International Staple, Nail and Tool Association, 512 West Burlington Ave., Suite 203, LaGrange, IL 60525-2245. A report prepared by National Evaluation Service, Inc., NER-272, Power - Driven Staples and Nails for Use in All Types of Building Construction (NES 1997), presents information about the performance of pneumatic nail guns and includes prescriptive nailing schedules. 13-20 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 is by pneumatic nail gun. Many nail guns use nails commonly referred to as "sinkers." Sinkers are slightly smaller in diameter and thus have lower withdrawal and shear capacities than common nails of the same size. Nail penetration is governed by air pressure for pneumatic nailers, and nail penetration is an important quality control issue for builders. Many prescriptive codes have nailing schedules for various building elements such as shearwalls and diaphragms. Another critical connection is the connection of the floor to the piles. Pile alignment and notching are critical not only to successful floor construction but also to the structural adequacy during a natural hazard event (see Section 13.1.1). Construction problems related to these issues are also inevitable, so solutions to pile misalignment and overnotching must be developed. Figure 13-16 illustrates a method of reinforcing an overnotched pile, including one that is placed on a corner. The most appropriate solution to pile misalignment is to re -drive a pile in the correct location. An alternative is illustrated in Figure 13-17, which shows a method of supporting a beam at a pile that has been driven "outside the layout" of the pile foundation. Figure 13-18 COASTAL CONSTRUCTION MANUAL 13-21 13 CONSTRUCTING THE BUILDING Volume II Figure 13-17. Beam support at misaligned piles Figure 13-18. Proper pile notching for two -member and four - member beams 13-22 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 illustrates the proper pile notching for both two -member and four -member beams. See Section 13.1.1 for more information on pile notching. After the "square" foundation has been built, the primary layout concerns about how the building will perform under loads are confined to other building elements being properly located so that load transfer paths are complete. 13.2.2 Floor Framing The connection between wood floor joists and the supporting beams and girders is usually a bearing connection for gravity V�10)� CROSS REFERENCE forces with a twist strap tie for uplift forces. Figure 13-19 shows a twist tie connection. This connection is subjected to large uplift See NFIP Technical Bulletin forces from high winds. In addition, the undersides of elevated 8-96, Corrosion Protection for structures, where these connectors are located, are particularly Metal Connectors in Coastal vulnerable to salt spray; the exposed surfaces are not washed Areas (FEMA 1996). by rain, and they stay damp longer because of their sheltered location. Consequently, the twist straps and the nails used to secure them must be hot -dipped galvanized or stainless steel. One way to reduce the corrosion potential for metal connectors located under the building is to cover the connectors with a plywood bottom attached to the undersides of the floor joists. (The bottom half of the joist -to -girder twist straps will still be exposed, however.) This covering will help keep insulation in the floor joist space as well as protect the metal connectors. Because the undersides of Zone V buildings are exposed, the first floor is more vulnerable to uplift wind and wave forces, as well as to the lateral forces of moving water, wave impact, and floating debris. These loads cause compressive and lateral forces in the normally unbraced lower flange of the joist. Solid blocking or 1x3 cross -bridging at 8-foot centers is recommended for at least the first floor joists unless substantial sheathing (at least 1/2-inch thick) has been nailed well to the bottom of these joists. Figure 13-19 also shows solid blocking between floor joists. Figure 13-19. Proper use of metal twist strap ties (circled); solid blocking between floor joists COASTAL CONSTRUCTION MANUAL 13-23 13 CONSTRUCTING THE BUILDING Volume II Floor framing materials other than 2x sawn lumber are becoming popular in many parts of the country. These materials include wood floor trusses and wood I -joists. Depending on the shape of the joist and the manufacturer, the proper installation of these materials may require some additional steps. For instance, some wood 1-joists require solid blocking at the end of the joist where it is supported so that the plywood web is not crushed or does not buckle. Figure 13-20 illustrates the use of plywood web 1-joists. As shown in the figure, the bottom flanges of the joists are braced with a small metal strip that helps keep the flange from twisting. Solid wood blocking is a corrosion -resistant alternative to the metal braces. Floor surfaces in high -wind, flood, or seismic hazard areas are required to act as a diaphragm. For the builder, this means that the floor joists and sheathing are an important structural element. Therefore, the following installation features may require added attention: Joints in the sheathing should fully bear on top of a joist, not a scabbed -on board used as floor support Nailing must be done in accordance with a shear diaphragm plan Construction adhesive is important for preventing "squeaky" floors, but the adhesive must not be relied on for shear resistance in the floor Joints in the sheathing across the joists must be fully blocked with a full -joist -height block. Horizontal floor diaphragms with lower shear capacities can be unblocked if tongue -and -groove sheathing is used. 13.2.2.1 Horizontal Beams and Girders Girders and beams can be solid sawn timbers, glue -laminated timbers (see Figure 13-20), or built-up sections (see "Material Durability in Coastal Environments" on the Residential Coastal Construction Web site at http://www.fema.gov/rebuild/mat/fema55.html). The girders span between the piles and support the beams and joists. The piles are usually notched to receive the girders. To meet the design intent, girders, beams, and joists must be square and level, girders must be secured to the piles, and beams and joists must be secured to the girders. Figure 13-20. Engineered joists used as floor joists with proper metal brace to keep the bottoms of the joists from twisting; engineered wood beam 13-24 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 The layout process involves careful surveying, notching, sawing, and boring. The bottom of the notch provides the bearing surface for downward vertical loads. The bolted connection between the girder and the vertical notch surface provides capacity for uplift loads and stability. Girder splices are made as required at these connections. Splices in multiple -member girders may be made away from the pile but should be engineered so that the splices occur at points of zero bending moment. This concept is illustrated in Figure 13-21. 0 0 0 0 0 0 0 � 0 0 = girder 0 = support 0 = splice 13.2.2.2 Substitution of Floor Framing Materials Figure 13-21. Acceptable locations for splices in multiple - member girders The considerations discussed in Section 13.1.8 for substitution of foundation materials also apply to substitutions of floor framing materials. 13.2.2.3 Floor Framing Inspection Points Proper connections between elements of the floor framing help to guarantee that the load path is continuous and the diaphragm action of the floor is intact. If floor framing is not constructed properly, many construction details in the floor framing can become structural inadequacies during a severe natural hazard event or cause premature failure because of deterioration caused by the harsh coastal environment. Table 13-1 is a list of suggested critical inspection points in foundations and a guide for floor framing inspections. 13.2.3 Wall Framing Exterior walls and designated interior shear walls are an important part of the building's vertical and lateral force -resisting system. All exterior walls must be able to withstand in -plane (i.e., parallel to the wall surface), gravity, and wind uplift tensile forces, and out -of -plane (i.e., normal or perpendicular to the wall surface) wind forces. Exterior and designated interior shear walls must be able to withstand shear and overturning forces transferred through the walls to and from the adjacent roof and floor diaphragms and framing. The framing of the walls should be of the specified material and fastened in accordance with the design drawings and standard code practice. Exterior wall and designated shear wall sheathing panels must be of the specified material and fastened with accurately placed nails whose size, spacing, and durability are in accordance with the design. Horizontal sheathing joints in shear walls must be solidly blocked in accordance with shear wall capacity tables. Shear transfer can be better accomplished if the sheathing extends the full height from the bottom of the floor joist to the wall top plate (see Figure 13-22), but sheathing this long is often unavailable. COASTAL CONSTRUCTION MANUAL 13-25 13 CONSTRUCTING THE BUILDING Volume II The design drawings may show tiedown connections between large shearwall vertical posts and main girders. Especially in larger, taller buildings, these connections must resist thousands of pounds of overturning forces during high winds. See Section 8.7 for information regarding the magnitude of these forces. The connections must be accomplished with careful layout, boring, and assembly. Shear transfer nailing at the top plates and sills must be in accordance with the design. Proper nailing and attachment of the framing material around openings is very important; see Section 9.2.1 for a discussion of the difficulty of transferring large shear loads when there are large openings in the shearwall. It is very important that shearwall sheathing (e.g., plywood, oriented strand board [OSB]) with an exterior exposure be finished appropriately with pigmented finishes such as paint, which last longer than unpigmented finishes, or semitransparent penetrating stains. It is also important that these finishes be properly maintained. Salt crystal buildup in surface checks in siding can damage the siding. Damage is typically worse in siding that is sheltered from precipitation because the salt crystals are never washed off with fresh rainwater. To meet the design intent, walls must: Be plumb and square to each other and to the floor Be lined up over solid support such as a beam, floor joists, or a perimeter band joist Not have any more openings than designated by the plans Not have openings located in places other than designated on the plans Consist of material expected to resist corrosion and deterioration Be properly attached to the floors above and below the wall, including the holddown brackets required to transfer overturning forces 13-26 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 In addition, all portions of walls designed as shearwalls must be covered with sheathing nailed in accordance with either the plans or a specified prescriptive standard. 13.2.3.1 Substitution of Wall Framing Materials The considerations discussed in Section 13.1.8 for substitution of foundation materials also apply to substitutions of wall framing materials. 13.2.3.2 Wall Framing Inspection Points Proper connections between elements of the wall framing help to guarantee a continuous load path and the diaphragm action of the walls is intact. If not completed properly, there are many construction details in the floor framing that can become structural inadequacies and fail during a severe natural hazard event or cause premature failure because of deterioration caused by the harsh coastal environment. Table 13-2 is a list of suggested critical inspection points that can be used as a guide for wall framing inspections. Table 13-2. Wall Inspection Points 1. Wall framing attachment to floors Ensures that nails are of sufficient size, type, and number 3. Wall stud blocking Ensures that there is support for edges of sheathing material 5. Material storage - protection from Ensures that the wood does not absorb too much moisture prior to elements prior to installation installation —exposure promotes checks and splits in wood, warp, and separation in plywood 7. Header support over openings Ensures that vertical and lateral loads will be transferred along the continuous load path 13.2.4 Roof Framing Proper roof construction is very important in high - wind and earthquake hazard areas. Reviews of wind damage to coastal buildings reveal that most damage starts with the failure of roof elements. The structural integrity of the roof depends on a complete load path, including the resistance to uplift of porch and roof overhangs, gable end overhangs, roof sheathing nailing, roof framing nailing and strapping, roof member -to -wall strapping, and gable end -wall bracing. WARNING The most common roof structure failure is the uplift failure of porch, eave, and gable end overhangs. The next most common is roof sheathing peeling away from the framing. Nailing the sheathing at the leading edge of the roof, the gable edge, and the joints at the hip rafter or ridge is very important, as is securing the roof framing to prevent uplift. This failure point (leading edge of sheathing at gable edge, ridge, and hip) is also the most likely place for progressive failure of the entire structure to begin. COASTAL CONSTRUCTION MANUAL 13-27 13 CONSTRUCTING THE BUILDING Volume II All of this construction must use the specified wood materials, straps, and nails. The appropriate nails must be used in all of the holes in the straps so that the straps develop their full strength. Sheathing nails must be of the specified length, diameter, and head, and the sheathing must be nailed at the correct spacing. In addition, sheathing nails must penetrate the underlying roof framing members and must not be overdriven, which frequently occurs when pneumatic nail guns are used. When prefabricated roof trusses are used, handling precautions must be observed, and the trusses must be laterally braced as specified by the design professional or manufacturer. Fact Sheets 7.1 through 7.4 in FEMA P-499 discuss roof construction, including sheathing installation, asphalt shingle roofing, and tile roofing. To meet the design intent, roofs must meet the following requirements: Roof trusses and rafters must be properly attached to the walls Roof sheathing must be nailed according to either the construction plans or a specified prescriptive standard Roofs must consist of materials expected to resist corrosion and deterioration, particularly the connectors 13.2.4.1 Substitution of Roof Framing Materials The considerations discussed in Section 13.1.8 for substitution of foundation materials also apply to substitutions of roof framing materials. 13.2.4.2 Roof Frame Inspection Points Proper connections between elements of the roof frame help to guarantee a continuous load path and the diaphragm action of the walls is intact. If not completed properly, there are many construction details in the roof framing that can become structural inadequacies and fail during a severe natural hazard event or cause premature failure because of deterioration caused by the harsh coastal environment. Table 13-3 contains suggestions of critical inspection points as a guide for roof framing inspections. 13.2.5 Top Structural Frame Issues for Builders The top structural frame issues for builders are as follows: WARNING Do not substitute nails, fasteners, or connectors without approval of the designer. Connections between structural elements (e.g., roofs to walls) must be made so that the full natural hazard forces are transferred along a continuous load path. Care must be taken to nail elements so that the nails are fully embedded. Compliance with manufacturers' recommendations on hardware use and load ratings is critically important. 13-28 COASTAL CONSTRUCTION MANUAL Volume II Table 13-3. Roof Frame Inspection Points 1. Roof framing attachment to walls 3. "H" clips or roof frame blocking 5. Material storage - protection from elements prior to installation CONSTRUCTING THE BUILDING 11 Ensures that the sufficient number, size, and type of nails are used in the proper connector Ensures that there is support for edges of the sheathing material Ensures that the wood does not absorb too much moisture prior to installation —exposure promotes checks and splits in wood, warp, and separation in plywood 7. Gable -end bracing Ensures that bracing conforms to design requirements and specifications Only material that is rated and specified for the expected use and environmental conditions should be used. Builders should understand that the weakest connections fail first and that it is therefore critical to pay attention to every connection. The concept of continuous load path must be considered for every connection in the structure. Exposed steel in the structural frame corrodes even in places such as the attic space. The builder should plan for it by installing hot -dipped galvanized or stainless steel hardware and nails. Compliance with suggested nailing schedules for roof, wall, and floor sheathing is very important. 13.3 Building Envelope The building envelope comprises the exterior doors, windows, skylights, non -load -bearing walls, wall coverings, soffits, roof systems, and attic vents. The floor is also considered a part of the envelope in buildings elevated on open foundations. Building envelope design is discussed in detail in Chapter 11. The key to successful building envelope construction is having a detailed plan that is followed carefully by the builder, as described below. A suitable design must be provided that is sufficiently specified and detailed to allow the builder to understand the design intent and to give the contractor adequate and clear guidance. Lack of sufficient and clear design guidance regarding the building envelope is common. If necessary, the contractor should seek additional guidance from the design professional or be responsible for providing design services in addition to constructing the building. COASTAL CONSTRUCTION MANUAL 13-29 13 CONSTRUCTING THE BUILDING Volume II The building must be constructed as intended by the design professional (i.e., the builder must follow the drawings and specifications). Examples are: Installing flashings, building paper, or air infiltration barriers so that water is shed at laps Using the specified type and size of fasteners and spacing them as specified Eliminating dissimilar metal contact Using materials that are compatible with one another Installing elements in a manner that accommodates thermal movements so that buckling or jacking out of fasteners is avoided Applying finishes to adequately cleaned, dried, and prepared substrates Installing backer rods or bond breaker tape at sealant joints Tooling sealant joints For products or systems specified by performance criteria, the contractor must exercise care in selecting those products or systems and in integrating them into the building envelope. For example, if the design professional specifies a window by requiring that it be capable of resisting a specified wind pressure, the contractor should ensure that the type of window that is being considered can resist the pressure when tested in accordance with the specified test (or a suitable test if a test method is not specified). Furthermore, the contractor needs to ensure that the manufacturer, design professional, or other qualified entity provides guidance on how to attach the window frame to the wall so that the frame can resist the design pressures. When the selection of accessory items is left to the discretion of the contractor, without prescriptive or performance guidance, the contractor must be aware of and consider special conditions at the site (e.g., termites, unusually severe corrosion, and high earthquake or wind loads) that should influence the selection of the accessory items. For example, instead of using screws in plastic sleeves to anchor elements to a concrete or masonry wall, a contractor can use metal expansion sleeves or steel spikes intended for anchoring to concrete, which should provide a stronger and more reliable connection, or the use of plastic shims at metal doors may be appropriate to avoid termite attack. Adequate quality control (i.e., inspection by the contractor's personnel) and adequate quality assurance (i.e., inspection by third parties such as the building official, the design professional, or a test lab) must be provided. The amount of quality control/quality assurance depends on the magnitude of the natural hazards being designed for, complexities of the building design, and the type of products or systems being used. For example, installing windows that are very tall and wide and make up the majority of a wall should receive more inspection than isolated, relatively small windows. Inspecting roof coverings and windows is generally more critical than inspecting most wall coverings because of the general susceptibility of roofing and glazing to wind and the resulting damage from water infiltration that commonly occurs when these elements fail. 13.3.1 Substitution of Building Envelope Materials The considerations discussed in Section 13.1.8 for substitution of foundation materials also apply to substitutions of envelope materials. Proposed substitutions of materials must be thoroughly evaluated and 13-30 COASTAL CONSTRUCTION MANUAL Volume II CONSTRUCTING THE BUILDING 11 must be approved by the design professional (see Section 13.1.8). The building envelope must be installed in a manner that will not compromise the building's structural integrity. For example, during construction, if a window larger than originally intended is to be installed because of delivery problems or other reasons, the contractor should obtain the design professional's approval prior to installation. The larger window may unacceptably reduce the shear capacity of the wall, or different header or framing connection details may be necessary. Likewise, if a door is to be located in a different position, the design professional should evaluate the change to determine whether it adversely affects the structure. 13.3.2 Building Envelope Inspection Points Table 13-4 is a list of suggested critical inspection points that can be used as a guide for building envelope inspections. Fact Sheet 6.1, Window and Door Installation, in FEMA P-499 discusses proper window and door installation and inspection points. Table 13-4. Building Envelope Inspection Points 1. Siding attachment to wall framing Ensures there are sufficient number, type, and spacing of nails 3. Flashings around wall and roof openings, roof perimeters, and at Prevents water penetration into building envelope changes in building shape 5. Attachments of vents and fans at Reduces chance that vents or fans will blow off and allow wind - roofs and walls driven rain into the building 13.3.3 Top Building Envelope Issues for Builders The top building envelope issues for builders are as follows: Many manufacturers do not rate their products in a way that it is easy to determine whether the product will really be adequate for the coastal environment and the expected loads. Suppliers should be required to provide information about product reliability in the coastal environment. Wind -driven rain finds a way into a building if there is an open path. Sealing openings and shedding water play significant parts in building a successful coastal home. Window and door products are particularly vulnerable to wind -driven rain leakage and air infiltration. These products should be tested and rated for the expected coastal conditions. The current high -wind techniques of adding extra roof surface sealing or attachments at the eaves and gable end edges should be used. Coastal buildings require more maintenance than inland structures. The maintenance requirement needs to be considered in the selection of materials and the care with which they are installed. COASTAL CONSTRUCTION MANUAL 13-31 13 CONSTRUCTING THE BUILDING Volume II 13.4 References ACI (American Concrete Institute). 2008. Building Code Requirements for Structural Concrete. ACI 318-08. AWPA (American Wood Protection Association). 1991. Care ofPressure-Treated Wood Products. AWPA Standard M4-91. Woodstock, MD. AWPA. 1994. Standards. Woodstock, MD. FEMA (Federal Emergency Management Agency). 1996. Corrosion Protection for Metal Connectors in Coastal Areas. NFIP Technical Bulletin 8-96. FEMA. 2006. Recommended Residential Construction for the Gulf Coast. FEMA P-550. FEMA. 2011. Home Builder's Guide to Coastal Construction Technical Fact Sheets. FEMA P-499. ICC (International Code Council). 2008. Standard for Residential Construction in High -Wind Regions, ICC 600-2008. ICC: Country Club Hills, IL. ICC. 2011a. International Building Code. 2012 IBC. Country Club Hills, IL: ICC. ICC. 2011b. International Residential Code for One -and Two -Family Dwellings. 2012 IRC. Country Club Hills, IL: ICC. NES (National Evaluation Service, Inc.). 1997. Power -Driven Staples and Nails for Use in All Types of Building Construction. National Evaluation Report NER-272. TMS (The Masonry Society). 2008. Building Code Requirements and Specification for Masonry Structures and Commentaries. TMS 402-08/ACI 530-08/ASCE 5-08 and TMS 602-08/ACI 530.1-08/ ASCE 6-08. USDN (U.S. Department of the Navy). 1982. Foundation and Earth Structures Design. Design Manual 7.2. 13-32 COASTAL CONSTRUCTION MANUAL i r"I j[a77Xiningthe Building This chapter provides guidance on maintaining the building structure and envelope. CROSS REFERENCE For maximum performance of a building in a coastal area, the or resources that augment building structure and envelope (i.e., exterior doors, windows, the guidance and other skylights, exterior wall coverings, soffits, roof systems, and attic information in this Manual, vents) must not be allowed to deteriorate. Significant degradation see the Residential Coastal Construction Web site (http:// by corrosion, wood decay, termite attack, or weathering increases www.fema.gov/rebuild/mat/ the building's vulnerability to damage from natural hazards. fema55.shtm). Figure 14-1 shows a post that appears on the exterior to be in Figure 14-1. Pile that appears acceptable from the exterior but has interior decay COASTAL CONSTRUCTION MANUAL 14-1 14 MAINTAINING THE BUILDING Volume II acceptable condition but is weakened by interior decay, which can , Jr be determined only through a detailed inspection. This post failed COST under the loads imposed by a natural hazard event. CONSIDERATION Long-term maintenance and repair demands are influenced Maintenance and repair costs directly by decisions about design, materials, and construction are related directly to original design decisions, materials methods during building design and construction. Using less selection, and construction durable materials will increase the frequency and cost of required methods. maintenance and repair. The design and detailing of various building systems (e.g., exposed structural, window, or roof systems) also significantly influence maintenance and repair demands. 14.1 Effects of Coastal Environment The coastal environment can cause severe damage to the building structure and envelope. The damage arises primarily from salt -laden moisture, termites, and weathering. 14.1.1 Corrosion The corrosive effect of salt -laden, wind -driven moisture in coastal areas cannot be overstated. Salt -laden, moist air can corrode exposed metal surfaces and penetrate any opening in the building. The need to protect metal surfaces through effective design and maintenance (see Section 14.2.6 for maintenance of metal connectors) is very important for the long-term life of building elements and the entire building. Stainless steel is recommended because many galvanized (non -heavy -gauge) products and unprotected steel products tin nnr lacr in dip parch rnictil anvirnnmanr Corrosion is most likely to attack metal connectors (see Section 14.2.6) that are used to attach the parts of the structure to one another, such as floor joists to beams and connectors used in cross - bracing below the finished lowest floor. Galvanized connectors coated with zinc at the rate of 0.9 ounce per square foot of surface area (designated G-90) can corrode in coastal environments at a rate of 0.1 to 0.3 millimeter/year. At this rate, the zinc protection will be gone in 7 years. A G-185 coated connector, which provides twice as much protection as G-90, can corrode in less than 20 years. More galvanized protection (more ounces of zinc per square foot of surface area to be protected) increases service life. CROSS REFERENCE For additional information on corrosion, see Section 9.4.5 in this Manual and FEMA Technical Bulletin 8-96, Corrosion Protection of Metal Connectors in Coastal Areas for Structures Located in Special Flood Hazard Areas (FEMA 1996). Corrosion can also affect fasteners for siding and connectors for attaching exterior -mounted heating, ventilation, and air-conditioning units, electrical boxes, lighting fixtures, and any other item mounted on the exterior of the building. These connectors (nails, bolts, and screws) should be stainless steel or when they must be replaced, replaced with stainless steel. These connectors are small items, and the increased cost of stainless steel is small. 14-2 COASTAL CONSTRUCTION MANUAL Volume II MAINTAINING THE BUILDING 14.1.2 Moisture There are many sources of exterior moisture from outside the home in the coastal environment. Whenever an object absorbs and retains moisture, the object may decay, mildew, or deteriorate in other ways. Figure 14-2 shows decay behind the connection plate on a beam. Significant sources of interior moisture, such as kitchens, baths, and clothes dryers, should be vented to the outside in such a way that condensation does not occur on interior or exterior surfaces. Figure 14-2. Wood decay behind a metal beam connector Connectors should be designed to shed water to prevent water from accumulating between the connector and the material the connector is attached to. Trapped moisture increases the moisture content of the material and potentially leads to decay. Moisture is most likely to enter at intersections of materials where there is a hole in the building envelope (e.g., window, door) of where two surfaces are joined (e.g., roof to wall intersection). If properly installed, the flashings for the openings and intersections should not require maintenance for many years. However, flashings are frequently not properly installed or installed at all, creating an ongoing moisture intrusion problem. The potential for wood framing in crawlspaces in low-lying coastal areas to decay is high. Moisture migration into the floor system can be reduced if the floor of the crawlspace is covered with a vapor barrier of at least 6-millimeter polyethylene. Where required by the local building code, wood framing in the crawlspace should be preservative -treated or naturally decay -resistant. The building code may have ventilation requirements. COASTAL CONSTRUCTION MANUAL 14-3 14 MAINTAINING THE BUILDING Volume II Many existing crawlspaces are being converted to "conditioned crawlspaces." A moisture barrier is placed on the floor and walls of the crawlspace interior, insulation is added to the floor system (commonly sprayed -on polyurethane foam), and conditioned air is introduced into the space. In order for a conditioned crawlspace to be successful in low-lying coastal areas, moisture control must be nearly perfect so that the moisture content of the floor system does not exceed 20 percent (the minimum water content in wood that promotes mold growth). Conditioned crawlspaces are typically not practical in a floodplain where flood vents are required. Sprinkler systems used for landscaping and other exterior water distribution systems (e.g., fountains) must be carefully tested so they do not create or increase water collection where metal connectors are fastened. Water collection can be prevented easily during installation of the exterior water distribution system by making sure the water distribution pattern does not increase the moisture that is present in the building materials. 14.1.3 Weathering The combined effects of sun and water on many building materials, particularly several types of roof and wall coverings, cause weathering damage, including: Fading of finishes Accelerated checking and splitting of wood Gradual loss of thickness of wood Degradation of physical properties (e.g., embrittlement of asphalt shingles) In combination, the effects of weathering reduce the life of building materials unless they are naturally resistant to weathering or are protected from it, either naturally or by maintenance. Even finishes intended to protect exterior materials fade in the sun, sometimes in only a few years. 14.1.4 Termites The likelihood of termite infestation in coastal buildings can be reduced by maintenance that makes the building site drier and otherwise less hospitable to termites, specifically: Storing firewood and other wood items that are stored on the ground, including wood mulch, well away from the building Keeping gutters and downspouts free of debris and positioned to direct water away from the building Keeping water pipes, water fixtures, and drainpipes in good repair Avoiding dampness in crawlspaces by providing adequate ventilation or installing impervious ground cover membranes Avoiding frequent plant watering adjacent to the house and trimming plants away from the walls If any wood must be replaced under the house in or near contact with the ground, the new wood should be treated. Removing moisture and treating the cellulose in wood, which is the termite's food source, are the most frequently used remedies to combat termites. 14-4 COASTAL CONSTRUCTION MANUAL Volume II MAINTAINING THE BUILDING 114 14.2 Building Elements That Require Frequent Maintenance To help ensure that a coastal building is properly maintained, this Manual recommends that buildings be inspected annually by professionals with the appropriate expertise. The following building elements should be inspected annually: Building envelope — wall coverings, doors, windows, shutters, skylights, roof coverings, soffits, and attic vents Foundation, attic, and the exposed structural frame Exterior -mounted mechanical and electrical equipment Table 14-1 provides a maintenance inspection checklist. Items requiring repair or replacement should be documented and the required work scheduled. Table 14-1. Maintenance Inspection Checklist COASTAL CONSTRUCTION MANUAL 14-5 14 MAINTAINING THE BUILDING Volume II Table 14-1. Maintenance Inspection Checklist (concluded) Sheathing under floors - attachment to framing, nail corrosion fastening sheathing to floor joists, buckling/warping caused by excessive moisture Glazing - cracked panes, condensation between panes of insulated glass, nicks in glass surface, sealant cracked/dried out Trim - deterioration, discoloration, separation at joints, caulking dried out or separated Shutters - permanent shutters should be operated at least twice/year and temporary panels should be checked once/year for condition Asphalt shingles - granule loss, shingles curled, nails withdrawing from sheathing, de -bonding of tabs along eaves and corners Wood shakes - splits, discoloration, deterioration, moss growth, attachment to framing (nails missing, withdrawn, or not attached to framing) Metal - corrosion, discoloration, connection of fasteners or fastening system adequacy Flashings - corrosion, joints separated, nails withdrawing Framing - condition of truss plates sagging or bowed rafters or truss chords, deterioration of underside of roof sheathing, evidence of water leaks, adequate ventilation Other items that should be inspected include cavities through which air can freely circulate (e.g., above soffits and behind brick or masonry veneers) and, depending on structural system characteristics and access, the structural system. For example, painted, light -gauge, cold -formed steel framing is vulnerable to corrosion, and the untreated cores of treated timber framing are vulnerable to decay and termite damage. Depending on visual findings, it may be prudent to determine the condition of concealed items through nondestructive or destructive tests (e.g., test cuts). The following sections provide information on the building elements that require frequent maintenance in coastal environments: glazing, siding, roofs, outdoor mechanical and electrical equipment, decks and exterior wood, and metal connectors. 14-6 COASTAL CONSTRUCTION MANUAL Volume II MAINTAINING THE BUILDING 14.2.1 Glazing Glazing includes glass or a transparent or translucent plastic sheet in windows, doors, skylights, and shutters. Glazing is particularly vulnerable to damage in hurricane -susceptible coastal areas because high winds create wind-borne debris that can strike the glazing. Maintenance suggestions for glazing include the following: Checking glazing gaskets/sealants for deterioration and repairing or replacing as needed. Broken seals in insulated glass are not uncommon in coastal areas. Checking wood frames for decay and termite attack, and checking metal frames for corrosion. Frames should be repainted periodically (where appropriate), and damaged wood should be replaced. Maintaining the putty in older wood windows minimizes sash decay. Metal frames should be cleaned of corrosion or pitting and the operation of the windows tested on some frequency. Checking vinyl frames for cracks especially in the corners and sealing any cracks with a sealant to prevent water entry into the window frame. Vinyl may become discolored from the ultraviolet (UV) rays of the sun. Checking for signs of water damage (e.g., water stains, rust streaks from joints) and checking sealants for substrate bond and general condition. Repair or replace as needed. Checking glazing for stress cracks in corners. Stress cracks might be an indication of either settlement of the house or of lateral movement that is causing excessive stress in the lateral load system. Checking shutters for general integrity and attachment and repainting periodically where appropriate. Replacing or strengthening the attachment of the shutter system to the building as appropriate. Checking the shutters for ease of operation. Sand can easily get into the hinges and operators and render shutters inoperable. Checking locks and latches frequently for corrosion and proper operation. Lock mechanisms are vulnerable to attack by salt -laden air. Applying a lubricant or rust inhibitor improves the operation of these mechanisms over the short term. Installing double hung and awning windows, which generally perform better than sliding or jalousie windows in the coastal environment, primarily because the sliding and jalousie windows allow more water, sand, and air infiltration because of the way the windows open and close. Replacing sliding and jalousie windows to reduce infiltration. 14.2.2 Siding Solar UV degradation occurs at a rate of about 1/16 inch over 10 years on exposed wood. This rate of degradation is not significant for dimension lumber, but it is significant for plywood with 1/8-inch veneers. If the exterior plywood is the shearwall sheathing, the loss will be significant over time. Maintenance suggestions for siding materials include the following: COASTAL CONSTRUCTION MANUAL 14-7 14 MAINTAINING THE BUILDING Volume II Protecting plywood from UV degradation with pigmented finishes rather than clear finishes. Pigmented finishes are also especially recommended for exposed shearwall sheathing. Protecting wood siding with a protective sealant —usually a semi -transparent stain or paint. The coating should be re -applied regularly because the degradation will occur nearly linearly if re -application is done but will progress faster if allowed to weather with no regular sealing. Keeping siding surfaces free of salt and mildew and washing salt from siding surfaces not washed by rain, taking care to direct the water stream downward. Mildew should be washed as needed from siding using commercially available products or the homemade solution of bleach and detergent described in Finishes for Exterior Wood: Section, Application and Maintenance (Williams et al. 1996). Power washing is another technique to keep the siding clean as long as the siding sealant is not removed. Mildew grows on almost any surface facing north, no matter how small the surface. Caulking seams, joints, and building material discontinuities with a sealant intended for severe exterior exposures and renew the sealant every 5 years at a minimum or when staining or painting the siding and trim. Sealant applied at large wood members should be renewed about 1 year after the wood has shrunk away from the caulked joint. Caulking carefully to avoid closing off weep or water drainage holes below windows or in veneers that are intended to drain will prevent sealing the moisture inside the wall cavity, which can lead to significant, long-term deterioration. Renailing siding when nails withdraw (pop out) and renailing at a new location so the new nail does not go into the old nail hole. Ensuring vinyl siding has the ability to expand and contract with temperature changes. Buckling in the siding is an indication that the siding was installed too tightly to the wall sheathing with an insufficient amount of room under the siding nails to allow for the normal horizontal movement of the siding. 14.2.3 Roofs Roof coverings are typically the building envelope material most susceptible to deterioration from weathering. Also, depending on roof system design, minor punctures or tears in the roof covering can allow water infiltration, which can lead to serious damage to the roof system and other building elements. Maintenance suggestions for roof materials include the following: Checking the general condition of the roof covering. Granule loss from asphalt shingles is always a sign of some deterioration, as is curling and clawing (reverse curling) although some minor loss is expected even from new shingles. Dabbing roofing cement under the tabs of the first layer of shingles, including the base course, to help ensure that this layer stays down in high winds. Dabbing roofing cement under any shingle tabs that have lifted up from the existing tack strip. Checking the nails that attach the shingles to the roof for corrosion or pullout. Checking metal flashings and replacing or repairing as necessary. Cleaning dirt, moss, leaves, vegetative matter, and mildew from wood shakes. 14-8 COASTAL CONSTRUCTION MANUAL Volume II MAINTAINING THE BUILDING 114 Cleaning corroded surfaces of ferrous metal roofs and applying an appropriate paint or sealer. Checking the attachment of the roof surface to the deck. Screws and nails can become loose and may require tightening. Gasketed screws should be added to tighten the metal deck to the underlayment. Some roofing systems are attached to the underlayment with clips that can corrode —these clips should be inspected and any corroded clips replaced, but in many cases, the clips will be concealed and will require some destructive inspection to discover the corroded clips. Removing debris from the roof and ensuring that drains, scuppers, gutters, and downspouts are not clogged. Removing old asphalt shingles before recovering. This is recommended because installing an additional layer of shingles requires longer nails, and it is difficult to install the new asphalt shingles so that they lay flat over the old. New layers installed over old layers can therefore be susceptible to wind uplift and damage, even in relatively low wind speeds. New layers installed over old shingles could void the warranty for the new shingles. Checking attachments of eave and fascia boards. Deterioration in these boards will likely allow flashings attached to them to fail at lower than design wind speeds. 14.2.4 Exterior -Mounted Mechanical and Electrical Equipment Most outdoor mechanical and electrical equipment includes metal parts that corrode in the coastal environment. Life expectancy improves if the salt is washed off the outside of the equipment frequently. This occurs naturally if the equipment is fully exposed to rainwater, but partially protected equipment is subject to greater corrosion because of the lack of the natural rinsing action. Using alternative materials that do not include metal parts can also help reduce the problems caused by corrosion. In all cases, electrical switches should be the totally enclosed type to help prevent moisture intrusion into the switch, even if the switch is located on a screened porch away from the direct effects of the weather. Building owners should expect the following problems in the coastal environment: Electrical contacts can malfunction and either short out or cause intermittent operation Housings for electrical equipment; heating, ventilation, and air-conditioning condensers; ductwork; and other elements deteriorate more rapidly Fan coils for outside condensers can deteriorate more rapidly unless a coastal environment is specified Typical metal fasteners and clips used to secure equipment can deteriorate more rapidly in a coastal environment than a non -coastal environment 14.2.5 Decks and Exterior Wood The approach to maintaining exterior wood 2x members is different from the approach for thicker members. The formation of small checks and splits in 2x wood members from cyclical wetting and drying can be reduced by using water-repellent finishes. The formation of larger checks and splits in thicker wood members is caused more by long-term drying and shrinking and is not as significantly reduced by the COASTAL CONSTRUCTION MANUAL 14-9 14 MAINTAINING THE BUILDING Volume II use of water-repellent finishes. Installation of horizontal 2x members with the cup (concave surface) down minimizes water retention and wood deterioration. Cyclical wetting and drying, such as from dew or precipitation, causes the exterior of a wood member to swell and shrink more quickly than the interior. This causes stress in the surface, which leads to the formation of checks and splits. This shrink -swell cycling is worst on southern and western exposures. Checks and splits, especially on horizontal surfaces, provide paths for water to reach the interior of a wood member and remain, where they eventually cause decay. Maintaining a water-repellent finish, such as a pigmented paint, semi -transparent stain, or clear finish, on the wood surface can reduce the formation of checks and splits. These finishes are not completely water- or vapor- repellent, but they significantly slow cyclical wetting and drying. Of the available finishes, pigmented paints and semi- transparent stains have the longest lifetime; clear finishes must be reapplied frequently to remain effective. Matte clear finishes are available that are almost unnoticeable on bare wood. These finishes are therefore attractive for decking and other "natural" wood, but they must be renewed when water no longer beads on the finished surface. Wood deck surfaces can be replaced with synthetic materials, which are sold under a variety of trade names. Many of these products should be attached with stainless screws or hidden clips to preservative - treated framing. Moisture -retaining debris can collect between deck boards and in the gaps in connections. Periodic cleaning of this debris from between wood members, especially at end grains, allows drying to proceed and inhibits decay. Larger timbers can also be vulnerable to checks, splits, and other weather -related problems. The best way to maintain larger timbers is to keep water away from joints, end grain surfaces, checks, and splits. Much can be learned by standing under the house (given sufficient headroom) during a rain with the prevailing wind blowing to see where the water goes. Measures, such as preservative treatments, can then be taken or renewed to minimize the effect of this water on the larger timbers. Connections of deck band boards to the structure should be inspected periodically for moisture intrusion. These connections frequently leak from wind -driven rain and moisture accumulation. Leakage can occur at the flashing to structure interface or at the bolts connecting the band board to the structure. 14.2.6 Metal Connectors Most sheet -metal connectors, such as tiedown straps, joist hangers, and truss plates used in structural applications in the building, should be specified to last the lifetime of the building without the need for maintenance. However, the use of corrosion -prone connectors is a common problem in existing coastal houses. Galvanized connectors may have corrosion issues. If galvanized connectors remain gray, the original strength is generally unaffected by corrosion. When most of the surface of the connector turns rust red, the sacrificial galvanizing has CROSS REFERENCE The selection of metal connectors for use within the building envelope and in exposed locations is addressed in Section 9.4 of this Manual. 14-10 COASTAL CONSTRUCTION MANUAL Volume II MAINTAINING THE BUILDING 114 been consumed and the corrosion rate of the unprotected steel can be expected to accelerate by up to a factor of 50 times. Figure 14-3 illustrates severe corrosion under an exterior deck. Sheet -metal connectors can be susceptible to rapid corrosion and are frequently without reserve strength. During routine inspections, any sheet -metal connectors found to have turned rust red or to show severe, localized rusting sufficient to compromise their structural capacity should be replaced immediately. However, the replacement of sheet metal connectors is usually difficult for a number of reasons: the connection may be under load, the nails or bolts used WARNING to secure connectors are usually hard to remove, and the location of a connector often makes removal awkward. Using corrosion -prone sheet metal connectors increases Salt -laden air can increase corrosion rates in building maintenance requirements materials. Covering exposed connectors with a sheathing and potentially compromises material reduces their exposure and therefore increases their structural integrity. life expectancy. COASTAL CONSTRUCTION MANUAL 14-11 14 MAINTAINING THE BUILDING Volume II 14.3.1 Flooding When designing for the lateral force capacity of an unbraced or braced pile foundation, the designer should allow for a certain amount of scour. Scour in excess of the amount allowed for reduces the embedment of the piles and causes them to be overstressed in bending during the maximum design flood, wind, or earthquake. As allowed by local regulations and practicality, the grade level should be maintained at the original design elevation. Scour and long-term beach erosion may affect pile maintenance requirements. If tidal wetting was not anticipated in the original design, the piles may have received the level of preservative treatment required only for ground contact and not the much higher marine treatment level that provides borer resistance. If the pile foundation is wetted by high tides or runup, borer infestation is possible. Wrapping treatments that minimize borer infestation are available for the portions of the piles above grade that are subject to wetting. 14.3.2 Seismic and Wind Many seismic and wind tiedowns at shearwall vertical chords use a vertical threaded rod as the tension member. Each end of the threaded rod engages the tiedown hardware or a structural member. Over time, cross -grain shrinkage in the horizontal wood members between the threaded rod connections loosens the threaded rod, allowing more rocking movement and possible damage to the structure. Whenever there is an opportunity to access the tiedowns, the nuts on the rods should be tightened firmly. New proprietary tiedown systems that do this automatically are available. Shearwall sill plates bearing directly on continuous footings or concrete slabs -on -grade, if used in coastal construction, are particularly susceptible to decay in moist conditions. Figure 14-4 shows a deteriorated sill plate. Even if the decay of the preservative -treated sill plate is retarded, the attached untreated plywood can easily decay and the shearwall will lose strength. Conditions that promote sill and plywood decay include an outside soil grade above the sill, stucco without a weep screed at the sill plate, and sources of excessive interior water vapor. Correcting these conditions helps maintain the strength of the shearwalls. Figure 14-4. Deteriorated wood sill plate 14-12 COASTAL CONSTRUCTION MANUAL Volume II MAINTAINING THE BUILDING 114 14.4 References FEMA (Federal Emergency Management Agency). 1996. Corrosion Protection ofMetal Connectors in CoastalAreas for Structures Located in Special Flood Hazard Areas. NFIP Technical Bulletin 8-96. Shifler, D.A. 2000. Corrosion and Corrosion Control in Saltwater Environments. Pennington, NJ: Electrochemical Society. Williams, R., M. Knaebe, and W. Feist. 1996. Finishes for Exterior Wood- Section, Application and Maintenance. Forest Products Society. COASTAL CONSTRUCTION MANUAL 14-13 i r"I 11 ing Buildings for Hazards This chapter provides guidance on retrofitting existing residential structures to resist or mitigate the consequences of natural hazards in the coastal environment. The natural hazards that are addressed are wildfires, seismic events, floods, and high winds. Specific retrofitting methods and implementation are discussed briefly, and resources with more in-depth information are provided. Some retrofitting methods are presented together with broader, non -retrofitting mitigation methods when retrofitting and non -retrofitting methods are presented together in the referenced guidance. For retrofitting to mitigate high winds, the new three -tiered wind retrofit program that is provided in FEMA P-804, Wind Retrofit Guide for Residential Buildings (FEMA 2010c), is discussed. The program includes systematic and programmatic guidance. Retrofitting opportunities present themselves every time maintenance is performed on a major element of a building. Retrofitting that increases resistance to natural hazards should focus on improvements that provide the largest benefit to the owner. CROSS REFERENCE For resources that augment the guidance and other information in this Manual, see the Residential Coastal Construction Web site (http://www. fema.gov/rebuild/mat/fema55.shtm). U NOTE FEMA's Hazard Mitigation Assistance (HMA) grant programs provide funding for eligible mitigation activities that reduce disaster losses and protect life and property from future disaster damage. Currently, FEMA administers the following HMA grant programs: Hazard Mitigation Grant Program, Pre - Disaster Mitigation, Flood Mitigation Assistance, Repetitive Flood Claims, and Severe Repetitive Loss. COASTAL CONSTRUCTION MANUAL 15-1 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II If an existing building is inadequate to resist natural hazard loads, retrofitting should be considered. 15.1 Wildfire i i i Thousands of residential and non-residential buildings are damaged or destroyed every year by wildfires, resulting in more than $200 million in property damage annually. More than $100 million is spent every year on fire suppression and even more on recovering from catastrophic natural and manmade hazards. Studies cited by IBHS in Mega Fires (IBHS 2008) have shown that financial losses can be prevented if simple measures are implemented to protect existing buildings. FEMA offers funding through the HMGP and the PDM Program for wildfire mitigation projects. Projects funded through these programs involve retrofits to buildings that help minimize the loss of life and damage to the buildings from wildfire. Eligible activities for wildfire mitigation per FEMXs Hazard Mitigation Assistance Unified Guidance (FEMA 2010a) may include: Provision of defensible space through the creation of perimeters around residential and non-residential buildings and structures by removing or reducing flammable vegetation. The three concentric zones of defensible space are shown in Figure 15-1. Figure 15-1. The three concentric zones of defensible space SOURCE: ADAPTED FROM FEMA P-737 15-2 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Application of non-combustible building envelope assemblies that can minimize the impact of wildfires through the use of ignition -resistant materials and proper retrofitting techniques. The components of the building envelope are shown in Figure 15-2. Reduction of hazardous fuels through vegetation management, vegetation thinning, or reduction of flammable materials. These actions protect life and property that are outside the defensible space perimeter but close to at -risk structures. Figure 15-3 shows a fire that is spreading vertically through vegetation. Figure 15-2. The building envelope SOURCE: ADAPTED FROM FEMA P-737 COASTAL CONSTRUCTION MANUAL 15-3 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II FEMA may fund above -code projects in communities with applicable fire -related codes. For homes and structures constructed or activities completed prior to the adoption of local building codes, FEMA may fund mitigation that meets or exceeds the codes currently in effect. For communities without fire codes, FEMA may fund mitigation when the materials and technologies are in accordance with the ICC, FEMA, U.S. Fire Administration, and the National Fire Protection Association (NFPA). Firewise recommendations, as appropriate. The Firewise program provides resources for communities and property owners to use in the creation of defensible space. Additional fire -related information and tools can be found at http://www. firevise.org and http://www.nfpa.org. Wildfire mitigation is required to be in accordance with the applicable fire -related codes and standards, including but not limited to the following: IWUIC, International Wildland- Urban Interface Code (ICC) NFPA 1144, Standard for Reducing Structure Ignition Hazards from Wildland Fire NFPA 1141, Standard for Fire Protection Infrastructure for Land Development in Suburban and Rural Areas NFPA 703, Standard for Fire -Retardant Treated Wood and Fire -Retardant Coatings for Building Materials Code for Fire Protection of Historical Structures (NFPA) FEMA P-737, Home Builder's Guide to Construction in Wildfire Zones (FEMA 2008a), is a Technical Fact Sheet Series (see Figure 15-4) that provides information about wildfire behavior and recommendations for building design and construction methods in the wildland/urban interface. The fact sheets cover mitigation topics for existing buildings including defensible space, roof assemblies, eaves, overhangs, soffits, exterior walls, vents, gutters, downspouts, a= windows, skylights, exterior doors, foundations, decks and other attached structures, landscape �} fencing and walls, fire sprinklers, and utilities and exterior equipment. Implementation of the recommended design and construction methods in FEMA P-737 can greatly increase the probability that a building will survive a wildfire. Home Builder's Guide to Construction in Wildfire Zones TedinicaI Fact Sheet Series F fh4.A � i 37 / Sgptnn ci )00{ . Figure 15-4., FEMA P-737, Home Builder's Guide to Construction FEMA in Wildlife Zones: Technical Fact Sheet Series 15-4 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Since it may not be financially possible for the homeowner to implement all of the measures that are recommended in FEMA P-737, homeowners should consult with local fire and building code officials or their fire management specialists to perform a vulnerability assessment and develop a customized, prioritized list of recommendations for remedial work on defensible space and the building envelope. Helpful information about the vulnerabilities of the building envelope is available at err ;i. firc.ccn rcc~,bci-kc lcy,ediif -)uiIdin g_in_ ildfire prone areas. The homeowner can use the Homeowner's Wildfire Assessment survey on this Web site to learn about the risks a particular building has and the measures that can be taken to address them. 15.2 Seismic Mitigation Seismic hazard, which is well documented and defined in the United States, is mitigated in existing residential buildings primarily through retrofitting. Although modifications to existing residential structures have the potential to reduce earthquake resistance, it is possible to take advantage of these modifications to increase resistance through earthquake retrofits (upgrades). FEMA has produced documents, including those referenced below, that address the evaluation and retrofit of buildings to improve performance during seismic events. For nationally applicable provisions governing seismic evaluation and rehabilitation, the design professional should reference ASCE 31 and ASCE 41. In addition, FEMA offers funding for seismic retrofits through the HMGP and the PDM Program to reduce the risk of loss of life, injury, and damage to buildings. Seismic retrofits, which are classified as structural and non-structural, are subject to the same HMGP and PDM funding processes as wind retrofits (see Section 15.4.3). FEMA 232, Homebuilders' Guide to Earthquake Resistant Design and Construction (FEMA 2006) (see Figure 15-5), contains descriptions of eight earthquake upgrades that address common seismic weaknesses in existing residential construction. The upgrades are foundation bolting, cripple wall bracing, weak- and soft -story bracing, open -front bracing, hillside house bracing, split-level floor interconnection, anchorage of masonry chimneys, and anchorage of concrete and masonry walls. The upgrades are summarized below. For in-depth information on these upgrades, see FEMA 232. Figure 15-5. FEMA 232, Homebuilders Guide to Earthquake Resistant Design and Construction Homebuilders' Guide to Earthquake Resistant Design and Construction FENIA 232 - June 2006 FEMA °"' rtebrp COASTAL CONSTRUCTION MANUAL 15-5 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II Foundation bolting. Inadequate attachment of the sill plate to the foundation can allow the framed structure to separate and shift off the foundation. Sill plate anchor bolts (either adhesive or expansion type depending on the foundation material) can be added provided there is sufficient access to the top surface of the sill plate. Alternately, proprietary anchoring hardware is available that is typically attached to the face of the foundation wall for greater ease of installation when access is limited. Reinforcing sill plate anchorage offers a generally high benefit in return for low cost. Cripple wall bracing. Another relatively inexpensive foundation -level retrofit is bracing the cripple walls. Cripple walls are framed walls occasionally installed between the top of the foundation and first - floor framing in the above -grade wall sections of basements and crawl spaces. Because of their location, cripple walls are particularly vulnerable to seismic loading, as shown in Figure 15-6. These walls can be braced through the prescribed installation of wood structural panel sheathing to the interior and/or exterior wall surface. Weak and soft -story bracing. Although first -story framed walls must bear greater seismic loads than the roof and walls above, they frequently have more openings and therefore less bracing. As a result, first -story framed walls, and any other level with underbraced wall sections, may be referred to as weak or soft stories. These walls can be retrofit by removing the interior finishes at wall corners and installing hold-down anchors between the corner studs and continuous reinforced foundation below. If renovations or repairs require removing larger areas of interior wall sheathing, additional hold- down anchors can be installed to tie in the floor or roof framing above. Additional wall bracing can be achieved by adding blocking for additional nailing and wood structural panel sheathing. Open -front bracing. An open -front configuration is one in which braced exterior walls are absent or grossly inadequate. Frequently, open -front configurations are found in garage entry walls where overhead garage doors consume most of the available wall area, as shown in Figure 15-7. Possible retrofits include reinforcing the existing framed end walls and replacing the framed wall ends with steel moment frames; common heights and lengths of steel moment frames are available commercially. Figure 15-6. A house with severe damage due to cripple wall failure 15-6 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Figure 15-7. Common open -front configurations in one - and two- family detached houses COASTAL CONSTRUCTION MANUAL 15-7 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Figure 15-8. FEMA 530, Earthquake Safety Guide for Homeowners 15.3 Flood Mitigation FEMA 259, Engineering Principles and Practices of Retrofitting Floodprone Structures (FEMA 2011), addresses retrofitting flood -prone residential structures. The objective of the document is to provide engineering design and economic guidance to engineers, architects, and local code officials about what constitutes technically feasible and cost-effective retrofitting measures for flood -prone residential structures. Volume II Earthquake Safety Guide for Homeowners l I MA t 1:) tirp'rm Fr! ?ili)S FEMA nehrp The focus in this chapter in regard to retrofitting for the flood hazard is retrofitting one- to four -family residences that are subject to flooding without wave action. The retrofitting measures that are described in this section include both active and passive efforts and wet and dry floodproofing. Active efforts require human intervention preceding the flood event and may include activities such as engaging protective shields at openings. Passive efforts do not require human intervention. The flood retrofitting measures are elevating the building in place, relocating the building, constructing barriers (levees and floodwalls), dry floodproofing (sealants, closures, sump pumps, and backflow valves), and wet floodproofing (using flood damage -resistant materials and protecting utilities and contents). Flood retrofitting projects may be eligible for funding through the following FEMA Hazard Mitigation Programs: HMGP, PDM, Flood Mitigation Assistance, Repetitive Flood Claims, and Severe Repetitive Loss. More information on obtaining funding for flood retrofitting is available in Hazard Mitigation Assistance Unified Guidance (FEMA 2010a). 15.3.1 Elevation Elevating a building to prevent floodwaters from reaching damageable portions of the building is an effective retrofitting technique. The building is raised so that the lowest floor is at or above the DFE to avoid damage from the design flood. Heavy- duty jacks are used to lift the building. Cribbing is used to support the building while a new or extended foundation is constructed. In lieu of constructing new support walls, open CROSS REFERENCE For definitions of DFE and BFE, see Section 8.5.1 of this Manual. 15-8 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Figure 15-9. Home elevated on piles foundations such as piers, columns, posts, and piles are often used (see Figure 15-9). Elevating the building on fill may be an option. Closed foundations are not permitted in Zone V and are not recommended in Coastal A Zones. See Table 10-1 for the types of foundations that are acceptable in each flood zone. The advantages and disadvantages of elevation are listed in Table 15-1 Table 15-1. Advantages and Disadvantages of Elevation SOURCE: FEMA 259 BFE = base flood elevation NFIP = National Flood Insurance Program COASTAL CONSTRUCTION MANUAL 15-9 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II 15.3.2 Relocation Relocation involves moving a structure to a location that is less prone to flooding or flood -related hazards such as erosion. The structure may be relocated to another portion of the current site or to a different site. The surest way to eliminate the risk of flood damage is to relocate the structure out of the floodplain. Relocation normally involves preparing the structure for the move (see Figure 15-10), placing it on a wheeled vehicle, transporting it to the new location, and setting it on a new foundation. Relocation is an appropriate measure in high hazard areas where continued occupancy is unsafe and/or owners want to be free of the risk of flooding. Relocation is also a viable option in communities that are considering using the resulting open space for more appropriate floodplain activities. Relocation may offer an alternative to elevation for substantially damaged structures that are required under local regulations to meet NFIP requirements. Table 15-2 lists the advantages and disadvantages of relocation. Figure 15-10. Preparing a building for relocation 15-10 COASTAL CONSTRUCTION MANUAL Volume II 15.3.3 Dry Floodproofing RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 In dry floodproofing, the portion of a structure that is below the chosen flood protection level (walls and other exterior components) is sealed to make it watertight and impermeable to floodwaters. The objective is to make the walls and other exterior components impermeable to floodwaters. Watertight, impervious membrane sealant systems include wall coatings, waterproofing compounds, impermeable sheeting, and supplemental impermeable wall systems, such as cast -in -place concrete. Doors, windows, sewer and water lines, and vents are closed with permanent or removable shields or valves. Figure 15-11 is a schematic of a dry floodproofed home. Non-residential techniques are also applicable in residential situations. See Table 15-3 for the advantages and disadvantages of dry floodproofing. WARNING Dry floodproofing is not allowed under the NFIP for new and substantially damaged or improved residential structures in an SFHA. For additional information on dry floodproofing, see FEMA FIA-TB-3, Non - Residential Floodproofing - Requirements and Certification for Buildings Located in Special Flood Hazard Areas in Accordance with the NFIP (FEMA 1993a) and the Substantial Improvement/Substantial Damage Desk Reference (FEMA 2010N The expected duration of flooding is critical when deciding which sealant system to use because seepage can increase over time, rendering the floodproofing ineffective. Waterproofing compounds, sheeting, and sheathing may deteriorate or fail if exposed to floodwaters for extended periods. Sealant systems are also subject to damage (puncture) in areas that experience water flow of significant velocity, ice, or debris flow. COASTAL CONSTRUCTION MANUAL 15-11 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Table 15-3. Advantages and Disadvantages of Dry Floodproofing SOURCE: FEMA 259 NFIP = National Flood Insurance Program DFE = design flood elevation 15. .4 Wet Floodproofing Wet floodproofing involves modifying a building to allow floodwaters to enter it in such a way that damage to the structure and its contents is minimized. A schematic of a home that has been wet floodproofed is shown in Figure 15-12. See Table 15-4 for a list of the advantages and disadvantages of wet floodproofing. Wet floodproofing is often used for structures with basements and crawlspaces when other mitigation techniques are technically infeasible or too costly. Wet floodproofing is generally appropriate if a structure has space available to temporarily store damageable items during the flood event. Utilities and furnaces situated below the DFE should be relocated to higher ground while remaining sub-DFE materials vulnerable to flood damage should be replaced with flood damage -resistant building materials. FEMA TB-2, Flood Damage -Resistant Materials Requirements (FEMA 2008b), provides guidance concerning the use of flood damage -resistant building components. Volume II WARNING Wet floodproofing is not allowed under the NFIP for new and substantially damaged or improved structures located in an SFHA. Refer to FEMA FIA-TB-7, Wet Floodproofing Requirements for Structures Located in Special Flood Hazard Areas in Accordance with the NFIP (FEMA 1993b). 15-12 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Figure 15-12. Wet floodproofed structure COASTAL CONSTRUCTION MANUAL 15-13 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II A levee is typically a compacted earthen structure that blocks floodwaters from coming into contact with the structure. To be WARNING effective over time, levees must be constructed of suitable materials (i.e., impervious soils) and have the correct side slopes for stability. While floodwalls and levees are allowed under NFIP Levees may completely surround the structure or tie to high regulations, they do not make ground at each end. Levees are generally limited to homes where a noncompliant structure floodwaters are less than 5 feet deep. Otherwise, the cost and the compliant under the NFIP. land area required for such barriers usually make them impractical for the average owner. See Table 15-5 for a list of the advantages and disadvantages for retrofitting a home against flooding hazards using floodwalls and levees. Table 15-5. Advantages and Disadvantages of a Floodwall or Levee 15-14 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Figure 15-13. Home protected by a floodwall and a levee COASTAL CONSTRUCTION MANUAL 15-15 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II Hurricane -force winds are most common in coastal areas but also occur in other areas. ASCE 7-05 defines the hurricane -prone regions as the U.S. Atlantic Ocean and Gulf of Mexico coasts where the design wind speed is greater than 90 mph, and Hawaii, Puerto Rico, Guam, Virgin Islands, and American Samoa. 15.4.1 Evaluating Existing Homes Executing a successful retrofit on any home requires an evaluation of its existing condition to determine age and condition; overall structural integrity; any weaknesses in the building envelope, structure, or foundation; whether the home can be retrofitted to improve resistance to wind -related damage; how the home can be retrofit for the Mitigation Packages (see Section 15.4.2); how much the Mitigation Packages would cost; and the most cost-effective retrofit project for the home. A qualified individual should evaluate the home and provide recommendations to the homeowner. Qualified professionals may include building science professionals such as registered architects and engineers, building officials, and evaluators who are certified through other acceptable wind retrofit programs such as the FORTIFIED for Existing Homes Program from the Insurance Institute for Business & Home Safety (IBHS 2010). The purposes of the evaluation are to identify any repairs that are needed before a wind retrofit project can be undertaken, the feasibility of the retrofit project, whether prescriptive retrofits can be performed on the home or whether an engineering solution should be developed, and whether the home is a good candidate for any of the wind retrofit Mitigation Packages described in Section 15.4.2. The purpose of the evaluation is not to determine whether the building meets the current building code. 15.4.2 WindRetrofit Mitigation Packages The wind retrofit projects described in this section, and more fully in FEMA P-804, are divided into the Basic Mitigation Package, Intermediate Mitigation Package, and Advanced Mitigation Package. Additional mitigation measures are presented at the end of this section. The packages should be implemented cumulatively, beginning with the Basic Mitigation Package. This means that for a home to successfully meet the criteria of the Advanced Mitigation Package, it must also meet the criteria of the Basic and Intermediate Mitigation Packages. The retrofits in each package are shown in Figure 15-15. NOTE In wind retrofitting, the most cost-effective techniques normally involve strengthening the weakest structural links and improving the water penetration resistance of the building envelope. To identify the weakest links, the designer should start at the top of the building and work down the load path. The wind mitigation retrofits for each package, if implemented correctly, will improve the performance of residential buildings when subjected to high winds. Although the information in this section can be helpful to homeowners, it is intended primarily for evaluators, contractors, and design professionals. The retrofits described for each Mitigation Package and throughout this section are not necessarily listed in the order in which they should be performed. The order in which retrofits should be performed depends on the configuration of the home and should be determined once the desired Mitigation Package is chosen. For example, when the Advanced Mitigation Package is selected, the homeowner should consider retrofitting the roof -to -wall connections when retrofitting the soffits (part of the Basic Mitigation Package). 15-16 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Figure 15-15. Wind Retrofit Mitigation Packages SOURCE: FEMA P-804 COASTAL CONSTRUCTION MANUAL 15-17 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II Figure 15-16. Bracing gable end overhangs 15-18 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 15.4.2.2 Intermediate Mitigation Package For the Intermediate Mitigation Package to be effective, the measures in the Basic Mitigation Package must first be successfully completed. The Intermediate Mitigation Package includes protecting windows and entry doors from wind-borne debris, protecting garage doors from wind pressure and garage door glazing from wind-borne debris, bracing gable end walls over 4 feet tall, and strengthening the connections of attached structures such as porches and carports. 15.4.2.3 Advanced Mitigation Package The Advanced Mitigation Package is the most comprehensive package of retrofits. This package can be effective only if the Basic Mitigation Package (with or without replacing the roof covering) and Intermediate Mitigation Package are also implemented. The Advanced Mitigation Package requires a more invasive inspection than the other two packages. Homes that are undergoing substantial renovation or are being rebuilt after a disaster are typically the best candidates for the Advanced Mitigation Package. The Advanced Mitigation Package requires the homeowner to provide a continuous load path as shown in Figure 15-18 and further protect openings. 15.4.2.4 Additional Mitigation Measures The wind retrofit Mitigation Packages include important retrofits that reduce the risk of wind -related damage, but the risk cannot be eliminated entirely. By maintaining an awareness of vulnerabilities of and around a home, the homeowner can reduce the risk of wind -related damage even further. Although the mitigation measures prescribed to address these vulnerabilities are important to understand, they are not a part of the Mitigation Packages and are not eligible for HMA program funding. These additional measures, described in greater detail in FEMA P-804, include securing the exterior wall covering, implementing tree fall prevention measures, and protecting exterior equipment. 15.4.3 FEMA Wind Retrofit Grant Programs Despite the significant damage experienced by all types of buildings during high -wind events, grant applications for wind retrofit projects have focused more on non-residential and commercial buildings than on residential buildings. FEMA developed FEMA P-804 to encourage wind mitigation of existing residential buildings. FEMA administers two HMA grant programs that fund wind retrofit projects: HMGP and the PDM Program. Hazard mitigation is defined as any sustained action taken to reduce or eliminate long-term risk to people and property from natural hazards and their effects. The HMA process has five stages, starting with mitigation planning and ending with successful execution of a project (see Figure 15-19). Through FEMA's HMA grant programs, applications for an individual home or groups of homes undergoing wind retrofit projects can be submitted for approval. If applications are approved, Federal funding is provided for 75 percent of the total project cost, significantly reducing the homeowner's expenses for the project. The remaining 25 percent of eligible project costs can be paid for directly or covered by donated labor, time, and materials. Refer to current HMA guidance for more details on cost -sharing (FEMA 2010a). More information on Federal assistance through HMA programs is also available in Chapter 5 of FEMA P-804. COASTAL CONSTRUCTION MANUAL 15-19 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II Figure 15-18. Continuous load path for wind -uplift of a residential, wood -frame building 15-20 COASTAL CONSTRUCTION MANUAL Volume II RETROFITTING BUILDINGS FOR NATURAL HAZARDS 11 Figure 15-19. HMA grant process SOURCE: FEMA P-804 COASTAL CONSTRUCTION MANUAL 15-21 15 RETROFITTING BUILDINGS FOR NATURAL HAZARDS Volume II FEMA. 2008a. Home Builder's Guide to Construction in Wildfire Zones. FEMA P-737. FEMA. 2008b. Flood Damage -Resistant Materials Requirements. Technical Bulletin 2. FEMA. 2009. Benefit -Cost Analysis Tool, Version 4.5.5. Available at http://www.bchelpline.com/ Download.aspx. Accessed January 2011. FEMA. 2010a. Hazard Mitigation Assistance Unified Guidance. Available at http://www.fema.gov/library/ viewRecord.do?id=4225. Accessed June 2011. FEMA. 2010b. Substantiallmprovement/Substantial Damage Desk Reference. FEMA P-758. FEMA. 2010c. Wind Retrofit Guide for Residential Buildings. FEMA P-804. FEMA. 2011. Engineering Principles and Practices of Retrofitting Floodprone Structures. FEMA 259. IBHS (Insurance Institute for Business & Home Safety). 2008. Mega Fires: The Case for Mitigation — The Witch Creek Wildfire, October 21-31, 2007 IBHS. 2010. FORTIFIED for Existing Homes Engineering Guide. ICC (International Code Council). 2006. International Residential Code for One- and Two -Family Dwellings. 2006 IRC. ICC. 2009a. International Residential Code for One- and Two -Family Dwellings. 2009 IRC. ICC. International Wildland- Urban Interface Code (IWUIC). NFPA (National Fire Protection Association). Code for Fire Protection of Historical Structures. NFPA. Standard for Fire Protection Infrastructure for Land Development in Suburban and RuralAreas. NFPA 1141. NFPA. Standard for Fire -Retardant Treated Wood and Fire -Retardant Coatings for Building Materials. NFPA 703. NFPA. Standard for Reducing Structure Ignition Hazards from Wildland Fire. NFPA 1144. 15-22 COASTAL CONSTRUCTION MANUAL Acronyms I:1 AAMA American Architectural Manufacturers Association ACI American Concrete Institute AF&PA American Forest & Paper Association AHJ Authority Having Jurisdiction AISI American Iron and Steel Institute ANSI American National Standards Institute ASCE American Society of Civil Engineers ASD Allowable Stress Design ASTM American Society for Testing and Materials AWPA American Wood Protection Association BCA Benefit -Cost Analysis BCEGS Building Code Effectiveness Grading Schedule BFE base flood elevation BUR built-up roof C C&C components and cladding COASTAL CONSTRUCTION MANUAL A-1 ACRONYMS Volume II CBRA Coastal Barrier Resources Act CBRS Coastal Barrier Resource System CCM Coastal Construction Manual CEA California Earthquake Authority CMU concrete masonry unit CRS Community Rating System DASMA Door & Access Systems Manufacturers Association DFE design flood elevation EIFS exterior insulating finishing system ELF Equivalent Lateral Force F FBC Florida Building Code FEMA Federal Emergency Management Agency FIRM Flood Insurance Rate Map FIS Flood Insurance Study FM Factory Mutual FRP fiber -reinforced polymer FS factor of safety GSA General Services Administration A-2 COASTAL CONSTRUCTION MANUAL Volume II ACRONYMS HMA Hazard Mitigation Assistance HMGP Hazard Mitigation Grant Program IBC International Building Code IBHS Institute for Business and Home Safety ICC International Code Council IRC International Residential Code ISO Insurance Services Office L lb pound(s) LEED Leadership in Energy and Environmental Design LiMWA Limit of Moderate Wave Action LPS lightning protection system LRFD Load and Resistance Factor Design MEPS molded expanded polystyrene mph miles per hour MWFRS main wind force -resisting system NAHB National Association of Home Builders COASTAL CONSTRUCTION MANUAL A-3 ACRONYMS Volume II NAVD North American Vertical Datum NDS National Design Specification NFIP National Flood Insurance Program NFPA National Fire Protection Association NGVD National Geodetic Vertical Datum NRCA National Roofing Contractors Association NRCS Natural Resources Conservation Service O.C.0 on center OH overhang OSB oriented strand board PDM Pre -Disaster Mitigation (Program) plf pound(s) per linear foot psf pound(s) per square foot psi pound(s) per square inch L J SBC Standard Building Code SBS styrene-butadiene-styrene S-DRY surface -dry lumber with <=19 percent moisture content SFHA Special Flood Hazard Area SFIP Standard Flood Insurance Policy SPRI Single -Ply Roofing Institute A-4 COASTAL CONSTRUCTION MANUAL Volume II ACRONYMS TMS The Masonry Society UBC Uniform Building Code UL Underwriters Laboratories USACE U.S. Army Corps of Engineers USDN U.S. Department of the Navy USGBC U.S. Green Buildings Council USGS U.S. Geological Survey UV ultraviolet WFCM Wood Frame Construction Manual Wind -MAP Windstorm Market Assistance Program (New Jersey) WPPC Wood Products Promotion Council Y yr year(s) COASTAL CONSTRUCTION MANUAL A-5 Glossary 0-9 100-year flood — See Base flood. 500-year flood — Flood that has as 0.2-percent probability of being equaled or exceeded in any given year. "MI Acceptable level of risk — The level of risk judged by the building owner and designer to be appropriate for a particular building. Adjacent grade — Elevation of the natural or graded ground surface, or structural fill, abutting the walls of a building. See also Highest adjacent grade and Lowest adjacentgrade. Angle of internal friction (soil) — A measure of the soil's ability to resist shear forces without failure. Appurtenant structure — Under the National Flood Insurance Program, an "appurtenant structure" is "a structure which is on the same parcel of property as the principal structure to be insured and the use of which is incidental to the use of the principal structure." Barrier island — A long, narrow sand island parallel to the mainland that protects the coast from erosion. Base flood — Flood that has as 1-percent probability of being equaled or exceeded in any given year. Also known as the 100-year flood. Base Flood Elevation (BFE) — The water surface elevation resulting from a flood that has a 1 percent chance of equaling or exceeding that level in any given year. Elevation of the base flood in relation to a specified datum, such as the National Geodetic Vertical Datum or the North American Vertical Datum. The Base Flood Elevation is the basis of the insurance and floodplain management requirements of the National Flood Insurance Program. COASTAL CONSTRUCTION MANUAL G-1 GLOSSARY Volume II Basement — Under the National Flood Insurance Program, any area of a building having its floor subgrade on all sides. (Note: What is typically referred to as a "walkout basement," which has a floor that is at or above grade on at least one side, is not considered a basement under the National Flood Insurance Program.) Beach nourishment — A project type that typically involve dredging or excavating hundreds of thousands to millions of cubic yards of sediment, and placing it along the shoreline. Bearing capacity (soils) — A measure of the ability of soil to support gravity loads without soil failure or excessive settlement. Berm — Horizontal portion of the backshore beach formed by sediments deposited by waves. Best Practices — Techniques that exceed the minimum requirements of model building codes; design and construction standards; or Federal, State, and local regulations. Breakaway wall — Under the National Flood Insurance Program, a wall that is not part of the structural support of the building and is intended through its design and construction to collapse under specific lateral loading forces without causing damage to the elevated portion of the building or supporting foundation system. Breakaway walls are required by the National Flood Insurance Program regulations for any enclosures constructed below the Base Flood Elevation beneath elevated buildings in Coastal High Hazard Areas (also referred to as Zone V). In addition, breakaway walls are recommended in areas where flood waters flow at high velocities or contain ice or other debris. Building code — Regulations adopted by local governments that establish standards for construction, modification, and repair of buildings and other structures. Building use — What occupants will do in the building. The intended use of the building will affect its layout, form, and function. Building envelope — Cladding, roofing, exterior walls, glazing, door assemblies, window assemblies, skylight assemblies, and other components enclosing the building. Building systems — Exposed structural, window, or roof systems. Built-up roof covering — Two or more layers of felt cemented together and surfaced with a cap sheet, mineral aggregate, smooth coating, or similar surfacing material. Bulkhead — Wall or other structure, often of wood, steel, stone, or concrete, designed to retain or prevent sliding or erosion of the land. Occasionally, bulkheads are used to protect against wave action. C Cladding — Exterior surface of the building envelope that is directly loaded by the wind. Closed foundation — A foundation that does not allow water to pass easily through the foundation elements below an elevated building. Examples of closed foundations include crawlspace foundations and stem wall foundations, which are usually filled with compacted soil, slab -on -grade foundations, and continuous perimeter foundation walls. G-2 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY Coastal A Zone — The portion of the coastal SFHA referenced by building codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many NFIP-compliant structures on shallow or solid wall foundations. Coastal barrier — Depositional geologic feature such as a bay barrier, tombolo, barrier spit, or barrier island that consists of unconsolidated sedimentary materials; is subject to wave, tidal, and wind energies; and protects landward aquatic habitats from direct wave attack. Coastal Barrier Resources Act of 1982 (CBRA) — Act (Public Law 97-348) that established the Coastal Barrier Resources System (CBRS). The act prohibits the provision of new flood insurance coverage on or after October 1, 1983, for any new construction or substantial improvements of structures located on any designated undeveloped coastal barrier within the CBRS. The CBRS was expanded by the Coastal Barrier Improvement Act of 1991. The date on which an area is added to the CBRS is the date of CBRS designation for that area. Coastal flood hazard area — An area subject to inundation by storm surge and, in some instances, wave action caused by storms or seismic forces. Usually along an open coast, bay, or inlet. Coastal geology — The origin, structure, and characteristics of the rocks and sediments that make up the coastal region. Coastal High Hazard Area — Under the National Flood Insurance Program, an area of special flood hazard extending from offshore to the inland limit of a primary frontal dune along an open coast and any other area subject to high -velocity wave action from storms or seismic sources. On a Flood Insurance Rate Map, the Coastal High Hazard Area is designated Zone V, VE, or Vl V30. These zones designate areas subject to inundation by the base flood, where wave heights or wave runup depths are 3.0 feet or higher. Coastal processes — The physical processes that act upon and shape the coastline. These processes, which influence the configuration, orientation, and movement of the coast, include tides and fluctuating water levels, waves, currents, and winds. Coastal sediment budget — The quantification of the amounts and rates of sediment transport, erosion, and deposition within a defined region. Coastal Special Flood Hazard Area — The portion of the Special Flood Hazard Area where the source of flooding is coastal surge or inundation. It includes Zone VE and Coastal A Zone. Code official — Officer or other designated authority charged with the administration and enforcement of the code, or a duly authorized representative, such as a building, zoning, planning, or floodplain management official. Column foundation — Foundation consisting of vertical support members with a height -to -least -lateral - dimension ratio greater than three. Columns are set in holes and backfilled with compacted material. They are usually made of concrete or masonry and often must be braced. Columns are sometimes known as posts, particularly if they are made of wood. Components and Cladding (C&C) — American Society of Civil Engineers (ASCE) 7-10 defines C&C as "... elements of the building envelope that do not qualify as part of the MWFRS [Main Wind Force Resisting System]." These elements include roof sheathing, roof coverings, exterior siding, windows, doors, soffits, fascia, and chimneys. COASTAL CONSTRUCTION MANUAL G-3 GLOSSARY Volume II Conditions Greater than Design Conditions — Design loads and conditions are based on some probability of exceedance, and it is always possible that design loads and conditions can be exceeded. Designers can anticipate this and modify their initial design to better accommodate higher forces and more extreme conditions. The benefits of doing so often exceed the costs of building higher and stronger. Connector — Mechanical device for securing two or more pieces, parts, or members together, including anchors, wall ties, and fasteners. Consequence — Both the short- and long-term effects of an event for the building. See Risk. Constructability — Ultimately, designs will only be successful if they can be implemented by contractors. Complex designs with many custom details may be difficult to construct and could lead to a variety of problems, both during construction and once the building is occupied. Continuous load paths — The structural condition required to resist loads acting on a building. The continuous load path starts at the point or surface where loads are applied, moves through the building, continues through the foundation, and terminates where the loads are transferred to the soils that support the building. Corrosion -resistant metal — Any nonferrous metal or any metal having an unbroken surfacing of nonferrous metal, or steel with not less than 10 percent chromium or with not less than 0.20 percent copper. Dead load — Weight of all materials of construction incorporated into the building, including but not limited to walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items and fixed service equipment. See also Loads. Debris — Solid objects or masses carried by or floating on the surface of moving water. Debris impact loads — Loads imposed on a structure by the impact of floodborne debris. These loads are often sudden and large. Though difficult to predict, debris impact loads must be considered when structures are designed and constructed. See also Loads. Deck — Exterior floor supported on at least two opposing sides by an adjacent structure and/or posts, piers, or other independent supports. Design event — The minimum code -required event (for natural hazards, such as flood, wind, and earthquake) and associated loads that the structure must be designed to resist. Design flood — The greater of either (1) the base flood or (2) the flood associated with the flood hazard area depicted on a community's flood hazard map, or otherwise legally designated. Design Flood Elevation (DFE) — Elevation of the design flood, or the flood protection elevation required by a community, including wave effects, relative to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum. The DFE is the locally adopted regulatory flood elevation. If a community regulates to minimum National Flood Insurance Program (NFIP) requirements, the G-4 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY DFE is identical to the Base Flood Elevation (BFE). If a community chooses to exceed minimum NFIP requirements, the DFE exceeds the BFE. Design flood protection depth — Vertical distance between the eroded ground elevation and the Design Flood Elevation. Design stillwater flood depth — Vertical distance between the eroded ground elevation and the design stillwater flood elevation. Design stillwater flood elevation — Stillwater elevation associated with the design flood, excluding wave effects, relative to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum. Development — Under the National Flood Insurance Program, any manmade change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation, or drilling operations or storage of equipment or materials. Dry floodproofing — A flood retrofitting technique in which the portion of a structure below the flood protection level (walls and other exterior components) is sealed to be impermeable to the passage of floodwaters. Dune — See Frontal dune and Primary frontal dune. Dune toe — Junction of the gentle slope seaward of the dune and the dune face, which is marked by a slope of 1 on 10 or steeper. E Effective Flood Insurance Rate Map — See Flood Insurance Rate Map. Elevation — Raising a structure to prevent floodwaters from reaching damageable portions. Enclosure — The portion of an elevated building below the lowest floor that is partially or fully shut in by rigid walls. Encroachment — The placement of an object in a floodplain that hinders the passage of water or otherwise affects the flood flows. Erodible soil — Soil subject to wearing away and movement due to the effects of wind, water, or other geological processes during a flood or storm or over a period of years. Erosion — Under the National Flood Insurance Program, the process of the gradual wearing away of land masses. Erosion analysis — Analysis of the short- and long-term erosion potential of soil or strata, including the effects of flooding or storm surge, moving water, wave action, and the interaction of water and structural components. Exterior -mounted mechanical equipment — Includes, but is not limited to, exhaust fans, vent hoods, air conditioning units, duct work, pool motors, and well pumps. COASTAL CONSTRUCTION MANUAL G-5 GLOSSARY Volume II F Federal Emergency Management Agency (FEMA) — Independent agency created in 1979 to provide a single point of accountability for all Federal activities related to disaster mitigation and emergency preparedness, response, and recovery. FEMA administers the National Flood Insurance Program. Federal Insurance and Mitigation Administration (FIMA) — The component of the Federal Emergency Management Agency directly responsible for administering the flood insurance aspects of the National Flood Insurance Program as well as a range of programs designed to reduce future losses to homes, businesses, schools, public buildings, and critical facilities from floods, earthquakes, tornadoes, and other natural disasters. Fill — Material such as soil, gravel, or crushed stone placed in an area to increase ground elevations or change soil properties. See also Structural fill. Flood — Under the National Flood Insurance Program, either a general and temporary condition or partial or complete inundation of normally dry land areas from: (1) the overflow of inland or tidal waters; (2) the unusual and rapid accumulation or runoff of surface waters from any source; (3) mudslides (i.e., mudflows) that are proximately caused by flooding as defined in (2) and are akin to a river of liquid and flowing mud on the surfaces of normally dry land areas, as when the earth is carried by a current of water and deposited along the path of the current; or (4) the collapse or subsidence of land along the shore of a lake or other body of water as a result of erosion or undermining caused by waves or currents of water exceeding anticipated cyclical levels or suddenly caused by an unusually high water level in a natural body of water, accompanied by a severe storm, or by an unanticipated force of nature, such as flash flood or abnormal tidal surge, or by some similarly unusual and unforeseeable event which results in flooding as defined in (1), above. Flood -damage -resistant material — Any construction material capable of withstanding direct and prolonged contact (i.e., at least 72 hours) with flood waters without suffering significant damage (i.e., damage that requires more than cleanup or low-cost cosmetic repair, such as painting). Flood elevation — Height of the water surface above an established elevation datum such as the National Geodetic Vertical Datum, North American Vertical Datum, or mean sea level. Flood hazard area — The greater of the following: (1) the area of special flood hazard, as defined under the National Flood Insurance Program, or (2) the area designated as a flood hazard area on a community's legally adopted flood hazard map, or otherwise legally designated. Flood insurance — Insurance coverage provided under the National Flood Insurance Program. Flood Insurance Rate Map (FIRM) — Under the National Flood Insurance Program, an official map of a community, on which the Federal Emergency Management Agency has delineated both the special hazard areas and the risk premium zones applicable to the community. (Note: The latest FIRM issued for a community is referred to as the "effective FIRM" for that community.) G-6 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY Flood Insurance Study (FIS) — Under the National Flood Insurance Program, an examination, evaluation, and determination of flood hazards and, if appropriate, corresponding water surface elevations, or an examination, evaluation, and determination of mudslide (i.e., mudflow) and flood -related erosion hazards in a community or communities. (Note: The National Flood Insurance Program regulations refer to Flood Insurance Studies as "flood elevation studies.") Flood -related erosion area or flood -related erosion prone area — A land area adjoining the shore of a lake or other body of water, which due to the composition of the shoreline or bank and high water levels or wind -driven currents, is likely to suffer flood -related erosion. Flooding — See Flood. Floodplain — Under the National Flood Insurance Program, any land area susceptible to being inundated by water from any source. See also Flood. Floodplain management — Operation of an overall program of corrective and preventive measures for reducing flood damage, including but not limited to emergency preparedness plans, flood control works, and floodplain management regulations. Floodplain management regulations — Under the National Flood Insurance Program, zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances (such as floodplain ordinance, grading ordinance, and erosion control ordinance), and other applications of police power. The term describes State or local regulations, in any combination thereof, that promulgate standards for the purpose of flood damage prevention and reduction. Floodwall — A flood retrofitting technique that consists of engineered barriers designed to keep floodwaters from coming into contact with the structure. Footing — Enlarged base of a foundation wall, pier, post, or column designed to spread the load of the structure so that it does not exceed the soil bearing capacity. Footprint — Land area occupied by a structure. Freeboard — Under the National Flood Insurance Program, a factor of safety, usually expressed in feet above a flood level, for the purposes of floodplain management. Freeboard is intended to compensate for the many unknown factors that could contribute to flood heights greater than the heights calculated for a selected size flood and floodway conditions, such as the hydrological effect of urbanization of the watershed. Freeboard is additional height incorporated into the Design Flood Elevation, and may be required by State or local regulations or be desired by a property owner. Frontal dune — Ridge or mound of unconsolidated sandy soil extending continuously alongshore landward of the sand beach and defined by relatively steep slopes abutting markedly flatter and lower regions on each side. Frontal dune reservoir — Dune cross-section above 100-year stillwater level and seaward of dune peak. COASTAL CONSTRUCTION MANUAL G-7 GLOSSARY Volume II G Gabion — Rock -filled cage made of wire or metal that is placed on slopes or embankments to protect them from erosion caused by flowing or fast-moving water. Geomorphology — The origin, structure, and characteristics of the rocks and sediments that make up the coastal region. Glazing — Glass or transparent or translucent plastic sheet in windows, doors, skylights, and shutters. Grade beam — Section of a concrete slab that is thicker than the slab and acts as a footing to provide stability, often under load -bearing or critical structural walls. Grade beams are occasionally installed to provide lateral support for vertical foundation members where they enter the ground. H High -velocity wave action — Condition in which wave heights or wave runup depths are 3.0 feet or higher. Highest adjacent grade — Elevation of the highest natural or regraded ground surface, or structural fill, that abuts the walls of a building. Hurricane — Tropical cyclone, formed in the atmosphere over warm ocean areas, in which wind speeds reach 74 miles per hour or more and blow in a large spiral around a relatively calm center or "eye." Hurricane circulation is counter -clockwise in the northern hemisphere and clockwise in the southern hemisphere. Hurricane clip or strap — Structural connector, usually metal, used to tie roof, wall, floor, and foundation members together so that they resist wind forces. Hurricane -prone region — In the United States and its territories, hurricane -prone regions are defined by The American Society of Civil Engineers (ASCE) 7-10 as: (1) The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed for Risk Category II buildings is greater than 115 mph, and (2) Hawaii, Puerto Rico, Guam, the Virgin Islands, and American Samoa. Hydrodynamic loads — Loads imposed on an object, such as a building, by water flowing against and around it. Among these loads are positive frontal pressure against the structure, drag effect along the sides, and negative pressure on the downstream side. Hydrostatic loads — Loads imposed on a surface, such as a wall or floor slab, by a standing mass of water. The water pressure increases with the square of the water depth. Initial costs — Include property evaluation, acquisition, permitting, design, and construction. G-8 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY Interior mechanical equipment — Includes, but is not limited to, furnaces, boilers, water heaters, and distribution ductwork. LJ Jetting (of piles) — Use of a high-pressure stream of water to embed a pile in sandy soil. See also Pile foundation. Jetty — Wall built from the shore out into the water to restrain currents or protect a structure. Joist — Any of the parallel structural members of a floor system that support, and are usually immediately beneath, the floor. L Lacustrine flood hazard area — Area subject to inundation from lakes. Landslide — Occurs when slopes become unstable and loose material slides or flows under the influence of gravity. Often, landslides are triggered by other events such as erosion at the toe of a steep slope, earthquakes, floods, or heavy rains, but can be worsened by human actions such as destruction of vegetation or uncontrolled pedestrian access on steep slopes. Levee — Typically a compacted earthen structure that blocks floodwaters from coming into contact with the structure, a levee is a manmade structure built parallel to a waterway to contain, control, or divert the flow of water. A levee system may also include concrete or steel floodwalls, fixed or operable floodgates and other closure structures, pump stations for rainwater drainage, and other elements, all of which must perform as designed to prevent failure. Limit of Moderate Wave Action (LiMWA) — A line indicating the limit of the 15-foot wave height during the base flood. FEMA requires new flood studies in coastal areas to delineate the LiMWA. Littoral drift — Movement of sand by littoral (longshore) currents in a direction parallel to the beach along the shore. Live loads — Loads produced by the use and occupancy of the building or other structure. Live loads do not include construction or environmental loads such as wind load, snow load, rain load, earthquake load, flood load, or dead load. See also Loads. Load -bearing wall — Wall that supports any vertical load in addition to its own weight. See also Non - load -bearing wall. Loads — Forces or other actions that result from the weight of all building materials, occupants and their possessions, environmental effects, differential movement, and restrained dimensional changes. Loads can be either permanent or variable. Permanent loads rarely vary over time or are of small magnitude. All other loads are variable loads. COASTAL CONSTRUCTION MANUAL G-9 GLOSSARY Volume II Location — The location of the building determines the nature and intensity of hazards to which the building will be exposed, loads and conditions that the building must withstand, and building regulations that must be satisfied. See also Siting. Long-term costs — Include preventive maintenance and repair and replacement of deteriorated or damaged building components. A hazard -resistant design can result in lower long-term costs by preventing or reducing losses from natural hazards events. Lowest adjacent grade (LAG) — Elevation of the lowest natural or regraded ground surface, or structural fill, that abuts the walls of a building. See also Highest adjacent grade. Lowest floor — Under the National Flood Insurance Program (NFIP), "lowest floor" of a building includes the floor of a basement. The NFIP regulations define a basement as "... any area of a building having its floor subgrade (below ground level) on all sides." For insurance rating purposes, this definition applies even when the subgrade floor is not enclosed by full -height walls. Lowest horizontal structural member — In an elevated building, the lowest beam, joist, or other horizontal member that supports the building. Grade beams installed to support vertical foundation members where they enter the ground are not considered lowest horizontal structural members. 1�1 Main Wind Force Resisting System (MWFRS) — Consists of the foundation; floor supports (e.g., joists, beams); columns; roof raters or trusses; and bracing, walls, and diaphragms that assist in transferring loads. The American Society of Civil Engineers (ASCE) 7-10 defines the MWFRS as "... an assemblage of structural elements assigned to provide support and stability for the overall structure." Manufactured home — Under the National Flood Insurance Program, a structure, transportable in one or more sections, built on a permanent chassis and designed for use with or without a permanent foundation when attached to the required utilities. Does not include recreational vehicles. Marsh — Wetland dominated by herbaceous or non -woody plants often developing in shallow ponds or depressions, river margins, tidal areas, and estuaries. Masonry — Built-up construction of building units made of clay, shale, concrete, glass, gypsum, stone, or other approved units bonded together with or without mortar or grout or other accepted methods of joining. Mean return period — The average time (in years) between landfall or nearby passage of a tropical storm or hurricane. Mean water elevation — The surface across which waves propagate. The mean water elevation is calculated as the stillwater elevation plus the wave setup. Mean sea level (MSL) — Average height of the sea for all stages of the tide, usually determined from hourly height observations over a 19-year period on an open coast or in adjacent waters having free access to the sea. See also National Geodetic Vertical Datum. G-10 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY Metal roof panel — Interlocking metal sheet having a minimum installed weather exposure of 3 square feet per sheet. Minimal Wave Action area (MiWA) — The portion of the coastal Special Flood Hazard Area where base flood wave heights are less than 1.5 feet. Mitigation — Any action taken to reduce or permanently eliminate the long-term risk to life and property from natural hazards. Mitigation Directorate — Component of the Federal Emergency Management Agency directly responsible for administering the flood hazard identification and floodplain management aspects of the National Flood Insurance Program. Moderate Wave Action area (MoWA) — See Coastal A Zone. IL National Flood Insurance Program (NFIP) — Federal program created by Congress in 1968 that makes flood insurance available in communities that enact and enforce satisfactory floodplain management regulations. National Geodetic Vertical Datum (NGVD) — Datum established in 1929 and used as a basis for measuring flood, ground, and structural elevations, previously referred to as Sea Level Datum or Mean Sea Level. The Base Flood Elevations shown on most of the Flood Insurance Rate Maps issued by the Federal Emergency Management Agency are referenced to NGVD or, more recently, to the North American Vertical Datum. Naturally decay -resistant wood — Wood whose composition provides it with some measure of resistance to decay and attack by insects, without preservative treatment (e.g., heartwood of cedar, black locust, black walnut, and redwood). New construction — For the purpose of determining flood insurance rates under the National Flood Insurance Program, structures for which the start of construction commenced on or after the effective date of the initial Flood Insurance Rate Map or after December 31, 1974, whichever is later, including any subsequent improvements to such structures. (See also Post -FIRM structure.) For floodplain management purposes, new construction means structures for which the start of construction commenced on or after the effective date of a floodplain management regulation adopted by a community and includes any subsequent improvements to such structures. Non -load -bearing wall — Wall that does not support vertical loads other than its own weight. See also Load -bearing wall. Nor'easter — A type of storm that occurs along the East Coast of the United States where the wind comes from the northeast. Nor'easters can cause coastal flooding, coastal erosion, hurricane -force winds, and heavy snow. North American Vertical Datum (NAVD) — Datum established in 1988 and used as a basis for measuring flood, ground, and structural elevations. NAVD is used in many recent Flood Insurance Studies rather than the National Geodetic Vertical Datum. COASTAL CONSTRUCTION MANUAL G-11 GLOSSARY Volume II ,J Open foundation — A foundation that allows water to pass through the foundation of an elevated building, which reduces the lateral flood loads the foundation must resist. Examples of open foundations are pile, pier, and column foundations. Operational costs — Costs associated with the use of the building, such as the cost of utilities and insurance. Optimizing energy efficiency may result in a higher initial cost but save in operational costs. Oriented strand board (OSB) — Mat -formed wood structural panel product composed of thin rectangular wood strands or wafers arranged in oriented layers and bonded with waterproof adhesive. Overwash — Occurs when low-lying coastal lands are overtopped and eroded by storm surge and waves such that the eroded sediments are carried landward by floodwaters, burying uplands, roads, and at -grade structures. Pier foundation — Foundation consisting of isolated masonry or cast -in -place concrete structural elements extending into firm materials. Piers are relatively short in comparison to their width, which is usually greater than or equal to 12 times their vertical dimension. Piers derive their load -carrying capacity through skin friction, end bearing, or a combination of both. Pile foundation — Foundation consisting of concrete, wood, or steel structural elements driven or jetted into the ground or cast -in -place. Piles are relatively slender in comparison to their length, which usually exceeds 12 times their horizontal dimension. Piles derive their load -carrying capacity through skin friction, end bearing, or a combination of both. Platform framing — A floor assembly consisting of beams, joists, and a subfloor that creates a platform that supports the exterior and interior walls. Plywood — Wood structural panel composed of plies of wood veneer arranged in cross -aligned layers. The plies are bonded with an adhesive that cures when heat and pressure are applied. Post -FIRM structure — For purposes of determining insurance rates under the National Flood Insurance Program, structures for which the start of construction commenced on or after the effective date of an initial Flood Insurance Rate Map or after December 31, 1974, whichever is later, including any subsequent improvements to such structures. This term should not be confused with the term new construction as it is used in floodplain management. Post foundation — Foundation consisting of vertical support members set in holes and backfilled with compacted material. Posts are usually made of wood and usually must be braced. Posts are also known as columns, but columns are usually made of concrete or masonry. Precast concrete — Structural concrete element cast elsewhere than its final position in the structure. See also Cast -in -place concrete. G-12 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY Pressure -treated wood — Wood impregnated under pressure with compounds that reduce the susceptibility of the wood to flame spread or to deterioration caused by fungi, insects, or marine borers. Premium — Amount of insurance coverage. Primary frontal dune — Under the National Flood Insurance Program, a continuous or nearly continuous mound or ridge of sand with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and subject to erosion and overtopping from high tides and waves during major coastal storms. The inland limit of the primary frontal dune occurs at the point where there is a distinct change from a relatively steep slope to a relatively mild slope. Rating factor (insurance) — A factor used to determine the amount to be charged for a certain amount of insurance coverage (premium). Recurrence interval — The frequency of occurrence of a natural hazard as referred to in most design codes and standards. Reinforced concrete — Structural concrete reinforced with steel bars. Relocation — The moving of a structure to a location that is less prone to flooding and flood -related hazards such as erosion. Residual risk — The level of risk that is not offset by hazard -resistant design or insurance, and that must be accepted by the property owner. Retrofit — Any change or combination of adjustments made to an existing structure intended to reduce or eliminate damage to that structure from flooding, erosion, high winds, earthquakes, or other hazards. Revetment — Facing of stone, cement, sandbags, or other materials placed on an earthen wall or embankment to protect it from erosion or scour caused by flood waters or wave action. Riprap — Broken stone, cut stone blocks, or rubble that is placed on slopes to protect them from erosion or scour caused by flood waters or wave action. Risk — Potential losses associated with a hazard, defined in terms of expected probability and frequency, exposure, and consequences. Risk is associated with three factors: threat, vulnerability, and consequence. Risk assessment — Process of quantifying the total risk to a coastal building (i.e., the risk associated with all the significant natural hazards that may impact the building). Risk category — As defined in American Society of Civil Engineers (ASCE) 7-10 and the 2012 International Building Code, a building's risk category is based on the risk to human life, health, and welfare associated with potential damage or failure of the building. These risk categories dictate which design event is used when calculating performance expectations of the building, specifically the loads the building is expected to resist. Risk reduction — The process of reducing or offsetting risks. Risk reduction is comprised of two aspects: physical risk reduction and risk management through insurance. COASTAL CONSTRUCTION MANUAL G-13 GLOSSARY Volume II Risk tolerance — Some owners are willing and able to assume a high degree of financial and other risks, while other owners are very conservative and seek to minimize potential building damage and future costs. Riverine SFHA — The portion of the Special Flood Hazard Area mapped as Zone AE and where the source of flooding is riverine, not coastal. Roof deck — Flat or sloped roof surface not including its supporting members or vertical supports. 0 Sand dunes — Under the National Flood Insurance Program, natural or artificial ridges or mounds of sand landward of the beach. Scour — Removal of soil or fill material by the flow of flood waters. Flow moving past a fixed object accelerates, often forming eddies or vortices and scouring loose sediment from the immediate vicinity of the object. The term is frequently used to describe storm -induced, localized conical erosion around pilings and other foundation supports, where the obstruction of flow increases turbulence. See also Erosion. Seawall — Solid barricade built at the water's edge to protect the shore and prevent inland flooding. Setback — For the purpose of this Manual, a State or local requirement that prohibits new construction and certain improvements and repairs to existing coastal buildings in areas expected to be lost to shoreline retreat. Shearwall — Load -bearing wall or non -load -bearing wall that transfers in -plane lateral forces from lateral loads acting on a structure to its foundation. Shoreline retreat — Progressive movement of the shoreline in a landward direction; caused by the composite effect of all storms over decades and centuries and expressed as an annual average erosion rate. Shoreline retreat is essentially the horizontal component of erosion and is relevant to long-term land use decisions and the siting of buildings. Single -ply membrane — Roofing membrane that is field -applied with one layer of membrane material (either homogeneous or composite) rather than multiple layers. The four primary types of single -ply membranes are chlorosulfonated polyethylene (CSPE) (Hypalon), ethylene propylene diene monomer (EPDM), polyvinyl chloride (PVC), and thermoplastic polyolefin (TPO). Siting — Choosing the location for the development or redevelopment of a structure. Special Flood Hazard Area (SFHA) — Under the National Flood Insurance Program, an area having special flood, mudslide (i.e., mudflow), or flood -related erosion hazards, and shown on a Flood Hazard Boundary Map or Flood Insurance Rate Map as Zone A, AO, Al-A30, AE, A99, AH, V, Vl V30, VE, M, or E. The area has a 1 percent chance, or greater, of flooding in any given year. Start of construction (for other than new construction or substantial improvements under the Coastal Barrier Resources Act) — Under the National Flood Insurance Program, date the building permit was issued, provided the actual start of construction, repair, reconstruction, rehabilitation, addition placement, or other improvement was within 180 days of the permit date. The actual start means either the first placement of permanent construction of a structure on a site such as the pouring of slab or footings, G-14 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY the installation of piles, the construction of columns, or any work beyond the stage of excavation; or the placement of a manufactured home on a foundation. Permanent construction does not include land preparation, such as clearing, grading, and filling; nor the installation of streets or walkways; excavation for a basement, footings, piers, or foundations or the erection of temporary forms; or the installation on the property of accessory buildings, such as garages or sheds not occupied as dwelling units or not part of the main structure. For a substantial improvement, the actual start of construction means the first alteration of any wall, ceiling, floor, or other structural part of a building, whether or not that alteration affects the external dimensions of the building. State Coordinating Agency — Under the National Flood Insurance Program, the agency of the State government, or other office designated by the Governor of the State or by State statute to assist in the implementation of the National Flood Insurance Program in that State. Stillwater elevation — The elevations of the water surface resulting solely from storm surge (i.e., the rise in the surface of the ocean due to the action of wind and the drop in atmospheric pressure association with hurricanes and other storms). Storm surge — Water pushed toward the shore by the force of the winds swirling around a storm. It is the greatest cause of loss of life due to hurricanes. Storm tide — Combined effect of storm surge, existing astronomical tide conditions, and breaking wave setup. Structural concrete — All concrete used for structural purposes, including plain concrete and reinforced concrete. Structural fill — Fill compacted to a specified density to provide structural support or protection to a structure. See also Fill. Structure — For floodplain management purposes under the National Flood Insurance Program (NFIP), a walled and roofed building, gas or liquid storage tank, or manufactured home that is principally above ground. For insurance coverage purposes under the NFIP, structure means a walled and roofed building, other than a gas or liquid storage tank, that is principally above ground and affixed to a permanent site, as well as a manufactured home on a permanent foundation. For the latter purpose, the term includes a building undergoing construction, alteration, or repair, but does not include building materials or supplies intended for use in such construction, alteration, or repair, unless such materials or supplies are within an enclosed building on the premises. Substantial damage — Under the National Flood Insurance Program, damage to a building (regardless of the cause) is considered substantial damage if the cost of restoring the building to its before -damage condition would equal or exceed 50 percent of the market value of the structure before the damage occurred. Substantial improvement — Under the National Flood Insurance Program, improvement of a building (such as reconstruction, rehabilitation, or addition) is considered a substantial improvement if its cost equals or exceeds 50 percent of the market value of the building before the start of construction of the improvement. This term includes structures that have incurred substantial damage, regardless of the actual repair work performed. The term does not, however, include either (1) any project for improvement of a structure to correct existing violations of State or local health, sanitary, or safety code specifications which have been identified by the local code enforcement official and which are the minimum necessary to ensure COASTAL CONSTRUCTION MANUAL G-15 GLOSSARY Volume II safe living conditions, or (2) any alteration of a "historic structure," provided that the alteration will not preclude the structure's continued designation as a "historic structure." Super typhoons — Storms with sustained winds equal to or greater than 150 mph. �I Threat — The probability that an even of a given recurrence interval will affect the building within a specified period. See Risk. Tornado — A rapidly rotating vortex or funnel of air extending groundward from a cumulonimbus cloud Tributary area — The area of the floor, wall, roof, or other surface that is supported by the element. The tributary area is generally a rectangle formed by one-half the distance to the adjacent element in each applicable direction. Tropical cyclone — A low-pressure system that generally forms in the tropics, and is often accompanied by thunderstorms. Tropical depression — Tropical cyclone with some rotary circulation at the water surface. With maximum sustained wind speeds of up to 39 miles per hour, it is the second phase in the development of a hurricane. Tropical disturbance — Tropical cyclone that maintains its identity for at least 24 hours and is marked by moving thunderstorms and with slight or no rotary circulation at the water surface. Winds are not strong. It is a common phenomenon in the tropics and is the first discernable stage in the development of a hurricane. Tropical storm — Tropical cyclone that has 1-minute sustained wind speeds averaging 39 to 74 miles per hour (mph). Tsunami — Long -period water waves generated by undersea shallow -focus earthquakes, undersea crustal displacements (subduction of tectonic plates), landslides, or volcanic activity. Typhoon — Name given to a hurricane in the area of the western Pacific Ocean west of 180 degrees longitude. Underlayment — One or more layers of felt, sheathing paper, non -bituminous saturated felt, or other approved material over which a steep -sloped roof covering is applied. Undermining — Process whereby the vertical component of erosion or scour exceeds the depth of the base of a building foundation or the level below which the bearing strength of the foundation is compromised. Uplift — Hydrostatic pressure caused by water under a building. It can be strong enough lift a building off its foundation, especially when the building is not properly anchored to its foundation. G-16 COASTAL CONSTRUCTION MANUAL Volume II GLOSSARY V Variance — Under the National Flood Insurance Program, grant of relief by a community from the terms of a floodplain management regulation. Violation — Under the National Flood Insurance Program (NFIP), the failure of a structure or other development to be fully compliant with the community's floodplain management regulations. A structure or other development without the elevation certificate, other certifications, or other evidence of compliance required in Sections 60.3(b)(5), (c)(4), (c)(10), (d)(3), (e)(2), (e)(4), or (e)(5) of the NFIP regulations is presumed to be in violation until such time as that documentation is provided. Vulnerability — Weaknesses in the building or site location that may result in damage. See Risk. Water surface elevation — Under the National Flood Insurance Program, the height, in relation to the National Geodetic Vertical Datum of 1929 (or other datum, where specified), of floods of various magnitudes and frequencies in the floodplains of coastal or riverine areas. Wave — Ridge, deformation, or undulation of the water surface. Wave height — Vertical distance between the wave crest and wave trough. Wave crest elevation is the elevation of the crest of a wave, referenced to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum. Wave overtopping — Occurs when waves run up and over a dune or barrier. Wave runup — Is the rush of water up a slope or structure. Wave runup occurs as waves break and run up beaches, sloping surfaces, and vertical surfaces. Wave runup depth — At any point is equal to the maximum wave runup elevation minus the lowest eroded ground elevation at that point. Wave runup elevation — Is the elevation reached by wave runup, referenced to the National Geodetic Vertical Datum or other datum. Wave setup — Increase in the stillwater surface near the shoreline due to the presence of breaking waves. Wave setup typically adds 1.5 to 2.5 feet to the 100-year stillwater flood elevation and should be discussed in the Flood Insurance Study. Wave slam — The action of wave crests striking the elevated portion of a structure. Wet floodproofing — A flood retrofitting technique that involves modifying a structure to allow floodwaters to enter it in such a way that damage to a structure and its contents is minimized. COASTAL CONSTRUCTION MANUAL G-17 GLOSSARY Volume II Z Zone A — Under the National Flood Insurance Program, area subject to inundation by the 100-year flood where wave action does not occur or where waves are less than 3 feet high, designated Zone A, AE, Al- A30, A0, AH, or AR on a Flood Insurance Rate Map. Zone AE — The portion of the Special Flood Hazard Area (SFHA) not mapped as Zone VE. It includes the Moderate Wave Action area, the Minimal Wave Action area, and the riverine SFHA. Zone B — Areas subject to inundation by the flood that has a 0.2-percent chance of being equaled or exceeded during any given year, often referred to the as 500-year flood. Zone B is provided on older flood maps, on newer maps this is referred to as "shaded Zone X." Zone C — Designates areas where the annual probability of flooding is less than 0.2 percent. Zone C is provided on older flood maps, on newer maps this is referred to as "unshaded Zone X." Zone V — See Coastal High Hazard Area. Zone VE — The portion of the coastal Special Flood Hazard Area where base flood wave heights are 3 feet or greater, or where other damaging base flood wave effects have been identified, or where the primary frontal dune has been identified. Zone X — Under the National Flood Insurance Program, areas where the flood hazard is lower than that in the Special Flood Hazard Area. Shaded Zone X shown on recent Flood Insurance Rate Maps (Zone B on older maps) designate areas subject to inundation by the 500-year flood. Unshaded Zone X (Zone C on older Flood Insurance Rate Maps) designate areas where the annual probability of flooding is less than 0.2 percent. Zone X (Shaded) — Areas subject to inundation by the flood that has a 0.2-percent chance of being equaled or exceeded during any given year, often referred to the as 500-year flood. Zone X (Unshaded) — Designates areas where the annual probability of flooding is less than 0.2 percent. G-18 COASTAL CONSTRUCTION MANUAL Index, Volume II Bold text indicates chapter titles or major headings. Italicized page numbers indicates a figure or table. A Acceptable level of risk, 7-4 Access to elevated buildings, 7-7, 8-6, 9-34, 9-38, 9-39 Allowable Stress Design (ASD), 8-2, 8-17, 8-48, 8-55, Example 8.5, 8-74, 10-9, 10-13 Anchor air-conditioning condenser, 12-4 bolts, 9-11 building envelope, 13-29 concrete and masonry walls, 9-27, 15-5, 15-7 corrosion of, 11-7, 11-13, 11-17, 12-3 exterior -mounted mechanical equipment in high winds, 12-2 hillside house bracing, 15-7 hold-down, 15-6 masonry chimney, 15-5, 15-7 sill plate anchor bolts in foundations, 15-6 split-level floor, 15-7 stainless steel frame, 11-7, 11-13 spacing, 9-11 truss, 9-27 Anchorage system, 7-17, 11-6 Angle of internal friction, 10-9, 10-10, 10-15 Appurtenances, 9-38 access to elevated buildings, 9-39 decks and covered porches, 9-38 handrails, 9-39 pools and hot tubs, 9-40, 9-41 stairways, 9-39 Attic vents, 11-50, 12-3, 14-5 B Base flood, 7-10, 8-5, 8-6 breakaway walls, 11-20 erosion and subsidence as a result of, 8-8 stillwater elevation of, 8-8 Base flood elevation (BFE) building elements allowed below, 9-38 buildings elevated above, 7-10, 7-19, 7-20, 9-30 deck, 9-38 designing for flood levels above, 7-10 elevators, 9-40, 12-1 flood -damage -resistant materials below, 9-34 flood insurance rates for buildings above the, 7-16 foundation, below the, 10-2 freeboard above, 8-6, 8-10 items below, covered by NFIP, 7-17 FIRMS, BFEs on, 8-6 wave setup included in, 8-15 Basement, 7-14, 7-17, 7-19, 13-12, 15-6, 15-12, 15-13 NFIP definition of, 7-13 Beach nourishment, 7-7, 7-20, 8-11, Example 8.1 Bearing capacity (see Soils) Benefit -cost model, 7-12 BFE (see Base flood elevation) Blockage coefficient, 8-33 Breakaway walls, 7-8, 7-16, 9-1, 9-30, 11-20 areas with no earthquake hazard, breakaway walls in, 13-9 collapse of, 11-21 designing, 8-24 enclosures, 7-16, 9-30, 11-20 failure, 9-32 flood and wind mitigation, 7-8 flood openings in, 11-20 foundation issues, 13-18 garage doors in, 11-4 high winds, 11-20 inspection, 7-25 not covered by NFIP, 7-18 solid, 7-21 utilities and wiring on, 12-7 wave loads, 8-21 COASTAL CONSTRUCTION MANUAL I-1 INDEX Volume II Building envelope, 13-29, 15-3 breach, 9-2 designing, 11-1 inspection points, 13-31 maintaining, 14-1 substitution of materials, 13-30 top building envelope issues for builders, 13-31 Buildings Coastal A Zones, buildings in, 7-8, 8-24 coastal, with large number of windows and doors, 7-7 coastal residential, proper siting, design, and construction of, 7-1 costs, 7-6 elevated foundation, buildings on, 7-6 elevating, 7-7, 7-10 elevating, insurance discount points for, 7-20 envelope, 11-1 (see also Building envelope) footprint, 7-12, 10-7 hazard insurance, 7-12, 7-13, 7-21, 7-24 height restrictions, 7-8, 7-13 inspection of, 7-25 L-shaped, 9-27 maintaining, 14-1 materials, 9-33 materials, selection of, 9-33 performance and roof system, 11-24 residential, 7-1 SFHAs, buildings in, 7-13 site, 7-1, 7-2, 7-7, 7-11 site, inspection of, 7-25 slab -on -grade, 7-25 sustainable design of, 7-24 substantially damaged, 7-15 substantially improved, 7-16 use of, 7-2 Zone A, buildings in, 7-7, 7-15, 7-16, 7-19 Zone V, buildings in, 7-7, 7-10, 7-14, 7-16, 7-19 Zones B, C, and X, buildings in, 7-15 Building Code Effectiveness Grading Schedule (BCEGS), 7-22 Building materials, 9-33 above the DFE, 9-35 below the DFE, 9-34 combinations, 9-35 corrosion, 9-37 fire safety, 9-36 piles, 10-12 selection of, 9-33 Bulkhead, 7-17, 9-38 C California Earthquake Authority (CEA), 7-24 Cast -in -place concrete, 13-10, 15-11 CBRA (see Coastal Barrier Resources Act of 1982) CBRS (see Coastal Barrier Resource System) CEA (see California Earthquake Authority) Cladding (see also Components and cladding), 7-9 Closed/shallow foundation, 10-35 breakaway wall enclosures in, 9-30 buildings in, 7-8, 8-24 Coastal A Zone, 7-8, 10-2 flood loads in, 8-17, 8-37 8-38, 8-44 flood openings in breakaway walls in, 11-20 foundation styles in, 7-8, 10-2, 10-3, 10-4, 10-5, 10-10, 10-34, 10-35, 10-36, 13-2, 13-5, 13-9, 13-12, 15-9 load combinations in, 8-38, 8-74, 8-75, Example 8.10, 8-77 masonry frames in, 9-27 septic systems in, 12-11 warning box, buildings in Coastal A Zones, 8-24 Coastal Barrier Resource System (CBRS), 7-15 Coastal Barrier Resources Act of 1982 (CBRA), 7-15 Coastal flood hazard areas, 7-15, 8-15, 13-9, 13-12 (see also Zone A) Coastal flood zones, 8-17 Coastal hazards, 7-4, 9-2, 9-37, 10-45, 13-1 Coastal high hazard flooding, 7-14 (see also Zone V) Coastal residential buildings design, 8-1, 9-1, 10-1, 11-1 Column foundation (see Foundation) Community Rating System (CRS), 7-18 Components and cladding (C&C), 8-48, 8-51, 8-52, 8-61 calculating pressures, 8-50 definition from ASCE 7-10, 8-61 wind pressures of, 8-62 Concrete bond beam, 9-12 cold weather, concrete in, 13-12 columns, 8-68, 10-31, 10-32, 10-33, 10-34 concrete/masonry construction, 9-27 cover, 13-11 damage -resistant to flooding, 13-19 decks, 11-37, 11-38 deterioration, 13-2 embedment of connectors, 9-35 fire-resistant, 7-22 floodwalls, 15-1 footings, 10-36, 10-37, 10-38 foundation, 9-30, 10-32, 10-33, 10-34 13-2, 13-3, 13-10, 13-11, 13-19, 14-5, 14-12 house, 13-11 mat, 10-37 minimum cover, 13-11 I-2 COASTAL CONSTRUCTION MANUAL Volume II INDEX piers, 9-34, 10-36 pile caps, 9-35 piles, 9-34, 10-4, 10-11, 10-12, 10-15, 10-24, 13-7 pool deck, 9-41 pools, 9-40 reinforced, 9-33 roof decks, 11-37, 11-39 roofs, 7-23, 11-50 the roofs, 11-38, 11-39 walls, 9-11, 9-34, 11-7, 11-13, 11-16, 11-20, 11-24, 13-30, 15-5, 15-7, 15-12 weight of, 8-17 Connectors column, 10-24 corrosion of metal connectors, 9-37 corrosion protection for metal connectors, 13-23 corrosion -resistant, 9-24 design event, connectors in, 13-19 failure of, 13-20 floor framing to support beam, 9-17 floor support beam to foundation, 9-19 metal, maintenance of, 14-10 roof framing to exterior wall, 9-8 roof sheathing to roof framing, 9-4, 9-6 roof to exterior wall, 9-8, 9-9, Example 9.2 roof -to -wall uplift, 8-54, Example 8.5 roof truss -to -masonry wall connection, 9-11 roof uplift connector loads, 8-52, 8-54, Example 8.5 structural, 13-19 wall sheathing to window header, 9-12, 9-13 wall to floor framing, 9-15 wall -to -floor, 8-66, Example 8.8 wall top plate -to -wall stud, 9-10 wall -to -roof, 8-66, Example 8.8 warning box, connections, 13-9 warning box, corrosion -prone sheet metal connectors, 14-11 warning box, nail selection and installation, 13-20 window header to exterior wall, 9-12, 9-13 wood pile -to -beam, 10-26 Constructability, 13-17 Construction, categories of frame, 7-23 masonry 7-23 masonry veneer, 7-23 superior, 7-23 Continuous load paths (see Loads) Contraction joint layout for slab -on -grade below elevated building, 9-42 Corrosion, 14-2, 10-12, 11-7, 11-13, 11-18, 11-24, 11-38, 11-43 corrosion -prone sheet metal, 14-11 corrosion protection for metal connectors, 12-3, 13-23 deck connectors, 14-11 metal connectors, corrosion of, 9-37 nails in plywood panels, corrosion of, 11-5 Corrosion -resistant, 9-25, 9-37 connectors, 9-24, 9-25, 11-48, 13-20 cost implications of, 7-9 materials, 9-33, 9-37 recommendations on connectors, 9-25 solid wood blocking, 13-23 Costs construction decisions, cost of, 7-8, 7-11 design decisions, cost of, 7-7, 7-11 erosion -control measures, cost of, 7-7 initial, 7-6 long term, 7-6 maintenance and repair, cost of, 14-2 natural hazards in coastal areas, cost of, 7-5 siting decisions, cost of, 7-7, 7-11 operational, 7-6 CRS (see Community Rating System) Dead loads, 8-3 (see also Loads) Debris (see also Floodborne debris; Waterborne debris; Wind-borne debris) floodborne debris, 8-3, 12-5, 12-7, 12-10 impact load calculation, 8-32, Equation 8.9 impact loads, 8-15, 8-31 (see also Loads) velocity, 8-32 waterborne, 8-32 Decks covered porches and, 9-38 maintenance, 14-9 warning box, decks, 9-38 Defensible space, 15-2 Depth coefficient, 8-32, 8-33 Design breaking wave height, 8-15 building, 9-1 building envelope, 11-1 coastal environment, 7-2 flood, 8-5 flood conditions, 10-5 flood elevation (DFE), 7-11, 8-6 flood protection depth, 8-9 flood velocity, 8-15, 8-16, Equation 8.2 flood velocity vs. design stillwater flood depth, 8-17 foundation design criteria, 10-2 framework, 7-3 process, 7-2 requirements, 7-3 COASTAL CONSTRUCTION MANUAL I-3 INDEX Volume II stillwater flood depth, 8-7, 8-9, 8-10, Equation 8.1 stillwater flood depth calculations, 8-11, Example 8.1 stillwater flood elevation, 8-10, 8-11, Equation 8.1 sustainable building, 7-24 wind pressure, 8-58, Example 8.6, 8-66, Example 8.8 wind pressure for low-rise buildings, 8-50, Equation 8.14 Design flood relationship to base flood, 8-5, 8-6 Design flood elevation (DFE), 7-11, 8-6 building, elevating to, 15-8 community without, 7-25 design flood protection depth, 8-9 electric utility, telephone, and cable TV systems, placement of, 12-6, 13-1 elevating a building above, cost of, 7-11 exterior -mounted mechanical equipment, placement of, 12-5 flood damage -resistant materials below, 9-34 foundation, 10-5 freeboard, 8-5 generator, placement of, 12-9 inspection, 7-25 interior mechanical equipment, placement of, 12-6 materials above, 9-32, 9-35 materials below, 9-32, 9-34 non-100-year frequency -based, 8-10 non -submersible well pumps, placement of, 12-10 perimeter walls below, 10-3 piles, 13-5 pools, 9-40 utilities, 12-6 utilities and furnaces below, 15-12 Design stillwater flood elevation, 8-10, Equation 8.1, 10-10 DFE (see Design flood elevation) Diaphragm, 13-24 floor framing, 13-24, 13-25 lateral diaphragm loads, 8-57, Example 8.6 loads, 8-52, 8-53 nailing schedule, 13-20 roof, 13-28, 13-29 shear, 13-18, 13-20 stiffening, 9-20 wall, 13-27 Doors durability, 11-7 exterior, 11-4 flashing, 11-8 frame attachment, 11-6 gap between threshold and door, 11-8 garage, 11-6 high winds, 11-6 loads and resistance, 11-6 sliding glass, 11-5 swing, 11-8 wall integration and, 11-8 water infiltration, 11-7 weatherstripping, 11-8 wind-borne debris and, 11-7 Drag coefficients, 8-29 Dry floodproofing, 15-11 advantages and disadvantages of, 15-12 warning box, dry floodproofing, 15-11 Dune frontal, 8-12, Example 8.1, 8-15, 8-38, Example 8.4 primary frontal, regulations for, 9-40 reservoir, 8-12, Example 8.1, 8-38, Example 8.4 toe, 8-14, Example 8.1, 8-38, Example 8.4 Dynamic pressure coefficient, 8-23 E EarthAdvantage, 7-24 Earthquake (see also Seismic hazard; Seismic hazard area; Seismic mitigation) base shear, 8-69, Equation 8.15 building envelope, 11-3, 13-30 dead load, 8-3 elevating a building and damage from, 7-7 insurance, 7-13, 7-24 live load, 8-3, 8-73 load, 8-68, 8-70, Example 8.9 low -sloped roofs, 11-49 mitigation, 15-5 multihazard mitigation, 15-14 non -load -bearing walls, wall coverings, and soffits, 11-24 open masonry foundation, 13-8 piles, 14-12 reinforced masonry foundation, 13-10 roof framing, 13-27 roof tiles, 11-45 vertical distribution of seismic forces, 8-70, Equation 8.16 Eaves, 11-31, 11-32, 11-38 pressures, 8-48 top building envelope issues for builders, 13-31 wildfire mitigation, 15-4 EIFS (see Exterior insulating finishing system) Electric utility, telephone, and cable TV systems, 12-6 design, 12-7 electric service meters, damaged, 12-7 emergency power, 12-9 routing and installation, 12-7, 12-8 wiring methods, 12-7 I-4 COASTAL CONSTRUCTION MANUAL Volume II INDEX Elevation, 15-8 advantages and disadvantages of, 15-9 above BEE, 7-10, 7-19, 7-20 design flood, 8-6 required, 7-8 Elevators, 9-39, 12-1 accessory equipment, 12-2 enclosure, 12-2 installation, 9-40 negative discount points, below the BFE, 7-21 NFIP coverage, 7-18 one- to four -family residential structures, 9-40 safety, 12-2 shaft, 12-2 Embedment, 7-8 connectors, 9-35 piles, 7-8, 7-21, 7-25, 8-3, 10-12, 10-13, 10-20, 10-21, 10-23, 13-6, 14-12 treated timber piles, 10-25 wood piles, 10-15, 10-18 Emergency generator, size of, 12-9 warning box, backfeeding emergency power, 12-10 Enclosure below the BFE, 7-14 below the lowest floor, 7-14, 7-16 breakaway walls, 7-8 breaking wave load on vertical walls, 8-23 flood and wind mitigation, 7-8 inspection points, 7-25 localized scour around, 8-36, 8-37, Equation 8.12 NFIP requirements, 7-16, 7-17, 7-180 EnergyStar, 7-24 Erosion, 7-1, 7-7, 7-8, 7-10, 10-4 control device, 7-20 depth, 10-5 during base flood, 8-8 during design flood, 8-10 effect on flood hazard, 8-7 effect on ground elevation, 8-8 flood and wind mitigation, 7-8 flood loads and, 8-5 hazard areas, 7-7 long-term, 7-7, 8-7, 8-11, Example 8.1 primary frontal dune, 8-15 short-term warning box, erosion, long-term and storm -induced, 13-6 wind -induced, 7-7 Exterior doors, 11-4 Exterior insulating finishing system (EIFS), 11-16, 11-19 Exterior -mounted mechanical equipment, 12-2 air-conditioning condenser, damaged, 12-4 air-conditioning condenser, elevation of, 12-4 flooding, 12-3 high winds, 12-2 maintenance, 14-9 seismic events, 12-6 F 500-year flood elevation, 8-6 safe rooms, 8-67 FAIR Plan, 7-21 Fasteners, 7-9, 8-64, 9-6, 9-11, 9-24, 13-10 corrosion, 11-4, 11-48, 14-2, 14-5, 14-6 corrosion resistant, 9-38 felt, 11-28 flood and wind mitigation, 7-9 frame, 11-6, 11-10 galvanized, 9-35 heads, 11-43 laminated, 11-35 mechanical, 11-19 metal, 7-9, 9-25, 9-37, 14-9 shingle, 11-25, 11-30, 11-35, 11-37 siding, 11-17 slate, 11-47 spacing, 9-4 stainless steel, 11-23, 11-47, 11-48, 12-3 substitution, 13-28 tie, 11-18, 11-19 tile, 11-43 vertical, 13-14 wood frame building, 13-20 Fill (see Structural fill), 7-8 Fire sprinkler systems, 12-12 FIRM (see Flood Insurance Rate Map) Flashing, 7-8, 11-21 door and window, 11-22 roof -to -wall, 11-22 deck -to -wall, 11-22 Flood depth parameters, 8-9 depth, wave setup contribution to, 8-15 design, 8-5 design flood elevation, 8-6 insurance, 7-10, 7-13 (see also National Flood Insurance Program) load calculation, 8-44, Worksheets 1, 2 load combinations, 8-37, 8-38, Example 8.4 loads, 8-5 mitigation measures, 7-8, 15-8 (see also Flood mitigation) velocities during tsunamis, 8-15 COASTAL CONSTRUCTION MANUAL I-5 INDEX Volume II Floodborne debris dead load, 8-3 electric service, 12-7 piles, 12-5 water supply line riser, 12-10 Flood damage -resistant material, 9-36, 10-2, 12-2, 13-18 inspection considerations, 7-26 flood mitigation, 15-8, 15-13 Flood elevation, 8-5 advisory, 8-7 design stillwater, 8-10 regulatory, 8-6 Flood hazard area elevators, 9-40 safe rooms, 8-68 Flood insurance (see also National Flood Insurance Program) Flood Insurance Rate Map (FIRM), 7-4, 7-10, 7-14, 7-15 BFE, 8-6 NFIP, 7-15, 7-19 pre -FIRM, 7-15 post -FIRM, 7-15, 7-16, 7-17, 7-19 use of, 8-6, 8-10 Flood Insurance Study (FIS) (see also National Flood Insurance Program), 7-4, 8-10 500-year flood elevation, 8-6 Flood mitigation, 7-8, 15-8 dry floodproofing, 15-11, 15-12 elevation, 15-8, 15-9 floodwalls and levees, 15-13, 15-14 multihazard mitigation, 15-16 relocation, 15-10 wet floodproofing, 15-12, 15-13 Floodproofing (see Dry floodproofing; Wet floodproofing) Flooding (see Flood) Floodplain 100-year (see Base flood), 7-15, 8-5, 8-6, 8-10 500-year, 8-67 administrator, 7-16 crawlspaces, 14-4 elevators, 12-2 inspection, 7-25 management program, 7-18 management regulations, 7-16, 7-17, 12-6 managers, 7-25, 9-40 NFIP regulations, 7-15 ordinances, 8-18, 9-40 relocation out of, 15-10 septic systems, 12-11 Flood retrofitting (see flood mitigation) Floodwalls, 15-13 advantages and disadvantages of, 15-14 warning box, floodwalls and levees, 15-14 Flood zones, 7-19, 10-5 Floor framing, 13-23 horizontal beams and girders, 13-24 inspection points, 13-25 substitution of materials, 13-25 Floors elevated buildings, floors in, 11-4 framing, 13-23 (see also Floor framing) framing to support beam connection, 9-17 lowest floor below the BFE, 9-34 support beam to foundation connection, 9-18, 9-19 Footings continuous, 9-27, 10-37, 10-45, 14-12 Force hydrostatic, 8-18, Equation 8.3, 8-19 vertical hydrostatic, 8-19, Equation 8.4, 8-20 Foundations (see also Foundation construction), 10-1 column, 7-8 closed, 10-3 closed, failure of, 10-4 closed/shallow, 10-35 construction, 13-2 (see also Foundation construction) design, 10-1 design criteria, 10-2 design process, 10-10 design requirements and recommendations, 10-4 deep, 10-4 erosion, long- and short-term, 10-5 open, 7-8, 10-3 open/deep, 10-25 (see also Open/deep foundation) open/shallow, 10-34 (see also Open/shallow foundation) perimeter wall, 7-8 pile, 7-8, 10-11 (see also Pile foundation; Foundation construction) pier, 7-8, 10-36 (see also Pier foundation) shallow, 10-4 site considerations, 10-5 site elevation, 10-5 site soils, 10-5 soils data, 10-5 style selection, 10-5 styles, 10-2 styles in coastal areas, 10-3 Foundation construction, 13-2 concrete, 13-10, 13-11 field preservative treatment, 13-17 inspection points, 13-18 layout, 13-2, 13-3 masonry, 13-8, 13-9, 13-10 material durability, 13-13 pile driving resistance, 13-8 piles, 13-3, 13-4 13-5, 13-6 I-6 COASTAL CONSTRUCTION MANUAL Volume II INDEX substitutions, 13-17 top foundation issues for builders, 13-18 wood, 13-12 Framing system floor, 13-23 townhouse, 9-37 steel frame on wood piles, 9-36 Freeboard 100-year flood, 8-10 design flood elevation, 8-6, 8-11, Example 8.1 NFIP requirements, 8-6 required by community, 8-6 terminology box, 8-5 wave slam, 8-25 G Gable braced gable frames, 9-28 end bracing, 9-26, 13-29 end failure, 9-2, 9-25, 9-31 gable edge, 13-27, 13-31 gable end overhangs, 13-27, 15-18, 15-19 gable end vents, 11-52 gable end walls, 15-20 masonry, 9-28 roof, 8-52, 8-61, 9-30 wall support, 9-21, 9-24 Garage doors attachment to frame, 11-6 blown out of tracks, 11-6 breakaway walls, garage doors in, 11-4 exterior doors, 11-4 open -front bracing, 15-7 wind mitigation, 8-61, 15-19 Glazing (see also Windows), 11-9 impact -resistant, 7-7, 7-24, 8-49, 9-39 maintenance of, 14-7 protection from debris, 7-8, 11-10, 11-12, 15-19 wind -driven rain and, 7-7, 11-14 Grade beam, 8-35, 10-11, 10-12, 10-18 concrete column and grade beam foundation, 10-32 continuous, 10-34 open/deep pile foundations, 10-31 pier foundations, 10-36 pile foundations, 10-23 scour around, 8-35, 8-36, Equation 8.11a, 10-26 timber pile treatment, 10-31 treated timber pile foundation, 10-25, 10-32 Green building programs, 7-24 Groundwater septic tanks, 12-11 Gutter blow -off, 11-25 H 100-year stillwater flood elevation, 8-8, 8-15 Hail, 7-13, 7-21, 11-15, 11-36, 11-37, 11-38, 11-45, 11-46, 11-48, 11-49, 11-50 Handrails, 9-39 Hazard insurance, 7-12 earthquake, 7-24 flood, 7-13 wind, 7-21 High -Velocity Hurricane Zone, 11-7 High -wind mitigation, 15-15 Advanced Mitigation Package, 15-19 Basic Mitigation Package, 15-17 evaluating existing homes, 15-16 FEMA wind retrofit grant programs, 15-19 Intermediate Mitigation Package, 15-19 wind retrofit mitigation packages, 15-16 Hurricane -prone region terminology box, 8-49 Hurricanes, 15-16 Andrew, 7-5, 9-2, 9-25, 11-1, 11-38 Bertha, 11-48 Charley, 7-5, 9-3, 9-4 11-1, 11-3, 11-5, 11-6, 11-9, H- 13, 11-23, 11-25, 11-26, 11-39, 11-40, 11-41, 11-42 Eloise, 7-4 Fran, 9-2 Frances, 7-5 Georges, 11-1, 11-9, 11-37, 12-4 Hugo, 9-32, 11-1 Ike, 7-5, 8-35, 11-1 Iniki, 11-1 Ivan, 7-5, 11-1, 11-43 Jeanne, 7-5 Katrina, 7-5, 8-6, 9-4, 10-2, 10-13, 10-24, 10-36, 10-37 11-1, 11-46, 11-47 Marilyn, 9-30, 9-31, 11-1, 12-9 Opal, 9-32, 12-7 Rita, 7-5 Wilma, 7-5 Hydrodynamic load, 8-5, 8-15, 8-28, 8-29, Equation 8.8 piles vs. breaking wave load on piles, 8-30, Example 8.3 Hydrostatic load, 8-17 lateral, 8-18, Equation 8.3a Hydrostatic force lateral, 8-18, Equation 8.3b vertical, 8-19, Equation 8.4 COASTAL CONSTRUCTION MANUAL I-7 INDEX Volume II IBHS (see Insurance Institute for Business and Home Safety) Ice loads, 11-25 sealant systems, 15-11 waterborne, 15-14 Initial costs, 7-6 Insurance (see Hazard insurance) Insurance Institute for Business and Home Safety (IBHS), 7-5, 7-21, 15-2, 15-16 Insurance Services Office (ISO), 7-22, 7-23 Interior mechanical equipment, 12-6 Inspection, 7-25 building envelope, 13-31 floor framing, 13-25 roof framing, 13-28, 13-29 wall framing, 13-27 ISO (see Insurance Services Office) J Jalousie louvers, 11-13, 11-14 Jetting, of piles, 10-20, 10-21, 13-7 Joints tooled concave and V-joints, 13-9 Joists floor, 13-23, 13-24, 14-5 L Landslide, 10-6 Lateral wave slam, 8-25, 8-26, Equation 8.7 Lattice, 9-33 Leadership in Energy and Environmental Design (LEED), 7-11, 7-24 LEED (see Leadership in Energy and Environmental Design) Levees, 15-13 advantages and disadvantages of, 15-14 warning box, floodwalls and levees, 15-14 Limit of Moderate Wave Action (LiMWA), 8-37, 8-74, 8-77, Example 8.10 terminology box, 10-2 LiMWA (see Limit of Moderate Wave Action) Liquid -applied membranes, 11-37 Live loads, 8-3 (see also Loads) Load -bearing wall exterior, 9-36 Load combinations, 8-73 Load and Resistance Factor Design (LRFD), 8-2 Loads breaking wave loads on vertical piles, 8-21, Equation 8.5 breaking wave loads on vertical walls, 8-22, Equation 8.6 combinations, 8-73, 8-75, Example 8.10 combination computation worksheet, 8-80 concrete/masonry framing system, 9-27, 9-29 continuous load path, 9-1, 15-20 dead, 8-3 debris impact, 8-31, 8-32, Equation 8.9 determining for flood, wind, and seismic events, 8-2 diaphragm, 8-52 flood, 8-5, 8-15 flood load combinations, 8-37, 8-38, Example 8.4 floor load computation worksheet, 8-44, 8-46 floor diaphragm, 8-60, Example 8.6 floor support beam to pile, uplift load path, 9-19, Example 9.6 floor to support beam framing, uplift load path, 9-18, Example 9.5 gable wall support, 9-24 hydrodynamic, 8-28, 8-29, Equation 8.8 hydrostatic, 8-17 ice, 11-25 L-shaped building, 9-27 lateral connector loads from wind and building end zones, 8-62, 8-63 lateral connector loads for wall -to -roof and wall -to -floor connections, 8-66, Example 8.8 lateral hydrostatic, 8-18, Equation 8.3 live, 8-3 moment -resisting frames, 9-28, 9-29 path, 9-5, 9-21 path failure, 9-2, 9-3 platform framing, 9-28 roof shape, 9-30 roof sheathing suction, 8-64, Example 8.7 roof -to -wall uplift connection, 8-54, Example 8.5 roof uplift connector, 8-52, 8-53, 8-54, Example 8.5 seismic, 8-68, 8-70, Example 8.9 site -specific, 8-1 snow, 8-5 tornado,8-67 tsunami, 8-47 tributary area, 8-4, 8-53, 9-14, Example 9.3 uplift, 7-24, 8-5, 8-61, 9-1, 9-10, 10-1, 10-15, 10-42, 11-33, 11-37, 13-7 uplift due to shear wall overturning, 9-21, Example 9.7, 9-24 wall sheathing suction, 8-64, Example 8.7 wall -to -floor framing, uplift and lateral load path, 9-15, Example 9.4 I-8 COASTAL CONSTRUCTION MANUAL Volume II INDEX wave, 8-20 wave slam, 8-25 wind, 8-47 wind, determining, 8-49 window header, uplift and lateral load path, 9-14, Example 9.3 Localized scour, 8-34 Losses from natural hazards in coastal areas, 7-5 Lowest floor below the BFE, 9-34 corrosion below, 14-2 DFE, 15-8 elevation of, 7-8, 7-10, 7-14, 7-15, 7-16, 7-20, 8-6, 8-28, 15-8 elevator, 9-40, 10-5 enclosures below, 7-16, 7-17 flood damage above, 7-10 inspection, 7-25 penalties related to areas below the lowest floor, 7-16 piles, 10-25 pool, 9-40 Zone A, lowest floor in, 7-15 Zone V, lowest floor in, 7-15 Lowest horizontal structural member, 7-8„ 7-14, 7-15, 7-16, 10-23, 13-5 M Main wind force resisting system (MWFRS), 8-48, 8-52 determining pressures, 8-49, 8-51 elements of shear walls and roof diaphragms, 8-61 Maintenance, 14-1, 14-5 decks and exterior wood, 14-9 exterior -mounted mechanical and electrical equipment, 14-9 glazing, 14-7 inspection checklist, 14-5 metal connectors, 14-10 roofs, 14-8 siding, 14-7 techniques, 14-11 (see also Maintenance techniques) Maintenance techniques, 14-11 flooding, 14-12 seismic and wind, 14-12 Manufactured home, 7-14 Masonry building material, 9-33 buildings, 7-22 chimneys, 15-5, 15-7 concrete masonry unit (CMU), 11-16, 11-20 construction, 9-12, 9-27, 9-32 deterioration, 13-2 exterior walls, 7-23, 9-27 foundation, 9-30, 13-3, 13-8, 13-18, 14-5 frames, 9-27 gables, 9-28 grouted masonry cell, 9-11 joints, 13-8 materials, 9-35, 10-36, 15-14 piers, 9-34 termites, 11-13 unreinforced masonry walls, 8-24 veneer, 7-23, 14-6 walls, 9-11, 11-7, 13-30, 15-5 MEPS (see Molded expanded polystyrene) Metal connectors (see also Fasteners), 7-9 maintenance, 14-10 Metal roof panel, 11-45 Mitigation elevation, 15-8, 15-9 flood, 7-8, 15-8 (see also Flood mitigation) floodwalls and levees, 15-13 high wind, 15-15 (see also High wind mitigation) muhihazard, 15-14 relocation, 15-10 retrofitting, 15-2 seismic, 15-5 (see also Seismic mitigation) wildfire, 15-2 wind, 7-8 Moisture, 9-35, 11-28, 12-11 barrier, 11-16, 11-22, 13-9 corrosion, 14-2 exterior, 14-3 framing construction, 13-14 inspection, 13-18, 13-27, 13-29, 14-6 interior, 14-3 intrusion, 9-33, 11-20, 13-1, 13-8 penetration or retention, 13-9 stairs, 13-16 sustainable design considerations, 7-24 termites, 14-4 Molded expanded polystyrene (MEPS), 11-19 Municipal water connections, 12-12 MWFRS (see Main wind force resisting system) NAHB (see National Association of Home Builders) National Association of Home Builders (NAHB), 7-24 National Flood Insurance Program (NFIP), 7-13 building occupancy, 7-14 building type, 7-14 contents, 7-17 covered items, 7-17 COASTAL CONSTRUCTION MANUAL I-9 INDEX Volume II date of construction, 7-15 discount points, 7-20 elevation of lowest floor or bottom, 7-16 enclosures below lowest floor, 7-16 flood insurance zone, 7-14 flood rating factors, 7-13 foundations, 10-4 lowering premiums, 7-20 lowest horizontal structural member of lowest floor, 7-16 non -covered items, 7-18 premiums, 7-19, 7-20 regulations, 7-8 replacement value, 7-17 warning box, differences between floodplain management regulations and NFIP flood insurance, 7-16 Natural hazard risk in coastal areas, 7-3 losses from natural hazards in coastal areas, 7-5 New construction, 9-34, 10-11, 11-52, 12-1 NFIP (see National Flood Insurance Program) Non -coastal flood zone flood loads in, 8-17 Non -load -bearing walls, wall coverings, and soffits, 11-15 breakaway walls, 11-20, 11-21 brick veneer, 11-18 concrete and CMU, 11-20 durability, 11-23 exterior walls, 11-16 exterior insulating finish system (EIFS), 11-19 exterior insulating finish system (EIFS), blown off, 11-20 fiber -cement siding, blown off, 11-18 flashings, 11-21 high winds, 11-16 seismic, effects of, 11-24 siding, 11-17 soffits, 11-22 vinyl siding, blown off, 11-17 Nor'easter, 7-6, 15-15 n J 100-year flood (see Base flood), 8-5, 8-6, 8-10 Open/deep foundation, 10-25 diagonal bracing, 10-27, 10-28, 10-29, Example 10.2 knee bracing, 10-30 pile bracing, 10-27 reinforced concrete beams and columns, 10-33 steel pipe pile and grade beam, 10-32 timber pile treatment, 10-25, 10-26, 10-30 treated timber piles and grade beams, 10-32 wood pile -to -beam connections, 10-26 Open/shallow foundation, 10-34 Operational costs, 7-2, 7-6, 7-7 OSB (see Oriented strand board) Oriented strand board (OSB) factory -applied wax, 11-27 rotted, 11-22 sheathing, 11-16 Overwash, 7-7 P Panels plywood, 11-4, 11-5 Pier foundation, 7-8, 10-36, 10-38 footing under gravity load, 10-41, Example 10.3 footing under uplift and lateral loads, 10-44, Example 10.5 footing under uplift load, 10-42, Example 10.4 soil pressure, 10-43, Equation 10.6 spread footing and, 10-38, 10-39 square footing size for gravity loads, 10-40, Equation 10.5 Pile foundation, 10-11 angering, 10-20, 13-7 bearing capacity, 10-14 compression capacity of, 10-12, 10-14, Equation 10.2 column connection failure, 10-24 concrete, 10-12 driving, 10-20 earth pressure coefficient, 10-14 effects of scour and erosion on, 10-21, 10-23 embedment, insufficient, 10-13 grade beams for, 10-23 installation, 10-20 installation methods, 10-20, 10-21 jetting, 10-20 lateral capacity, 10-18, 10-19, Equation 10.4, 10-19 modulus of subgrade reaction, 10-19 scouring around grade beams, 10-25 steel, 10-12 tension capacity, 10-15, Equation 10.3 wood, 10-12, 10-16, Example 10.1, 10-18 Pile notching, 7-21, 10-26, 10-31, 13-4, 13-5, 13-15, 13-18, 13-21, 13-22, 13-23 Platform framing, 9-27, 9-28 Plywood, 11-4, 11-16, 11-23, 13-12, 13-14, 13-23 decks, 11-37 inspection, 13-18, 13-27, 13-29 sheathing, 11-44, 13-26 untreated, 14-12 UV degradation, 14-7 I-10 COASTAL CONSTRUCTION MANUAL Volume II INDEX Pneumatic nail guns, 13-20 Pools coastal high hazard areas, pools in, 9-40 hot tubs and, 9-40, 9-41, 9-42 insurance coverage, 7-17, 7-18 Zone V, pools in, 9-40 Precast concrete, 13-7 Pre -design considerations, 7-1 Pressure -treated wood, 13-13, 13-19 Primary frontal dune, 9-40 erosion, 8-15 Protective devices, 7-23 R Rating factor (insurance), 7-13, 7-18 Recurrence interval, 7-4, 8-52 Reinforced concrete building material, 9-34 Relocation, 15-10 advantages and disadvantages of, 15-12 Reroofing in high -wind areas, 11-24 Residual risk, 7-11 Retaining wall, 7-17, 7-18 Retrofitting, 7-7, 7-21 flood mitigation, 15-8 (see also Flood mitigation) high wind mitigation, 15-15 (see also High wind mitigation) seismic mitigation, 15-5 (see also Seismic mitigation) terminology box, 15-2 wildfire mitigation, 15-2 Revetment, 7-7, 7-18 Risk, 7-1 acceptable level of, 7-4 category, 8-48 coastal flooding, 13-1 flood, 15-9, 15-10, 12-7 high winds, 13-1 Homeowner's Wildfire Assessment, 15-5 long-term, 15-19 natural hazard risk in coastal areas, 7-3 tolerance of owner, 7-2 wildfire, 11-3 wind -related damage, 15-19 Roof (see also Roof framing) aggregate roof surfacing, 11-49 asphalt shingles, 11-25, 11-30 asphalt shingles, wind resistance of, 11-31 bleeder strips, 11-33, 11-34 decking, blown off, 11-22 eave, 11-32 exterior wall connection, 9-8, 9-9, Example 9.2 fiber -cement shingles, 11-37 fire-resistant, 11-3 framing to exterior wall connection, 9-8 hail, 11-36 high winds, 11-25 hip, 9-31 liquid -applied membranes, 11-37 low -slope, 11-49 maintenance, 14-8 metal panels, 11-46 metal shingles, 11-46 pressures, 8-62, 8-63 rake, 11-32, 11-33 roof -to -wall uplift connection load, 8-54, Example 8.5 shakes, 11-48 sheathing nail spacing for wind uplift, 9-6, Example 9.1 sheathing suction loads, 8-64, Example 8.7 sheathing to roof framing connection, 9-4, 9-6 shingles, 11-30 (see also Shingles) slate, 11-47 systems, 11-24 tiles, blown off, 11-39, 11-40, 11-41, 11-42, 11-43, H- 44 tiles, clay and extruded concrete, 11-38 truss connection to wood -frame wall, 9-10 truss -to -masonry wall connection, 9-11 underlayment, 11-26 (see also Underlayment) uplift connector load, 8-52, 8-53, 8-54, Example 8.5 wall top plate -to -wall stud connection, 9-10, 9-11 warning box, roof structure failure, 13-27 wood shingles, 11-48 Roof deck, 9-3, 11-10, 11-24, 11-38, 11-46 blown off, 11-22 concrete, 11-38 panels, 15-18 Roof framing, 13-27 inspection points, 13-28, 13-29 substitution of materials, 13-28 0 Salt spray, 9-25, 13-23 Sanitary systems, 12-11 Scour, 7-7, 7-8, 7-10, 8-34, 10-4 deep around foundation piles, 8-35 localized around a vertical pile, 8-34 8-35, Equation 8.10, 8-36, Equation 8.11 localized around vertical walls and enclosures, 8-37, Equation 8.12 Sea level rise, 7-10 Sea spray, 7-7 COASTAL CONSTRUCTION MANUAL I-11 INDEX Volume II Seawall, 7-7, 7-17, 7-18 Seismic hazard base shear, 8-69, Equation 8.15 effect of seismic forces on supporting piles, 8-69 load, 8-68, 8-70, Example 8.9 mitigation, 15-5 (see also Seismic mitigation) vertical distribution of seismic forces, 8-70, Equation 8.16 Seismic hazard area building elevation, 15-9 diagonal bracing, 9-37 floor surfaces, 13-24 reinforced and grouted masonry, 9-27 roof sheathing, 11-50 warning box, open masonry foundations in earthquake hazard area, 13-8 Seismic mitigation, 15-5 anchorage of concrete and masonry walls, 15-7 anchorage of masonry chimneys, 15-7 cripple wall bracing, 15-5 foundation bolting, 15-5 hillside house bracing, 15-5 open -front bracing, 15-5 split-level floor interconnection, 15-5 weak- and soft -story bracing, 15-5 Septic systems, 12-10 warning box, septic tanks below expected level of erosion and scour, 12-11 SFHA (see Special Flood Hazard Area) SFIP (see Standard Flood Insurance Policy) Shakes, 11-48 Shearwall, 8-70, Example 8.9, 13-21, 13-26, 14-7, 14-12 sill plates, 14-12 Shingles, 11-30 asphalt, 11-25 asphalt, wind resistance of, 11-31 fasteners, 11-35 fiber -cement, 11-37 loss of underlayment and, 11-31 metal, 11-46 unzipped, 11-36 wood, 11-48 Shutters, 7-9, 7-23, 8-49, 11-10, 11-12, 11-13 Skylights, 11-1, 11-15 windows and, 11-9 Siding, 11-17 fiber -cement, blown off, 11-18 maintenance of, 14-7 vinyl, blown off, 11-17 Single -ply membrane, 11-50 Site -specific loads, 8-1 Siting, 7-7 benefits and cost implications, 7-11 Slate, 11-47 Snow loads, 8-5 Soffits, 11-15, 11-22, 11-23, 13-29 Soils angle of internal friction/soil friction angle, 10-9, 10-10, 10-15 bearing capacity, 10-7, 10-14 classifications, 10-7, 10-8 compressive strength, 10-7, 10-8 data from site investigations, 10-6 modulus of subgrade reaction, 10-10, 10-19 pressure, determining, 10-43, Equation 10.6 sliding resistance, 10-10, Equation 10.1 subgrade modulus, 10-10 Special Flood Hazard Area (SFHA) acquisition of buildings in, 7-13 fills allowed in, 7-25 foundation in, 10-42 residential structures in, 15-11, 15-12 substantially damaged or improved structures in, 15-11, 15-12 zones outside, 7-15 Stairways, 9-39 Standard Flood Insurance Policy (SFIP), 7-17 (see also National Flood Insurance Program) Steel building material, 9-33 Stillwater flood depth, 8-9 calculations, 8-9, 8-10, Example 8.1 Stillwater elevation, 8-7, 8-15, 8-21, 10-10 100-year, 8-8, 8-15 Storm surge, 7-4, 7-11, 10-1, 10-22 depths, 8-6 elevation, 8-6 evacuation maps, 8-6 Straps, 12-3, 13-27, 14-10 cast -in, 9-11 connector, 13-19 metal, 15-7 stainless steel, 11-37, 11-43, 11-45, 11-47 tiedown, 14-10 twist, 13-23 Structural frame, 13-19 connections, 13-19 connector failure, 13-20 durability, 13-15 floor framing, 13-23 (see also Floor framing) maintenance, 14-5 roof framing, 13-27 (see also Roof framing) top structural frame issues for buildings, 13-28 wall framing, 13-25 (see also Wall framing) Structure, maintaining, 14-1 I-12 COASTAL CONSTRUCTION MANUAL Volume II INDEX Subsidence, 8-7, 8-8 Substantial damage dry floodproofing, 15-11 tsunami, 8-47 Substantial improvement, 9-34 dry floodproofing, 15-11 Sustainable building design, 7-24 Substitutions, 13-17 warning box, 13-17, 13-28 T Termites, 9-33, 11-7, 11-13, 13-30, 14-2, 14-4 Tiles, 11-38 (see also Roof) Topography, 8-16 Tornado, 8-47, 11-10, 15-15 loads, 8-67 warning box, safe room location, 8-67 Tributary area and application of loads to a building, 8-4 Tropical cyclones, 8-47 Tropical storms, 7-5, 15-15 Allison, 7-5 Tsunamis, 7-6 load, 8-47 warning box, flood velocity during tsunamis, 8-15 Typhoon, 8-24, 11-37, 15-15 Paka, 11-1 U Underlayment, 7-9, 11-26 attachment, 11-26 enhanced Option 1, 11-26, 11-27 enhanced Option 2, 11-28 enhanced Option 3, 11-29 loss of shingles and, 11-31 not lapped over hip, 11-30 Uplift, 8-17, 8-21, 8-37, 8-61, 9-21, 14-9, 15-20 capacity, 13-19 force, 8-3, 9-1, 9-4, 9-6, Examples 9.1 through 9.9, 9-8, 9-10, 9-12, 9-17, 9-18, 10-34, 10-42, Example 10.4, 10-44, Example 10.5, 10-45, 12-3, 13-23, 13-27 inspection, 13-29 loads (see Loads) resistance, 10-15, 10-34, 10-38, 11-47, 13-19 roof uplift connector load, 8-52, 8-53, 8-54, Example 8.5 shear wall overturning, 9-21 solar panel system, 7-24 wind, 9-8, 9-15, 10-22 1 Vents attic, 11-50, 12-3, 14-5 continuous ridge, 11-50, 11-52 V Zone Risk Factor Rating Form, 7-20 W Wall (see also Wall framing) coverings, 11-15, 11-16 fire-resistant, 11-3 floor framing connection, 9-15 non -load -bearing, 11-15 sheathing to window header connection, 9-12, 9-13 suction pressures, 8-62, 8-63 Wall framing, 13-25 inspection points, 13-27 substitution of materials, 13-27 Water and wasterwater systems, 12-10 fire sprinkler systems, 12-11 municipal water connections, 12-12 sanitary systems, 12-11 septic systems, 12-11 wells, 12-10 Waterborne debris, 8-32, 9-33 Wave action, 7-7 crest, 8-24 height, 8-25 load, 8-20 setup, 8-15 slam, 7-10, 8-25, 8-26 slam calculation, 8-27, Example 8.2 Weatherstripping, 7-8, 11-8 Wet floodprooling, 15-12, 15-13 advantages and disadvantages of, 15-13 warning box, under NFIP, 15-12 Wildfire fire-resistant walls and roof, 11-3 mitigation, 15-2 Wind design wind pressure for low-rise buildings, 8-50, Equation 8.14 determining loads, 8-49 effect on enclosed building vs. building with an opening, 8-48 high -wind mitigation, 15-15 insurance, 7-21 load, 8-47 mapped speeds, 8-48 mitigation measures, 7-8 COASTAL CONSTRUCTION MANUAL I-13 INDEX Volume II velocity pressure, 8-50, Equation 8.13 Wind-borne debris, 11-7 doors and, 11-7 exterior wall assemblies, 11-16 glazing and, 11-22 scars on exterior wall, 11-3 Wind -driven rain, 7-7, 11-52 building envelope, 11-4, 11-52, 13-31 concrete and concrete masonry unit, 11-20 deck connections to structure, 14-10 deck surface, 9-38 door/wall integration, 11-8 exterior door assemblies, 11-7 exterior non -load -bearing walls, wall coverings, and soffits, 11-16 flood mitigation, 7-8 foundations, 13-13 glazing, 7-7 high winds, 11-7 rain screen on fiber -cement siding, 11-17 resistance in windows, 11-15 sealant joints protected by a stop, 11-15 soffit blow -off, 11-15, 11-22, 11-23 threshold/door gap, 11-8 vents and fans, 13-31 wall coverings, 11-16 windows and skylights, 11-9 Wind -driven saltwater spray, 9-33 Wind -driven water infiltration, 11-2, 11-7, 11-14 Wind -MAP, 7-21 Windows (see also Glazing) design pressure and impact -resistant ratings, 11-10, 11-11, 11-12 durability, 11-13 frame, inadequate attachment of, 11-9 hail, 11-15 header to exterior wall connection, 9-12, 9-13 high winds, 11-9 installation, 11-14 jalousie louvers, 11-13, 11-14 loads and resistance, 11-9 seismic effects on, 11-15 skylights and, 11-9 uplift and lateral load path at window header, 9-14, Example 9.3 water infiltration, 11-14 wind-borne debris, 11-10 Wood building material, 9-33 Z Zone A, 7-7, 7-15, 7-16, 7-19 recommended foundation styles in, 10-3 Zone AE, 7-15 Zone B, 7-15 Zone C, 7-15 Zones Vl—V30, 7-14 Zone V, 7-14, 7-16 recommended foundation styles in, 10-3 Risk Factor Rating Form, 7-20 warning box, solid foundation walls in Zone V, 8-24 Zone VE, 7-14 Zone X, 7-15 I-14 COASTAL CONSTRUCTION MANUAL FEMA P-55 Catalog No. 08352-1 BOCC AGENDA ROUTING SLIP r Z BUILDING DEPARTMENT�� Agenda Item Subject: Resolution adopting FEMA P-85, Second Edition "Protecting Manufactured Homes from Floods and Other Hazards" Date: August 17, 2015 Prepared By: Ed Koconis, AICP, Permit Manager Agenda Deadline: August 20, 2015 BOCC meeting date: September 16, 2015 # Reviewer ***Internal Deadline to Teresa:*** Notes Initials Date Permit Manager_ Senior Director of Building County Attorney Deadline: Assistant County Administrator Deadline: FINAL review by legal _XBulk Approval Time Approximate Requested Type of Proceeding: Ad (Ad map, if applicable) Public Hearing Yes Legislative Deadline Surrounding Property Owner Notice: Deadline NIA Discussion Time Quasi -Judicial Publish Date ***Reminder*** Once your item is complete and includes all corrections, email all final word documents to Teresa Smith.