Resolution 178-2020 1
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9 MONROE COUNTY,FLORIDA
10 MONROE COUNTY BOARD OF COUNTY COMMISSIONERS
11 RESOLUTION NO. 178 -2020
12
13 A RESOLUTION OF THE MONROE COUNTY BOARD OF
14 COUNTY COMMISSIONERS ADOPTING FEMA TECHNICAL
15 BULLETIN 1 "REQUIREMENTS FOR FLOOD OPENINGS IN
16 FOUNDATION WALLS AND WALLS OF ENCLOSURES" DATED
17 MARCH 2020 AS REQUIRED PURSUANT TO MONROE
18 COUNTY CODE SECTION 122-2(C)
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21 WHEREAS, Monroe County is currently a participating community in the National
22 Flood Insurance Program (NFIP)and is working on internal County policies to improve upon its
23 interpretation of NFIP regulations; and
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25 WHEREAS, Monroe County desires to maintain eligibility and improve its standing in
26 FEMA's Community Rating System(CRS); and
27
28 WHEREAS, Monroe County Code Section 122-2(c), in part, requires that in interpreting
29 other provisions of this chapter, the building official shall be guided by the current edition of
30 FEMA's 44 CFR, and FEMA's interpretive letters, policy statements and technical bulletins as
31 adopted by resolution from time to time by the Board of County Commissioners;
32
33 NOW, THEREFORE, BE IT RESOLVED BY THE BOARD OF COUNTY
34 COMMISSIONERS OF MONROE COUNTY,FLORIDA:
35
36 Section 1. Pursuant to Monroe County Code Section 122-2(c), the Board hereby adopts
37 FEMA Technical Bulletin 1 "Requirements for Flood Openings in Foundation Walls and Walls
38 of Enclosures"dated March 2020,a copy of which is attached hereto.
39
40 Section 2. The Clerk of the Board is hereby directed to forward one (1) certified copy of
41 this Resolution to the Building Department.
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I PASSED AND ADOPTED by the Board of County Commissioners of Monroe County,
2 Florida,at a regular meeting held on the 17th of June, 2020.
3
4
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6 Mayor Heather Carruthers Yes
7 Mayor pro tem Michelle Coldiron Yes
8 Commissioner Craig Cates Yes
9 Commissioner Sylvia Murphy Yes
10 Commissioner David Rice Yes
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13
14 BOARD OF COUNTY COMMISSIONERS
15 OF MONROE CO TY,FLORIDA
16
17 BY:
18 Mayor eath titers
19
20 (SEAL)
21 ATTEST�MADOK,CLERK
23
24- As Deputy Clerk
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Requirements for Flood Openings
in Foundation Walls and Walls
of Enclosures
Below Elevated Buildings in Special Flood Hazard Areas
In Accordance with the National Flood Insurance Program
NFIP Technical Bulletin 1 / March 2020
�ynxrM
����� FEMA
,LAND SECJ,
Comments on the Technical Bulletins should be directed to:
Department of Homeland Security/Federal Emergency Management Agency
Federal Insurance and Mitigation Administration (FIMA) Risk Management Directorate
Building Science Branch
400 C Street, S.W., Sixth Floor
Washington, DC 20472-3020
NFIP Technical Bulletin 1 (2020) replaces NFIP Technical Bulletin 1 (2008), Openings in Foundation Walls
and Walls of Enclosures.
Photograph credits:
Cover: Leigh Chapman, Salters Creek Consulting
Figure 3. Bill Bryant, Anne Arundel County, Maryland
Figure 17. North Carolina Emergency Management/T. Riddle
NFIP Technical Bulletin 1 contains information that is proprietary to and copyrighted by the American
Society of Civil Engineers and information that is proprietary to and copyrighted by the International Code
Council, Inc. All information is used with permission.
For more information, see the FEMA Building Science
Frequently Asked Questions website at http://www.fema.gov/ To order publications, contact the FEMA
frequently-asked-questions-building-science. Distribution Center:
Call: 1-800-480-2520
If you have any additional questions on FEMA Building (Monday—Friday, 8 a.m.-5 p.m., EST)
Science Publications, contact the helpline at FEMA- Fax: 719-948-9724
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You may also sign up for the FEMA Building Science email Additional FEMA documents can be
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FEMA Building Science activities. Subscribe at https://public. https://www.fema.gov/media-library/.
govdelivery.com/accounts/USDHSFEMA/subscriber/new.
Please scan this QR code
Visit the Building Science Branch of the Risk Management to visit the FEMA Building ❑ '_❑�
Directorate at FEMA's Federal Insurance and Mitigation Science web page. '
Administration at https://www.fema.gov/building-science.
Table of Contents
Acronyms.............................................................................................................................................................iv
1 Introduction......................................................................................................................................................I
2 National Flood Insurance Program Regulations...............................................................................................3
3 Building Codes and Standards.........................................................................................................................5
3.1 International Residential Code.............................................................................................................5
3.2 International Building Code and ASCE 24..........................................................................................6
4 NAP Flood Insurance Implications...................................................................................................................8
5 Documenting Building Elevations and Flood Openings Using the NFIP Elevation Certificate ..........................8
6 Use of Enclosed Areas Below Elevated Buildings............................................................................................9
7 Foundation Walls and Enclosure Walls that Require Flood Openings............................................................10
7.1 Solid Perimeter Foundation Walls (Crawlspacesand Under-Floor Spaces) .....................................11
7.2 Solid Perimeter Foundation Walls (Below-Grade Crawlspaces) .......................................................12
7.3 Garages Attached to Elevated Buildings............................................................................................13
7.4 Enclosed Areas Under Buildings Elevated on Open Foundations...................................................14
7.5 Enclosed Areas with Breakaway Walls Under Buildings Elevated on Open Foundations ..............15
7.6 Above-Grade (Elevated) Enclosed Areas............................................................................................16
7.7 Two-Level Enclosed Areas ...................................................................................................................17
7.8 Solid Perimeter Foundation Walls on which Manufactured Homes Are Installed.........................18
7.9 Accessory Structures............................................................................................................................19
8 Requirements and Guidance for Installation of Flood Openings....................................................................20
8.1 Location and Minimum Number of Flood Openings.......................................................................20
8.2 Height of Flood Openings Above Grade or Floor.............................................................................21
8.3 Examples of Flood Opening Installations..........................................................................................22
8.3.1 Interior Grade or Floor Higher than the Exterior Grade ....................................................22
8.3.2 Sloping Sites.............................................................................................................................23
8.3.3 Buildings with Large Enclosed Areas.....................................................................................24
8.3.4 Townhouses with Limited Exterior Walls..............................................................................24
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 i
8.3.5 Buildings with Multiple Enclosures........................................................................................25
8.3.6 Flood Openings in Areas with Shallow Flooding..................................................................26
9 Non-Engineered Flood Openings and Engineered Flood Openings................................................................27
9.1 Measures Not Acceptable as Flood Openings....................................................................................28
9.2 Non-Engineered Flood Openings.......................................................................................................28
9.3 Engineered Flood Openings...............................................................................................................33
9.3.1 Design and Performance Requirements................................................................................33
9.3.2 Documentation of Engineered Openings for Compliance..................................................36
9.3.3 Engineered Openings with Certification Reports ................................................................36
9.3.4 Engineered Openings Individually Certified for Specific Buildings...................................37
9.3.5 NFIP Elevation Certificate and Documentation of Engineered Openings for Flood
Insurance .................................................................................................................................39
10 References.....................................................................................................................................................41
List of Figures
Figure 1: Equalizing flood forces (hydrostatic loads) on exterior walls.......................................................I
Figure 2: Typical enclosures with flood openings in Zone A........................................................................2
Figure 3: Full-height, solid perimeter walls surrounding a garage and storage area with flood
openings..........................................................................................................................................11
Figure 4: Backfilled stem wall foundation; flood openings not required...................................................12
Figure 5: Limitations on below-grade crawlspaces in shallow flood hazard areas.....................................13
Figure 6: Engineered openings in garage doors..........................................................................................14
Figure 7: Enclosure with flood openings under a house elevated on pilings.............................................15
Figure 8: Above-grade enclosures..................................................................................................................17
Figure 9: Two-level enclosure with non-load-bearing walls under building elevated on pilings or
columns; configuration also applies if walls are load-bearing....................................................18
Figure 10: Manufactured home supported on interior piers and masonry perimeter wall with
floodopenings................................................................................................................................19
Figure 11: Foundation plan of home with multiple enclosed areas, each with flood openings.................21
Figure 12: Manufactured home installed on columns above a full-height,framed garage (note
elevation of thick driveway slab on left; the flood openings are within 1 foot of interior
floorsurface) ..................................................................................................................................22
Figure 13: Flood openings in enclosure walls on a sloping site ....................................................................23
Figure 14: Flood openings that are stacked and closely grouped to satisfy the required total net
openarea.........................................................................................................................................24
ii NFIP TECHNICAL BULLETIN 1 MARCH 2O20
Figure 15: Suggested flood openings in enclosures under elevated townhouses ........................................25
Figure 16: Bottom of the flood opening positioned as close as possible to grade (or floor) when
any portion of the opening extends above the BEE.....................................................................26
Figure 17: Standard air vent that is unacceptable as a flood opening because it is not disabled in
theopen position............................................................................................................................28
Figure 19: Example of non-engineered opening: Typical standard air vent with fixed, angled
blades providing approximately 44 square inches of net open area; measurement of
net open area uses slot width of 13 inches times the sum of the spaces between the blades....29
Figure 18: Example of non-engineered opening: Typical standard air vent faceplate providing
42 square inches of net open area if disabled in the open position; measurement of net
open area uses a slot width of 0.5 inch times a slot height of 0.65 inch times the total
numberof slots...............................................................................................................................29
Figure 20: Typical air vents with insect screens blocked by flood debris......................................................30
Figure 21: Examples of typical air vents in crawlspace foundation walls used as flood openings
withvarying net open areas...........................................................................................................31
Figure 22: Decorative masonry units and closely spaced holes in brickwork; the area of each hole
counts toward the total net open area..........................................................................................32
Figure 23: Concrete blocks turned sideways with insect screening; a typical 8-by 16-inch block
provides approximately 60 square inches of net open area.........................................................32
Figure 24: Wood frame with insect screen inserted in void in poured concrete foundation wall;
inside dimensions of frame determine net open area.................................................................33
Figure 25: Equation used to determined total net area of engineered openings........................................34
Figure 26: Completing the NFIP Elevation Certificate when engineered openings are used....................40
List of Tables
Table 1: Comparison of Selected 2018 IRC and NFIP Flood Opening Requirements..............................6
Table 2: Comparison of Selected 2018 IBC and ASCE 24-14 Flood Opening Requirements with
NFIPRequirements..........................................................................................................................7
Table 3: Flood Opening Coefficient of Discharge......................................................................................35
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 iii
Acronyms
ASCE American Society of Civil Engineers
BFE base flood elevation
CFR Code of Federal Regulations
DHS Department of Homeland Security
FEMA Federal Emergency Management Agency
FIRM Flood Insurance Rate Map
IBC International Building Code°
ICC International Code Council®
ICC-ES ICC Evaluation Service
I-Codes International Codes°
IRC International Residential Code°
LiMWA Limit of Moderate Wave Action
NFIP National Flood Insurance Program
NFPA National Fire Protection Association
SEI Structural Engineering Institute
SFHA Special Flood Hazard Area
iv NFIP TECHNICAL BULLETIN 1 MARCH 2O20
1 Introduction
This Technical Bulletin explains the National Flood Insurance Program (NFIP) requirements for flood
openings in foundation walls and walls of enclosures below elevated buildings in Special Flood Hazard
Areas (SFHAs) that are designated as Zone A (A,AE,Al-30,AH,and AO) on Flood Insurance Rate Maps
(FIRMs). The flood opening requirements are intended to equalize hydrostatic forces (loads or pressure
caused by standing or slow-moving water) on walls, thus preventing damage to or collapse of the building
(see Figure 1). The requirements are not intended to reduce flood damage caused by hydrodynamic loads
associated with fast-moving water (e.g.,faster than 10 feet per second),wave impacts, or debris impacts.
Qvp�F OOp RO P�`ZEp FLOOp FOR J�� R�Fs �av eFs
Exterior Exterior °' Interior
flood flood flood
level level level
Q_
Interior
flood _a. .
level Flood
• opening
Accumulated --------
seepage
•d,
Figure 1:Equalizing flood forces(hydrostatic loads)on exterior walls
This Technical Bulletin includes the following:
• Examples of foundation walls and enclosure walls that require openings. Figure 2 illustrates typical
enclosures with flood openings in Zone A: a crawlspace foundation wall, a non-load-bearing wood-
framed wall surrounding an enclosed area under a piling-or column-supported building,and a
concrete or masonry load-bearing foundation wall surrounding an enclosed area. Other types of
enclosures or situations may require the advice of a registered design professional.
• Information on installing flood openings, including the minimum number and minimum height
above grade, and examples of installations.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 1
• Guidance on prescriptive (non-engineered) and engineered flood openings. Non-engineered
openings do not have moving parts and may be used to meet the NFIP prescriptive requirement
for 1 square inch of net open area for every square foot of enclosed area. Engineered openings
may be used if designed and certified by a registered design professional as meeting certain
performance characteristics.
• Description of how flood openings affect NFIP flood insurance premiums.
• Guidance on documenting building elevations and flood openings using the NFIP Elevation
Certificate (FEMA Form 086-0-33) (FEMA, 2015).
"°6 F Load-bearing
Solid perimeter
foundation wall Non-load-bearing R•a? concrete or
•b•.•
wood framed wall masonry
(concrete
masonry unit) around enclosure perimeter
or poured Joist/truss below building 4:: a. foundation wall
p supported on ° enclosing
concrete) ::va.
pilings or columns :::a: under-floor space
(%awlspace Flood opening p.a
i
Flood Flood Interior
opening Interior openings No more — grade/floor
R'• ';
No more — grade/floor No more — Interior than 1 foot
than 1 foot ----' than 1 foot grade/floor _ :•`.• :o'•::'•\::.'.:o.": :o'.:.'
9..•':6
,.:.:.o.':. :; .:.:••c•::.o.' Exterior
Exterior grade Footing grade :':Q° Footing
Exterior
depth per
o....oc P °':..:r depth per
grade ,..:.
building :o'a: :s ;:.:.. building code
code
Crawlspace foundation wall Non-load-bearing wood-framed wall Load-bearing foundation wall
Figure 2:Typical enclosures with flood openings in Zone A
Questions about enclosure and flood opening requirements should be directed to the appropriate
local official, NFIP State Coordinating Office, or Federal Emergency Management Agency (FEMA)
Regional Office.
NFIP TECHNICAL BULLETIN 0
NFIP Technical Bulletin 0, User's Guide to Technical Bulletins, should be used as a reference in
conjunction with this Technical Bulletin. Technical Bulletin 0 describes the purpose and use of the
Technical Bulletins, includes common concepts and terms, lists useful resources, and includes a
crosswalk of the sections of the NFIP regulations identifying the Technical Bulletin that addresses each
section of the regulations and a subject index.
Readers are cautioned that the definitions of some of the terms that are used in the Technical Bulletins
are not the same when used by the NFIP for the purpose of rating flood insurance policies.
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2 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
NFIP TERMS USED IN THIS TECHNICAL BULLETIN
• Basement: Area of a building that has its floor subgrade(below ground level) on all sides. NFIP
regulations do not allow basements to extend below the base flood elevation (BFE)except in
dry-floodproofed, non-residential buildings.
• Enclosed area (enclosure): An area below an elevated building that is enclosed by walls on all sides.
• Lowest floor: Lowest floor of the lowest enclosed area of a building, including basement. An
unfinished or flood-resistant enclosure that is used solely for parking of vehicles, building access,
or storage is not the lowest floor, provided the enclosure is built in compliance with applicable
requirements.
• Net open area: Permanently open area of a non-engineered flood opening.
• Special Flood Hazard Area (SFHA): Area subject to flooding by the base flood (1-percent-annual-
chance flood)and shown on Flood Insurance Rate Maps(FIRMs)as Zone A or Zone V.
• Zone A: Flood zones shown on FIRMs as Zone A, AE, Al-30, AH, AO, A99, and AR.
• Zone V: Flood zones shown on FIRMs as Zone V, VE, V1-30, and VO.
2 National Flood Insurance Program
Regulations
An important NFIP objective is protecting buildings constructed in SFHAs from damage caused by
flooding. The SFHA, composed of Zones A and V, is the areal extent of the base flood shown on Flood
Insurance Rate Maps (FIRMs) prepared by FEMA. The base flood is the flood that has a 1 percent chance
of being equaled or exceeded in any given year (commonly called the "100-year" flood).
The NFIP floodplain management regulations include minimum building design criteria that apply to:
• New construction
• Work determined to be Substantial Improvements, including improvements, alterations, and additions
• Repair of buildings determined to have incurred Substantial Damage
A defining characteristic of the NFIP regulations applicable in Zone A is the requirement for the lowest
floor (including basement) to be elevated to or above the BFE. Non-residential buildings in Zone A must
be elevated or dry floodproofed. The requirements in Zone V, not addressed in this Technical Bulletin,
also specify building elevation, foundation,and enclosure requirements.
Enclosed areas (enclosures) are permitted below elevated buildings if the enclosed areas meet
requirements, including limitations on use (parking of vehicles, building access, or storage), use of flood
damage-resistant materials, and installation of flood openings that allow automatic entry and exit of
floodwater (i.e., free inflow and outflow in both directions) to equalize the hydrostatic flood loads.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 3
The NFIP regulations for enclosures and flood openings are codified in Title 44 of the Code of Federal
Regulations (CFR) Part 60. Specific to NFIP Technical Bulletin 1, 44 CFR § 60.3(c)(5) states that a
community shall:
Require, for all new construction and substantial improvements, that fully enclosed areas
below the lowest floor that are usable solely for parking of vehicles, building access or storage
in an area other than a basement and which are subject to flooding shall be designed to
automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry
and exit of floodwaters. Designs for meeting this requirement must either be certified by a
registered professional engineer or architect or meet or exceed the following minimum
criteria: A minimum of two openings having a total net area of not less than one square inch
for every square foot of enclosed area subject to flooding shall be provided. The bottom of
all openings shall be no higher than one foot above grade. Openings may be equipped with
screens, louvers, valves, or other coverings or devices provided that they permit the automatic
entry and exit of floodwaters.
NFIP REQUIREMENTS AND HIGHER REGULATORY STANDARDS
State or Local Requirements. State or local requirements that are more restrictive or stringent than the
minimum requirements of the NFIP take precedence. The Technical Bulletins and other FEMA publications
provide guidance on the minimum NFIP requirements and describe best practices. Design professionals,
builders, and property owners should contact local officials to determine whether more restrictive
requirements apply to buildings or sites in question. All other applicable requirements of state or local
building codes must also be met for buildings in flood hazard areas.
Substantial Improvement and Substantial Damage.As part of issuing permits, local officials must
review not only proposals for new construction but also for work on existing buildings to determine
whether the work constitutes Substantial Improvement or repair of Substantial Damage. If the work is
determined to constitute Substantial Improvement or repair of Substantial Damage, the buildings must
be brought into compliance with the NFIP requirements for new construction. Some communities modify
the definitions of Substantial Improvement and/or Substantial Damage to be more restrictive than the
NFIP minimum requirements. For more information on Substantial Improvement and Substantial Damage,
see FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference (2010), and FEMA 213,
Answers to Questions About Substantially Improved/Substantially Damaged Buildings (2018).
Elevation Above Minimum NFIP Requirements. Some communities require that buildings be elevated
above the NFIP minimum requirement. The additional elevation is called freeboard. Design professionals,
builders, and property owners should check with local officials to determine whether a community has
freeboard requirements. References to building elevations in this Technical Bulletin should be construed
as references to the community's elevation requirement where freeboard is required.
Legal Nonconforming Buildings. Owners of older, legal nonconforming buildings that are elevated with
enclosures below the BFE may wish to retrofit the enclosures to conform to current requirements for
enclosures, even when the enclosure is below grade on all sides. Lower NFIP flood insurance rates may
apply if retrofit enclosures have flood openings that meet the requirements in this Technical Bulletin and
other requirements for enclosures(e.g., limited use, flood damage-resistant materials, elevated utilities).
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4 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
3 Building Codes and Standards
In addition to complying with the NFIP requirements, all new construction, Substantial Improvements,
and repair of Substantial Damage must comply with the applicable building codes and standards adopted
by states and communities.
The International Codes° (I-Codes°),published by the International Code Council® (ICC®),are a family
of codes that includes the International Residential Code° (IRC®), International Building Code° (IBC°),
International Existing Building Code° (IEBC®), and codes that govern the installation of mechanical,
plumbing, fuel gas service, and other aspects of building construction. FEMA has deemed that the latest
published editions of the I-Codes meet or exceed NFIP requirements for buildings and structures in
flood hazard areas. Excerpts of the flood provisions of the I-Codes are available on FENINs Building
Code Resource webpage (htti2s://www.fema.gov/building-code-resources).
3.1 International Residential Code
The IRC applies to one- and two-family dwellings and
townhomes not more than three stories above grade IRC COMMENTARY
plane. The IRC requirements related to flood openings, The ICC publishes companion
summarized in Table 1, are similar to but generally exceed commentary for the IRC. Although not
NFIP requirements. regulatory, the commentary provides
Table 1 refers to selected requirements of the 2018 IRC guidance that is useful in complying
and notes changes from the 2015 and 2012 editions; With, interpreting, and enforcing the
subsequent editions of the IRC should include comparable requirements of the code.
requirements.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 5
Table 1: Comparison of Selected 2018 IRC and NFIP Flood Opening Requirements
Summary of Selected 2018 IRC Requirements Comparison
and Changes from 20151
Flood openings Section R322.2.2(2) Enclosed area below design flood elevation. Equivalent to NFIP
Requires enclosed areas below the design flood elevation, including 44 CFR§60.3(c)(5) but
crawlspaces, to have flood openings (non-engineered or engineered) with more specificity:
that meet listed criteria and that are installed in accordance with measurement of
R322.2.2.1. The enclosed area is measured on the exterior of the enclosed area and
enclosure. The listed criteria are equivalent to non-engineered and minimum dimensions of
engineered openings, with the addition of a minimum size (not less opening.
than 3 inches in any direction in the plane of the wall).
Change from 2015 to 2018 IRC: No change.
Change from 2012 to 2015 IRC: No change.
Installation of Section R322.2.2.1 Installation of openings. More specificity
flood openings Specifies the following for the installation of flood openings: than NFIP 44 CFR
• At least two openings on different sides of an enclosure are §60.3(c)(5): openings on
required, and if more than one enclosed area is present, each must different sides, openings
have openings on exterior walls. installed above higher
of interior and exterior
• The bottom of each opening must be not more than 1 foot above the grade or floor, and
higher of the final interior grade(or floor) and the finished exterior openings installed in
grade immediately under each opening. doors.
• Openings are permitted to be installed in doors and windows.
Change from 2015 to 2018 IRC: No change.
Change from 2012 to 2015 IRC: Installation requirements moved to
new section.
Breakaway Section R322.3.5 Walls below design flood elevation. Exceeds NFIP 44 CFR
walls Requires walls below elevated dwellings in Coastal High Hazard Areas §60.3(e)(5): openings
(Zone V) and Coastal A Zones that are intended to break away under in breakaway walls and
flood loads to have flood openings that meet the requirements of Zone V requirements
Section R322.2.2(2). applied in Coastal A
Change from 2015 to 2018 IRC: Section number was R322.3.4. Zones if delineated.
Change from 2012 to 2015 IRC: New requirement in Coastal High
Hazard Areas(Zone V) and Coastal A Zones if delineated.
3.2 International Building Code and ASCE 24 IBC AND ASCE 24
The flood provisions of the latest published editions of the IBC meet or COMMENTARIES
exceed NFIP requirements for buildings, largely through reference to The ICC publishes
the standard ASCE 24,Flood Resistant Design and Construction, developed companion commentary
by the American Society of Civil Engineers (ASCE). The IBC applies for the IBC, and ASCE
to all applicable buildings and structures. While primarily used for publishes companion
buildings and structures other than dwellings within the scope of the commentary for ASCE 24.
IRC, the IBC may be used to design dwellings. ASCE 24 requirements Although not regulatory,
for flood openings, summarized in Table 2, are similar to but generally the commentaries
exceed and are more specific than NFIP requirements. Table 2 refers to provide guidance that is
selected requirements of the 2018 IBC and ASCE 24-14 (noting changes useful in complying with,
from 2015 and 2012 IBC and ASCE 24-05); subsequent editions of the interpreting, and enforcing
IBC and ASCE 24 should include comparable requirements. the requirements.
6 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
Table 2: Comparison of Selected 2018 IBC and ASCE 24-14 Flood Opening Requirements with NFIP Requirements
Summary of Selected 1Comparison
and Changes from 2015124-05 NFIP Requirements
Certification Section 1612.4(1.2). Equivalent to NFIP
of engineered Requires submission of a certification statement that the design provides 44 CFR§60.3(c)(5).
openings for equalization of hydrostatic flood forces in accordance with ASCE 24,
Section 2.7.2.2 (for engineered openings), if flood openings do not meet the
requirements of ASCE 24, Section 2.7.2.1 (for non-engineered openings).
Change from 2015 to 2018 IBC: Section number was 1612.5.
Change from 2012 to 2015 IBC: No change.
Breakaway ASCE 24 Section 2.7.1.1. Exceeds
walls Requires openings in breakaway walls. NFIP 44 CFR
Change from ASCE 24-05: New requirement for openings in breakaway §60.3(e)(5) by
walls in Coastal High Hazard Areas and Coastal A Zones. requiring openings
in breakaway walls.
Non- ASCE 24 Section 2.7.2.1. Equivalent to
engineered Specifies non-engineered openings, requires enclosed areas to be NFIP 44 CFR
openings measured on the exterior, specifies minimum size(not less than 3 inches §60.3(c)(5) but with
in any direction in the plane of the wall), and requires that the presence more specificity:
of louvers, blades, screens, faceplates or other covers, and devices be measurement of
accounted for in determining net open area. enclosure area,
Change from ASCE 24-05: Specifies measurement of enclosed areas minimum dimension
to determine square footage. Clarifies that the presence of louvers, of openings, and
blades, screens, faceplates, and devices must be accounted for in the measurement of net
measurement of net open area of flood openings. open area.
Engineered ASCE 24 Section 2.7.2.2. Equivalent to
openings Specifies engineered openings with emphasis on performance accounting NFIP 44 CFR
for the presence of louvers, blades, screens, grilles, faceplates or other §60.3(c)(5) but with
covers, and devices and ensuring that the difference between exterior more specificity:
and interior flood levels does not exceed 1 foot, with guidance related to minimum rate
the rate of rise and fall in excess of(or less than)5 feet per hour. Specifies of rise and fall,
minimum size(not less than 3 inches in any direction in the plane of the minimum dimension
wall). Provides the formula for calculating the total net area of required of openings,
engineered openings. and formula
Change from ASCE 24-05: Greater emphasis on performance and the for engineered
effects of louvers, blades, screens, grills, faceplates, and devices and openings.
revises the table of coefficients of discharge
Installation of ASCE 24 Section 2.7.3. Equivalent to
flood openings Specifies the following for the installation of openings: NFIP 44 CFR
• At least two openings in at least two walls of each enclosed area §60.3(c)(5) but with
more specificity:
• The bottom of each opening not more than 1 foot above the higher of the openings on
final interior grade or floor and the finished exterior grade immediately different sides,
under each opening bottom of openings
• Openings in doors and windows permitted above higher of
Change from ASCE 24-05: Consolidates installation requirements, which interior and exterior
apply to both non-engineered and engineered openings, and clarifies that grade or flood, and
the position is relative to the higher of the interior and exterior grade or floor. openings in doors
and windows.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 7
4 NFIP Flood Insurance Implications
Careful attention to compliance with NFIP requirements for enclosures below elevated lowest floors and
flood openings is important during the design, plan review, construction, and inspection of buildings in
SFHAs. Compliance influences vulnerability to flood damage and also the cost of NFIP flood insurance
policies. The presence of enclosures may result in higher NFIP flood insurance premiums. If flood
openings are not compliant, the floor of a crawlspace or the floor of an enclosure will be deemed the
lowest floor for insurance rating purposes, which may result in higher NFIPflood insurance premiums,
especially if the floor of the crawlspace or enclosure is more than 1 foot below the BFE.
5 Documenting Building Elevations
and Flood Openings Using the NFIP
Elevation Certif icate
Communities are required to obtain the following from permit holders for buildings in SFHAs: the
surveyed elevation of lowest floors of new buildings and buildings that have been Substantially Improved
or repaired after incurring Substantial Damage. The elevations may be provided on the NFIP Elevation
Certificate or in other formats.
The NFIP Elevation Certificate is designed to facilitate the collection of information that will help local
officials evaluate compliance with floodplain management requirements and to provide the information
necessary for the proper rating of NFIP flood insurance policies. For guidance on completing the
certificate, see NFIP Elevation Certificate and Instructions (FEMA, 2015) and FEMA 467-1, Floodplain
Management Bulletin:Elevation Certificate (FEMA, 2004).
The required information includes the following
characteristics of crawlspaces, enclosures, and NFIP ELEVATION CERTIFICATE COMMENTS
attached garages:
The comment section of the NFIP Elevation
• Square footage of the enclosed area, measured Certificate should be used to note
on the outside of the enclosure walls characteristics of enclosures and flood
openings that comply with the requirements but
• Number of permanent flood openings within that, without close inspection, may appear to be
1.0 foot above adjacent grade non-compliant. In particular, without clarifying
• Total net open area of flood openings comments on engineered openings, local
officials and insurance agents may inadvertently
• Whether engineered openings are used determine that enclosures are non-compliant
According to the NFIP Elevation Certificate and deem the floor of the enclosure the lowest
instructions, when an enclosed area has no flood floor, resulting in unnecessarily high NFIP flood
openings or if all flood openings (non-engineered insurance premiums.
8 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
or engineered) are higher than 1.0 foot above the adjacent grade, "N/A' (not applicable) should be
entered for both the number of flood openings within 1.0 foot above adjacent grade and total net open
area of flood openings. If the bottoms of some flood openings are within 1.0 foot above the adjacent
grade, only the number and net open area of those openings should be recorded (openings that are
higher than 1.0 foot are not included).
The certificate does not require users to determine whether any portion of a flood opening is above the
BFE. However, for compliance purposes, see Section 8.3.6 of this Technical Bulletin for guidance on
flood openings that extend above the BFE,which can occur in areas with shallow flooding. In these areas,
even if the bottom of an opening is less than 1.0 foot above grade, a portion of the opening may extend
above the BFE.
The NFIP Elevation Certificate has space for comments. Comments must be entered when engineered
openings are used. Section 9.3.2 of this Technical Bulletin describes the documentation that is required
for engineered openings and that must be attached to the certificate.
6 Use of Enclosed Areas Below Elevated
Buildings
The NFIP regulations specify that enclosed areas under
elevated buildings in SFHAs may be allowed if the enclosed DRY FLOODPROOFED BUILDINGS
areas are used solely for: The only buildings with enclosed
• Parking of vehicles (attached garages or parking areas areas that are not required to have
below elevated buildings) flood openings are non-residential
buildings that are engineered to be
• Building access (stairwells, foyers) dry floodproofed. For information on
• Storage (recommended to be limited to storage of low- dry foodproofing, see FEMA P-936,
value items) Floodproofing Non-Residential
Buildings (FEMA, 2013), and NFIP
The NFIP regulations do not list crawlspaces and under-floor Technical Bulletin 3, Non-Residential
spaces as allowable uses of enclosed areas.However,buildings Floodproofing-Requirements and
in Zone A may be elevated using perimeter foundation walls Certification. FEMA has granted
that create these enclosed areas. Crawlspaces and under- exceptions to a small number of
floor spaces provide access to under-floor utilities such as communities to allow engineered,
pipes, ductwork, and electric conduits. dry-floodproofed basements in
specific circumstances.
---------------------------------------------
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 9
A compliant enclosed area below the BFE can be
rendered non-compliant by installing features NON-CONVERSION AGREEMENTS
that are inconsistent with the limitations on uses. When some communities issue permits for
Examples of features that are not allowed below buildings with enclosed areas below the BFE,
the BFE are: permittees are required to execute Non-
• Appliances Conversion Agreements. These agreements
document the permittees' understanding that
• Heating and air conditioning equipment the allowed use of enclosures is limited, that
• Ventilation conversion to other uses is not allowed, and that
modifying enclosed areas may render a building
• Ductwork non-compliant with minimum requirements and
• Plumbing fixtures result in higher NFIP flood insurance rates.
• Materials that are not flood damage-resistant
materials
• More than the minimum electric service required to address life-safety and electric code requirements
for vehicle parking, building access, or storage
7 Foundation Walls and Enclosure Walls
that Require Flood Openings
The NFIP regulations require that enclosed areas below the lowest floors of elevated buildings in
Zone A have flood openings to equalize the hydrostatic flood forces (loads) on the enclosure walls. This
requirement applies whether the walls are crawlspace, load-bearing, or non-load-bearing walls.
Examples of foundation and enclosure walls that require openings are listed below and described in
Sections 7.1 through 7.9.
• Solid perimeter foundation walls (crawlspaces and under-floor spaces)
• Solid perimeter foundation walls (below-grade crawlspaces)
• Garages attached to elevated buildings
• Enclosed areas under buildings elevated on open foundations
• Enclosed areas with breakaway walls under buildings elevated on open foundations
• Above-grade (elevated) enclosed areas
• Two-level enclosed areas
• Solid perimeter foundation walls on which manufactured homes are installed
• Accessory structures (detached garages and storage sheds)
10 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
7.1 Solid Perimeter Foundation Walls (Crawlspaces
and Under-Floor Spaces)
The crawlspace or under-floor space that is created when
a building is elevated on a solid perimeter foundation CONDITIONED CRAWLSPACES
wall that is below the BFE (see Figure 2) must meet all MUST HAVE FLOOD OPENINGS
of the requirements for enclosed areas, including flood In many parts of the country, a common
openings. If brick veneer, siding, or other material covers practice is to build "conditioned
the wall, the openings in the wall must penetrate into the crawlspaces" that are sealed and have
enclosed area.A crawlspace access door does not qualify as mechanical ventilation. In SFHAs, all
a flood opening unless the door has an opening installed Crawlspaces must have flood openings
in it or otherwise meets the performance requirement to that meet the NFIP requirements and
allow automatic entry and exit of floodwater. building codes.
Section 8.2 of this Technical Bulletin explains that the
bottom of each opening must be no higher than 1 foot above the higher of the finished interior grade (or
floor) or the finished exterior grade immediately under the opening. Therefore, the expected finished
exterior grade and the final interior grade (or floor) of a crawlspace must be known before the location
of the openings in a perimeter foundation wall can be determined.
Building codes may require ventilation of under-floor spaces.Ventilation openings are typically positioned
near the top of the foundation wall to facilitate air flow. In most cases, ventilation openings are too far
above grade to satisfy flood opening requirements.
In SFHAs where BFEs are several feet above grade or when owners want enough head room in an under-
floor space to allow for parking of vehicles and storage, solid perimeter foundation walls may be used to
create a full-height, under-floor space (see Figure 3). The walls surrounding an under-floor space must
meet all flood-opening requirements.
Flood openings ,
(only three shown)
Figure 3: Full-height, solid perimeter walls surrounding a garage and
storage area with flood openings(only three openings are shown)
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 11
Full-height, under-floor spaces must also meet all other NFIP requirements, which will minimize the
likelihood of future conversion to uses other than the allowed uses (parking of vehicles, building access,
or storage). Features that are inconsistent with the allowed uses are not permitted (see Section 6).
A backfilled stem wall foundation (also called
chain wall, raised-slab-on-grade, and slab- BACKFILLED STEM WALLS
on-stem-wall-with-fill) can look like a solid AND NFIP ELEVATION CERTIFICATES
perimeter foundation wall from the outside, but When the NFIP Elevation Certificate for a building
a backfilled stem wall foundation is backfilled elevated on a backfilled stem wall is completed,
with compacted structural fill, concrete, or the foundation should be described in the
gravel that supports the floor slab (see Figure 4). comment section to clarify that the foundation is
Because stem wall foundations are backfilled, not a crawlspace and therefore does not require
flood openings are not required and should not and should not have flood openings.
be installed.
Concrete slab
Compacted
structural fill
Figure 4: Backfilled stem wall foundation;flood openings
not required
7.2 Solid Perimeter Foundation Walls (Below-Grade Crawlspaces)
The NFIP regulations do not allow buildings in
SFHAs to have basements (areas below grade on LIMITATIONS ON
all sides) except for engineered, non-residential BELOW-GRADE CRAWLSPACES
buildings in Zone A that are designed and Before authorizing below-grade crawlspaces,
certified to be dry floodproofed. Therefore, communities are required to adopt specific
crawlspaces that are below grade on all sides provisions in their ordinances to be consistent
are not allowed because they are basements. An with the limitations specified in NFIP Technical
exception is available only in SFHAs with shallow Bulletin 11. Communities should consult NFIP
flooding and then only if specific requirements State Coordinators or FEMA Regional Offices for
and limitations are met. For more information, the appropriate language.
12 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
see NFIP Technical Bulletin 11, Crawlspace Construction for Buildings Located in Special Flood Hazard Areas:
National Flood Insurance Program Interim Guidance.
According to Technical Bulletin 11, below-grade
crawlspaces may be allowed if the foundation wall
height is less than 4 feet from the bottom of the
floor joist/truss to the top of the footing or interior
grade/floor (whichever is higher). The top of the
footing or interior grade/floor must be no more than Joist/truss
2 feet below grade (see Figure 5). Flood openings
are required in the foundation walls surrounding Flood
below-grade crawlspaces and, as noted in Section 7.1, opening 4-foot
ventilation may be required. Because below-grade more maximum
Y h q g than 1 foot
crawlspaces may contribute to increased humidity Interior
and mold growth,Technical Bulletin 11 requires that 2-foot grade/
below-grade crawlspaces have adequate drainage Exterior grade maximum floor
systems to minimize moisture damage.
Y g ..4 .�
Footing
Although crawlspaces that meet the limitations in
Technical Bulletin 11 are not considered basements Figure 5: Limitations on below-grade crawlspaces in
for floodplain management purposes, they are shallow flood hazard areas(see NFIP Technical Bulletin 11
considered basements for NFIP flood insurance for more information)
purposes, and premiums will be higher if the grade
inside a crawlspace is below the exterior grade on
all sides.
7.3 Garages Attached to Elevated Buildings
Many buildings, especially homes, have an attached garage that extends laterally from the building and
may or may not have living space above it. The floor of a garage that is attached to a building in an SFHA
is allowed to be below the BFE if the garage meets all of the requirements for an enclosed area below the
BFE. The use of the garage space must be limited to parking of vehicles, building access, or storage.
Flood openings are required in the exterior walls of garages in Zone A. Openings may be installed
in garage doors (see Figure 6). However, because garage doors are likely to be replaced over the life
of a building and subsequent owners may inadvertently replace garage doors without openings, flood
openings should be installed in garage doors only when there is insufficient wall area in which to install
the required number of openings.
Garage doors themselves do not meet the requirements for openings because human intervention would
be needed to open garage doors when flooding is expected. Human intervention is inconsistent with
the requirement that openings allow for the automatic entry and exit of floodwater. Garage doors with
mechanisms that open the doors when water is detected do not meet the requirements because electric
service cannot be guaranteed even if a backup power source is provided. Similarly, gaps that may be
present between the garage door and the doorjamb or walls do not guarantee automatic entry and exit of
floodwater and do not count toward the net open area requirement.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 13
!/y f
f
u __
y r.
Figure 6: Engineered openings in garage doors
7.4 Enclosed Areas Under Buildings Elevated on Open Foundations
A building that is elevated on an open foundation (e.g.,piers,posts,columns,pilings) in Zone A may have
enclosed areas below the elevated floor (see Figure 7). Sometimes, only part of the footprint is enclosed,
such as for a stairwell or storage room. All of the requirements for enclosed areas apply. Requirements
include openings, elevated utilities, flood damage-resistant materials, and limitations on use (parking of
vehicles, building access, or storage).
Skirting used to enclose areas under
manufactured homes or other elevated NATIONAL FIRE PROTECTION ASSOCIATION
(NFPA) INSTALLATION STANDARD
buildings is typically made of weather-resistant AND SKIRTING
material and extends from the bottom of the
floor system down to grade. Rigid vinyl and NFPA 225, Model Manufactured Home Installation
aluminum skirting must have flood openings. Standard(NFPA, 2017), specifies that the installation
Flood openings are not required when flexible of skirting does not trigger the requirement for flood
skirting is used, but flexible skirting may be openings if the skirting does not provide structural
support and would collapse under wind and water
pushed against foundations if floodwater loads that are less than those expected during the
rises rapidly, in which case open lattice may base flood event without causing structural damage
be more appropriate. Unattached skirting to the elevated home or foundation.
can become dislodged during flooding and
generate damaging debris.
14 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
0 0
-nil
o ❑ LIJ
Q-j
Figure 7: Enclosure with flood openings under a house elevated on pilings
UTILITY CHASES
For floodplain management and NFIP flood insurance purposes, utility chases designed to protect utility
lines from freezing are not considered enclosures. Utility chases must be small and not allow access for a
person to enter the space(access panels for servicing the lines are appropriate).
Because a utility chase is not considered an enclosure, it does not have to have flood openings(but flood
openings may be provided). The utility chase must be constructed of flood damage-resistant materials
below the BFE, and the enclosed utility lines must meet the requirement to be watertight and capable of
withstanding flood loads (hydrostatic, hydrodynamic, wave).
7.5 Enclosed Areas with Breakaway Walls Under Buildings Elevated
on Open Foundations
Open foundations (e.g., piers, posts, columns, pilings) are recommended in riverine SFHAs where flow
velocities are expected to exceed 10 feet per second and in coastal areas where breaking wave heights
during base flood conditions are expected to be between 1.5 and 3 feet (called Coastal A Zones).
Buildings in these areas may be exposed to significant hydrodynamic loads, debris impact, and scour,
any of which could be sufficient to damage typical perimeter foundation walls and enclosure walls even
when there are flood openings.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 15
Many Flood Insurance Rate Maps (FIRMs) for
coastal communities that have been revised since I-CODES AND COASTAL A ZONE
2009 show a Limit of Moderate Wave Action Starting with the 2015 editions, I-Codes treat
(LiMWA), which delineates the inland extent of Coastal A Zones like Zone V if the LiMWA
the 1.5-foot wave. In Coastal A Zones, identified is delineated on FIRMs or if communities
as Zone A on FIRMs, FEMA recommends that designate Coastal A Zones. In addition,
walls surrounding enclosed areas be designed the I-Codes and ASCE 24-14 require flood
as breakaway walls. To comply with the NFIP openings in all breakaway walls, including
requirements, flood openings are required in those in Coastal A Zones and Zone V.
breakaway walls in Zone A. Post-flood assessments indicate that
The NFIP regulations require that enclosures breakaway walls with openings prevent wall
below elevated buildings in SFHAs identified as failure under frequent, shallow flood events.
Zone V meet the same requirements for enclosures Preventing frequent wall failures reduces
in Zone A, except that (1) walls must be non- debris, keeps enclosure interiors and contents
supporting breakaway walls, open lattice-work, or protected from wind-driven rain and sand,
insect screening and (2) flood openings are not and reduces the cost of replacing walls.
required (see NFIP Technical Bulletin 9, Design
and Construction Guidance for Breakaway Walls). The
guidance in Technical Bulletin 9 should be used when flood openings are installed in breakaway walls to
minimize wall failure under flooding that occurs more frequently than the base flood.
7.6 Above-Grade (Elevated) Enclosed Areas
In flood hazard areas that experience frequent
flooding, some owners construct enclosures with "HANGING ENCLOSURE"
floor systems that are elevated above grade, not in The term "hanging enclosure" has been used
contact with the ground, but still below the BFE to refer to raised, above-grade enclosures
(see Figure 8). Placing the enclosure floor above although above-grade enclosures are typically
grade minimizes the potential for damage to the supported by other means and do not actually
enclosure and contents during frequent, low-level hang from elevated buildings.
flood events.
Above-grade enclosures must meet all requirements
applicable to enclosures (flood openings, flood damage-resistant materials, and used only for storage or
building access). The floor system of above-grade enclosures may be independently supported on piers or
posts, or enclosures may be structurally attached to the building's column or piling foundation.Although
the floors of above-grade enclosures are not the lowest floor for floodplain management purposes, the
enclosure floors are the lowest floor for NFIP flood insurance rating purposes.
One or more floor grates should be installed in the enclosure floor to reduce the potential for structural
damage. Damage could result from buoyancy loads on the enclosure floors before water enters through
the flood openings installed in walls. Openings in floors also allow enclosures to drain completely,
reducing the potential for damage caused by the added weight of water.
16 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
—Base flood—— — ————————————
Elevated building
elevation (BFE) Enclosure walls span
Non-load-bearing pilings or columns
framed wall around
enclosure _ __Base flood———— —— - ——— —
Flood opening 3, elevation (BFE)
Install floor grate
to facilitate o
drainage Pilings or
No more columns
than 1 foot 4_
Wood frame floor system Flood opening 0
Floor system
Piers 3P attached to pilings
or columns Install floor grate to
facilitate drainage
(� �I; ,a Stairway not shown
`Pier footings_
or deck blocks
Enclosure floor on piers under house supported Enclosure floor attached to pilings or column
on pilings or columns(pilings/columns not shown)
Figure 8:Above-grade enclosures
ABOVE-GRADE ENCLOSURES AND NFIP FLOOD INSURANCE
NFIP flood insurance policies for elevated buildings with above-grade enclosures are rated assuming
the above-grade enclosure is the lowest floor(i.e., the floor of the enclosure instead of the floor of the
elevated building). See the "Lowest Floor Guide" section of the NFIP Flood Insurance Manual(FEMA,
2019). Above-grade enclosures can result in higher NFIP flood insurance premiums than enclosures
with floors that are at-grade or close to grade. Owners should ask their insurance companies to submit
requests to the NFIP for a special rating for buildings with above-grade enclosures.
---------------------------------------------------------
7.7 Two-Level Enclosed Areas
In flood hazard areas where the BFE is more than one story
above the ground, some owners want to build two-level TERMS USED
enclosures (see Figure 9). For compliance purposes, to avoid FOR TWO-LEVEL ENCLOSURES
the second-level enclosure from being identified as the lowest Two-level enclosures are also
floor, both enclosure levels must meet all of the requirements referred to as two-story enclosures,
for enclosed areas, including openings, elevated utilities, flood double enclosures, and stacked
damage-resistant materials, and limitations on use (parking enclosures.
of vehicles, building access, or storage). To facilitate drainage
from the upper level of the enclosure, an opening with a grate
should be installed in the floor.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 17
Figure 9 shows a two-level enclosure in which
the surrounding walls are not load-bearing; the
Base flood——— — ———————————— same configuration and requirement apply if the
elevation(BFE) surrounding walls are load-bearing perimeter walls.
Floor system Two-level enclosures are unusual and warrant
Flood opening 3P connected to
pilings/columns consideration of flood loads based on site-specific
(pilings/columns flood conditions. Local officials may require that
No more than not shown)
1 foot buildings with two-level enclosures be designed
and certified by a registered design professional
rather than rely on non-engineered foundations and
Floor grate
to facilitate enclosure configurations.
drainage
TWO-LEVEL ENCLOSURES
Non-load-bearing AND NFIP FLOOD INSURANCE
wood-framed walls
around enclosure Designers and owners should be aware that a
building with a two-level enclosure, even if allowed
by permit, will have a higher NFIP flood insurance
Flood opening 3P premium than if the building has a one-level
enclosure. Even if a two-level enclosure complies
No more than Interior grade/floor with building codes and floodplain management
1 foot
requirements for enclosures, the upper floor of
' the two-level enclosure will be deemed the lowest
a'
Exterior grade floor for insurance rating purposes(the lowest
floor for flood insurance purposes is the first
Figure 9:Two-level enclosure with non-load-bearing floor elevated above ground). Owners should ask
walls under building elevated on pilings or columns; their insurance companies to submit requests
configuration also applies if walls are load-bearing to the NFIP for a special rating for buildings with
two-level enclosures.
7.8 Solid Perimeter Foundation Walls on which Manufactured Homes
Are Installed
Manufactured homes may be installed on solid perimeter foundation walls that enclose the space below the homes
(see Figure 10). Even if not part of a home's load-bearing support system, a solid perimeter foundation wall is
required to have openings; otherwise, hydrostatic loads may damage the wall, which could lead to damage of the
home's supporting foundation and anchor system.
18 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
Manufactured home
Ground anchors
Floor not shown
for clarity
W IF Masonry
perimeter wall
Cross member Pier
Flood opening
Figure 10: Manufactured home supported on interior piers
and masonry perimeter wall with flood openings(ground
anchors not shown)
7.9 Accessory Structures
Communities participating in the NFIP are required to regulate all development in SFHAs, including
detached garages, detached storage buildings, and small storage sheds. Accessory structures may be
elevated in accordance with the requirements for elevated buildings or dry floodproofed.
When communities have FEMA-approved
limitations on the size of accessory structures ADDITIONAL ACCESSORY
or when communities grant variances for non- STRUCTURE CONSIDERATIONS
elevated accessory structures, the structures Some communities have FEMA-approved
may be allowed without elevation provided regulations that specify limitations on the size
the structures are wet floodproofed (see of accessory structures that are allowed in
NFIP Technical Bulletin 7, Wet Floodproofing SFHAs without having to comply with elevation
Requirements for Certain Buildings Located in Special requirements. Other considerations for accessory
Flood Hazard Areas). Alternatively, communities structures are set forth in FEMA policies
without FEMA-approved size limits may consider and guidance.
granting variances for non-elevated accessory Local officials should consult NFIP State
structures in accordance with FEMA policies Coordinators or FEMA Regional Offices for
and guidance. additional guidance and for appropriate size limits
and language to include in local regulations.
-----------------------------------------------------------------------------------------------
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 19
Wet-floodproofed accessory structures must comply with the following measures:
• Use is limited to parking of vehicles and storage
• Utilities are elevated
• Materials below the BFE are flood damage-resistant materials
• Flood opening requirements are satisfied
• Structures are anchored to resist flotation, collapse, or lateral movement under flood conditions
A best practice is to require Non-Conversion Agreements when non-elevated accessory structures
are allowed. These agreements, when recorded with property deeds, inform future owners about
the limitations and the wet-floodproofing measures. Accessory structures that are allowed to be wet
floodproofed must not be used for any habitable or other prohibited purpose.
8 Requirements and Guidance
for Installation of Flood Openings
The NFIP regulations specify installation requirements for all flood openings, whether non-engineered
or engineered. See Section 9 of this Technical Bulletin for information on non-engineered and
engineered flood openings. Installation requirements specify the minimum number of openings and the
maximum height of openings above grade. The requirements and guidance on installation are provided
in Sections 8.1 through 8.3.
8.1 Location and Minimum Number of Flood Openings
Every enclosed area is required to have at least two
flood openings on exterior walls. Flood openings LOCATION OF FLOOD OPENINGS
should be installed in at least two sides of each The IRC and IBC(by reference to ASCE 24)
enclosed area to decrease the chance that all require flood openings "on different sides of
openings will be blocked by floating debris and to each enclosed area" (IRC R322.2.2.1) and
allow for more even filling and drainage of enclosed "in at least two walls of each enclosed area"
areas than if openings are installed on only one side. (ASCE 24, Section 2.7.3).
FEMA recommends that openings be distributed
around the perimeter of enclosed areas unless
there is clear justification for putting all of the openings on only one or two sides, such as in townhouses
with limited exterior walls (see Section 8.3.4) and buildings set into sloping sites (see Section 8.3.2). If
openings are not distributed around the perimeter, an imbalance in flood loads could result in damage
to or collapse of walls.
Figure 11 shows a foundation plan with multiple enclosures and openings in the perimeter wall of each
enclosed area.Note that the number of openings shown is for illustration purposes only;the total number
of openings and the adequacy of the net open area of the openings depend on the type of opening and
whether air-vent devices or engineered openings are installed.
20 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
Crawlspace Storage
Pigs
i❑i i❑i i❑i
Garage
Flood openings
Figure 11: Foundation plan of home with multiple enclosed areas,each with flood
openings(number of openings for illustration purposes only)
In some situations, openings in interior walls or partitions are necessary to ensure that floodwater can
reach all enclosed areas and minimize unbalanced hydrostatic loads on interior and exterior walls.When
openings are used in interior walls, the total number of openings and their net open area should be
based on the size of the enclosed area,but openings in interior walls are not counted toward the required
total opening requirement based on the exterior measurement of the enclosed area. To maintain safe fire
separation, flood openings should not be placed in the wall separating a garage from living spaces and
crawlspaces unless devices used as flood openings that are designed to satisfy fire-separation requirements
are used.
8.2 Height of Flood Openings Above Grade or Floor
The bottom of each flood opening must be positioned no higher than 1 foot above the higher of the final
(finished) interior or exterior grade or the floor that is immediately under each opening so water will
begin to flow through the opening when water rises just above the bottom of the opening. The purpose
of this requirement is to satisfy the performance
expectation that the difference in water levels
between the interior and exterior will not ENCLOSURES BELOW GRADE
exceed 1 foot as floodwater begins to rise and as ON ALL SIDES ARE BASEMENTS
it recedes from the site. To reduce the amount An enclosure that is below grade on all sides is
of water trapped inside, a good practice is to a basement regardless of whether the interior
install some openings closer to grade than the grade or floor is below grade because backfill,
maximum 1 foot allowed. See Section 8.3.6 for topsoil, or landscaping materials were added or
information on openings that extend above the because the footing trenches inside the perimeter
BFE in areas with shallow flooding. foundation walls are not completely backfilled.
Basements do not comply with the minimum
When interior and exterior grades are different, NFIP requirements. In addition, the presence of
the higher of (1) the finished exterior grade such below-grade enclosures will result in higher
immediately under each opening and (2) the NFIP flood insurance premiums.
final interior grade or floor is used to determine _
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 21
the position of flood openings. The following should be considered when determining which grade or
floor to use:
• Finished exterior grade. Care should be taken when placing backfill, topsoil, or landscaping materials
around the outside of enclosures, especially solid perimeter foundation walls. If the finished exterior
grade is higher than the interior grade on all sides of the building, the enclosed area will be a
basement as defined by the NFIP.
• Final interior grade or floor. The trench that is excavated to construct footings and foundation walls
must be backfilled completely; otherwise, a basement will be created. If the interior grade or floor is
higher than the exterior grade, the openings must be no higher than 1 foot above the interior grade
or floor.
8.3 Examples of Flood Opening Installations
The following examples of flood opening installations are described in Sections 8.3.1 through 8.3.6:
• Interior grade or floor higher than the exterior grade
• Sloping sites
• Buildings with large enclosed areas
• Townhouses with limited exterior walls
• Buildings with multiple enclosures
• Openings in areas with shallow flooding
8.3.1 Interior Grade or Floor Higher than the Exterior Grade
This section describes enclosures in which
the interior grade or floor is higher than
the exterior grade. As water rises against
the outside of the foundation, the interior -
fill or slab resists the hydrostatic load. When
water rises above the interior grade or slab,
the lateral load will become unbalanced
and therefore must be equalized with
openings that allow water to automatically -
enter and exit.
Figure 12 is an example of a framed
enclosure below a manufactured home
that is elevated on columns. As indicated
by the driveway on the left, the interior slab
is higher than the exterior grade along the
side of the building. The flood openings are Figure 12: Manufactured home installed on columns above a full-
within 1 foot of the interior floor surface. height, framed garage(note elevation of thick driveway slab on left;
Here, the full-height enclosed area is used the flood openings are within 1 foot of interior floor surface)
for parking of vehicles and storage.
22 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
When viewed from the outside, an enclosure with
the interior grade or floor higher than the exterior INTERIOR GRADE
grade may appear non-compliant with the installation OR FLOOR ABOVE BFE
requirements for openings because the openings When the interior grade or floor of an
appear to be too high above the exterior grade. enclosure below an elevated building is
Therefore, the final documentation of as-built entirely above the BFE, flood openings are
elevations should note the difference in interior and recommended but not required. When the
exterior grades. For example, if the NFIP Elevation floor of an enclosure is above the BFE, the
Certificate is used, the comments should indicate NFIP flood insurance policy will be rated
whether the openings are (or are not) within 1 foot of using the enclosure floor as the lowest floor
the higher of the two grades and should explain that rather than the next higher floor above the
the interior grade or floor is higher than the exterior enclosure. Installing flood openings in these
grade. Without the explanation, NFIP flood insurance situations will result in lower NFIP flood
premiums may be higher than necessary. insurance premiums.
------------------------------
8.3.2 Sloping Sites
Buildings on solid perimeter foundation walls set into sloping sites present a special situation for the
installation of flood openings. Careful attention must be paid to the following:
• The interior grade or floor along the lowest side of the building must be at or above the exterior grade
across the entire length of the lowest side, and there must be positive surface drainage away from the
building; otherwise, the enclosure will be considered a basement as defined by the NFIP.
• The bottom of each opening must be no higher than 1 foot above the exterior or interior grade
immediately below the opening,whichever is higher (see Figure 13).
• For flood openings to perform their intended function, they should be below the BFE.
Elevated lowest floor
L��
Base flood
elevation
(BFE)
Mill f:::::::::: 0
:•:•:.••..
......
0
Each flood opening
no more than 1 foot
above grade Interior floor or grade must be at or above
the exterior grade along the entire length of
the lowest side to prevent being a basement
Figure 13: Flood openings in enclosure walls on a sloping site
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 23
• Interior partitions and load-bearing walls must have openings to allow water to readily reach every
enclosed area (see Section 8.3.5 for information on buildings with multiple enclosures).
8.3.3 Buildings with Large Enclosed Areas
Some buildings, especially commercial and industrial buildings, have large under-floor spaces,
crawlspaces,or enclosures.Flood openings may be stacked or grouped (see Figure 14),or large-dimension
openings may be used, provided all of the requirements for openings are satisfied. Vertically stacked or
closely spaced openings function together as one opening, and the bottom of the lowest opening must be
no higher than 1 foot above the exterior grade or interior grade,whichever is higher.
Base flood elevation (BFE)
-----------------------------
IIIIIII IIIIII�
IIIIIII IIIIIII
Figure 14: Flood openings that are stacked and closely grouped to
satisfy the required total net open area
8.3.4 Townhouses with Limited Exterior Walls
Townhouses are single-family dwelling units constructed in groups of three or more attached units in
which each unit extends from foundation to roof with exterior walls on at least two sides. Flood openings
are required for townhouses in SFHAs that are constructed with solid perimeter foundation walls or solid
walls surrounding enclosed areas under the elevated portion of the building.
Because interior townhouse units have less linear exterior wall length than end units, meeting all of the
requirements for flood openings can be a challenge, especially the requirement for adequate opening
area and the requirement that each enclosed area have openings. If openings cannot be provided in at
least two exterior walls of each enclosed area, the NFIP allows all openings to be installed in one wall.
24 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
The design of interior townhouse units can satisfy the guidance that openings should be located on
different sides of each enclosed area if interior partitions and walls have openings to connect enclosed
spaces from front to back. Figure 15 shows suggested locations for openings. Note that the number of
openings in Figure 15 is for illustration purposes only; the total number of openings and the adequacy of
the opening area depend on the type of opening and whether non-engineered or engineered openings are
installed. Fire-safety limitations generally preclude openings in the walls that separate townhouse units.
Providing adequate openings in enclosures below elevated townhouse units, other than end units,may be
even more challenging if a multi-unit building is set into a sloping site. In this case, it may be appropriate
to consider an open foundation or a backfilled stem wall foundation that does not require openings.
T
2 T
Storage room Storage room Storage room
3
2 Garage Garage Garage 2
All stairs open o
underneath
Foyer i---� ---, i---� ---, Foyer i---� ---, Foyer
1 3
1O Openings in garage door O2 Openings in exterior wall O3 Openings in interior wall/door
Figure 15:Suggested flood openings in enclosures under elevated townhouses(number of openings for illustration
purposes only)
8.3.5 Buildings with Multiple Enclosures
Every enclosed area is required to meet the requirements for enclosures, including the requirement for
flood openings in exterior walls. Figure 11 in Section 8.1 shows a home foundation plan with multiple
enclosures. In some situations, openings in interior walls or partitions may be necessary to ensure that
floodwater can reach all areas to minimize unbalanced hydrostatic loads on load-bearing interior walls
and exterior walls (see middle townhouse in Figure 15 in Section 8.3.4). When openings are used in
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 25
interior walls, the total number of openings in exterior walls and the total opening area should be based
on the size of the entire enclosed area. Openings in interior walls do not count toward the total opening
requirements based on the exterior measurement of the enclosed area.
8.3.6 Flood Openings in Areas with Shallow Flooding
Some FIRMs show mapped SFHAs where the depth
of floodwater above grade will be shallow (2 feet or NFIP ELEVATION CERTIFICATE
less during the base flood). Shallow flooding occurs AND SHALLOW FLOODING
toward the landward boundary of SFHAs and in areas The NFIP Elevation Certificate requires
identified as being subject to sheet flow or ponding. users to input the number of flood openings
The NFIP regulations require flood openings in Within 1.0 foot above the adjacent grade or
enclosures even if the depth of flooding is only 1 foot floor. The certificate does not require users
and the difference in water depth between the inside to determine how much of a flood opening
and outside of enclosures is 1 foot or less. is above or below the BFE.
Depending on the depth of floodwater in areas with --------
shallow flooding, flood openings may extend above
the BFE if the bottom of the opening is no higher than 1 foot above the higher of the final interior grade
or floor and the finished exterior grade of the crawlspace or enclosure. When flood openings extend
above the BFE, alternatives to satisfy the requirements include:
• Raise the floor of the enclosure to be at or above the BFE, perhaps by using a thicker slab, resulting in
no need for openings. Although this alternative satisfies the construction requirement, for NFIP flood
insurance rating purposes, the top of the slab is the elevation of the lowest floor, not the next higher
floor (see the text box"Interior Grade or Floor above BFE" in Section 8.3.1).
• Install openings as close to grade (or floor) as possible to maximize the open area available for inflow
and outflow of floodwater (see Figure 16). The total net open area of the openings must be based on
the enclosed area even if some portion of the opening is above the BFE.
4obd.ipenln:g.'. .:
• u
(BFE)—
L16§� harN4 0' .. .=
i
Figure 16: Bottom of the flood opening positioned as close as
possible to grade(or floor)when any portion of the opening extends
above the BFE
26 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
9 Non-Engineered Flood Openings
and Engineered Flood Openings
The NFIP regulations, described in previous sections, identify
options for providing sufficient size and number of flood I-CODE REQUIREMENTS
openings to allow for the automatic (free) entry and exit of FOR FLOOD OPENINGS
floodwater. This section describes how the automatic entry The IRC includes requirements for
and exit of floodwater can be accomplished by the use of: non-engineered and engineered
flood openings, and the IBC
• Non-engineered openings that meet the prescriptive includes the same requirements by
requirement to provide 1 square inch of net open area reference to ASCE 24.
for each square foot of enclosed area,where the enclosed
area is measured on the exterior of the enclosure walls.
Section 9.2 describes a variety of options that can serve as
non-engineered openings. FLOOD DAMAGE-RESISTANT
MATERIALS
• Engineered openings for which Evaluation Reports are
issued by the ICC Evaluation Service (ICC-ES), a subsidiary Flood openings must made of
of the ICC, or equivalent reports issued by other product flood damage-resistantt materials
certification organizations. in order to satisfy the requirement
that materials used below the
• Engineered openings designed and certified by a BFE be resistant to flood damage.
registered design professional for a specific building and Metals should be corrosion
site-specific conditions. resistant, and plastics should be
weather resistant. For guidance,
All of the following requirements for installation apply see NFIP Technical Bulletin 2,
regardless of whether engineered openings or non-engineered Flood Damage-Resistant
openings are used to satisfy the NFIP requirements (also see Materials Requirements.
Section 8):
• Each enclosed area must have a minimum of two openings.
When multiple enclosed areas are present, each area must have openings in its exterior walls.
Section 8.3.5 describes connecting multiple areas by installing openings in interior walls or partitions
to ensure that floodwater can reach all enclosed areas.
• The bottom of each opening must be no more than 1 foot above the higher of the final interior grade
or floor or the finished exterior grade immediately under the opening.
• Insect screens, grates, grilles, fixed louvers, blades,faceplates, or other devices, if any, must not block
the automatic flow of floodwater into and out of the enclosed area.
Section 9.1 provides a list of measures that are not acceptable as flood openings.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 27
9.1 Measures Not Acceptable as Flood Openings
FEMA has determined that the following measures do not satisfy the requirements for flood openings:
• Standard foundation air-ventilation devices that can be closed manually unless they are permanently
disabled in the open position because otherwise, they do not allow for the automatic entry and exit of
floodwater (see Figure 17).
• Standard foundation air-ventilation devices that have detachable solid covers intended to be manually
installed over the vent because they do not allow for the automatic entry and exit of floodwater when
the cover is in place.
• Standard foundation air-ventilation devices that are designed to open and close based on temperature
unless they are also designed to allow for the automatic entry and exit of floodwater.
• Devices with covers or panels that are intended to displace when floodwaters rise on only one side
of a wall because they do not satisfy the requirement for automatic entry and exit of floodwater in
both directions.
• Windows below the BFE because the automatic entry and exit of floodwater cannot be satisfied by the
expectation that windows will break under rising floodwater.
• Garage doors without openings because human intervention is required to open garage doors when
flooding is expected. Gaps between the garage door and the doorjamb or walls do not count toward
the net open area requirement.
Figure 17:Standard air vent that is unacceptable as a flood opening
because it is not disabled in the open position
9.2 Non-Engineered Flood Openings
Flood openings without moving parts are non-engineered openings, while those with moving parts
should be certified as engineered openings (see Section 9.3). Non-engineered openings are used to
provide 1 square inch of net open area for each square foot of enclosed area. The size of an enclosed
28 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
area in square feet should be measured
on the exterior of the enclosure walls. A MEASUREMENT MUST ACCOUNT
variety of non-engineered opening options FOR OBSTRUCTIONS
are available. Section C2.7.2.1 of the ASCE 24 commentary
Net open area" refers to the permanently
emphasizes that the measurement of net open area
open area of a non-engineered opening. is not based on the dimensions of the opening (void)
The NFIP regulations indicate that flood in the wall. The measurement must account for any
portion of the void that is obstructed or covered in
openings may be equipped with "coverings any way(other than by screening).
or devices" if they permit the automatic
----------------------------------------------------------------------------
(free) entry and exit of floodwater in
both directions.
The measurement of the net open area must 16.7 inches
take into consideration any solid obstructions
such as grilles, fixed blades and louvers, or
faceplates. Methods used by the ventilation
industry to account for such obstructions 6.5 OPEN
when determining net open area for air inches
flow may be used. Figure 18 shows a typical
standard air-vent faceplate and measurements
of the net open area. Figure 19 shows a typical
ventilation louver with fixed blades and 0.5 inch Closure device disabled
in the open position
indicates how the net open area is determined.
Figure 18: Example of non-engineered opening:Typical standard
Some manufacturers of standard air vents air vent faceplate providing 42 square inches of net open area if
stamp the number of square inches the disabled in the open position; measurement of net open area uses a
device provides for air flow into the frame slot width of 0.5 inch times a slot height of 6.5 inch times the total
of the device or may note the number in the number of slots
packaging. The measurement accounts for
Front view Side view
0.89 inch
0.7 inch
13 inches
Figure 19: Example of non-engineered opening:Typical standard air vent with fixed,angled
blades providing approximately 44 square inches of net open area; measurement of net
open area uses slot width of 13 inches times the sum of the spaces between the blades
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 29
the presence of fixed blades, insect screens, and other obstructions. The same number of square inches
should be used for the net open area calculation when these devices are installed as non-engineered
openings. If not indicated by the manufacturer, the net open area must be measured. Guidance on
measuring the net opening area may be available from manufacturers or other sources.
To qualify as non-engineered flood openings that permit the automatic entry and exit of floodwater:
• Standard air vents must not have solid covers (detachable or integrated with the vent) that are
intended to be manually installed.
• Typical air-vent devices that are designed to be opened and closed manually must be disabled
permanently in the open position.
• Air-vent devices that are designed to open and close based on temperature must also be designed to
allow the automatic entry and exit of floodwater.
Insect screens that do not block the entry and exit
of floodwater are allowed and do not affect the AREAS LIKELY TO HAVE
determination of the net open area. Communities DEBRIS AND SEDIMENT
that administer the IBC or IRC should note the Section C2.7.2.1 of the ASCE 24 commentary
requirement to cover ventilation openings for suggests using caution in selecting or
crawlspaces and under-floor spaces. The codes specifying openings with louvers, blades,
provide a list of acceptable covering materials. screens, or faceplates that may be blocked
The IBC and IRC commentaries note that some by debris and sediment. In areas where
covering materials for ventilation openings may experience indicates that floodborne
reduce the gross open area of the vent by as much debris and sediment are likely, ASCE 24
recommends avoiding the use of openings
as 50 percent. Although the net open area is not with components that have been shown to
reduced by screens, in areas where floodwater is become blocked or clogged.
expected to carry debris such as grass clippings and
leaves, insect screens tend to clog (see Figure 20).
Engineers, architects, and local officials may determine that a different type of opening is appropriate
or that more than the minimum number of flood openings is required to increase the likelihood that
openings will perform as expected during flooding, even if some of them become clogged with debris.
f k +
b N�.
i
Figure 20:Typical air vents with insect screens blocked by flood debris
30 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
Examples of non-engineered openings are described
below and shown in Figures 21 through 24. MINIMUM DIMENSION
SPECIFIED BY I-CODES
• Figure 21 shows typical standard air-ventilation
devices that are intended for crawlspace foundation The IRC and IBC(by reference to
walls. If installed as flood openings, they must ASCE 24) require that openings be not less
be disabled permanently in the open position to than 3 inches in any direction in the plane
satisfy the requirement for automatic entry and exit of the wall. This requirement applies to the
of floodwater. opening in the wall, excluding any device
that may be inserted.
• Figure 22 shows decorative masonry units and
decorative brickwork with closely spaced, open
holes. Only the net open area of each hole is counted.
• Figure 23 shows standard concrete blocks that are turned sideways and have insect screening. The
voids in the blocks are measured to determine the net open area.
• Figure 24 shows a foundation in which a hole was created when the concrete was poured. The
horizontal dimension should be greater than the vertical dimension to facilitate flow-through. A
wood frame covered with insect screening is inserted into the hole. The framed void is measured
to determine the net open area.A similar situation results when a block is omitted from perimeter
foundation walls constructed of concrete masonry units, resulting in a void the size of the
omitted block.
G_
� O O ODO000 h O00 0 0
000000� G O�oo�oo� °
Grate Fixed blades Faceplate or grille Decorative faceplate
Figure 21: Examples of typical air vents in crawlspace foundation walls used as flood openings with varying net open areas
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 31
Figure 22: D8COr8bv8 masonry units and closely spaced hO|8S in brickwork;the area 0feach hO|8 counts toward the
total net open area
Figurn23: Concrete blocks turned sideways with insect screening;
o typical 8'by16'innh block provides approximately 60square
inches of net open area
32 NF|P TECHNICAL BULLETIN I MARCH 2020
Figure 24: Wood frame with insect screen inserted in void in poured
concrete foundation wall; inside dimensions of frame determine net
open area
9.3 Engineered Flood Openings
Engineered flood openings,which have moving parts, must be designed and certified by registered design
professionals as engineered flood openings (see Section 9.2 for openings without moving parts). The
certification must specifically address the performance required by the NFIP regulations. Devices with
moving parts should be certified as engineered openings. In general, engineered openings remain closed
until flood conditions trigger the movable parts to allow floodwater and debris to freely and automatically
enter or exit. This section describes the design and performance requirements and the certification and
documentation requirements for engineered openings.
9.3.1 Design and Performance Requirements
The design and performance criteria for engineered openings are in ASCE 24, Section 2.7.2.2.
Section C2.7.2.2 of the ASCE 24 commentary provides additional information on engineered openings
and the best means to test expected performance.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 33
The equation from ASCE 24, shown in Figure 25, is used to determine the total net area of engineered
openings required for a given total enclosed area, based on some of the characteristics of the openings.
The calculated minimum net area of engineered openings may be called the "coverage" or"rated" area.
Ao =0.033 [l/c]R Ae
Where: Ao = total net area of openings required(in2)
0.033 = coefficient corresponding to a factor of safety of 5.0(in2•hr/ft3)
c = opening coefficient(non-dimensional;see ASCE 24,Table 2-2)
R = worst case rate of rise and fall(ft/hr)
Ae = total enclosed area(ft2)
Figure 25: Equation used to determined total net area of engineered openings(ASCE 24-14; used
with permission)
The equation includes a coefficient (0.033) that
corresponds to a factor of safety of 5, which is ASCE 24 EMPHASIS ON PERFORMANCE
consistent with design practices related to the AND CERTIFICATION
protection of life and property. The ASCE 24 Engineered opening requirements changed
commentary provides additional background on between the 2005 and 2014 editions of ASCE 24.
the derivation of the equation. The 2014 edition places more emphasis on
Design and performance criteria for engineered evidence of performance and consideration of
openings specified in ASCE 24 include all of factors that represent expected flood conditions.
the following: Section C2.7.2.2 of the ASCE 24-14 commentary
notes that the best means to certify performance
• Performance must allow for the automatic is to test engineered openings under conditions
entry and exit of floodwater. The ASCE 24 that mimic a range of rates of rise and fall,
commentary notes that the certification including rates many times the minimum rate of
requires consideration of a number of 5 feet per hour.
factors that represent expected base flood Documentation of performance under faster rates
conditions and not simply application of the of rise and fall provides building designers and
equation. (Flood conditions in different areas local officials with sufficient information on which
can vary widely; in some areas, the onset of to base decisions regarding whether to increase
flooding may be rapid while in other areas, the number or size of openings to account for
flood conditions may develop over much faster rates. The ASCE 24 commentary also notes
longer periods.) that testing should be done with water containing
debris typical of flooding around buildings (e.g.,
• Performance must account for the presence leaves, grass clippings, small branches, trash).
of obstructions such as louvers, blades,
screens, grilles,faceplates, and devices that
are part of the engineered opening assembly itself. In accordance with ASCE 24, Table 2-2 (see Table
3 of this Technical Bulletin), the opening coefficient of discharge (c)is 0.20 for openings of all shapes
if partially obstructed during design flood conditions by"louvers, blades, screens, grilles,faceplates,
or other covers or devices [that] are present during the design flood," as opposed to blocked by debris.
34 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
(The coefficient of discharge, also called an orifice coefficient, is selected to characterize the shape of
the portion of an engineered opening through which water flows.)
Table 3: Flood Opening Coefficient of Discharge(')
Opening
All shapes, partially obstructed during design flood(2) 0.20
Circular, unobstructed during design flood 0.60
Rectangular, long axis horizontal, short axis vertical, unobstructed during design flood 0.40(3)
Square, unobstructed during design flood 0.35
Rectangular, short axis horizontal, long axis vertical, unobstructed during design flood 0.25(4)
Other shapes, unobstructed during design flood 0.30
Source:ASCE 24-14,Table 2-2(used with permission)
(1) Different coefficients of discharge shall be permitted:(1)where a designer has performed detailed,opening-specific
calculations,a coefficient of discharge up to 10%different than given in Table 2-2 shall be permitted;or(2)where
laboratory testing or numerical modeling of flow through the opening has been conducted,the resulting coefficient of
discharge shall be permitted. In no case shall a coefficient of discharge>0.60 be permitted.
(2) Openings shall be classified as partially obstructed if louvers,blades,screens,grilles,faceplates,or other covers or
devices are present during the design flood.
(3) When the horizontal dimension is twice or more the vertical dimension,use 0.4;as the dimensions approach a square,
interpolate from
0.4 to 0.35.
(4) When the horizontal dimension is half or less the vertical dimension,use 0.25;as the dimensions approach a square,
interpolate from 0.25 to 0.35.
• Performance must account for the potential
for debris blockage even if there are no FLOODWATER RATE OF RISE AND FALL
louvers, blades,screens, grilles, faceplates, or Section C2.7.2.2 of the ASCE 24 commentary
other devices, preferably by allowing typical notes that a rate of rise of 5 feet per hour, only
floodborne debris to pass through. 1 inch per minute, is not representative of
• Performance must ensure that the difference many flood hazard areas and advises building
between the exterior and interior water levels designers to be cautious about relying entirely
will not exceed 1 foot. (Because the minimum on that rate. Faster rates of rise and fall are
requirement allows the bottom of openings to likely in watersheds where rainfall runoff
be no more than 1 foot above the higher of the accumulates rapidly and in many areas that
are subject to storm surge flooding. ASCE 24
finished interior grade [or floor] or exterior advises that information on rates of rise may
grade, a difference of no more than 1 foot is be available from stream and tide gauges;
maintained when water begins to pass through federal, state, and local sources; and video
as it crests the bottom of the opening frame.) documentation of past flood events.
• The minimum dimension of an opening in
a wall must not be less than 3 inches in any
direction in the plane of the wall.
• Reliable data on the rates of rise and fall at specific locations are usually not readily available.
Therefore, engineered openings must be designed and must function based on the assumption that
the minimum rate of rise and fall will be 5 feet per hour. Reinforcing the importance of testing for
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 35
faster rates of rise and fall, building designers must increase the specified total net area of engineered
openings when site-specific data or analyses of anticipated flood conditions indicate that more rapid
rates of rise and fall are likely.
9.3.2 Documentation of Engineered Openings for Compliance
Engineered openings should be accepted by local
officials when the designs are certified and the I-CODES REQUIRE
certifications are submitted as part of permit DESIGN STATEMENTS
applications. Acceptable documentation of certification The IBC and IRC require that construction
are the certification reports (i.e., ICC-ES Evaluation documents submitted for building
Reports or equivalent reports from other product permits include design statements by
certification organizations) and individual certifications registered design professionals when
for specific buildings (see Section 9.3.4). applicants propose using engineered
Copies of the certifications must be kept in the openings. ICC-ES Evaluation Reports and
community's permanent permit files. Community equivalent certification reports satisfy this
retention of these documents is important not only requirement.
to demonstrate compliance but also in the event that Individual certifications prepared for
future building owners do not receive copies of the specific buildings also satisfy the
certifications when they buy buildings. Owners must requirement for design statements.
submit certifications with applications for NFIP flood
insurance policies.
9.3.3 Engineered Openings with Certification Reports
The ICC-ES and other product certification organizations develop criteria for acceptance of a variety of
building products, construction methods, and materials. Each organization issues certification reports
after technical evaluation of documentation that is submitted by manufacturers. Documentation typically
includes technical design reports, certifications,
and testing results to demonstrate performance and
compliance with codes and standards. Certification SITE-SPECIFIC APPLICABILITY
reports provide evidence that products comply with OF ENGINEERED OPENINGS
specific building codes and standards. Designers, When an engineered opening product
builders, and local officials who rely on these reports with a certification report issued by
must determine whether the reports identify the editions ICC-ES or an equivalent product
of the building codes and ASCE 24 that are applicable certification organization is specified in
to individual projects. If applicable editions of the codes construction documents, the engineer,
and standard are not identified, the certification report architect, or builder should determine
should not be used. whether the product, given its limitations
and conditions of use, is appropriate
Documentation submitted by manufacturers to obtain for the conditions of flooding the site,
an ICC-ES Evaluation Report or equivalent certification especially the rate of rise and fall of
report for engineered openings must be supported floodwater. Designers should consult
by certifications describing the performance of the with local officials regarding observations
openings and the name, title, address, type of license, of past rates of rise and fall during
license number,the state in which the license was issued, conditions of flooding.
and the signature and seal of the certifying registered
36 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
design professional. The certification reports must include a description of installation requirements or
limitations that,if not followed,would void the certification.FEMA considers the following documentation
important:
• Statement certifying that the openings,when properly installed, are designed to automatically
equalize hydrostatic flood loads on exterior walls by allowing the automatic entry and exit of
floodwater in accordance with the design and performance requirements in ASCE 24.
• Statement certifying that the performance accounts for the presence of louvers, blades, screens,
grilles, faceplates, or devices with consideration of the potential for debris blockage when these
features are present.
• Description of the measurement of the actual net area of the engineered opening that is being
certified and identification of the opening coefficient of discharge,which is the variable c in the
formula in ASCE 24 (see Figure 25 and Table 3 of this Technical Bulletin). The coefficient of
discharge is selected by the designer based on the shape and dimensions of the opening and whether
the engineered opening has features such as louvers, blades, screens, grilles,faceplates, or devices that
partially obstruct flow during conditions of flooding.
• The range of flood characteristics tested for which the certification is valid, specifically the rates of
rise and fall of floodwater,which is the variable R in the formula in ASCE 24 (see Figure 25),and
whether there are any limitations based on rates of rise and fall that are faster than 5 feet per hour.
Given the ASCE 24 performance expectations, engineered openings must function during conditions
of the minimum 5 feet per hour rate of rise and fall.
9.3.4 Engineered Openings Individually Certified for Specific Buildings
Engineered openings that do not have ICC-ES Evaluation Reports or equivalent certification reports must
be individually certified as meeting the design requirements described in Section 9.3.1 of this Technical
Bulletin and for acceptability in specific buildings based on site-specific conditions. The formula in
Section 9.3.1 includes the variable R, which is the worst-case rate of rise and fall at a specific location.
ASCE 24 allows the assumption of a minimum rate of rise and fall of 5 feet per hour only in the absence
of reliable data on site-specific rates of rise and fall. Building designers who specify engineered openings
that are individually certified should consult local officials regarding observations of past rates of rise and
fall during conditions of flooding.
Generic certifications for manufactured products
place the burden on users (who may not be design INDIVIDUAL CERTIFICATION
professionals) to determine whether a specific FOR SPECIFIC BUILDINGS MUST
location is subject to rates of rise and fall greater ADDRESS SEVERAL FACTORS
than 5 feet per hour. For this reason, generic "fill-in- Section C2.7.2.2 of the ASCE 24
the-blank" certifications are not acceptable when a commentary indicates that "certification
manufactured product is used for a specific building requires more than simply applying the
unless the builder or design professional for that equation ... it requires consideration of a
building, or the local official, determines that the number of factors that represent expected
rates of rise and fall at the specific location are no base flood conditions." The commentary
faster than 5 feet per hour. Alternatively, the builder also notes that engineered openings should
be tested unless uniquely designed for a
or design professional may submit documentation specific location.
that there are no reliable data for site-specific rates of
----------------------------------------------------------------------------
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 37
rise and fall, in which case the local official may concur that the rates may be assumed to be no faster
than 5 feet per hour.
When engineered openings that have been individually certified for specific buildings are used,the permit
application must include a certification that is signed and sealed by the registered design professional,
who must be licensed to practice in the state in which the building is located. In addition, the submitted
plans must identify the location for the openings and specify installation instructions.
The original certification for engineered openings prepared for specific buildings must include the
design professional's name, title, address, signature, type of license, license number, the state in which
the license was issued, and the signature and applied seal of the certifying registered design professional.
The original certification must identify the physical location of the building in which the engineered
openings will be installed.
This Technical Bulletin relies on the ASCE 24 requirements for engineered openings as the accepted
standard of practice. The certification must include a description of installation requirements or
limitations that, if not followed, will void the certification. In addition to the design and certification
criteria listed in Section 9.3.1, the certification must include the following:
• Statement certifying that the openings,when properly installed, are designed to automatically
equalize hydrostatic flood loads on exterior walls by allowing the automatic entry and exit of
floodwater in accordance with the design and performance requirements in ASCE 24.
• Statement certifying that the performance accounts for the presence of louvers, blades, screens,
grilles, faceplates, or devices with consideration of the potential for debris blockage when these
features are present.
• Description of the measurement of the actual net area of the engineered opening and identification
of the opening coefficient of discharge,which is the variable c in the formula in ASCE 24 (see
Figure 25 and Table 3 of this Technical Bulletin). The coefficient of discharge is selected by the
designer based on the shape and dimensions of the opening and whether the engineered opening
has features such as louvers, blades, covers, screens, grilles, faceplates, or other elements that partially
obstruct flow during conditions of flooding.
• Determination of the rate of rise and fall of floodwater at the site and a statement certifying that the
openings are designed for that rate of rise and fall or a statement that the opening is designed for a
minimum rate of rise and fall of 5 feet per hour because reliable data on site-specific rates of rise and
fall are not available.
38 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
9.3.5 NFIP Elevation Certificate and Documentation of Engineered Openings
for Flood Insurance
When engineered openings are used, the NFIP Elevation Certificate must be completed carefully. The
question "Engineered flood openings?" must be answered with "Yes" (see A8.d and A9.d in Figure 26).
The engineered opening documentation must be attached to the NFIP Elevation Certificate. Insurers
and insurance agents must ask property owners to provide the documentation as part of applications for
NFIP flood insurance policies. The following are acceptable forms of documentation:
• For engineered openings with ICC-ES Evaluation
Reports or equivalent reports from other product NFIP ELEVATION CERTIFICATES
certification organizations, a copy of the report AND NON-ENGINEERED OPENINGS
that identifies the manufacturer's model number When non-engineered openings are
and specifies the number of such openings that used, the total net open area of the
are required for a specified square footage of openings that are within 1.0 foot above
enclosed area the higher of the exterior or interior
• For engineered openings individually certified for grade or floor should be determined by
installation in a specific building, a certification measurement (see examples in
that is signed and sealed by a registered design Section 9.2) or by using the
professional who is licensed in the state where the manufacturers specifications.
building is located, and that addresses the statements
described in Section 9.3.4
To complete the NFIP Elevation Certificate with information required for proper rating of NFIP flood
insurance policies for buildings with engineered openings, Item A8.c, "Total net area of flood openings in
A8.b," must be filled in with the total coverage or rated area of engineered openings. The total coverage
or rated area is the number of engineered openings identified in Item A8.b multiplied by the "coverage"
area, "rated" area, or "enclosed area coverage" identified in the ICC-ES Evaluation Report, equivalent
report, or individual certifications. When engineered openings are used in attached garages, Item A9.c
must be completed in the same manner. The coverage or rated area usually is given in square feet of
enclosed area for which an engineered opening can provide automatic inflow and outflow of floodwater,
which is,in effect, equivalent to the performance that would be provided by that number of square inches
of non-engineered openings.
Also, in Section D, "Check here if attachments" must be selected, and a copy of the certification
report must be attached to the NFIP Elevation Certificate (see Figure 26). Notes must be added in the
Section D comment section to identify the manufacturer and the manufacturer's model number of the
engineered opening.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 39
A8. For a building with a crawlspace or enclosure(s):
a) Square footage of crawlspace or enclosure(s) 1,6757 sq ft
b) Number of permanent flood openings in t L
( within 1.0 foot above adjacent grade
c) Total net area of flood openings in A8.b $ n
Insert coverage/rated area times number
d) Engineered flood openings? ®Yes No
of engineering openings in A8.b and A9.b.
A9.For a building with an attached garage: Add comments to identify engineering
a) Square footage of attached garage 35-0Oithin
openings and attach copy of Evaluation
Report or certification
b) Number of permanent flood openings in the
c) Total net area of flood openings in A9.b 40
d) Engineered flood openings? ®Yes ❑ No
Comments(including type of equipment and location,per C2(e),if applicable)
As and Aq — Engineered openings maviufactured by
XXX Company, Inc., mode( number XX-XXX,
1CC-ES Report No. XXXX (attached). Rated
200 sq in per unrt.
FEMA Form 086-0-33(7/15) Replaces all previous editions. Form Page 1 of 6
Figure 26: Completing the NFIP Elevation Certificate when engineered openings are used
40 NFIP TECHNICAL BULLETIN 1 MARCH 2O20
10 References
This section lists the references cited in this Technical Bulletin. Additional resources related to NFIP
requirements are provided in Technical Bulletin 0.
ASCE/SEI. 2014.ASCE/SEI 24-14,Flood Resistant Design and Construction.Available at
https://www.asce.org/.
FEMA (Federal Emergency Management Agency).Various NFIP Technical Bulletins. Current editions
are available at https://www.fema.gov/nfip-technical-bulletins:
• Technical Bulletin 0, Users Guide to Technical Bulletins.
• Technical Bulletin 2,Flood Damage-Resistant Materials Requirements.
• Technical Bulletin 3, Non-Residential Floodproofing—Requirements and Certification.
• Technical Bulletin 7, Wet Floodproofing Requirements for Certain Buildings Located in Special
Flood Hazard Areas.
• Technical Bulletin 9, Design and Construction Guidance for Breakaway Walls.
• Technical Bulletin 11, Crawlspace Construction for Buildings Located in Special Flood Hazard
Areas:National Flood Insurance Program Interim Guidance.
FEMA. 2004. FEMA 467-1,Floodplain Management Bulletin:Elevation Certificate.Available at
htti2s://www.fema.gov/media-library/assets/documents/3539.
FEMA. 2010. FEMA P-758, Substantial Improvement/Substantial Damage Desk Reference.Available at
htti2s://www.fema.gov/media-library/assets/documents/18562.
FEMA. 2013.FEMA P-936,Floodproofing Non-Residential Buildings.Available at http://www.fema.gov/
media-library/as sets/documents/3 42 70.
FEMA. 2015. FEMA Form 086-0-33,NFIP Elevation Certificate and Instructions.Available at http://www.
fema.gov/media-library/as sets/documents/160.
FEMA. 2018. FEMA 213,Answers to Questions About Substantially Damaged Improved/Damaged Buildings.
Available at https://www.fema.gov/media-library/assets/documents/169099.
FEMA. 2019. NFIPFlood Insurance Manual.Available at https://www.fema.gov/flood-insurance-manual
ICC (International Code Council). International Codes.Available at https://codes.iccsafe.org/
category/I-Codes.
• 2012 International Building Code
• 2012 International Residential Code
• 2015 International Building Code
• 2015 International Residential Code
• 2018 International Building Code
• 2018 International Residential Code
NFPA (National Fire Protection Association). 2017. NFPA 225, Model Manufactured Home Installation
Standard.Available at www.nfpa.org.
NFIP TECHNICAL BULLETIN 1 MARCH 2O20 41