Item H09BOARD OF COUNTY COMMISSIONERS
AGENDA ITEM SUMMARY
Meeting Date: September 16, 2015 Department: Building
Bulk Item: Yes X No Staff Contact Person/Phone #: Christine Hurley, 289-2517
Ed Koconis 453-8727
AGENDA ITEM WORDING: Approval of a resolution of the Monroe County Board of County
Commissioners adopting FEMA Technical Bulletin 8 "Corrosion Protection for Metal Connectors in
Coastal Areas" dated. August 1996 as required pursuant to Monroe County Cade Section 122-2(c).
ITEM BACKGROUND: Chapter 122 of the Monroe County Code "Floodplain Management"
includes rules for interpreting flood hazard issues. The building official shall be guided by the current
edition of FEMA's 44 CFR, and FEMA's interpretive letters, policy statements and technical bulletins
as adopted from time to time by the board of county commissioners. FEMA's Technical Bulletins
("bulletins") provide guidance concerning the building performance standards of the National Flood
Insurance Program (NFIP), which are contained in Title 44 of the U.S. Code of Federal Regulations.
The bulletins are intended for use primarily by State and local officials responsible for interpreting and
enforcing NFIP regulations and by members of the development community, such as design
professionals and builders. New bulletins, as well as updates to existing bulletins, are issued
periodically as needed. The bulletins do not create regulations; rather they provide specific guidance
for complying with the minimum requirements of existing NFIP regulations. Adopting these
documents as well as internal County policies would serve to allow the County to not only remain in
the NFIP as stated in Section 122-1(b), but also to move forward with the intent of becoming eligible
to enter FEMA's Community .Rating System (CRS). The proposed resolution would adopt FEMA
Technical Bulletin 8 "Corrosion Protection for Metal Connectors in Coastal Areas" dated August 1996
as required pursuant to Monroe County Code Section 122-2(c).
PREVIOUS RELEVANT BOCC ACTION:
January 18, 1994 — BOCC approved Ordinance No. 002-1994 adding the language "as adopted by
resolution from time to time by the Board of County Commissioners" to the rules for interpreting flood
hazard issues.
July 15, 2015 — BOCC rejected proposed ordinance amending Section 122-2(c) and directed staff to
continue proposing resolutions for adoption of both new and amended documents to be used by the
building official for guidance on floodplain management.
STAFF ECOMMENDATION: Approval
COST:TOTAL s BUDGETED:
DIFFERENTIALPREFERENCE: N/A
COST TO COUNTY: N/A SOURCE OF FUNDS: N/A
REVENUE PRODUCING: Yes No N/A AMOUNT PER MONTH N/A Year
APPROVED BY: County Atty X OMB/Purchasing Risk Management
DOCUMENTATION: Included X Not Required
DISPOSITION: AGENI
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i ". i-. COUNTY,i 1
MONROE COUNTYBOARD OF 1 COMMISSIONERS
RESOLUTION i,
RESOLUTION OF •i BOARD OF
COUNTYi iNERS ADOPTING FEMA TECHNICAL
CULLETIN 8 "CORROSION PROTECTION i i' METAL
CONNECTORS IN COASTAL AREAS" DATED AUGUST 1996 AS
REQUIRED TO MONROE COUNTY1
SECTION 122-2(C)
WHEREAS, Monroe County is currently a participating community in the National
Flood Insurance Program (NFIP) and is working on internal County policies to improve upon its
interpretation ofNFIP regulations; and
WHEREAS, Monroe County desires to become eligible to enter FEMA's Community
Rating System (CRS); and
WHEREAS, Monroe County Code Section 122-2(c), in part, requires that in interpreting
other provisions of this chapter, the building official shall be guided by the current edition of
FEMA's 44 CFR, and FEMA's interpretive letters, policy statements and technical bulletins as
adopted by resolution from time to time by the board of county commissioners;
NOW, THEREFORE, BE IT RESOLVED BY THE BOARD OF COUNTY
COMMISSIONERS OF i iCOUNTY,i• 1
Section 1. Pursuant to Monroe County Code Section 122-2(c), the Board hereby adopts
FEMA Technical Bulletin 8 "Corrosion Protection for Metal Connectors in Coastal Areas" dated
August 1996, a copy of which is attached hereto.
Section 2. The Clerk of the Board is hereby directed to forward one (1) certified copy of
this Resolution to the Building Department.
PASSED AND ADOPTED by the Board of County Commissioners of Monroe County,
Florida, at a regular meeting held on the 16`h of September, 2015.
Mayor Danny L. Kolhage
Mayor pro tem Heather Carruthers
Commissioner Sylvia Murphy
Commissioner George Neugent
Commissioner David Rice
Ili'!! ! •
i
(SEAL)
ATTEST: AM`t' HEAVILIN, CLERK
Deputy Clerk
Mayor Danny L. Kolhage
A FORki
VENT. WI I. .
ate 21
Om
ethnical
ulletin
Corrosion Protection for Metal Connectors in Coastal Areas
for Structures Located in Special Flood Hazard Areas
in accordance with the
National Flood Insurance Program
21
- — --- -----
FEDERAL EMERGENCY MANAGEMENTAGENCY FIA-TB-8
MITIGATION Directorate (8196)
11 .
This index allows the user to locate key words and subjects in this Technical Bulletin.
The Technical Bulletin User's Guide (printed separately) provides references to key
words and subjects throughout the Technical Bulletins. For definitions of selected terms,
refer to the Glossary at the end of this bulletin.
Key WordiSubject Page
Corrosion, classes of building exposure to 5
Corrosion, causes of 3
Corrosion, planning for 7
Corrosion, identifying high -risk buildings 5
Corrosion -resistant materials for sheetmetal connectors 6,7,9
Galvanizing 2
Salt spray from breaking waves 3
An.y com7nents on the Technical Bulletins should be directed to:
FFMA / Mitigation Directorate
Program Develorment Branch
500 C Street, SW.
Washington, DC 20472
Graphic wave design on cover based on the Japanese print The Great Wave Off Kanagawa, by Katsushika Hokusi
(1760-1849), Asiatic Collection. Museum of Fine Arts, Boston.
En
M
on
NW-- Corrosion Protection for Metal Connectors in Coastal Are,-M
An important objective of the National Flood Insurance Program (NFIP) is to protect buildings
from the effects of hurricanes, The NFIP regulations include requirements concerning the
resistance of buildings to flood and wind forces (as described in the following section). For a
building in a Coastal High Hazard Area to comply with these requirements, many of its
components must be adequately anchored. In wood -frame buildings, the necessary anchoring is
usually achieved through the use of metal connectors such as joist hangers, truss plates, and
hurricane straps. The need for such connectors is especially great in coastal areas, where storm -
induced flooding and high winds pose significant threats. However, metal connectors are subject
to corrosion when exposed to moisture and salt, both of which are prevalent in coastal areas.
This bulletin describes the causes of accelerated corrosion of metal connectors in buildings
located near the ocean and some larger saltwater bays. The variation in the corrosive
environments within a typical building is also described. This bulletin outlines available
corrosion -resistant materials and methods of maintaining proper anchorage for the life of the
building. It recommends connector materials for buildings at various distances from the ocean
and for different exposure conditions within an individual building. Few local building codes and
no national building codes address accelerated corrosion near the coast. This bulletin describes
areas where corrosion is known to be a problem and recommends a variety of solutions.
1UM277=
Section 60.3(a)(3) of the NFIP regulations states that the community shall:
"Review all permit applications to determine whether proposed building sites will be
reasot?ably ,,,vafe.fi-onifleroditig. IJ'a proposed building site is in, aflood-prone area, all
new, construction and substantial improvernentsshall (i) be designed (or tri.odifted) and
adequatel, anchored to preventflotation, collapse, or lateral movement Qfthe
structure... "
And Section 60.3(e)(4) states that the community shall:
"Provide that new construction and substantival improvements in ... (the coastal high
hazard area) —are elevated on pilings and columns so that...(ii) the pile or colunm
,foundation and structure attached thereto is anchored to resist flotation, collapse and
lateral movement due, to the feats of'wind and water loads acting simultaneousl ' y on all
buildingcomponents. Water loading values shall be those associated with the base flood.
Wind loading values used shall be those required bY applicable State or local building
standards, A registered pr(afessional engineer or architect shall develop or review the
structural design specifications and playas for the construction, and shall certifv that the
design and methods of construction to be used are in accordance with accepted standards
o f Para graphs— (it) ofis section
.
.fpracticefior meeting the provisions o
When buildings are damaged by natural hazards
such as high wind, waves, flooding, and
earthquakes. the structural damage usually does
not start with a wood board breaking. The weak
link is normally the connection between
individual wooden members, and it is here that
structural failure often begins. In many cases,
replacing conventional nailing with a sheetmetal
connector produces a connection over 10 times
stronger, Hurricanes and earthquakes have
demonstrated repeatedly that for most buildings,
good connections often make the difference
between survival and severe damage.
Double
Double
Floor Band
jots[
I-Lulger
Do I I
joist
Joist
Hanger
Figure 2. Single and double joisr hangers
Figure 1, Wind anchor and truss plate
Typical metal connectors that are potentially
subject to corrosion include hurricane straps
and wind anchors used to connect roofs to
walls (see Figure 1)% truss plates that connect
the separate members of premanufactured
roof and floor systems (see Figure 1); joist
hangers used on floor joists, beams, and
rafters (see Figure 2); and various other metal
straps used to connect wood components
throughout the building. These include straps
that attach the roof to the walls and prevent
the aerodynamic lift of high winds from
removing the roof or displacement caused by
lateral forces during earthquakes.
Most connectors are fabricated from steel sheetmetal. In thin sheets, steel is sufficiently strong,
readily workable, and relatively inexpensive, characteristics that make it well -suited for
connectors, However, bare steel is subject to corrosion, or rusting, even in inland areas, and it
corrodes rapidly in salt air. Most sheetmetal connectors, therefore, are galvanized for corrosion
protection. Galvanizing is the process of coating steel with zinc. After careful cleaning, the steel
sheet is dipped into a vat of molten zinc. The high temperature melts the surface of the steel and
forms several steel/zinc alloys to tightly bond the zinc coating to the steel base metal. The
coating ofzinc still corrodes. but generally over 50 times more slowly than steel in the same salt
an- environment.
Galvanizing is particularly effective for steel because, unlike most other coatings, the zinc
sacrificially protects any bare steel edges or scratches. The zinc surface near a scratch will
corrode ,slightly faster than the zinc surrounding it and will fill small scratches with zinc
Pon
corrosion products, preventing the steel from rusting until the nearby zinc is consumed. Zinc also
differs from other coatings (or paints) and most metals by corroding at a relatively steady rate in
most atmospheric exposures. Therefore, doubling the thickness of the zinc coating approximately
doubles the protection period.
Most connectors are fabricated after the steel sheetmetal has been galvanized, The American
Society for Testing and Materials (ASTM) has established national standards for galvanizing that
are accepted by the Standard (Southern Building Code Congress International), National
(Building Officials & Code Administrators International), Uniform (International Conference of
Building Officials), and most local building codes. Most connector manufacturers specify ASTM.
A-525 G 60 for the galvanized steel sheetmetal from which connectors are fabricated. ASTM A-
525 is a general standard that establishes a variety of galvanizing thicknesses identified by
different G number-,. The G 60 designation used for most connectors indicates a zinc coating
thickness of 0.5 mil (I mil = 0.001 inch) on each side of the steel, The numerical G designation
increases or decreases proportionally with the coating thickness. For example, the coating of zinc
on a G 90 connector is 1.5 times thicker than that on a G 60 connector.
The conditions that accelerate corrosion near the coast have been studied in a few corrosion field
stations and research laboratories around the world. Several of these conditions occur along most
shorelines. Understanding the causes of accelerated corrosion can help identify some of the worst
corrosion exposures that affect coastal buildings.
Al� Salt Spray from Breaking Waves and Onshore Winds
Salt spray from breaking waves and onshore winds significantly accelerates the corrosion of
metal connectors. The ocean salts, which are primarily sodium chloride but include other
compounds, accumulate on the metal surfaces and accelerate the electrochemical react -Ions that
cause rusting and other forms of corrosion. The combination of salt accumulation on the surface
and the high humidity common to many coastal areas significantly accelerates the corrosion race
of steel and other metals commonly used for connectors or other building materials, The longer a
surface remains damp during normal daily fluctuations in humidity, the higher the corrosion rate.
Onshore winds carry both salt and moisture inland. Therefore, corrosion rates along shorelines
with predominately onshore winds will be higher than those along shorelines with predominately
offshore winds.
Corrosion rates vary considerably from community to community. But the amount of salt spray
in the air is greatest near the breaking waves and can decline rapidly in the first 300 to 3000 feet
(roughly 100 to 1000 meters) landward of the shoreline. Farther landward, corrosion is akin to
that which occurs in milder, inland conditions. The width of the high -corrosion zone must be
determined in each community, but oceanfront buildings will always be more severely affected
than buildings farther inland.
One series of tests in North Carolina in the 1940s found that sarnples of iron corroded 10 times
faster at 80 feet ( 25 meters) landward of the shoreline than samples of the same type at 800 feet
(250 meters) landward of the shoreline (Lague, 1975, see #6 in the section titled "Further
Information"). Similar results have been noted around the world, Where waves break, salt is
tossed into the air and the wind tends to distribute the salt spray to inland areas.
Corrosion Rate
Variation with Elevation
35
-
800 Ft,] 80 Ft.
30-
from from
Ocean Ocean
25
peak
10
Corrosion
Rate
15
to-
P11
5-
0
0 to 20 30
Corrosion Rate (mils/yr)
A
Other tests conducted in North Carolina found
that corrosion reached a peak at about 12 feet
(3.6 meters) above the ground (see Figure, 3),
approximately equal to the lowest floor
elevation of an elevated buildinc, with lower
level parking. Several rows of buildings
farther inland, the overall corrosion rate is
lower, but it is highest at an elevation above
the roofs of small buildings. Figure 3 also
indicates that the worst corrosion nearest the
ocean was more than double the worst farther
inland.
Figure 3, The variazion in the corrosion rate of steel Bold exposures such as building exteriors are
with eles,,arionjbr Kure Beach, NC coated with large amounts of salt spray and
can be expected to suffer high corrosion rates. But partially sheltered exposures, such as
underneath open, piling -supported buildings or underneath decks and walkways, can sustain
even worse corrosion than bold exposures. I'he results of other exposure tests from near the
ocean in Kure Beach are shown in Figure 4 (LaQue, 1975). Steel samples were weighed, then
exposed under a wooden roof. After 2 years, rust and other corrosion products were stripped
from the samples, and the samples were weighed again to measure the weight loss.
'The study reported that salt spray accumulations on bold exposures are rinsed periodically by
rainfall tPositious 4 and 5), reducing the surface salt concentrations. Sheltered exposures receive
little salt spray (Position 1). Partially sheltered exposures (Positions 2 and 3) receive almost as
much incoming spray as bold exposures. However, the surface concentrations remain high,
400
0
North
Ea:t South West
(ocean)
Shelter
Test
Roof
Plate Position # IQ
t
� 3
Figure 4. The effec! ofsheher and orientation under rhe rest roof shown on the right
4
4
5
because of the shelter from cleansing rain. An additional factor is the duration of surface
wetness. Accelerated corrosion occurs primarily when a certain level of surface wetness is
exceeded, initiating electrochemical reactions among the metal, salts, and air. Bold exposures are
more rapidly dried because they are exposed to sunlight. Drying slows the corrosion rate.
Partially sheltered exposures stay damp longer and therefore corrode faster. The effect of
building orientation on corrosion is also shown in Figure 4. The metals on the side of a building
facing the ocean will corrode Much faster than those facing away from the ocean.
C�
Weather affects the rate of corrosion in all exposures, both coastal and inland. Most chemical
reactions, including corrosion rates, are affected by temperature, humidity, wind speed, and other
factors. Like any weather -driven condition, the corrosion rate can vary considerably from year to
year. Average conditions for factors like rainfall seldom occur. The measured rainfall is often
either much higher or much lower than the average. Average years seldom occur. Likewise, the
annual corrosion rate in any individual year will be significantly higher or lower than the long-
term average. Therefore, annual measurements of corrosion can be very misleading unless
compared to long-term averages for nearby locations.
In a few communities, corrosion test facilities can predict the distance from the shoreline at
which corrosion will be most severe. Unfortunately, in most communities, corrosion data will not
be available. Estimates of the width of the zone where corrosion -resistant materials and methods
are necessary should be based on local experience. Metal connectors should be observed in older
buildings at various distances from the shoreline. If oceanfront buildings are experiencing severe
corrosion problems in less than 10 years, then the second or third row buildings will experience
severe corrosion over a typical useful lifetime of 50 to 70 years.
2=7
Corrosion exposures for metal connectors in most buildings can be grouped into five classes,
four of which are shown in Figure 5. The five
classes are listed below in order of decreasing
corrosion severity.
Eaqi j1_v !iheltffed exterior eXDOSures.
Examples include open, underhouse storage and
parking areas below a piling-, column-, or post -
supported building and areas underneath roof
overhangs, decks, and walkways. Corrosion can
significantly weaken standard shectrnetal
connectors after 5 to 10 years in these exposures
on oceanfront buildings.
Boldly exposed exterior exposures. Examples
include exterior walls with the connector fully
exposed, If the exposed connector is fully dried
Unvented
Enclosed
Exposure
(wall cavtty)
_. Vented
Enclosed
Exposure
Boldly Exposed
Exterior E or xposure
SSheliered
Partially
Exterior
Exposure
Fa ure 5. The locations trf various clu.;.Yes of
corrosion
between wettings by the ocean spray, the corrosion rate will be lower than that in partially
sheltered exterior exposures. Otherwise, the corrosion rate can match that in partially sheltered
exterior exposures. I-
V S.nted enclosed ex osures. Attics„ which must be vented to release excess heat and moisture,
are typical examples of this type of exposure. Corrosion will vary with the location of the
connector in the enclosed space. Corrosion rates for connectors near exterior vents, where
outside airflow is concentrated, are often similar to those for connectors in partially sheltered
exterior exposures. For connectors that are away from the vents or covered by insulation, the
corrosion rate is expected to be much lower.
Lnven Led enclosed e oures. Examples include enclosed floor systems with solid joists or
_xp_
trusses, Because of the limited airflow and incoming salt spray, corrosion rates for connectors in
these exposures are expected to be lower than those for connectors in the previous three
exposures.
Interior livings pace ex sur -. These spaces are sealed from most salt spray, and normal
heating and cooling further reduce interior humidity below the threshold needed for rapid
C-1
corrosion. Connectors in these spaces should have the lowest corrosion rates.
Irriproved corrosion resistance can be obtained by fabricating connectors from more resistant
C�
sheetmetal or by treating standard connectors after they have been fabricated. The relative
improvement in corrosion resistance for different options is estimated in this section. Better
materials can sometimes mean higher cost. Typical cost differences for the alternative materials
are also estirriated in this section.
Thicker Galvanizing
There are two methods of producing thicker galvanizing on connectors: 1) fabricating connectors
frorn steel sheet with thicker initial galvanizing, or 2) regalvanizing standard connectors after
fabrication. Galvanized sheet steel is available in a variety of coating thicknesses, Several
Zn
nian u facture rs now market standard connectors in various designs fabricated from G 180 or G
2100 grades of galvanized steel, which, compared to the, standard G 60 connector, have zinc
coatings that are 3 or 3.3 times thicker, respectively. Since the corrosion resistance of zinc is
proportional to the thickness of the zinc, these connectors should last approximately 3 or, 3.3
times longer, respectively, than standard connectors. Advertised costs for connectors with thicker
galvanizing have been known to range from 13 to 1.7 times the cost of standard connectors.
Thicker galvanizing can also be obtained by hot -dipping standard connectors after fabrication.
9 L7
The manufacturer usually sends the connectors to an outside galvanizing company for dipping.
Several variables can affect the thickness of' the galvanizing, but the result is typically a coating
Zl>
of zinc four times thicker than that on a standard G 60 connector. A few types of these connectors
are regularly available. Other connector designs are available by special order. The cost estimate
1'(--lr SheeLmetal connectors hot -dipped after fabrication has been known to be roughly 1.75 times
the cost of standard G 60 grade connectors.
0
Stainless Steel
1%W Several connector manufacturers also produce a variety of the most commonly used connectors
in stainless steel. Stainless steel is very resistant to corrosion in salt air and should last longer in
a wood -frame building than most other materials, even in the most corrosive oceanfront
situation. For extended lifetimes, stainless connectors must be attached with stainless steel nails
when separate fasteners are needed. Stainless steel sheetmetal is a more costly raw material than
the sheetmetal used to make galvanized connectors. It is also harder; therefore, stainless steel
connectors are more difficult to fabricate. The cost of a stainless steel connector, including the
cost of the necessary stainless steel nails, can be 6 to 15 times the cost of the same connector in
G 60 grade galvanized steel,
C�
Paint Coatings
Painting standard galvanized steel connectors can significantly improve their corrosion
resistance. However many paints commonly used for buildings do not adhere well to galvanized
surfaces. The Truss Plate Institute (TPI) has considered the use of truss plates in corrosive
environments, like coastal buildings, The TPI design specifications, which are accepted by the
national model codes, recommend that one of three types of industrial paint systems be applied
by brush to embedded plates after delivery of the completed truss to the job site or after truss
installation (see TPI-85). The paints are specific formulations of (1) epoxy -po lyamide, () coal -
tar epoxy-polyanilde, and (3) zinc chromate vinyl butyrai primer with asphaltic mastic.
The increased corrosion resistance provided by the recommended paint coatings in coastal
buildings is difficult to estimate. Unlike changes in galvanizing thickness, changes in paint
thickness do not proportionally change the corrosion resistance. Paint lifetimes are significantly
affected by salt spray, but exposure conditions can affect paints and galvanizing differently.
Surface preparation and care In application are critical for improved corrosion resistance with
paints. The added cost of these coatings will vary with local labor costs. In general, other types
of paints should not he assumed to significantly improve the corrosion resistance of standard
connectors or truss plates. For other types of connectors, the alternatives described previously
are recommended over any type of painting. However, for maintenance, zinc -rich coatings of
paint may be better than nothing.
All construction materials deteriorate with time. The average useful lifetime of the Structural
components of a wood -frame building is approximately 70 years in the United States. Continued
use of a building requires that (a) the original materials be durable enough to last the expected
lifetime, (b) periodic maintenance be conducted to extend the life of original materials, or (c) the
material be replaced one or more times during the lifetime of the building.
Most connectors are intended for inland uses with mild corrosion and, under normal conditions,
appear to last as long as or longer than other materials in the building. Many buildings in
communities near the coast are likely to experience only slightly 'increased corrosion rates, and
standard connectors appear appropriate for those buildings. But close to the ocean, drastically
higher corrosion rates can be expected. The use of standard connectors in these areas may
necessitate care in controlling the exposure.
Otherwise, alternative materials should be used.
For some uses, corrosion can be partially
avoided by altering the exposure of the
connectors. For example, on exteriors, a
connector should be fully covered if possible or
otherwise protected from salt spray and
moisture. Exterior siding should be designed to
completely cover connectors. Applying siding
in this way changes the exposure from boldly
exposed to unvented enclosed, An easy, but
more costly, way to protect joist oist hangers and
truss plates in the floors of piling -supported
buildings is to sheath the underside of the floor
joists to reduce the exposure to salt air. Adding
such sheathing transforms one of the worst
L�
Nails Through
Bearns into
Floor
Wind Anchor
Joist
Floor Beams
(,-i k. ➢d e n
Wind Anchors
01
13,lisThrou h
Beams and Pile
Square Wood Pile
Fgure 6. Traditional ivooden ledger boards used in
place of joist Irangers in higir-corrosion areas
exposures, partially sheltered exterior, into a
less corrosive, unvented enclosed.
For some connections, corrosion may be
avoided by not using sheetmetal. Underneath
unsheathed floors and decks, the traditional use
of ledger boards avoids the need for joist
hangers in the worst corrosion exposures (see
Figure 6). The wooden wind anchors in Figure
7 attach piling -supported floor beams to floor
joists. Commonly used on the Texas coast,
these anchors proved effective during
Hurricane A] ic ia's 90- to I 00-mph winds in
t981
Figure 7 Woodept ivind anchors used to con t nec floor Maintenance and Replacement
joists to floor learns In some uses. connectors may be placed
where thev are accessible and maintainable, In milder exposures, applying a regular coat of
exterior house paint may be enough to extend the life, of the connector. But in severe exposures,
even annual painting is unlikely to prolong the life of a connector to that of the rest of the
building. In these exposures, accessible connectors may be inspected for corrosion and, if
C�
necessary, replaced. Galvanized sheeLmeLaI connectors should be replaced as soon as partial
surface rusting appears. The presence of more than thin rusty edges indicates that the zinc
coating has been consumed and the sacrificial effects have been lost. Corrosion of the thin, steel
sheet will occur quickly and will rapidly deteriorate the structural integrity of the connector.
When the option of'periodic replacement is evaluated, the cost over the lifetime of the building
0
should be considered. Corrosion -resistant connectors, available for a moderately higher price,
can have significantly Ionizer lifetimes than standard connectors, The cost of labor for initial
i nsLal lation is the sarne for both materials. The material and labor cost for even one replacement
cm
cm
el
is often greater than the added initial cost for corrosion -resistant materials. By using better
NW- materials initially, one can avoid the cost of two or three replacements of standard 'materials. In
the worst exposures, where standard connectors may have to be replaced as often as every 5
years. even the use of stainless steel connectors may prove less costly over the long run.
LOM
Given the low likelihood of regular inspection by most building owners and the brief expected
lifetime of standard connectors in the worst exposures, replacement is usually a poor option.
Furthermore, many connectors are hidden structural components that are difficult or impossible
to maintain or replace. In such cases, replacement is rarely an option and more corrosion -
resistant materials should be selected. Replacement may be the only option in existing buildings
where connectors have already been damaged by corrosion or were, never installed. In existing
buildings, adding roof connectors can significantly improve the wind resistance and is therefore
worthwhile, even if some dismantling is needed to gain access.
For manv connector applications in corrosion -prone buildings, the use of corrosion -resistant
C,
materials is the best solution for new construction.. The choice of alternative connector material
or coating specifications should be guided by the location of the building relative to the observed
corrosion hazards in each community and by the class of exposure in the building.
Recommended materials for a typical community are listed in Table 1,
Table 1 -Recommendations for Corrosion —Resistant Materials and
Methods*
Location
Oceanfront Buildings
Intermediate Rows of Buildings in
Buildings Farther
Carrosion-Prone Areas
Landward
Class of
(300 feet or less from the shorelinc)'"
(3Wto 3M0 feet front the
(Greater than
Exposure
3,(,)(.X) feet from
the shoreline)***
Parvally
I Avoid sheeirricial connectors where pawbic
Use connectors with thicker
Use connectors with
sheltered
2 L" ""nlcss ""' c"'necto"'
galvanizing.
standard galvanizing,
I Use connectors with thicker galvanizing and
(OptionaL staintess steel)
7OtnionaL thicker
exteriors
replace them when necessary.
gals'aDIZIng)
Boldly
l Avoid iheettnetaJ connevorswhere possible.
Use connector, with this galvanizing.
Use connector's with
exposed
2 Use stainless oecl conncc(ors�
;Opflorwl stainless steel)
standard gab; arnzing
.1, Use conneclors with thicker galvanizing and
4olaainal thicker
exteriors
replace them when necessary
galvanizing )
Vented
I Uic connectors with thicker galvartwing
I Use connvoors with thicker gatVMILZIng
Use Diane tars voLh
enciosures
(Opiionjl' stainless wel)
near vents
standard galvanizin g
2 Use TPI paints on truss pial"i
live TPI paints on Miss plates near vents
iOptionaj thicker'
for iniss plaE" Thicker galvanizing, TPI
fOratonal thicker galvainzing for all
galvanizing)
paints over this galvaWing. or stainless steel)
ccam( ciorsi
Unvented
I Use connecior.s\4,ithiiiiLkergai%,anizing
Use coninotom wrath clandard galvanizing,
Use connector with
enclosures
2, Use TPI paints on truss plates
i0pnonal mickergals anizing)
%iandard galvanizing
Optional for truss plaies thicker galvanizing)
tOpucinal thicker
galvanizing)
Interior
Use wrinecTors with Mandard galvanizing,
Use connectorr with standard galvanizing
Use Wnnecsori with
living space
(OpTiOnal thicker galvanizing
(C)ptional thicker galvanizing
Standard galvanizing
(Optional - thicker
aJv4mzing1t
Revonitnendnuons ate txtsed on ibe avwlahle reearch and are suhjeti to dunge in future Technical Buliriins
Soc Fi4wc 5 lot, curruimn ' Tasws.
w� m Drinceay ary dqnjing on lm-al cinnatt, Me xEdth of dW o"ar'j j7r't whu'e to C w"m 'lusiij N. dCi,,'n11inCd ") inO
imniwiirty rom h6d obs'!rvaklons 'Anci mlv mqlng sonxi%lor. 'ii;dies
In Table 1, building locations are categorized as oceanfront buildings, intermediate rows of
buildings in corrosion -prone areas, and buildings near the coast but far enough away from the
ocean that excessive corrosion is not anticipated. In most communities, connectors on
oceanfront buildings can be expected to corrode at high rates. Corrosion rates should approach
inland levels 300 to 3000 feet (roughly 100 to 1000 meters) landward of the ocean in most
communities. The types of connector exposures in a building are listed in Table I in order of
decreasing severity of location. Truss plate treatments are noted separately, based on TPI
recommendations for corrosive environments, Recommendations in the table are in some cases
based on limited research. When the severity of the exposure is unknown, selecting more
corrosion -resistant materials prudent. Optional materials for superior corrosion resistance are
also noted.
MM nmr"�=
This publication is one of a series of Technical Bulletins FEMA has produced to provide
guidance concerning the building performance standards of the NFIP. These standards are
contained in Title 44 of the U.S. Code of Federal Regulations at Section 60.3. The bulletins are
intended for use primarily by State and local officials responsible for interpreting and enforcing
NFIP regulations and by members of the development community, such as design professionals
and builders. New bulletins, as well as updates of existing bulletins, are issued periodically, as
necessary, The bulletins do not create regulations; rather they provide specific guidance for
c()rnply1ng with the minirnUm requirements of existing NFIP regulations. Users of the Technical
Bulletins who need additional guidance concerning NFIP regulatory requirements should
contact the Mitigation Division of the appropriate FEMA regional office, The User's Guide to
Technical Bulletins (FIA-TB-0) lists the bulletins issued to date and provides a key word/subject
index for the entire series.
Ordering Information
Copies of the Technical Bulletins can be obtained from the appropriate FEMA regional office.
Technical Bulletins can also be ordered from the FERIA publications warehouse. Use of FENIA
Form 60-8 will result in a more timely delivery from the warehouse. The form can be obtained
from FEMA regional offices and Your state's Office of Emergency Management. Send
publication requests to FENIA Publications, P.O. Box 2012, Jessup, MD 20794-2011
Further Information
1. Atmospheric Corrosion, edited by W. H. Ailor, John Wiley & Sons, 1982.
2. "Coastal Construction Manual," FEMA, 1986, FEMA-55,
3 Corrosion Engineering, by M. G. Fontana & N. D. Greene, McGraw-Hill, 1986.
4, Corrosion Prevention by Protective ,.CoaLin-g_s, by C, G. Munger, National Association of
Corrosion Engineers, 1984.
5. "Design Specification for Metal Plate Connected Wood Trusses," American National
Standards Institute, ANSI/TP1 1-95, Commentary and Appendix, 1995,
6. Nlar.ine Corrosion: Causes and Prevention, by F. R. Lague, John Wiley & Sons, 1975,
10
7, "Selected Specifications for Hot Dip Galvanizing," by the American Society for Testing and
N111-- Materials (ASTM), 1994, available from the American Galvanizers Association.
8. "Standard Specification for General Requirements for Steel Sheet, Zinc -Coated (Galvanized)
by the Hot -Dip Process." ASTM, 1987, ASTM A 525-90.
on
1�=
Base Flood — The flood that has a I -percent probability of being equaled or exceeded in any
given year (also referred to as the I} -year flood).
Base Flood Elevation (BFE) — The height of the base flood, usually in feet, in relation to the
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National Geodetic Vertical Datum of 1929 or other datum as specified,
Coastal -High Hazard Area — An area of special flood hazard extending from offshore to the
inland limit of a primary frontal dune along an open coast and any other area subject to high- C_
velocity wave action from storms or seismic sources. These areas are identified as V zones,
Federal Emergency Management Agency (FEMA) —The independent Federal agency that, in
addition to carrying out other activities, oversees the administration of the National Flood
Insurance Program.
Federal Insurance Administration (FIA) — The component of FEMA directly responsible for
administering the flood insurance aspects of the National Flood Insurance Program.
Flood Insurance Rate Map (FIRM) — The insurance and floodplain management map issued
by FEMA that identifies, on the basis of detailed or approximate analyses, areas of 100-year
flood hazard in a community.
Floodprone Area — Any land area susceptible to being inundated by floodwater frorn any
source.
Lowest Floor— The lowest floor of the lowest enclosed area of a structure, including a
basement. An unfinished or flood -resistant enclosure useable solely for parking of vehicles,
building access, or storage in an area other than a basement area is not considered a building's
lowest floor, as long as the enclosure is not built in such a way that It violates the non -elevation
design requirements of Section 60.3 of the National Flood Insurance Program regulations.
Mitigation Directorate — The component of FEMA directly responsible for administering the
floodplain management aspects of the National Flood Insurance Program and for carrying out
hazard mitigation activities related to flood and other disasters.
New Construction/Structure — For floodplain management purposes, new construction means
structures for which the start of construction commences on or after the effective date of a
floodplain management regulation adopted by a community and includes subsequent
improvements to the structure. These structures are often referred to as "Post -FIRM" structures.
Special Flood Hazard Area (SFHA) — Area delineated on a Flood Insurance Rate Map as
being subject to inundation by the base flood and designated Zone A, AE, A I -A30, AR, AO, AR
V, 'VE, or V I - V 30.
II
Substantial Damage — Damage of any origin sustained by a structure whereby the cost of
restoring the structure to its before -damaged condition would equal or exceed 50 percent of the
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market value of the structure before the damage occurred.
Substantial Improvement — Any reconstruction, rehabilitation, addition, or other improvement
of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure
before the "start of construction" of the improvement. This term includes structures that have
incurred "substantial damage," regardless of the actual repair work performed.
Eq
12
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