CAZ CRS Credit for Coastal A Zones

CRS Credit for Coastal A Zone Regulations
Background
Coastal FIRMs depict A Zones the same way as inland FIRMs do. There is no
designation for a ―Coastal A Zone‖. Likewise, NFIP regulations treat building standards
for A Zones in riverine and coastal areas the same.
The V Zone is known also as the Coastal High Hazard Area (CHHA), and extends from
offshore to an inland limit based on one or more mapping criteria. The mapping criteria
relate to high velocity wave action effects (e.g., the 3-foot breaking wave height, the 3foot wave runup depth, or a wave overtopping rate exceeding a threshold rate), and to
the physical presence of a primary frontal dune (PFD).

Coastal floodplain on a FIRM

The A Zone is that
portion of the SFHA
that is not subject to
high velocity wave
action during the base
flood and is not
designated as Zone V
due to primary frontal
dune considerations.
The source of flooding
in an A Zone can be a
stream or river that
overflows its banks; a
lake; or coastal storm
surge accompanied by
wave
heights
and
wave runup depths
less than 3 feet.

NFIP building standards in Coastal A Zones are identical to those in riverine A Zones. A
coastal building in an area subject to a 2.9 ft breaking wave height during the base flood
would be mapped today as an A Zone, and conformance with A Zone building
standards only would be required – despite the fact that breaking waves of that size are
capable of destroying or heavily damaging typical residential wood-frame walls which
could be used as foundation walls in an A Zone.
In recognition of the problem, CRS encourages local governments to adopt regulations
that require the foundation design in a Coastal A Zone comply with the more stringent
requirements applied to V Zones.

Coastal A Zone Regulations

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The ―Coastal A Zone‖
is a term that is used
to draw a distinction
between coastal and
inland A Zones, and to
highlight
similarities
between V Zones and
A Zones in coastal
areas. The rationale
for these efforts is
based on post-storm
field studies that have
shown flood hazards
in Coastal A Zones are
more like those in V
Zones than those in
riverine A Zones, and
that building damage
in Coastal A Zones is
consistent with those
observed in V Zones,
not riverine A Zones.

Post-storm field studies have shown that minimally
compliant A Zone foundations in Coastal A Zones
often fail. (Hurricane Fran)

Mapping the Coastal A Zone
Identifying the area of the Coastal A Zone is the first step toward regulating the hazard.
For purposes of CRS credit the Coastal A Zone is the area landward of a V Zone, or
landward of an open coast without mapped V Zones. In a coastal A Zone, the principal
source of flooding will be astronomical tides, storm surges, seiches or tsunamis, not
riverine flooding. During base flood conditions the potential for breaking wave heights
between 1.5 feet and 3.0 ft will exist.
Following Hurricane Katrina FEMA
prepared Recovery Maps for the
Mississippi coastline. The maps
included Advisory Base Flood
Elevations (ABFEs). One of the
ABFE lines represents the inland
limit of wave action where the wave
height is 1.5 feet. Katrina Recovery
Maps are for advisory purposes
only; they do not supersede
effective Flood Insurance Rate
Maps (FIRMs) for insurance rating
purposes. However, some local
governments
in
Mississippi
Coastal A Zone Regulations

Example of a Local Coastal A Zone Map

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designated Coastal A Zones and adopted V Zone standards for these areas.
While the Mississippi coastline is the only area where FEMA has mapped the inland
limit of the 1.5 foot wave so far, local governments in other states have identified
Coastal A Zone areas and adopted building regulations that traditionally applied only to
V Zone construction. Local governments looking to designate a Coastal A Zone should
make sure two conditions are met:
1) there should be a water depth sufficient to support waves between 1.5 and 3.0 feet
high, and
2) there should be an expectation that wave heights between 1.5 and 3.0 feet will occur
during the 1 percent chance storm.

Transect shows 1 percent annual chance stillwater elevation, stillwater
depth and ABFE, and inland limit of V zone and Coastal A zone.

Condition 1 requires stillwater depths (vertical distance between the 100-year stillwater
elevation and the ground elevation) of 2 to 4 feet at the site.
Condition 2 requires wave heights at the shoreline greater than 1.5 feet (under the 100year flood conditions), sufficient water depth between the shoreline and the building site
and few, if any obstructions (buildings, dense tree stands, etc.) that may block or
dampen the waves, between the shoreline and the site.
The figure to the right illustrates the relationships between the stillwater flood elevation,
ground elevations, the associated 1 percent annual chance (100-year) stillwater flood
depths, ABFEs, and associated flood hazard zones (For more information see
Hurricane Katrina Recovery Advisory Reconstruction Guidance Using Hurricane Katrina
Surge Inundation and ABFE Maps).

Coastal A Zone Regulations

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Communities, designers, and owners can obtain the information necessary to make a
Coastal A Zone determination by observing the site and its surroundings, knowing site
ground elevations, and using 1 percent annual chance stillwater elevations from the
Flood Insurance Study. Additionally, FEMA has recently advised its Regional Offices
that the landward limit of waves 1.5 feet in height (called the Limit of Moderate Wave
Action (LiMWA)) may be shown as an informational layer on the FIRM.
CRS Credit for Coastal A Zone Regulations
Coastal A Zone design and
construction practices described
herein are not mandated by the
NFIP, but are recommended for
communities that wish to adopt
higher floodplain management
standards. Community Rating
System (CRS) credits are
available for doing so. Note that
some Coastal A Zone practices
may be required by the
International
Building Code,
through its reference to ASCE
24-98.

Coastal A Zone Regulation

Foundation Design
Engineers Certification
Reference Elevation
Landward of Mean High Tide
Protect Dunes and Mangroves
Prohibit Enclosures
CAZ Total

Potential
Points
225
125
100
25
25
150
650

Up to 650 credit points are available for local governments that map Coastal A Zones
and regulate these areas based on V Zone building standards. The 650 credit points are
subject to an impact adjustment described on page 6. The credit points are allocated
based on the following schedule:
a. Foundation Design
Post-storm damage assessments have documented that slab-on-grade foundations
elevated over structural fill, various types of enclosed perimeter foundations, and
masonry pier foundations have been
Foundation Design - Up to 225 points prone to failure in Coastal A Zones. In
with all of the following requirements:
contrast, open foundations free of
obstruction and consisting of piles or
1. Buildings on pile or column
columns with adequate embedment to
foundations.
resist scour, have proven to be less prone
2. Foundation and structure attached to to failure.
resist wind and water loads
CRS credits Coastal A Zone regulations
3. Areas below the lowest floor are free
that prohibit the use of fill for structural
of obstruction.
support, require buildings located in
Coastal A Zones to be elevated on pilings
4. Use of fill for structural support is
or columns and require enclosures below
prohibited
the BFE to be free-of-obstruction.

Coastal A Zone Regulations

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b. Engineers Certification
The building design must be certified by a
licensed engineer or architect that it will
resist flotation, collapse, and lateral
movement resulting from combined wind
and hydrostatic loads.

Structural Design, Specifications
and Plans - 125 points
Engineer’s Certification of structural
designs and methods of construction.

c. Reference Elevation
In inland areas, experience has shown that floods damage areas of buildings not
elevated above the flood level and destroy the contents of those areas. In coastal areas,
wave action causes even more damage, often destroying enclosed building areas below
the flood level (and any building areas above the flood level that depend on the lower
area for structural support). Once waves rise above the lowest structural member in a V
Zone or Coastal A Zone, the elevated portion of the building is likely to be severely
damaged or destroyed.
The Community Rating System encourages local governments to adopt Coastal A Zone
regulations that require all newly constructed, substantially damaged, and substantially
improved buildings to be elevated on pilings, posts, piers, or columns so that the bottom
of the lowest horizontal structural member of the lowest floor (excluding the vertical
foundation members) is at or above the BFE.

The Community Rating System
provides 100 points of credit when
a local government uses the bottom
of the lowest horizontal member as
the elevation reference point within
its Coastal A Zone.
Lowest Horizontal Structural Member Used as
the Elevation Reference Point
in the Coastal A Zone

d. Location landward of mean high tide
The single most common and costly siting mistake made by designers, builders, and
owners is failing to consider future
erosion and slope stability when an
Local governments that require Coastal
existing coastal home is purchased or
A zone buildings along a shoreline to be
when land is purchased and a new
located landward of the reach of mean
home is built. Purchase decisions—or
high tide can receive up to 25 CRS
siting, design, and construction
credit points.
decisions — based on present-day
Coastal A Zone Regulations

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shoreline conditions often lead to future building failures.
Over a long period of time, owners of poorly sited coastal buildings may spend more
money on erosion control and erosion-related building repairs than they spent on the
building itself.
CRS credit is available when the local regulation requires all newly constructed
buildings to be located landward of the reach of mean high tide (i.e., the mean high
water line) along all shorelines within the Coastal A Zone.
e. Alteration of sand dunes or mangrove stands.
The vulnerability of a barrier island to storm overwash and inundation is determined, in
part, by the elevation of the dune crest, the elevation of the base of the dune, and the
volume of the dune. Where a dune is not present,
Local
governments
that
the vulnerability of the barrier island to overwash is
prohibit the alteration of sand
determined, in part, by the elevation and width of
dunes or mangrove stands
the beach berm.
within Coastal A zones may
receive up to 25 CRS credit
CRS credit is available where local regulations
prohibit the alteration of sand dunes and
points.
mangroves if those alterations would increase
potential flood damage. Removing sand or vegetation from, or otherwise altering, a
sand dune may increase potential flood damage; therefore, such actions must not be
carried out without the prior approval of a local official.
f. Enclosures.
Floodborne debris produced by coastal flood events and storms typically includes
decks, steps, ramps, breakaway wall panels, fuel tanks, vehicles, and a variety of
smaller objects
Regulations to limit enclosures below
the base flood elevation have three
objectives. First, they minimize the
damage from floodborne debris that
may hit the building. Second, they
minimize the potential for the building
being a source of debris that may hit
other buildings. Third, they discourage
finishing the area below the base flood
elevation and storing valuable or
hazardous items in that area.

Coastal A Zone Regulations

CRS Credit Points for Coastal A Zone
Enclosure Limits
150 Prohibit all Enclosures
50 Limit enclosures to 299 Square feet
or less.
These points are in addition to the 300 points
provided for Enclosure Regulations in Section
430h of the CRS Coordinator’s Manual.

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Impact Adjustment
CRS credit points are adjusted to reflect the impact of the community’s activity on
floodplain development. The impact adjustment serves to adjust credits so that the
dollar impact of premium discounts is spread over the community’s entire premium
base.
Example:: Gulf Beach floodplain regulations state that all lands seaward of the
Coastal Highway shall be considered V Zones for building protection purposes. It
also states that no new buildings or substantial improvements seaward of the
Coastal Highway shall have enclosures below the level of the base flood elevation
plus two feet.
CAZ = 500 + 150 = 650.

Impact Adjustment: The area regulated as a Coastal A zone is 30 percent of
the SFHA in Gulf Beach.
rCAZ = 0.30

Credit Calculation:
cCAZ = 650 x 0.30 = 195

For More Information
Additional guidance for design and construction in Coastal A Zones can be found in:
FEMA 499, Home Builder’s Guide to Coastal Construction
(http://www.fema.gov/fima/mat/fema499.shtm). The publication is a series of 31 fact
sheets that provide recommended design and construction practices for foundations,
connections, building envelope, etc. Fact Sheet 2 summarizes recommended practices
for Coastal A Zones, and references other fact sheets that provide more details.
FEMA 55, Coastal Construction Manual (revised 2000)
FEMA 549, Hurricane Katrina in the Gulf Coast: Mitigation Assessment Team Report,
Building Performance Observations, Recommendations, and Technical Guidance, July
2006.
FEMA. 2005a. ―Design and Construction in Coastal A Zones.‖ Hurricane Katrina
Recovery Advisory. Available at
http://www.fema.gov/pdf/rebuild/mat/coastal_a_zones.pdf

Coastal A Zone Regulations

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