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Coastal Building Successes and Failures
Home Builder’s Guide to Coastal Construction

Technical Fact Sheet No. 1

Purpose: To discuss how coastal construction requirements are different from
those for inland construction. To discuss the characteristics that make for a
successful coastal building.

Is Coastal Construction That Different From Inland Construction?
The short answer is yes, building in a coastal environment is different from
building in an inland area:
--Flood levels, velocities, and wave action in coastal areas tend to make
coastal flooding more damaging than inland flooding.
--Coastal erosion can undermine buildings and destroy land, roads, utilities,
and infrastructure.
--Wind speeds are typically higher in coastal areas and require stronger
engineered building connections and more closely spaced nailing of building
sheathing, siding, and roof shingles.
--Wind-driven rain, corrosion, and decay are frequent concerns in coastal areas.

In general, homes in coastal areas must be designed and built to withstand
higher loads and more extreme conditions. Homes in coastal areas will require
more maintenance and upkeep. Because of their exposure to higher loads and
extreme conditions, homes in coastal areas will cost more to design, construct,
maintain, repair, and insure.

Building Success
In order for a coastal building to be considered a “success,” four things must
occur:
--The building must be designed to withstand coastal forces and conditions.
--The building must be constructed as designed.
--The building must be sited so that erosion does not undermine the building or
render it uninhabitable.
--The building must be maintained/repaired.

A well-built but poorly sited building can be undermined and will not be a
success (see Figure 1). Even if a building is set back or situated farther from
the coastline, it will not perform well (i.e., will not be a success) if it is
incapable of resisting high winds and other hazards that occur at the site (see
Figure 2).

Figure 1. Well-built but poorly sited building.

Figure 2. Well-sited building that still sustained damage.

What Should Owners and Home Builders Expect From a “Successful” Coastal
Building?
In coastal areas, a building can be considered a success only if it is capable
of resisting damage from coastal hazards and coastal processes over a period of
decades. This statement does not imply that a coastal residential building will
remain undamaged over its intended lifetime. It means that the impacts of a
design-level flood, storm, wind, or erosion event (or series of lesser events
with combined impacts equivalent to a design event) will be limited to the
following:
--The building foundation must remain intact and functional.
--The envelope (walls, openings, roof, and lowest floor) must remain
structurally sound and capable of minimizing penetration by wind, rain, and
debris.
--The lowest floor elevation must be sufficient to prevent floodwaters from
entering the elevated building envelope during the design event.
--The utility connections (e.g., electricity, water, sewer, natural gas) must
remain intact or be restored easily.
--The building must be accessible and usable following a design-level event.
--Any damage to enclosures below the Design Flood Elevation (DFE)* must not
result in damage to the foundation, the utility connections, or the elevated
portion of the building.

Recommended Practice
--Siting – Site buildings away from eroding shorelines and high-hazard areas.
Building Form – Flat or low-sloped porch roofs, overhangs, and gable ends are
subject to increased uplift in high winds. Buildings that are both tall and
narrow are subject to overturning. Each of these problems can be overcome
through the design process, but each must receive special attention. In the
design process, chose moderate-sloped hip roofs (4/12 to 6/12) if possible.

--Lowest Floor Elevation – Elevate above the DFE the bottom of the lowest
horizontal structural member supporting the lowest floor. Add “freeboard” to
reduce damage and lower flood insurance premiums.

--Free of Obstructions – Use an open foundation. Do not obstruct the area below
the elevated portion of the building.  Avoid or minimize the use of breakaway
walls. Do not install utilities or finish enclosed areas below the DFE (owners
tend to convert these areas to habitable uses, which is prohibited under the
National Flood Insurance Program and will lead to additional flood damage and
economic loss).

--Foundation – Make sure the foundation is deep enough to resist the effects of
scour and erosion; strong enough to resist wave, current, flood, and debris
forces; and capable of transferring wind and seismic forces on upper stories to
the ground.

--Connections – Key connections include roof sheathing, roof-to-wall, wall-to-
wall, and walls-to-foundation. Be sure these connections are constructed
according to the design. Bolts, screws, and ring-shanked nails are common
requirements. Standard connection details and nailing should be identified on
the plans.

--Exterior Walls – Use structural sheathing in high-wind areas for increased
wall strength. Use tighter nailing schedules for attaching sheathing. Care
should be taken not to over-drive pneumatically driven nails. This can result in
loss of shear capacity in shearwalls.

--Windows and Glass Doors – In high-wind areas, use windows and doors capable of
withstanding increased wind pressures. In windborne debris areas, use impact-
resistant glazing or shutters.

--Flashing and Weather Barriers – Use stronger connections and improved flashing
for roofs, walls, doors, and windows and other openings. Properly installed
secondary moisture barriers, such as housewrap or building paper, can reduce
water intrusion from wind-driven rain.

--Roof – In high-wind areas, select appropriate roof coverings and pay close
attention to detailing. Avoid roof tiles in hurricane-prone areas.

--Porch Roofs and Roof Overhangs – Design and tie down porch roofs and roof
overhangs to resist uplift forces.

--Building Materials – Use flood-resistant materials below the DFE. All exposed
materials should be moisture- and decay-resistant. Metals should have enhanced
corrosion protection.

--Mechanical and Utilities – Electrical boxes, HVAC equipment, and other
equipment should be elevated to avoid flood damage and strategically located to
avoid wind damage. Utility lines and runs should be installed to minimize
potential flood damage.

--Quality Control – Construction inspections and quality control are essential
for building success. Even “minor” construction errors and defects can lead to
major damage during high-wind or flood events. Keep this in mind when inspecting
construction or assessing yearly maintenance needs.

*The DFE is the locally mandated flood elevation, which will be equal to or
higher than the Base Flood Elevation (BFE). The BFE is the expected elevation of
flood waters and wave effects during the 100-year flood (also known as the Base
Flood).

Recommended practice and guidance concerning the topics listed above can be
found in the documents referenced in these fact sheets and in many trade
publications (e.g., the Journal of Light Construction,
http://www.jlconline.com).

Will the Likelihood of Success (Building Performance) Be Improved by Exceeding
Minimum Requirements?
States and communities enforce regulatory requirements that determine where and
how buildings may be sited, designed, and constructed. There are often economic
benefits to exceeding the enforced requirements (see box). Designers and home
builders can help owners evaluate their options and make informed decisions
about whether to exceed these requirements.

Benefits of Exceeding Minimum Requirements
--Reduced building damage during coastal storm events
--Reduced building maintenance
--Longer building lifetime
--Reduced insurance premiums*
--Increased reputation of builder

*Note: Flood insurance premiums can be reduced up to 60 percent by exceeding
minimum siting, design, and construction practices. See the V-Zone Risk Factor
Rating Form in FEMA’s Flood Insurance Manual
(
http://www.fema.gov/nfip/manual.shtm).