Coastal Construction Manual - National Ready Mixed Concrete ...

HISTORICAL PERSPECTIVE 2
Two other enclosure scenarios have design and flood insurance implications. Designers should be cautious
when an owner asks for either type of enclosure, and should consult with the community and a knowledgeable
flood insurance agent:
Enclosures that do not extend all the way to the ground (sometimes called “above-grade,”
“hanging,” or “elevated” enclosures). These enclosures have a floor system that is not in contact
with the ground, but that may be connected to the building foundation or supported on the primary
pile system or short posts (Figure 2-23). Having the floor of the enclosure above grade means frequent
flooding passes underneath, which may reduce the frequency and severity of damage. These enclosures
were not contemplated when flood insurance premium rate tables were prepared, and thus can result in
significantly higher flood insurance premiums. As of early 2011, the NFIP was working to address this
type of construction, but until such time as it is resolved, owners will pay a substantial premium penalty
for this type of enclosure.
Two-story enclosures. In flood hazard areas with very high BFEs, some owners have constructed twostory,
solid walls to enclose areas below elevated buildings, typically with a floor system approximately
midway between the ground and the elevated building (Figure 2-24). These enclosures present unique
problems. In Zone A, the walls at both levels of the enclosure must have flood openings; there must be
some means to relieve water pressure against the floor system between the upper and lower enclosures;
and special ingress and egress code requirements may apply. These enclosures may also result in
substantially higher flood insurance premiums.
Figure 2-23.
Above-grade enclosure
(Perry, FL)
COASTAL CONSTRUCTION MANUAL
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