The best method, and often the only legal method, of protecting new homes in flood-hazard areas is building above expected flood levels. Through the resources of the National Flood Insurance Program, a flood risk-estimation system is in place in much of the country. That risk-estimation system is most often represented in the Flood Insurance Rate Map (FIRM). These maps and the studies used to generate them form the basis for rating flood insurance and regulating floodplain development .
In most situations where development is regulated for flood protection, the builder/homeowner can choose any foundation system that results in the lowest floor of the inhabitable structure (and certain building equipment) being at the required elevation.
There are exceptions and limitations:
No construction on fill-in areas of Coastal Hazards (Velocity zones):
The NFIP minimum regulations prohibit the use of fill for structural support of buildings within Zones V1-30, VE or V. They further require new construction and substantial improvements in Zones V1-30, VE or V to be elevated so that the bottom of the lowest horizontal structural member of the lowest floor is at or above the BFE on a pile or column foundation. (For all other flood zones, the top of the elevated floor must be at or above BFE.)
Fill limitations imposed by the community:
Some Louisiana communities limit the amount of fill dirt that can be brought into flood hazard areas. These limits are imposed to preserve floodplain storage capacity. The extent of the limitation varies among communities, with most having no limitations. Some typical types of fill limitations in Louisiana are
No fill brought into the flood hazard area
Any fill placed in the flood hazard area below base flood elevation (BFE) must be compensated by creating an equal volume of flood storage capacity (a dry reservoir or other excavation that does not hold water in non-flood conditions). The communities may demand that the compensatory storage be in close proximity to the site at which fill is placed.
Fill may be placed under the footprint of the house only. In some cases the community allows only 2 feet under the house, and that must be sloped back to natural grade within 5 feet of the perimeter. The slab-on-backfill is the typical construction style in these situations.
The NFIP minimum regulations require the community to regulate development in Zones A1-30 and AE, for which no regulatory floodway is designated, so that the cumulative effect of any proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than 1 foot at any point within the community.