Breakaway walls are allowed both by the International Residential Code and by the National Flood Insurance Program (NFIP) rules. However, there are certain identified "disconnects" between what is allowed by law and what may result in higher insurance premiums. The use of breakaway walls in a V zone is one of these disconnects.
In accordance with the NFIP Flood Insurance Manual, insurance companies may charge higher premiums for an "elevated building with obstruction." The Flood Insurance Manual contains the following guidelines. (Note: The italicized text below is from the Manual. The most recent (May 1, 2013) Manual may be accessed at FEMA Manual.)
1. Elevated Building Without Obstruction
The area below the lowest elevated floor is open, with no obstruction, to allow the flow of floodwaters. Insect screening is permissible. Wooden or plastic lattice, slates, or shutters are also permissible if at least 40 percent of their area is open. Lattice can be no thicker than 1/2 inch; slats or shutters can be no thicker than 1 inch. In addition, buildings are considered without obstruction if the area below the lowest elevated floor is enclosed by a combination of 1 solid breakaway wall or garage door, and the other sides of the enclosure are insect screening, or wooden or plastic lattice, slats, or shutters. Machinery or equipment below the lowest elevated floor must be at or above the BFE. Use the rates from Table 3E. For unnumbered Zone V, use the Submit-for-Rate procedures.
2. Elevated Building With Obstruction
Buildings are rated "With Obstruction" if any of the following conditions are met:
a. The area below the lowest elevated floor is enclosed fully by solid breakaway walls.
b. The area below the lowest elevated floor is enclosed by a combination of 2 or more solid breakaway walls, the remaining sides constructed of insect screening, or wooden or plastic lattice, slats, or shutters.
c. Machinery or equipment below the lowest elevated floor is also below the BFE. Use the rates from Table 3F provided that the enclosure is less than 300 square feet with solid breakaway walls, or any machinery or equipment is below the BFE. For unnumbered Zone V, use Submit-for-Rate procedures.
Homeowners are permitted to enclose areas below the BFE with breakaway walls. However, they should be informed that this will result in higher insurance premiums. Under the Flood Insurance Manual, enclosed space of 300 square feet or more will be counted as the building's lowest floor even if it is enclosed with breakaway walls and is restricted to use for building access, parking or storage in accordance with the rules. "Without obstruction" in accordance with the above guidelines results in the best rates. How much higher will the rate be with obstructions? Most of the flood insurance rates in the V zone are shown as "submit for rate" which means that the information is submitted to the insurance company and the company determines the policy premium.