A. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated one foot or more* above the base flood elevation (BFE).
B. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria:
1. A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided;
2. The bottom of all openings shall be no higher than one foot above grade;
3. Openings may be equipped with screens, louvers, or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters.
Foundation vent standards required by the IBC/IRC outside the floodplain do not meet this standard and are often inadvertently permitted. Insurance rates reflect an “all or nothing” standard, meaning, partially ventilated crawlspaces may be subject to an additional loading fee of 20 to 25 percent attached to the annual insurance premium.
*Minimum FEMA standards require the lowest floor to be elevated “to or above” the BFE; however, adding an additional foot of freeboard increases safety and can reduce insurance premiums by as much as 30 percent. Adopting additional freeboard is strongly encouraged by FEMA. This note applies throughout this chapter.