Crawlspace foundations are commonly used in some parts of the nation to elevate the lowest floors of residential buildings located in Special Flood Hazard Areas (SFHAs) above the Base Flood Elevation (BFE). Crawlspeces should be constructed so that the floor of the crawlspace is at or above the lowest grade adjacent to the building. Crawspaces that have their floors below BFE must have openings to allow the equalization of flood forces.
Recent FEMA guidance now allows crawlspaces to have their floors up to two feet below lowest adjacent grade under certain circumstances although this is discouraged. Below-grade crawlspace foundation walls are exposed to increased forces during flood conditions, such as hydrostatic and saturated soil forces. Guidance on the National Flood Insurance Program (NFIP) minimum requirements for crawlspace construction in the SFHA is given in FIA-TB-11.
Buildings that have below-grade crawlspaces will have higher flood insurance premiums than buildings that have the interior elevation of the crawlspace at or above the lowest adjacent exterior grade.
National Flood Insurance Program (NFIP) Requirement
- 60.3 - Flood plain management criteria for flood-prone areas
- (a) (3) - Reasonably Safe From Flooding
- (c) (2) - A Zone Residential Buildings
- (c) (5) - Openings
- Technical Bulletin 11, Crawlspace Construction for Buildings Located in Special Flood Hazard Areas (FIA-TB-11)