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Proper Openings - Enclosures (Applicable to Zones A, A1-A30, AE, AO, AH, AR and AR Dual)

All enclosures below the lowest elevated floor must be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. A minimum of 2 openings, with positioning on at least 2 walls, having a total net area of not less than 1 square inch for every square foot of enclosed area subject to flooding must be provided. The bottom of all openings must be no higher than 1 foot above the higher of the exterior or interior (adjacent) or floor immediately below the openings.

Glossary Section
NFIP - National Flood Insurance Program