Size and place flood vents for an enclosure below the Base Flood Elevation (BFE)

Steps

1. Confirm the enclosure is below BFE in a mapped Special Flood Hazard Area (Zone A/AE/A1-A30/AR/AO/AH) subject to 44 CFR §60.3(c)(5) — this applies to unfinished/flood-resistant enclosures used only for parking, building access, or storage below an elevated structure's lowest floor, not to finished/habitable space, which must instead be elevated.
2. Place openings so each exterior wall has vents with bottom edges no more than 1 foot above the lowest adjacent (exterior) grade, allowing automatic floodwater entry/exit without human intervention (no manual gates/covers).
3. Size non-engineered openings for a minimum of 1 square inch of net open area per 1 square foot of enclosed floor area, distributed across at least two exterior walls where possible.
4. As an alternative, use engineered openings with a documented ICC-ES evaluation report or engineer's certification stating a rated coverage area in square feet per vent, which can allow fewer vents than the non-engineered default — keep the supporting report/certification on file.
5. Consult FEMA Technical Bulletin 1 (Requirements for Flood Openings in Foundation Walls and Walls of Enclosures) for full illustrated guidance, and confirm the local floodplain ordinance hasn't imposed stricter requirements than the federal minimum.