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Safe Room Sizing — FEMA P-361 (2024, 5th ed.) / ICC 500-2023

Required usable floor area for tornado or hurricane community safe rooms by occupant type, the one-wheelchair-space-per-200 rule, and a check of the usable area provided by the candidate spaces.

Occupants

Hazard

Standing or seated

Wheelchair users

Relocated to a bed or stretcher

Candidate spaces

One space per line: name, GROSS floor area (ft²), furnishing — concentrated (× 0.50), unconcentrated (× 0.65), open (× 0.85), or usable (× 1.00, already net of all unusable areas)

Residential safe room (≤ 16 occupants)

Dwelling

Occupants

Usable floor area (gross minus unusable) ft²

Residential: required usable area · check—

Results

Occupants · wheelchair spaces (≥ 1 per 200)—

Required usable floor area—

Usable area provided · check—

Standing/seated capacity of the spaces—

FEMA P-361 (Nov 2024, 5th ed.) · ICC 500-2023Section B5.2.1, Tables B5-1 (community tornado), B5-2 (community hurricane) and B5-3 (residential); usable-area percentage reductions are minimums applied to the GROSS floor area (ICC 500 §502.4). Restrooms: tornado — only areas outside toilet stalls count; hurricane — restrooms do not count.

VerifiedAll densities checked against the primary text of FEMA P-361 (2024). Earlier versions of this tool applied the reductions to net area (from a secondary source) — corrected. Standing and seated occupants share one value; a vendor figure of 6 ft² for seated occupants does not appear in FEMA or ICC 500.

Preliminary calculation tool. Final design requires the full text of the referenced standard (see the sources on this page) and review by a licensed PE.