The requirements in plain terms
- Design wind speed: 250 mph (3-second gust)
- Missile impact: 15 lb 2x4 at 100 mph horizontal, 67 mph vertical
- Anchoring: documented bolt schedule into a qualifying slab or foundation
- Door: tested as part of the assembly, not retrofitted
- Ventilation: passive minimums plus optional powered ventilation
- Usable floor area: 3 to 7 sq ft per person depending on case
How to verify a unit is genuinely P-320
Ask for the ICC 500 test report number for the exact model, the anchoring schedule in writing, and the ventilation calculation for your expected occupancy. For the full discussion of safe room types and costs, see our safe room guide.
Frequently Asked Questions
What does FEMA P-320 actually require?+
P-320 requires a residential safe room designed to a 250 mph wind event, tested against a 15 lb 2x4 missile at 100 mph horizontal, with documented anchoring, a tested door assembly, and ventilation that does not compromise the protected envelope.
Is FEMA P-320 the same as ICC 500?+
Not quite. FEMA P-320 references ICC 500 and adds residential-specific guidance. A P-320 safe room is also ICC 500 compliant. The reverse is not always true: a generic ICC 500 shelter may not meet every P-320 detail.
Does FEMA certify or approve shelter brands?+
No. FEMA publishes the P-320 guidance but does not approve individual products. Any claim of FEMA approval is a marketing shortcut. Verify the ICC 500 test report and confirm the installer documents P-320 compliance on the plans.
How many square feet do I need per person?+
P-320 recommends roughly 3 to 7 square feet per person depending on occupancy duration and mobility. A typical four person household is well served by a room of about 25 square feet of usable floor area.