FEMA P-361 and ICC 500, explained
The two names you will hear most when shopping for a storm shelter, and what they actually mean for your family.
The short version
- ICC 500 is the ICC/NSSA Standard for the Design and Construction of Storm Shelters. Building codes adopted in Texas cities reference it for storm shelters.
- FEMA P-361, Safe Rooms for Tornadoes and Hurricanes, is FEMA's guidance for community and residential safe rooms. It builds on ICC 500 and adds FEMA's own criteria.
- FEMA P-320, Taking Shelter from the Storm, is FEMA's homeowner-focused guide with prescriptive safe room designs for homes and small businesses.
Key tornado criteria
| Criterion | FEMA tornado safe room |
|---|---|
| Design wind speed | 250 mph (3-second gust) |
| Debris impact, walls (vertical surfaces) | 15 lb wood 2x4 at 100 mph |
| Debris impact, roof (horizontal surfaces) | 15 lb wood 2x4 at 67 mph |
| Doors and openings | Must be tested as an assembly, with the frame and hardware, to the same debris criteria |
| Siting | Not in high flood-hazard areas or floodways |
Summary of published FEMA guidance. Engineers and code officials should work from the current official documents, linked below.
Why the 2x4 test matters
FEMA notes that a 15 lb 2x4 carried by a 250 mph wind can reach a horizontal speed of about 100 mph, enough to penetrate most common residential wall and roof materials. Shelters are tested by firing a 2x4 at their walls, roof and door to show it does not get through.
What to ask for
- A test report or certification from an independent lab showing the specific model and door assembly met ICC 500 and FEMA P-361 debris tests.
- Engineering or anchoring details that match your slab or soil.
- Confirmation of who handles the permit and inspection.
A shelter described as "built to FEMA standards" is not the same as one that has been tested. Ask for the paperwork. Central Texas Storm Shelters does not test, certify or endorse any product.
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