- FEMA P-361 and ICC 500 set the design rules for tornado and hurricane safe rooms and storm shelters.
- Residential tornado designs use a 250 mph design wind speed and resist a 15-pound 2x4 striking at 100 mph.
- Storm shelter standards do not cover long-stay air, power, water or waste.
What the storm standards cover
FEMA P-361 is FEMA's guide for safe rooms, and ICC 500 is the building standard for storm shelters. FEMA P-320 gives prescriptive designs a homeowner can build. For tornadoes, those designs use a 250 mph design wind speed and must stop a 15-pound two-by-four flying at 100 mph. They also cover anchoring, doors, and ventilation for a short stay.
What a long stay needs
A safe room is designed for the storm to pass. A bunker is designed for the days after. That means filtered fresh air sized for summer heat, power that runs without the grid, stored water, a toilet that works, a place to cook and sleep, and a way to get out if the main entry is blocked.
Can one do both?
A buried structure can serve as a storm shelter when it is designed and certified to the storm standard, which covers things like the door assembly and anchoring. If you live in tornado country and want both, ask for the storm rating in writing, by standard and edition, rather than assume it.
Questions
Is a CUBE Bunker a FEMA safe room?
Not by default. CUBE Bunkers are designed as long-stay underground shelters. If you need a FEMA P-361 or ICC 500 rated shelter, tell your dealer at the start so the design and door can be specified for it.
What is the 250 mph rule?
FEMA's residential tornado safe room designs use a 250 mph design wind speed,, along with debris impact from a 15-pound two-by-four at 100 mph.
CUBE Bunker prices are preliminary until engineering for the cube system is complete and are confirmed in writing after a site visit. This guide is general information, not engineering, legal or medical advice. Updated 2026-11-02.