Storm shelter types
Every type below can be built to the same FEMA and ICC 500 tornado criteria. The real differences are stairs, space, flooding risk, permit type and price.
The common standard
- FEMA P-320 residential safe rooms are designed for 250 mph winds and to stop a 15-pound 2x4 board hitting at 100 mph (FEMA P-320 (2025)).
- For tornado use, FEMA's minimum is 3 square feet of usable floor space per person in a one- or two-family home (FEMA P-320 (2025)). A 4-person family needs at least 12 sq ft.
- The anchoring and slab matter as much as the box; FEMA publishes separate foundation and anchoring criteria (FEMA foundation and anchoring criteria).
Garage in-ground (below-ground) shelter
A steel box set into the garage slab with a sliding lid you can park over, often installed in one day. Needs stairs, so it is harder for people with limited mobility. In Oklahoma City it is permitted as an in-ground shelter, $99.50 (City of OKC Storm Shelter Permit page).
Above-ground safe room
A reinforced steel or concrete room bolted to a slab in a garage, closet or new addition. No stairs and no digging, the best choice for wheelchairs and older adults. OKC's above-ground safe room permit is $104.50 (City of OKC Storm Shelter Permit page); the slab must be able to take the anchors (FEMA foundation and anchoring criteria).
Outdoor underground shelter (storm cellar)
Concrete or steel shelter buried in the yard, sometimes slope-front. Needs yard access and excavation, and can flood or float if not engineered for groundwater, which is why OKC asks for an engineer's flotation letter (City of OKC Development Center).
Quick comparison
| Type | Stairs | Flood concern | Typical published price |
|---|---|---|---|
| Garage in-ground | Yes | Low-moderate | from about $3,300 |
| Above-ground safe room | No | Lowest | about $4,500-$14,000 |
| Outdoor underground | Yes | Highest | about $5,000-$15,000 |
Prices from installer pages on the costs page.
What to ask any installer
- Proof the design meets FEMA P-320 / P-361 and ICC 500 (see what those mean).
- Door type and impact testing.
- Who pulls the permit and schedules inspection.
- Warranty terms in writing.
Checked Oct 23, 2026.
Newer guides: Shelter rebate 2026 · Register your shelter · FEMA P-320 and ICC 500