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.
What wind speed are residential safe rooms built for?
250 mph, under FEMA P-320, plus a debris test (FEMA P-320 (2025)).
- 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 |
Garage shelter problems and how to avoid them
In-garage floor shelters held up well in Moore in 2013: Texas Tech documented 20 of them and found no major failures, but noted flooding, weak locking systems, worn roller bearings and awkward stairs in some (Texas Tech shelter performance report, Moore 2013). FEMA's team flagged the same weak spots (FEMA observation report, Moore tornado of May 20, 2013).
- Water. FEMA calls flooding a common issue that is not often considered for garage shelters: once the garage is destroyed, rain, flash flooding or broken water lines can flow in. Flush-to-slab units flooded more, and a 1 to 2 inch lip at the entrance gave better protection (FEMA observation report, Moore tornado of May 20, 2013). Ask your installer about the lip and how the slab drains.
- Parking over the lid. FEMA warns that a car parked over the shelter can block you getting in before the storm or out after it (FEMA observation report, Moore tornado of May 20, 2013). Park off the door on watch days, and register the shelter so responders know to look for you.
- Sliding door trouble. Check the tracks for debris and use a silicone-based lubricant if the door feels stiff (Oklahoma Shelters garage shelter checklist). A door that drags, will not latch or lets water past the gasket needs attention before storm season (OKC Shelters drainage and waterproofing guide).
- Clutter. Do not store boxes on top of or inside the shelter; you may have seconds to get in (Oklahoma Shelters garage shelter checklist).
Questions for a quote: how high the lip sits above the slab, how many locks the door has, what the rollers are rated for, and who services the door later.
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: Storm season checklist · Shelter rebate 2026 · Register your shelter · FEMA P-320 and ICC 500
Related: permits by city and storm shelter FAQ. When you are ready, request a quote.