Last updated: October 11, 2026
Size a home tornado safe room at a minimum of 3 square feet of usable floor space per person — that's FEMA's figure for safe rooms in one- and two-family homes — then add room for anyone in a wheelchair or who can't stand, for pets, and for the people who'll be at your house when the warning comes. Five occupants at that allocation need at least 15 usable square feet. Floor-area arithmetic alone does not establish a shelter’s rated capacity; residential safe rooms are limited to 16 occupants. Just as important: everyone has to be able to get in fast. If someone in your house can't reach the shelter in under a minute — our rule of thumb — the location or type needs rethinking.
How much space
FEMA's guidance sets these minimum usable floor areas per occupant for residential tornado safe rooms:
| Setting | Usable floor area per person |
|---|---|
| One- and two-family homes | 3 sq ft |
| Other residential | 5 sq ft |
Planning examples below assume the entire listed interior area is usable, before any additional accessibility needs. They are not manufacturer capacity ratings:
| Clear interior dimensions | Usable area assumed | People at 3 sq ft, capped at 16 | People at 5 sq ft, capped at 16 |
|---|---|---|---|
| 4 × 4 ft | 16 sq ft | 5 | 3 |
| 4 × 6 ft | 24 sq ft | 8 | 4 |
| 4 × 8 ft | 32 sq ft | 10 | 6 |
| 6 × 6 ft | 36 sq ft | 12 | 7 |
| 6 × 8 ft | 48 sq ft | 16 | 9 |
| 8 × 10 ft | 80 sq ft | 16 | 16 |
Use net usable space, not the outside shell footprint: subtract walls, partitions, columns and equipment or other obstructions that cannot be removed when sheltering. See FEMA P-361, usable floor area and residential occupancy.
A plan for more than 16 occupants requires community-safe-room design criteria, not just more floor area. Confirm the documented capacity and applicable requirements with the manufacturer and a licensed design professional. FEMA P-320 explains the residential/community distinction. Three square feet is close quarters; for a long warning, more room is kinder.
Who to plan for
- Everyone who lives there.
- Regular visitors — grandchildren on weekends, a caregiver, a nanny.
- Neighbors without a shelter, if you'd open the door to them. Many people would.
- Anyone who uses a wheelchair or walker — they need turning room and more floor area than a standing adult. The table above does not establish accessible capacity. Ask the seller and designer to verify the usable area, layout and occupant allowance for each wheelchair or walker user before selecting a unit.
- Pets in carriers, which take floor space.
Access: the one-minute test
Tonight, try this:
- Pick the person in your house who'd be slowest — the grandparent, the heavy sleeper, the toddler.
- From their bedroom, time how long it takes to get them into the shelter spot with shoes on.
- Do it with the lights off.
If it's over a minute, change something: the shelter's location, the type (above-ground opens at floor level — see above-ground vs underground), or the plan (who carries whom, what's left by the bed; see the household tornado plan).
Why this matters in St. Louis: many of the region's damaging tornadoes have struck in the evening or at night — 1967 at 6:55 p.m., 2011 at 7:55 p.m., 2013 at 7:50 p.m., and two in December 2021 after 7:30 p.m. Warning times are measured in minutes.
Access by shelter type
| Type | Access | Best for |
|---|---|---|
| Above-ground safe room | Floor-level door | Mobility needs, children, seniors |
| Basement safe room | Down the stairs, then a door | Households who use the basement daily |
| In-ground garage | Move the car, open hatch, steps down | Able-bodied households |
| Yard shelter | Go outside, then steps or ladder | Rural sites; able-bodied households |
Accessibility features to ask for
- Door width that fits a wheelchair or walker.
- A threshold you can roll over.
- Interior space for a wheelchair to turn or park without blocking others.
- Grab bars and seating.
- Lighting that works without house power.
- A latch that someone with limited hand strength can operate.
Related guides
Frequently asked questions
How big a shelter for a family of five? At least 15 usable square feet for five occupants at FEMA's 3-square-foot allocation for a one- or two-family home. A nominal 4 × 4 footprint alone does not establish capacity: account for obstructions, accessibility needs, pets and supplies, and confirm the unit's documented rating.
Can a wheelchair user use an underground shelter? Usually not practically. An above-ground safe room with a wide, low-threshold door is the better option.
How long would we be in there? Usually minutes, until the warning expires or the storm passes. FEMA's grant guidance uses a minimum two-hour protection period for tornado safe rooms.
Should we size it for neighbors? If you'd let them in, yes.
Sources
- NWS — Tornado safety: during — current; accessed 2026-10-10
- FEMA — Residential Tornado Safe Room Doors fact sheet — Nov/Dec 2024; accessed 2026-10-10
- FEMA — HMA Guide Part 12, B.8 Safe rooms — current; accessed 2026-10-10
- Survive-a-Storm — St. Louis storm shelters — pub. 2023-05-09, mod. 2024-05-17; accessed 2026-10-10
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