Protective design is not only about explosions. For most American families and schools, the extreme event most likely to threaten their lives is a violent tornado or a major hurricane. A properly designed safe room is the residential and community version of protective design: a space engineered to stay intact and keep occupants safe when the rest of the building may not. This guide explains the federal guidance and the consensus standard behind safe rooms and storm shelters, how to choose and size one, and how to tell a genuine safe room from a reinforced closet.

Safe room or storm shelter? The terms

FEMA uses "safe room" for a space that meets the criteria in FEMA P-361 and provides what FEMA calls near-absolute protection from extreme wind events. "Storm shelter" is the term used in ICC 500, the ICC/NSSA Standard for the Design and Construction of Storm Shelters, and in the building codes that reference it. In practice:

• ICC 500 storm shelters meet a consensus standard adopted through the International Building Code and International Residential Code.
• FEMA safe rooms meet ICC 500 plus FEMA's additional criteria. FEMA-funded projects must meet FEMA P-361.
• "Best available refuge areas" are the safest parts of ordinary buildings, used when no safe room exists. They reduce risk but are not engineered for extreme winds.

Since the 2015 edition, the International Building Code has required ICC 500 storm shelters for many new K-12 schools and certain emergency facilities, such as 911 call centers, fire, rescue, police stations and emergency operations centers, in areas where the shelter design wind speed for tornadoes is 250 mph. Check which code edition your jurisdiction has adopted.

What makes a safe room different

Design wind speed and pressures

FEMA designs all tornado safe rooms for a 250 mph wind speed regardless of location, because the strongest tornadoes can occur across much of the country. Hurricane safe room design wind speeds vary by location along the coast. The structure, roof, walls, connections and anchorage to the foundation must all resist the resulting pressures, including uplift.

Wind-borne debris

Tornado debris is what kills and injures most people who are in a building that fails. Safe room walls, roofs, doors and any openings must pass debris impact testing. For tornado safe rooms, the representative test missile is a 15-pound 2x4 wood board striking at 100 mph horizontally, with a lower vertical speed for roofs. Hurricane criteria use a lighter board at speeds based on the design wind speed.

Doors and openings

Doors are the most common weak point. A safe room door, frame and hardware must be tested together as an assembly for both pressure and debris impact. Ordinary steel doors, even heavy ones, generally do not qualify unless tested in that configuration. Vents and any other openings need tested protective covers.

Siting

Tornado safe rooms must be reachable quickly, because warning times can be short. Hurricane safe rooms must not be located where flooding or storm surge can reach them; people in surge and evacuation zones should evacuate when told to, not shelter in place. In-ground safe rooms should not be built where flooding is likely.

Residential options

FEMA P-320, Taking Shelter from the Storm, provides prescriptive construction plans for residential and small business safe rooms built with common materials, so a contractor can build one without a custom engineering design when the plans are followed exactly.

How big does a safe room need to be?

ICC 500 and FEMA guidance set minimum usable floor area per occupant. Residential safe rooms need about 3 square feet per person for tornadoes and 7 square feet per person for hurricanes, because hurricane sheltering can last many hours. Community safe rooms use larger values and add space for wheelchair users and people who must lie down.

How to verify a safe room is real

Cost and funding

Costs vary widely by type, size, region and whether the room is built during new construction or added to an existing home. Building a safe room into a new home is usually less expensive than retrofitting. Prefabricated interior and in-ground units are often priced in the thousands to low tens of thousands of dollars installed, depending on size and site work; get multiple quotes and confirm what is included. FEMA's safe room program provides guidance and funds safe rooms through hazard mitigation grants administered by states, and some states have run individual safe room rebate programs. Check with your state emergency management agency.

Beyond the structure: readiness

A safe room only works if people get into it in time and can stay safely until help arrives. Keep a NOAA Weather Radio with battery backup, phones charged, water, a first aid kit, flashlights, a whistle or air horn to signal rescuers and any essential medications. Practice going to the safe room, and tell local emergency officials or trusted neighbors that you have one so responders know to check after a storm. For larger facilities and infrastructure, our guide to protecting critical infrastructure from natural hazards covers the wider building, and our engineer selection guide explains who should design community safe rooms.