Can you build a DIY storm shelter that actually protects you?

Start with a tested design, not a sketch

The difference between a storm shelter and a strong room is testing. A real shelter is designed for tornado winds of 250 mph and for a 15-pound two-by-four hitting it end-on at 100 mph, which is the debris test FEMA describes in its homeowner guide, P-320. Walls that feel solid can still fail that test at a joint, a hinge or the point where the roof meets the wall.

The good news for a DIY storm shelter is that you do not have to design one from scratch. FEMA P-320, “Taking Shelter from the Storm”, is free to download and includes construction plans for safe rooms that a builder or a capable homeowner can follow. The plans cover wall types, how the room is tied to its foundation, the ceiling and the door. Building to those plans, without changes, is the closest a self-builder can get to the tested result.

What the FEMA plans cover

P-320 is written for homeowners and builders. Among other things it explains:

• How much room you need: at least 3 square feet of floor per person for a tornado safe room in a home, or 7 square feet for hurricanes.
• Where to put it: in a basement, in the ground, in the garage, inside the house, or detached within 150 feet of the home’s nearest door.
• Where not to: floodways, and coastal high-hazard flood zones. Below-ground rooms are a poor choice wherever floodwater could reach.
• Which wall systems work: reinforced concrete, concrete block filled with grout and steel, and certain steel and wood assemblies with protective layers.

It also says prefabricated units must be listed and labeled to show compliance with ICC 500 and FEMA P-361. That rule matters if you buy a kit: look for the label.

The parts that go wrong

Anchoring

Tornadoes do not just push; they lift. A room that is not tied to a foundation designed for it can be lifted or slid off its base. The plans specify the anchors, the slab and the connections. Swapping in a different anchor or skipping a few is where DIY rooms most often stop matching the design.

The door

The door, frame and hardware are part of the tested system. An ordinary steel entry door, even a heavy one, has not been tested to the same debris impact. HomeGuide puts a tornado-rated steel door at $500 to $2,500 or more. It is not a part to economize on, and it is the one most DIY builders underestimate.

Water

Any room below ground has to deal with water from above and from the soil around it. Digging, a gravel base, sealing, waterproofing the outside and grading the ground away from the entry all have to be done well, or the room fills with water just when you need it. Our guide to waterproof underground storm shelters goes into detail.

Ventilation

People in a small sealed room need air. ICC 500, the shelter standard, sets a minimum mechanical ventilation rate for tornado shelters, and the FEMA plans include vent openings that have to be protected from debris. A sealed box without vents is not a shelter.

Permits and digging safely

Most cities and counties want a building permit for a new shelter, a new slab or a cut in an existing one. The inspector will check the work against the plans, which is useful protection for you as well as a legal step.

Before any digging, call 811. It is free, and it gets public utility lines marked so you do not hit gas, power or water. Lines you own, such as power to a shed, are not marked by 811 and are your job to find.

If you hope to claim a state rebate or tax credit, read the rules before you build. Oklahoma’s SoonerSafe program, for example, does not accept shelters installed or started before an applicant is selected, and Alabama’s tax credit asks for an engineer-sealed design.

Does DIY save money?

Sometimes, but less than people expect. HomeGuide puts a DIY wood-frame safe room built to a published 8 by 8 foot design at $4,300 to $5,000 or more in materials, and compares prefab shelters installed at $3,000 to $12,000 or more. FEMA’s own estimates for building its designs into a new house are about $8,000 to $9,500 for an 8 by 8 foot room, in 2014 dollars.

Add up the tested door, concrete, rebar, anchors, tool hire and your time, and a small prefab unit installed by a crew in a day can come out close. Our cost calculator gives a range for an installed shelter so you can compare.

When to call a professional

DIY makes most sense when you are building a safe room into a new house or an addition, have building experience, and will follow the FEMA plans to the letter. It makes least sense below ground in wet or rocky soil, or where someone in the home needs step-free access and the room has to work for them.

If you would rather have it done, storm shelter installation is usually a day’s work once the permit is in hand. We can find an installer who covers your area and name them to you before anyone gets in touch. Whichever route you take, register the finished shelter with your local fire department and emergency management office, as FEMA recommends, so responders know to check it after a storm.