Is a shipping container storm shelter a good idea?

Why the idea is so appealing

A used 20-foot container is big, made of steel, built to be stacked several high on a ship, and easy to find. It seems obvious that it would make a strong, roomy shelter for less than a purpose-built unit. That is why “shipping container storm shelter” is searched hundreds of times a month.

The trouble is that a container is strong in one particular way, and a storm shelter needs to be strong in others. A shelter has to resist soil pressing in on every side if it is buried, or wind, uplift and flying debris if it sits on the surface, and it has to let people in quickly and get them out safely afterward. A container was designed for none of those jobs, and the gaps are expensive to close.

Where a container’s strength really is

A container carries its load through a steel frame: four corner posts, top and bottom rails, and corner castings. When containers are stacked, the weight goes straight down through those posts. The roof and side walls are thin corrugated steel panels that keep the weather out. They are not the structure.

A container dealer, Conexwest, says exactly this in its guide to burying containers: the roof and walls are not designed to hold back soil, soil pressure can bow the walls, and soil on top can make the roof sag. It adds that wet soil is heavier than dry soil and that trapped water creates extra pressure. Its conclusion is that a standard, unreinforced container should not be fully buried, and that there is no universal safe burial depth.

Buried: the soil problem

Underground, soil presses on every side of a box, all the time, and harder after rain. A container’s long side walls and roof take that load across their weakest direction. Over months or years, walls can bow and roofs can dish, and a collapse can happen without warning, with people inside.

Making a buried container safe means an engineer designing internal steel beams, columns and roof supports, and often retaining walls or other measures outside so the soil does not press straight on the steel. Add drainage, waterproofing and a protective coating, because buried steel in damp soil rusts. By then you have paid for a custom engineered structure, with a container inside it.

Above ground: the debris problem

On the surface, the threat is wind and flying debris. FEMA’s guide for homeowners, P-320, designs safe rooms for 250 mph winds and a 15-pound two-by-four striking at 100 mph. ICC 500, the shelter standard, sets impact and pressure tests for walls, roofs and doors.

A container’s thin panels and standard cargo doors have not been tested to those criteria, and an empty container is light for its size. The National Weather Service lists sheds and storage units among the places that are not safe in a tornado; an unanchored, unreinforced container sits in the same group. Tying it down well enough to resist uplift is an engineering job in itself.

The door, the air and the way out

Even a reinforced container needs a door and frame that are tested as part of a shelter, vents that are protected from debris, and a way for people to get out if debris lands on the entrance. Cargo doors open outward and lock from outside, which is the opposite of what you want. ICC 500 includes requirements for latches and hardware so people are not trapped.

What it really costs

The appeal of a container is price. But once you add an engineer, steel reinforcement, excavation, drainage, coatings, a rated door and vents, the saving is usually gone. HomeGuide puts prefab shelters installed at $3,000 to $12,000 or more, and shelters for six people at $3,800 to $7,800. A purpose-built unit arrives already designed, tested and labeled, and is often installed in a day.

Our cost calculator shows typical installed prices by type and size, so you can compare with what a container conversion would really involve.

Better options for the same budget

If you were drawn to a container because you want something big and steel:

• A steel above-ground storm shelter bolted to a slab avoids digging and is tested for debris.
• A precast concrete storm shelter is heavy, resists rust and is made to sit in the ground.
• If you want to build it yourself, FEMA P-320 includes free safe room plans. Our DIY storm shelter guide explains what that involves.

Whichever you choose, check that it is designed to ICC 500 and FEMA P-361, ask how it is anchored, and register it with your local fire department once it is in.

Containers make good sheds, workshops and storage. For a place to ride out a tornado, choose something designed and tested for that job, and if you want help finding an installer who covers your area, we can do that for free.