Modular steel or poured concrete

Where the work happens

A CUBE Bunker is welded, coated and finished inside a plant in Utah. The cubes arrive with walls, wiring and built-ins already in, and a crane sets them in the excavation. The hole is open for days instead of the weeks that forming, pouring and curing a structure in place usually takes.

Poured concrete is built where it stands. The excavation stays open while crews set forms and steel, pour, wait for the concrete to gain strength, strip the forms and waterproof. Weather and inspections set the pace.

Water and corrosion

Concrete and steel both fail when water gets to them. Reinforced concrete depends on a minimum cover of concrete over the rebar, waterproofing and drainage to keep the steel inside dry. A steel structure depends on its coating, waterproofing and drainage for the same reason. In both cases the drainage around the structure does as much work as the structure itself.

Shipping containers are a third option, and a poor one

Containers are built to carry their load on the corner posts and to be stacked, not to hold several feet of wet soil on a flat roof or soil pressure on long side walls. The international container safety tests check the roof with roughly 660 pounds over a small patch. Burying one without heavy reinforcement invites the walls and roof to bend in.

When each makes sense

• Modular steel fits when you want a fixed price for a known layout, a short time on site, and the option to add rooms later.
• Poured concrete fits very large or unusual shapes, or a shelter built into a new house foundation as the house goes up.

Questions