Sheath with two layers of ¾-inch plywood inside and one layer of ¾-inch plywood outside. Cover plywood with drywall or other interior wall finish.
Grout all cells and provide continuous bond beam at the top of walls. Embed straps into bond beam to tie the ceiling to the walls.
Use 8-inch concrete block with #5 rebar at corners and every 4 feet maximum.
Keep the safe room ceiling separate from house framing—don’t attach it to the floor or ceiling. Use two layers of ¾-inch plywood and one layer of 14-gauge steel, with steel as the inner surface.
Double 2x4s with stud-to-plate connectors at each stud. Bolt double-sill plate to slab.
Despite the fact that tornado and hurricane zones cover most of the country, the demand for safe rooms and storm shelters remains limited. Many builders offer them, but few buyers bite.
As a former builder, I hate to think of people being hurt in a house that I worked on. When I built and remodeled houses in Nashville, Tenn.—the buckle of the tornado belt—I never built a safe room or saw one installed. Now, not building one seems outright reckless. Extreme storms are making headlines on a regular basis, so why are safe rooms being ignored?
The problem is that safe rooms aren’t run-of-the-mill add-ons. They must be built exactly as designed because the result of a site-built safe room failure is unthinkable. But safe rooms are an undertaking. They can’t be bolted onto a wood frame floor over a crawlspace or basement. To build a safe room in a house over a crawlspace, the earth would need to be built up such that a slab could be poured at floor level, and that’s expensive.
The solution is to build a safe room into the floor plan. If you can’t build with a basement in tornado zones, don’t compromise with a crawlspace. It’s more practical to build a slab on grade house so that the safe room can be bolted directly to the slab. One way to defray material costs is to design the safe room into existing living space, such as an interior bathroom; you also can build one in the garage.
The payoff is that safe rooms and storm shelters can prevent fatalities, and saving lives is good business. As a dad, I can’t imagine not having one in Tornado Alley. Safe rooms are relatively affordable when rolled into a mortgage, and grants and incentives are available. Reinforcing an existing room in the center of a house is a great way to lower the cost of a safe room in dollars, feet, and lives.
Dry stack 4-inch solid masonry units to fill stud cavity; fur out framing with ½-inch drywall spacers along the bottom plate and ¾-inch wood furring strips on the outer face of studs.