Homes Built Slab-on-Grade

Homes built on a concrete slab that is installed on compacted or natural soil are said to be built "slab-on-grade." Most such concrete slabs are reinforced with steel that helps prevent cracking and bending.

In new home construction:
When building a new slab-on-grade house that will contain a concrete or masonry saferoom, the slab must be made thicker where the shelter will be built in order to serve as a footing for the shelter walls, and to provide structural support.

Basic saferoom design with concrete blocks, traditionally cast concrete, and for 4- and 6-inch flat ICF walls and 6-inch waffle grid ICF walls may be found in the FEMA publication Taking Shelter From the Storm: Building A Safe Room Inside Your House, which includes construction plans, materials, and construction cost estimates. It's available from FEMA at no charge by calling toll free (800) 480-2520.

In existing home construction:
Building a saferoom in an existing slab-on-grade house requires the removal of a part of the slab and replacing it with a thickened slab if a concrete or masonry block shelter is built. Since this is usually impractical, an alternative would be a properly designed and constructed wood-frame saferoom built with plywood and steel on wood studs.

In this type of construction, the shelter walls and ceiling structure must be isolated from the surrounding house structure. Layers of plywood and heavy gauge sheet metal are installed on the wall side selected for retrofit. This method requires anchorage of wall sill plates to the slab and the walls to the new ceiling joists installed below the existing ceiling.

In most cases, it will be more practical to purchase an in ground shelter or a shelter that attaches to the house.

Sample of in ground shelter

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