Enthusiasm abounds for earth-sheltered homes. They do have advantages, and to many who are not experienced in construction the concept seems like an ideal do-it-yourself project. In some cases this leads to disaster because there are plenty of pitfalls even for an experienced concrete contractor. Earth-covered houses require more attention to structural and waterproofing problems than conventional homes. Conventionally built homes rarely require structural engineering, or special know-how to keep the water out. Tried and true methods in above-grade houses are common knowledge because these dwellings have withstood the test of time.

HEAVY LOADS AND DRAINAGE PROBLEMS

There are two very important differences between earth-covered homes and conventional houses: The loads are real and permanent, and water is often present and may not run off quickly. The roofs on conventionally built houses are expected to support live loads ranging from 20 to 40 pounds per square foot. In earth-covered houses the permanent superimposed load is often 200 pounds per square foot, and temporary live loads can add another 50 pounds per square foot or more. And when water keeps coming into the living quarters of the house, you have a domestic crisis on your hands, not just a now-and- then problem.

DESIGN TIPS

In designing the roof slab system keep these points in mind: Short spans (12 to 16 feet) will have substantially less deflection than long spans (20 to 25 feet); slabs supported on three or four edges are much stiffer than those simply supported on two edges; deeper slabs and beams (12 to 24 inches) will behave much better than shallow depth systems (8 to 10 inches); slab or slab beam systems with end fixity (made continuous with vertical supports) will deflect less than systems which are simply supported; and, prestressed concrete slabs and beams are better for resisting heavy sustained loads with minimum deflection than mild steel reinforced concrete.