Edward R. Carr, big scale Washington area developer, saves $12.50 a house and eliminates slab cracking and settlement problems through the use of a residence foundation design called "intermediate pier floor slab construction." The new ground slab design has been required by FHA's District of Columbia office for approximately the past 5 years, with nearly 5,000 installations to date, many of them by Carr.
The important difference between the new floor design and conventional slab-on-ground construction is that the concrete floor, in combination with welded wire fabric, is a semi-structural slab somewhat similar to a bridge deck. The weight of the slab on its residential load actually is borne by the foundaton walls and the intermediate supporting piers which penetrate to undistribed soil. In contrast the conventional slab-on-ground is floating and in theory is supported entirely by the soil upon which it is poured.
The first construction step, after determining the floor level of the house, is to run up footing walls in the usual manner, and build piers to the same height of solid concrete block on 6 to 8 foot centers in each direction of the floor plan. The next operation, using available material, to with in 6 inches of the tops of the piers. Transite heating ducts are then placed, leading off from the furnance base which has been previously poured, and plumbing is roughed in.
The final operation is placing the ready mixed concrete. Here care is taken to be sure that the welded wire fabric is properly positioned in the 4 inch thick slab, about one inch from the bottom. The reinforcement must be near the bottom of the slab to lend tensile strength in the area of greater deflection.