A waffle slab foundation, also called a ribbed slab foundation, is an above-ground type of foundation used to provide load-bearing capacity in expansive, rocky or hydro collapsible soils. The foundation is created by placing a series of single-use plastic forms set directly on grade to create a grid of ribs, and then monolithically pouring a post tensioned, rebar or Fiber reinforced concrete slab, usually 4 to 8 inches thick between the ribs. Sometimes, expanded polystyrene blocks are used instead of plastic forms, to prevent creating an air space under the slab. The monolithic pour creates concrete beams running throughout the footprint and perimeter of the foundation, with voids between, in one operation. The completed slab then sits on the ground bearing on the ribs created between the forms. The void areas underneath the slab allow for soil movement.