Waffle raft slabs

Waffle raft slab construction is quite different from stiffened raft and footing slab structures. The slab ribs are formed on top of the ground using a grid of polystyrene void forms which are laid out on a levelled area. It is ideally suited to very reactive clay sites and does not have the problems associated with stiffened raft slabs that have their beams embedded in the reactive clays.

Diagram of a waffle slab with masonry veneer on the left wall resting on the edge beam.

Diagram of a waffle raft slab being set up displaying the cardboard void forms set in a rectangular pattern between the formwork on the left and rear edges of the diagram. There are bar chairs at each corner of the void forms.