Waffle raft construction

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. These are laid out on a levelled area. The construction is ideally suited to very reactive clay sites. It does not have the problems associated with stiffened raft slabs, which have their beams embedded in the reactive clays.

The slab would be designed to the engineer's specifications and installed to manufacturer's specifications.

Diagram of a section showing waffle raft slab. Waffle raft is 1,090 wide with spacing of 110 between waffles. It shows the vapour barrier, formed void and slab mesh (thickness of 85 mm).
Section showing waffle raft slab
Photo of polystyrene void forms below the reinforcement.

Polystyrene void forms below reinforcement