The waffle raft slab system involves building an ‘on-ground’ using perimeter formwork and expanded polystyrene Voidforms, separated by plastic spacers, to create reinforced concrete ribs beneath the slab surface.

The traditional ‘in-ground’ concrete slab requires digging of tyrnches, construction of a perimeter nib wall and subsequent backfilling. It is labour intensive, does not allow accurate measurement of concrete and can be subject to considerable delays if rain occurs.

Barnes VoidForm® improve energy efficiency of house slabs by increasing the R value of the floor, saving heating and cooling costs. Using 225mm Voidforms will give an R value of 1.86 approximately – 43% better than a conventional slab.

The waffle raft slab system has a number of advantages. The construction is simple as there are fewer stages in construction. Less site preparation is required, for example, on non expansive soils only topsoil and organic material must be removed. Construction is quicker as there are fewer stages in construction and all stages can be carried out by one trade, work can often continue in adverse weather conditions. Concrete volumes can be accurately calculated meaning wastage can be eliminated. All concrete is contained within formwork and defined areas. The Voidforms® provide ‘built in’ insulation. Quality control is simple, everything is open for inspection prior to pouring concrete. Only one concrete pour is required.