The insulated slab former produced by Isoquick and supplied by local company Logix ensures that neither the ground floor slab nor the timber frame touch the ground, therefore avoiding any cold bridges (direct paths for heat to be lost through the building fabric) which are really difficult to avoid in traditional construction!
In this instance, the house is sitting on 300mm (12 inches) of expanded BSAF Polystyrene built up in two interlocking layers. For comparison the minimum requirement for new-build construction would typically be in the range of 100-125mm of insulation!
This insulation slab is then surrounded by a Polystyrene up-stand, which acts as shuttering for the concrete slab while it is being poured, and ensures that the insulation is completely continuous between the floor and the walls. (again, usually very difficult to achieve in traditional cavity construction.)
On top of this 300mm insulation sits a 300mm reinforced concrete slab, this provides the ground floor slab, and also supports the timber frame- it is designed to be stiff enough that any point loads are evenly distributed to avoid crushing the polystyrene.
It may be bulky, but essential to the thermal performance of the house!