Sixteen years ago we had an Isoquick 300mm Peripor insulated raft foundation installed. The Structural Engineer specified 200mm compacted type 1 with 50mm thickness of 3mm granite fines on top, type 1 to be extended 700mm beyond outside edge of raft. The raft was 200mm thick with two layers of A393 reinforcing mesh and an additional third layer, 1200mm wide, around edge of two storey part of foundation. All this was for our ground conditions, yours could be very different.