A passive slab foundation is a raft that is fully insulated from contact with the ground below eliminating any thermal bridging. Insulation forms the shuttering for a concrete pour, and layering of the insulation allows a ring beam to be formed around the perimeter and thickening under load bearing internal walls. Reinforcing steel is added to the raft according to calculations from a structural engineer to ensure all loadings and ground conditions are accounted for. Due to the raft having a very large surface area compared to traditional strip foundations, the load at any given point under the house is much lower. The structural engineer needs to design the raft to suit ground conditions, which is why a full ground bearing test and soil analysis was undertaken at the start of the project.