Only perimeter insulation can be used as load-bearing thermal insulation under foundation slabs that has the appropriate building authority approval. Since a foundation slab as a rigid floor slab transfers the building load downwards, the perimeter insulation underneath the slab must also be sufficiently pressure-resistant to be able to pass on the load to the ground. The decisive factor for this is the maximum permissible compressive stress fcd of the insulation.
Source: bauwion
