A thick layer of foam on a bed of compacted gravel supports the building, prevents frost damage, and keeps the heat inside
The author occasionally uses a thin layer of flowable fill to create a void-free surface beneath the supporting foam layer.
An insulating layer of rigid foam forms a structural base for a monolithic slab foundation. The foam covers the foundation's entire footprint, extending beyond it by about 24 inches on all sides.
The author forms a monolithic, thickened-edge slab using 4-inch-thick foam board braced with framing lumber.
After the air-vapor barrier is installed, the interior is filled with compacted gravel that's contoured to form the thickened edge. Long screws pushed through the vertical foam hold it to the hardened concrete.
In this alternative to the monolithic slab method, ICFs outline the foundation and are poured first. Forms are stabilized with framing lumber cleats, staked through the foam into the gravel base.