Improving the energy efficiency of a structure’s building envelop doesn’t end with the walls, windows and attic. The foundation of a home whether a basement, crawl space or slab on grade needs to be insulated too.
The International Energy Conservation Code (IECC) requires slab edge insulation and 36 states have adopted this IECC standard. The IECC code requires R-10 at the slab edge. The requirement runs from the Canadian border (and Alaska) south, covering Climate Zones 4 and above. In California Title 24 mandates insulated edges for radiant slabs even if in Zones 1, 2, and 3, which predominate in the state.