According to EPA, the slab-edge insulation requirement in the TBC only applies to slab-on-grade floors with a floor surface less than 12" below grade. Basements are exempt under this definition, except for walkout basements. Vented crawlspaces don\'t require insulation because the slab is not part of the thermal envelope. Unvented crawls may need insulation, depending on the depth of the slab. Up to 25% of the slab edge may be uninsulated.