• Installing rigid insulation, typically foam board, directly against the exterior of the slab and footing
• Building a “contained” or “floating” slab with interior rigid insulation, typically foam board.

If insulation is installed on the exterior of the slab:

• Install it from the top of the slab to the bottom of the frost line unless a termite inspection gap is required.
• Encapsulate or cover the exterior face of the insulation with a protective membrane to serve as a capillary break and to protect the insulation from termites.
• Cover the above-grade portion of the insulation exposed to the outside air using a stucco coating, pressure-treated wood, brick, or aluminum flashing. When covering insulation, be conscious of how to detect termites in areas prone to termite infestation. Some states in termite-prone areas address this issue by requiring a termite inspection gap near the top of the slab insulation.

Source: EERE, U.S. Department of Energy