How to Install Insulation in a Slab Edge

Slab-on-grade foundations are suitable foundations only in areas where temperatures don't freeze. But adding insulation to the perimeter of such a slab nonetheless can improve the concrete's resistance to the effects of cold temperatures. Exterior insulation can serve as part of the barrier to moisture penetrating the concrete. Termites are a concern in some areas, though, and local regulations may specify measures for exterior slab insulation to prevent insect infiltration through foam board. Rubber membranes used for protection of the foam board insulation also act as termite shields.

Things You'll Need

• Rigid extruded polystyrene foam board, R-15 value (3-inch), approved for below-grade use
• Protection board, rubber membrane, ethylene propylene diene terpolymer (EPDM) type
• Gravel, crush or road mix
• Aluminum flashing
• Silicone caulking
• Caulking gun

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Instructions

1. • 1

     Install the foam board directly against the exterior slab edge, from the top of the slab to the bottom of the thickened edge of the slab. Insulate along the perimeter of the slab, making sure the coverage is continuous and complete. Add insulation between heated and unheated parts of the slab, such as between the house and the garage, as necessary.

   • 2

     Cover the exterior face of the foam board with the rubber membrane according to manufacturer instructions. Backfill against the slab with gravel material, sloping away from the house.

   • 3

     Place aluminum flashing above-grade below the bottom of the siding. Caulk the seam with the silicone caulking, using the caulking gun.