Perimeter foundation insulation is required in colder climates to reduce the heat-loss from a slab-on-grade to the below grade foundation wall. In most cases, the insulation is only required up to two feet below the grade since heat loss in the soil is negligible. In mild climates a 12-inch depth is sufficient.

Materials
Nominal 2-inch-thick extruded polystyrene, cellular glass, or other closed-cell type rigid board.

Adhesive material recommended by waterproofing system manufacturer.

Execution
Apply rigid insulation to vertical below grade foundation wall.

Backfill as required.