How can I insulate a concrete slab foundation that is on a sloped site?
To avoid having the slab lifted up off the ground by frost heaves, insulation must be applied at a 45-degree angle over a width of 4 feet along the entire length of the excavated face. The insulation must be buried at least 8 inches and placed flush against the wall, if the wall is already insulated on the inside. In general, the insulation rests on the gravel that surrounds the perimeter drain. Use water repellent polystyrene insulation (blue foam board for underground use) that is at least two inches thick.
