Insulating Foundations

Insulating Foundation Walls

Because foundation walls give up a significant amount of heat, it's important to insulate poured-concrete and block foundation walls with a minimum of 1 in. of extruded polystyrene insulation (expanded polystyrene (EPS), polyisocyanurate, and polyurethane rigid insulations are not recommended for below-grade applications).

COLD-CLIMATE FOUNDATION INSULATION

Install insulation running the full height of the foundation wall. In cold climates, “taper” exterior foundation insulation as follows:

• Install 1-in.-thick 2x8-ft. tongue-and-groove sheets vertically from footing to sill plate.
• Next, place a second layer of half-sheets (2x4-ft.) extending down 4 ft. with joints offset.
• Follow with a third layer of 2x8 sheets running horizontally across the top of the foundation.

Learn more about this topic in the JLC Field Guide.