Foundation perimeter and slab insulation would be required at which of the following?

• A. Walk out basement
• B. Fully finished basement with interior insulation
• C. Slab-on-grade with no basement
• D. Raised pier foundation

Answer: (A)

The key idea is insulating where heat can escape at the edge of the building’s thermal envelope, especially where concrete and ground meet. A walk-out basement has exterior foundation walls running around the perimeter and a slab-on-grade interface that sits against soil. Because the living space extends to those foundation edges and the slab edge is in contact with the ground, insulation around the full foundation perimeter plus at the slab edge creates a continuous thermal barrier and helps control moisture movement.

In contrast, a fully finished basement that relies on interior insulation uses insulation on the inside of the walls to meet the energy needs, so exterior foundation perimeter insulation is not required in that scenario. A slab-on-grade with no basement lacks a continuous perimeter foundation wall to insulate, so foundation perimeter insulation isn’t applicable there. A raised pier foundation also doesn’t form a continuous perimeter wall to insulate in the same way, so the same requirement wouldn’t apply.