Article #116 - Why is Perimeter Slab Insulation Important?

Heat loss through a slab foundation.

A substantial amount of heat is lost through an uninsulated slab, resulting in cold, uncomfortable floors. Even if the foundation wall is insulated vertically under the slab (see figure to the right), significant heat is still lost from the slab edge that is closest to the cold outside air.

In some cases, perimeter slab insulation can be "traded-off" using a software tool like REScheck or COMcheck. Additional insulation is added in another part of the structure to compensate for the missing insulation in the slab. The code permits this trade-off, but when carpet is placed on a cold slab, the higher humidity levels that result can attract dust mites and mold.