Article #22 - Where and How Should Perimeter Slab Insulation be Applied?
The insulation can be applied outside (see figure below) or inside (see figure below) the foundation wall.
Exterior applications require a metal flashing or durable finish for protection.
They must have a rigid, opaque, and weather-resistant covering that prevents the degradation of the insulation's performance. The protective covering must cover the exposed (above-grade) area of the insulation and extend to a minimum of 6 in. below grade.
The insulation can also be placed vertically along the foundation wall (figure above, interior) or horizontally under the slab (figure below).
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.