When exterior insulation board is used, how far below the grade must it extend?

When exterior insulation board is used, how far below the grade must it extend?

• A. 2 inches above, 5 inches below
• B. 12 inches below
• C. 3 inches above, 6 inches below
• D. 8 inches below

Answer: (B)

Extending exterior insulation below grade is about protecting the insulation and preserving a continuous thermal barrier where moisture and soil conditions can affect the wall. The minimum requirement is to have the insulation extend 12 inches below grade. This depth helps shield the insulation from moisture, soil contact, and potential damage during backfilling, while maintaining effective insulation along the foundation. Other options don’t meet the protection and continuity needs: extending only a shallow amount below grade doesn’t guard against moisture and damage, and including above-grade extensions isn’t addressing the below-grade exposure.

Extending exterior insulation below grade is about protecting the insulation and preserving a continuous thermal barrier where moisture and soil conditions can affect the wall. The minimum requirement is to have the insulation extend 12 inches below grade. This depth helps shield the insulation from moisture, soil contact, and potential damage during backfilling, while maintaining effective insulation along the foundation.

Other options don’t meet the protection and continuity needs: extending only a shallow amount below grade doesn’t guard against moisture and damage, and including above-grade extensions isn’t addressing the below-grade exposure.