Residential Building Inspector B1Wall Construction and Wall CoveringsEasy
A residential building inspector is reviewing the plans for a new single-family dwelling. The plans indicate that moisture-sensitive exterior wall coverings will be installed. According to the 2021 IRC, what is the minimum required air space between the exterior wall covering and the water-resistive barrier?
- A1/2 inch
- B3/8 inch
- C1/4 inch
- D1/8 inch
Show answer & explanationAnswer & explanation
Correct answer: C. 1/4 inch
For moisture-sensitive exterior wall coverings, the 2021 IRC requires a minimum 1/4-inch space between the exterior wall covering and the water-resistive barrier to allow for drainage and drying.
Why the other options are wrong
- A. This provides ample space but exceeds the minimum code requirement, potentially adding unnecessary cost or complexity.
- B. While providing more space, 3/8 inch is not the minimum required by code; 1/4 inch is sufficient.
- D. This spacing is insufficient for adequate drainage and drying of moisture-sensitive materials.
Moisture-Sensitive Exterior Wall Covering Air Space
A minimum 1/4-inch clear air space is required between moisture-sensitive exterior wall coverings and the water-resistive barrier.
- Applies to moisture-sensitive materials (e.g., wood siding, fiber cement siding).
- Promotes drainage and drying.
- Prevents moisture accumulation behind the siding.
Memory trick: Keep the 'Sensitive' walls 'Quarter' dry with an air gap.