Residential Building Inspector B1Wall Construction and Wall CoveringsMedium
A residential building inspector is observing the installation of a masonry chimney in a new single-family home. The chimney is constructed with solid masonry units. What is the minimum required thickness for the wall of the masonry chimney, not including the flue lining?
- A6 inches
- B4 inches
- C2 inches
- D8 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 4 inches
According to IRC Section R1003.8.1, masonry chimneys are required to have a minimum wall thickness of 4 inches (nominal) of solid masonry units, not including the flue lining.
Why the other options are wrong
- A. While structurally sound, 6 inches exceeds the minimum code requirement for a typical masonry chimney wall.
- C. 2 inches is insufficient for structural integrity and fire protection for a masonry chimney wall.
- D. 8 inches is typically the thickness for a structural masonry wall or foundation, not the minimum for a chimney wall.
Masonry Chimney Wall Thickness
Masonry chimney walls, excluding the flue lining, must have a minimum thickness of 4 inches of solid masonry units.
- Applies to masonry chimneys.
- Ensures structural stability and fire safety.
- Flue lining is a separate component and not included in this thickness.
Memory trick: A solid 'Four' inches of masonry makes a safe chimney wall.