Residential Building Inspector B1Public Safety and Special ConstructionMedium
An inspector is reviewing the construction of a masonry chimney serving a wood-burning fireplace. What is the minimum wall thickness required for the masonry of the chimney to be considered solid (not hollow or block with voids)?
- A8 inches (203 mm)
- B12 inches (305 mm)
- C4 inches (102 mm)
- D6 inches (152 mm)
Show answer & explanationAnswer & explanation
Correct answer: C. 4 inches (102 mm)
For masonry chimneys, the minimum wall thickness of solid masonry, such as brick, is 4 inches (102 mm). This thickness is necessary to provide adequate structural integrity and fire resistance for the flue. If unlined, 8 inches is required.
Why the other options are wrong
- A. This is the minimum thickness for unlined masonry chimneys, or for specific structural elements, but not general solid masonry walls with liners.
- B. This thickness is excessive and not required for standard solid masonry chimney walls.
- D. This is not a standard minimum for solid masonry chimney walls.
Solid Masonry Chimney Wall Thickness
The minimum thickness for the solid masonry (e.g., brick) of a chimney wall.
- Applies to solid masonry construction
- Minimum 4 inches (102 mm) thick
- Assumes the presence of a flue liner
Memory trick: Four inches of solid brick, for a chimney's quick trick.