CSLB General Building (B)Mechanical, Electrical, Plumbing CoordinationHard
A masonry chimney passes through a combustible wood-framed floor/ceiling assembly. What is the code-required treatment at this penetration to address fire safety?
- ANo fire blocking is required since masonry itself is noncombustible
- BStandard fiberglass batt insulation may fill the entire gap
- CWood fire blocking may directly contact the chimney masonry
- DA minimum 2-inch airspace must be maintained with noncombustible fire blocking, such as mineral wool
Show answer & explanationAnswer & explanation
Correct answer: D. A minimum 2-inch airspace must be maintained with noncombustible fire blocking, such as mineral wool
Where combustible framing surrounds a masonry chimney, code requires maintaining clearance (commonly a minimum 2-inch airspace) from combustibles, with the gap fire blocked using noncombustible material such as mineral wool rather than ordinary wood or standard fiberglass batts, to prevent heat transfer and ember intrusion.
Why the other options are wrong
- A. Fire blocking is still required at the penetration itself to seal the concealed space, even though masonry is noncombustible.
- B. Standard fiberglass batt insulation is not a substitute for the required noncombustible fire blocking material at this high-heat location.
- C. Wood must not be in direct contact with the chimney; combustible clearance must be maintained.
Chimney Penetration Fire Blocking
Where masonry chimneys pass through combustible floor/ceiling assemblies, code requires maintaining clearance from combustibles and fire blocking the gap with noncombustible material like mineral wool.
- Minimum airspace clearance protects framing from heat transfer.
- Noncombustible fire blocking (mineral wool) is required, not wood or standard batts.
- Direct wood-to-masonry contact at chimneys is prohibited.
Memory trick: 'Keep wood off the chimney's hot skin—mineral wool seals it in.'