Commercial Building Inspector B2Public Safety and Special ConstructionMedium
A building inspector is reviewing the plans for a new three-story Group R-2 apartment building. The plans indicate the use of fireblocking in concealed spaces of combustible construction. According to IBC, what is the maximum dimension permitted for a concealed space of combustible construction without the installation of fireblocking?
- A10 feet (3048 mm)
- B20 feet (6096 mm)
- C40 feet (12192 mm)
- D30 feet (9144 mm)
Show answer & explanationAnswer & explanation
Correct answer: A. 10 feet (3048 mm)
According to IBC Section 718.2.1, 'Concealed spaces in walls, floor/ceiling assemblies, attic spaces and crawl spaces shall be fireblocked such that the maximum dimension of any concealed space is not more than 10 feet (3048 mm) in any direction.' This is a fundamental requirement for preventing fire spread within concealed spaces.
Why the other options are wrong
- B. 20 feet is double the permitted length and would require fireblocking.
- C. 40 feet is a very large dimension and would promote rapid fire spread without fireblocking.
- D. 30 feet is far too large and would significantly violate fireblocking requirements.
Fireblocking Requirements
Fireblocking is required in concealed spaces of combustible construction to subdivide them into smaller compartments, limiting the spread of flame and smoke.
- Required in walls, floors, ceilings, attics, and crawl spaces.
- Limits concealed space dimension to 10 feet.
- Materials typically include 2-inch nominal lumber or 1/2-inch gypsum board.
Memory trick: Fireblocking: Keep the concealed fire within a 10-foot box.