CSLB General Building (B)Mechanical, Electrical, Plumbing CoordinationEasy
What is the primary purpose of fire blocking in a wood-framed residential structure?
- ATo reduce sound transmission between floors
- BTo restrict the spread of fire and hot gases through concealed spaces
- CTo provide structural support for load-bearing walls
- DTo prevent moisture intrusion into wall cavities
Show answer & explanationAnswer & explanation
Correct answer: B. To restrict the spread of fire and hot gases through concealed spaces
Fire blocking is installed to close off concealed draft openings, cutting off air movement that could allow fire to spread rapidly through hidden spaces such as stud cavities and soffits.
Why the other options are wrong
- A. Sound control uses different materials like resilient channels and insulation, not fire blocking.
- C. Fire blocking is not a structural element and carries no load.
- D. Moisture control relies on vapor barriers and flashing, not fire blocking.
Fire Blocking Purpose
Fire blocking material seals concealed spaces in framing to slow the spread of fire and combustion gases.
- Required in concealed wall and floor cavities
- Common materials include 2x lumber, gypsum board, and mineral wool
- Different from draft stopping, which limits air movement in larger concealed spaces
Memory trick: Block the path, stop the flash.