CSLB General Building (B)Mechanical, Electrical, Plumbing CoordinationHard
Which of the following materials is NOT an approved fire blocking material under the California Residential Code?
- AUnfaced expanded polystyrene foam board alone
- BTwo-inch nominal lumber
- CTwo thicknesses of 1-inch nominal lumber with broken lap joints
- DBatts or blankets of mineral wool or glass fiber
Show answer & explanationAnswer & explanation
Correct answer: A. Unfaced expanded polystyrene foam board alone
Unfaced foam plastic insulation alone is not an approved fire blocking material because it does not provide the required resistance to flame spread through concealed cavities; approved materials include solid lumber, mineral wool batts, and gypsum board.
Why the other options are wrong
- B. Two-inch nominal lumber is a code-approved fire blocking material.
- C. Two layers of 1-inch lumber with staggered joints are an approved fire blocking assembly.
- D. Mineral wool or glass fiber batts are approved fire blocking materials when properly installed.
Approved Fire Blocking Materials
Code specifies acceptable materials for fire blocking, including solid wood, mineral wool, and gypsum board; foam plastic alone is not acceptable.
- 2-inch nominal lumber is acceptable
- Two layers of 1-inch lumber with broken joints are acceptable
- Mineral wool, glass fiber batts, and gypsum board are also approved
- Unfaced foam plastic alone does not meet fire blocking requirements
Memory trick: Wood, wool, and gypsum block; foam alone just can't do the job.