Commercial Building Inspector B2General Administration, Permits, and PlansMedium
A commercial building inspector is evaluating the fire-resistance rating of a bearing wall separating two tenant spaces in a Type V-A building. The wall is constructed of 2x4 wood studs at 16 inches on center, with 5/8-inch Type X gypsum board installed on each side. There is no insulation in the wall cavity. What is the fire-resistance rating of this wall assembly according to the IBC?
- A0.5-hour
- B1-hour
- C2-hour
- D1.5-hour
Show answer & explanationAnswer & explanation
Correct answer: B. 1-hour
According to IBC Table 721.1(2), Item 2-1.1, a wood stud wall with 5/8-inch Type X gypsum board on each side, no insulation, and 2x4 studs at 16 inches on center provides a 1-hour fire-resistance rating.
Why the other options are wrong
- A. A 0.5-hour rating is for less protective assemblies, like 1/2-inch gypsum board.
- C. 2-hour ratings require significantly more fire protection, such as double layers of gypsum or heavier construction.
- D. 1.5-hour ratings typically involve more complex assemblies or specific fire-rated insulation.
Wood Stud Wall Fire Rating
The fire-resistance rating of a wood stud wall assembly is determined by the materials used (e.g., gypsum board type and thickness), stud size and spacing, and whether insulation is present, as specified in IBC Table 721.1(2).
- 5/8-inch Type X gypsum board is a common fire-rated material.
- Gypsum board thickness and type are crucial for fire resistance.
- IBC Table 721.1(2) provides prescriptive fire-resistance ratings for various wall assemblies.
Memory trick: For a 'Wall' to 'Resist Fire', check its 'Gypsum Shield' and 'Stud' strength.