CSLB General Building (B)Finishes and Building EnvelopeEasy
A drywall installer is finishing a one-hour fire-rated corridor wall required by code. Which type and thickness of gypsum board is typically specified to achieve this rating?
- A3/8-inch moisture-resistant board
- B1/2-inch regular gypsum board
- C5/8-inch Type X gypsum board
- D1/4-inch gypsum lath
Show answer & explanationAnswer & explanation
Correct answer: C. 5/8-inch Type X gypsum board
Type X gypsum board at 5/8-inch thickness contains glass fibers that slow heat transfer, and a single layer on each side of a wood or metal stud wall is the standard assembly used to achieve a one-hour fire rating.
Why the other options are wrong
- A. Moisture-resistant board addresses dampness, not fire rating.
- B. Regular board lacks the fire-resistive additives needed for a rated assembly.
- D. Gypsum lath is thin and used with plaster, not for rated wall assemblies.
Type X Gypsum Board
A fire-resistant drywall product with reinforcing glass fibers, commonly used in 5/8-inch thickness to achieve one-hour fire-rated assemblies.
- 5/8-inch Type X = standard 1-hour rating component
- Used in garages, corridors, and shared walls
- Different from standard 1/2-inch drywall
Memory trick: 'X marks the eXtra fire protection.'