Residential Building Inspector B1Wall Construction and Wall CoveringsEasy
A builder is constructing a new residential dwelling with 2x4 wood studs spaced 16 inches on center. What is the minimum nominal thickness required for gypsum board installed parallel to the framing members on a wall that is not a fire-resistance-rated assembly?
- A1/2 inch
- B1/4 inch
- C3/8 inch
- D5/8 inch
Show answer & explanationAnswer & explanation
Correct answer: C. 3/8 inch
For gypsum board applied parallel to framing members on walls, the 2021 IRC specifies a minimum 3/8-inch thickness when studs are 16 inches on center.
Why the other options are wrong
- A. 1/2-inch gypsum board is commonly used and permitted but not the minimum required for this specific scenario.
- B. 1/4-inch gypsum board is typically used for curved surfaces or as a base layer, not for general wall applications at 16 inches on center.
- D. 5/8-inch gypsum board is often used for fire-resistance-rated assemblies or where greater impact resistance is desired, exceeding the minimum for this condition.
Gypsum Board Thickness (Walls)
The minimum thickness of gypsum board required for wall applications depends on stud spacing and orientation (parallel or perpendicular to framing).
- 3/8 inch is minimum for 16" o.c. studs, parallel application.
- 1/2 inch is minimum for 24" o.c. studs, parallel application.
- Any thickness can be used for perpendicular application with studs up to 24" o.c.
Memory trick: Gypsum walls need the right thickness, based on how far apart the studs are.