Commercial Building Inspector B2Wall Construction and Wall CoveringsEasy
A commercial building inspector is reviewing the exterior wall sheathing for a new Type III-B construction. The design specifies gypsum sheathing. What is the minimum thickness of gypsum sheathing required for this application?
- A1/4 inch (6.4 mm)
- B1/2 inch (12.7 mm)
- C5/8 inch (15.9 mm)
- D3/8 inch (9.5 mm)
Show answer & explanationAnswer & explanation
Correct answer: D. 3/8 inch (9.5 mm)
For exterior wall sheathing, gypsum sheathing is typically required to be a minimum of 3/8 inch (9.5 mm) thick. This provides adequate substrate for exterior finishes and some fire resistance, depending on the assembly.
Why the other options are wrong
- A. 1/4 inch gypsum is generally for curved surfaces or as a base layer, not exterior sheathing.
- B. 1/2 inch is common for interior walls and often used for exterior, but not the minimum.
- C. 5/8 inch is typically used for higher fire ratings or impact resistance.
Gypsum Sheathing Minimum Thickness
The minimum nominal thickness required for gypsum sheathing used as an exterior wall substrate.
- Gypsum sheathing provides a noncombustible substrate.
- It contributes to fire resistance when part of a rated assembly.
- Minimum thickness ensures durability and proper fastening of finishes.
Memory trick: Gypsum's skin, 3/8ths within.