Residential Building Inspector B1Building Planning and Life SafetyHard
A residential building inspector is performing a framing inspection for a new dwelling. The plans indicate a wood structural panel subfloor. What is the minimum required nominal thickness for a wood structural panel subfloor where the floor joist spacing is 16 inches on center and the panel is not tongue and groove?
- A3/4 inch
- B3/8 inch
- C1/2 inch
- D5/8 inch
Show answer & explanationAnswer & explanation
Correct answer: C. 1/2 inch
According to IRC Table R503.2.1.1(1) for Allowable Spans for Wood Structural Panel Subfloor and Combined Subfloor Underlayment, for a joist spacing of 16 inches on center, a non-tongue-and-groove panel requires a minimum nominal thickness of 1/2 inch (12.7 mm).
Why the other options are wrong
- A. This thickness exceeds the minimum requirement for this scenario.
- B. This thickness is insufficient for a 16-inch joist spacing without tongue and groove.
- D. This thickness would be appropriate for larger joist spacing or combined subfloor/underlayment, but not the minimum for this scenario.
Subfloor Panel Thickness
Minimum nominal thickness of wood structural panels used for subflooring, based on joist spacing and panel type.
- Ensures structural integrity of the floor.
- Varies with joist spacing.
- Tongue and groove panels can span further.
Memory trick: For a 16-inch joist span, without T&G, a half-inch subfloor is the minimum to be.