A contractor is framing a wall for a bathroom, and the plumbing requires a 3-inch diameter waste pipe to pass horizontally through a 2x4 stud. What is the maximum diameter hole that can be bored through a 2x4 stud in a non-bearing wall, according to common building codes?
- A1-1/2 inches
- B1-3/4 inches
- C2-1/8 inches
- D2-1/2 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 1-3/4 inches
For 2x4 studs in a non-bearing wall, the maximum hole diameter permitted by common building codes is typically 40% of the stud's actual depth. A 2x4 stud has an actual depth of 3.5 inches, so 40% of 3.5 inches is 1.4 inches. However, codes often round up or specify a slightly larger practical limit, with 1-3/4 inches (1.75 inches) being the common maximum for plumbing in 2x4s, assuming the hole is not too close to the edge or other holes. A 3-inch pipe cannot pass through a 2x4.
Why the other options are wrong
- A. This is too restrictive; a larger hole is typically allowed.
- C. This exceeds the maximum allowable hole size for a 2x4 stud, potentially weakening the stud.
- D. This significantly exceeds the maximum allowable hole size for a 2x4 stud, which would compromise its structural integrity.
Stud Boring Limits
Maximum size and location of holes or notches permitted in wood studs to maintain structural integrity, varying by stud size, whether it's bearing or non-bearing, and the type of modification.
- Holes in non-bearing studs are generally limited to 40% of the stud's depth.
- Holes in bearing studs are typically limited to 60% of the stud's depth, but not more than 40% if the stud is part of a doubled stud.
- Notches are more restrictive, usually limited to 25% of the stud's depth and not permitted in the middle third of bearing studs.
Memory trick: Holes are simple, notches are tricky, bearing walls are picky.