Bathroom drain through exterior wall studs
What's wrong here?
- Nothing. This installation is compliant
- Holes in exterior wall studs may not exceed 40 percent of the stud width
- Steel shield plates are required wherever a pipe passes through a stud
- A drain may not pass through two studs in a row; one of them must be notched instead
Show the answer and the code reference
The answer
Nothing is wrong. The holes are about 2-5/8 in. in 5-1/2 in. studs (roughly 48 percent), which R602.6 allows in an exterior wall because each bored stud is doubled and only two successive doubled studs are bored.
Correct choice: 1. Nothing. This installation is compliant
R602.6 item 2 allows any stud to be bored up to 60 percent of its width, with the hole edge kept at least 5/8 in. from the stud edge and not in the same section as a notch. In exterior walls and bearing partitions, a stud bored more than 40 percent must be doubled, and no more than two successive doubled studs may be bored that way. Here the two bored studs are both doubled 2x6s, the holes are centered with about 1-7/16 in. of wood on each side, and the studs past the stack carry only small cable holes. Compare a notch, which in an exterior wall is limited to 25 percent of the stud width.
How to fix it
No correction needed. If a third stud in a row had to be bored over 40 percent, reroute or have the framing designed for it; if a pipe ends up close to the stud face, add the steel shield plates the plumbing code calls for.
Code reference
IRC 2018 R602.6 — Drilling and notching—studs
Item 2: any stud may be bored if the hole is not more than 60 percent of the stud width, is kept 5/8 in. from the stud edge (the 2018 printing says 'not more than 5/8 inch', a known wording error that later editions correct to 'not less than'), and is not in the same section as a cut or notch. Studs in exterior walls or bearing partitions bored over 40 and up to 60 percent must be doubled, with not more than two successive doubled studs bored.
Drills citing R602.6
2024 IRC:changed: The 2024 IRC rewords R602.6 as prohibitions, measures holes against the stud 'depth' rather than 'width', and states the edge distance as 'not less than 5/8 in.' The 60 percent maximum and the doubling requirement over 40 percent in exterior and bearing walls, with no more than two successive doubled studs bored, carry over. Based on published 2024 text seen in search results, not checked against the printed code. Confidence: medium
Minnesota
Minnesota adopts the 2018 IRC with Minnesota amendments as the Minnesota Residential Code (Minn. Rules ch. 1309). No Minnesota amendment to R602.6 is known. DLI is adopting the 2024 IRC as the next edition; see the 2024 IRC note.
About the Minnesota Residential CodeWhy the other choices are wrong
- Holes in exterior wall studs may not exceed 40 percent of the stud width. 40 percent is the point where doubling kicks in, not the limit. R602.6 allows holes up to 60 percent in exterior and bearing wall studs when those studs are doubled and no more than two successive doubled studs are bored, which is what was done here.
- Steel shield plates are required wherever a pipe passes through a stud. Shield plates are only needed where a pipe runs close to the face of the framing (within about 1 to 1-1/4 in., depending on the plumbing code). A 2-5/8 in. hole centered in a 2x6 leaves about 1-7/16 in. of wood on each side, and the pipe sits farther back than that.
- A drain may not pass through two studs in a row; one of them must be notched instead. The rule runs the other way: notches in exterior wall studs are limited to 25 percent of the width, while bored holes may go to 60 percent with doubling. Up to two successive doubled studs may be bored.