Vanity wall at rough-in
What's wrong here?
- The PEX in the notched middle stud sits at the face of the stud with no steel nail plate over it
- The notch is deeper than a stud may be cut
- Hot and cold PEX may not pass through the same notch or hole
- Nothing. This installation is compliant
Show the answer and the code reference
The answer
Both PEX lines run through a notch at the front edge of the middle stud, well within 1 in. of the face, and no steel nail plate covers them.
Correct choice: 1. The PEX in the notched middle stud sits at the face of the stud with no steel nail plate over it
UPC 312.9 requires plastic and copper piping that penetrates framing to within 1 in. of the exposed edge to be covered by a steel nail plate at least No. 18 gauge, extending at least 1-1/2 in. past the pipe. A notch at the stud face puts the PEX right where the drywall screws and the vanity or trim nails go. A screw through PEX may not leak until weeks after the wall is closed, and then it leaks inside the wall. The right stud is done correctly; the middle one was missed.
How to fix it
Nail an 18-gauge (or heavier) steel stud guard over the notch in the middle stud before insulation and drywall, sized to cover both lines with at least 1-1/2 in. to spare above and below. A centered bored hole, like the one in the left stud, avoids the need for a plate.
Code reference
UPC 2018 312.9 — Steel Nail Plates
Plastic and copper piping that penetrates framing members to within 1 in. of the exposed framing edge must be protected by steel nail plates not less than No. 18 gauge (0.0478 in.) thick, extending along the framing member at least 1-1/2 in. beyond the outside diameter of the pipe or tubing.
Drills citing 312.9
Minnesota
Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). Search-result snippets show Minn. Rules 4714.0312 (Minnesota's amendments to UPC 312) restating 312.9 with the same No. 18 gauge plate, 1 in. and 1-1/2 in. figures, but what Minnesota changed in 312.9, if anything, could not be confirmed. The requirement this drill turns on reads the same in the snippets as in the model code.
About the Minnesota Plumbing CodeWhy the other choices are wrong
- The notch is deeper than a stud may be cut. The notch is about 3/4 in. deep, roughly 20 percent of a 3-1/2 in. stud. The building code (IRC R602.6) allows 25 percent in a bearing wall and 40 percent in a non-bearing wall, so the cut itself is fine. The problem is that the pipe is unprotected.
- Hot and cold PEX may not pass through the same notch or hole. No UPC rule requires separate penetrations for hot and cold lines. They only need to be protected and supported.
- Nothing. This installation is compliant. The right stud shows the fix: a steel plate over the notch. The middle stud has the same notch and no plate, so a drywall screw or trim nail will find the PEX.