Spot the Violation

PlumbingDrainage piping & fittingsLevel 12018 UPC

New laundry standpipe in an older house

Laundry room wall opened up between two studs. An existing black ABS stack runs up the stud bay with a sanitary tee whose branch faces left. A new white PVC standpipe drops from below a washer valve box into a PVC P-trap, and the trap arm runs right into the branch of the black tee. The PVC joints show purple primer, a front-load washer stands to the right, and a laundry basket sits on the floor. 2 IN ABS DWV ASTM D2661 2 IN PVC DWV SCH 40
Main-floor laundry room, washer drain being replaced

What's wrong here?

  1. ABS and PVC may never be connected in the same drainage system
  2. A clothes washer standpipe and trap arm must be 3 in. pipe
  3. The PVC trap arm is solvent-cemented directly into an ABS fitting without a listed transition fitting
  4. Nothing. This installation is compliant
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Show the answer and the code reference

The answer

White PVC has been primed and glued straight into the hub of a black ABS sanitary tee. A joint between different plastic piping materials needs an approved adapter or transition fitting listed for that transition.

Correct choice: 3. The PVC trap arm is solvent-cemented directly into an ABS fitting without a listed transition fitting

ABS and PVC are different plastics, and ordinary PVC primer and cement (or ABS cement) are listed for one material, not for bonding the two together. A PVC-to-ABS solvent joint may hold at first, but it is not a true solvent weld and can pull apart or weep, inside a wall where no one will see it. UPC 705.10 covers joints between different materials, and 705.10.3 requires an approved adapter or transition fitting listed for the specific transition when plastic pipe joins another type of plastic or another material.

How to fix it

Cut the PVC trap arm back and join it to the ABS with a listed shielded transition coupling (an elastomeric sleeve with a stainless shield and clamps, rated for ABS to PVC). Or cut in a new ABS tee and run ABS from the trap. Then support the trap arm so the coupling is not carrying the trap's weight.

Code references

  • UPC 2018 705.10.3 — Plastic Pipe to Other Materials

    Where plastic pipe connects to another type of plastic or another piping material, approved adapter or transition fittings listed for the specific transition intended are to be used.

    Drills citing 705.10.3

  • UPC 2018 705.10 — Joints Between Various Materials

    Joints between different piping materials are to be made in accordance with the manufacturer's installation instructions and the subsections that follow, including 705.10.3 for plastic pipe.

    Drills citing 705.10

Minnesota

MN adopts this rule as writtenConfidence: medium

No Minnesota amendment to 705.10.3 is known; check ch. 4714 before relying on it.

About the Minnesota Plumbing Code

Citation under review. The 2018 UPC wording and numbering of 705.10 and 705.10.3 were not checked against the printed code. Confirm them in the book.

Why the other choices are wrong

  • ABS and PVC may never be connected in the same drainage system. They may be joined. 705.10.3 requires an approved adapter or transition fitting listed for that specific transition, such as a shielded transition coupling. What is not allowed is gluing one straight into the other.
  • A clothes washer standpipe and trap arm must be 3 in. pipe. UPC Table 702.1 sizes the trap and trap arm for a domestic clothes washer at 2 in., which is what is installed.
  • Nothing. This installation is compliant. PVC primer and cement do not make a reliable bond to ABS, and 705.10.3 requires a listed transition between different plastics.
Code complianceLevel 1 · Apprentice#materials#ABS#PVC#transition#joints#laundry

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