New laundry standpipe in an older house
What's wrong here?
- The PVC trap arm is solvent-cemented directly into an ABS fitting without a listed transition fitting
- A clothes washer standpipe and trap arm must be 3 in. pipe
- ABS and PVC may never be connected in the same drainage system
- Nothing. This installation is compliant
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: 1. 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 705.10.3UPC 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
Minnesota adopts the 2018 Uniform Plumbing Code with Minnesota amendments as the Minnesota Plumbing Code (Minn. Rules ch. 4714, effective Dec. 17, 2021). No Minnesota amendment to 705.10.3 is known; check ch. 4714 before relying on it.
About the Minnesota Plumbing CodeCitation under review. Confirm the 2018 UPC wording and numbering of 705.10 / 705.10.3, which came from search snippets of an up.codes page whose edition was not shown. Also check whether the 2018 UPC (or a Minnesota amendment) allows an ASTM D3138 transition solvent cement joint between ABS and PVC. Search snippets mention one, apparently limited to a single joint between building drain and building sewer. Even if allowed, it would not cover this above-floor trap arm glued with PVC primer, so the answer stands.
Why the other choices are wrong
- 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.
- 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.
- 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.