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We moved into a house in Oregon 3 months ago and were plagued by sewer smells both inside and outside one side of the house. We found in the crawl space an approximately 12 foot horizontal section of 2" ABS vent pipe had broken off. This was right below the area where we noticed the worst of the smells. On one side it came through a brick wall from a bathroom and toilet on the opposite side of the wall.

It was completely sheared of at a coupling about a foot from the wall. From that break, the pipe ran about 6 feet horizontally, then a 45 up to the joists, then another 45 running it horizontal for another 5 feet or so where it had sheared off about 5 or 6 inches before it disappeared into the opposite wall. A vertical vent pipe goes up somewhere in there.

I'm guessing the original install wasn't properly sloped and the abundant rainfall we get here built up and broke the pipe. Now I'm trying to figure out how I'm going to fix it.

There is a bathroom on the other side of this wall

I was thinking of using rubber couplings at both ends near the walls then a 45 section in the middle. I thought that might allow me the flexibility to bend it down a little if I need more slope and also the fact that on the second side I don't have a lot of pipe to work with. I also wanted the option to disassemble it in case critters got in there and nested and I need to clean them out.

Unfortunately there aren't many joists to suspend it from. In between the joists there are some thin slat-like boards.

Any suggestions on my approach? What are the slope requirements here? Suspension requirements? Many thanks all!

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    Are you sure it was "sheared off"? Plastic doesn't usually break like that. Maybe it was never cemented. Is there broken pipe inside the hub? That's not PVC, by the way. The distinction is important because cements may not be inter-compatible.
    – isherwood
    Dec 18, 2023 at 13:58

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Most code requires a metal enforced coupling like this one.

enter image description here

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  • a.k.a. a shielded coupling.
    – Huesmann
    Dec 18, 2023 at 13:20
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    Most code allows a shielded coupling. Your wording is misleading since other solutions exist.
    – isherwood
    Dec 18, 2023 at 13:54
  • I would think only a solvent weld or a shielded coupling is allowed on that. If there is play in the pipe, weld a fitting in there, otherwise, use a coupling. Are the non-shielded ones ever allowed?
    – Evil Elf
    Dec 18, 2023 at 18:34
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ABS should be supported every 4 ft under the International Plumbing Code. I can't imagine that your floor joists are spaced wider than that. Plastic banding works fine. Just wrap a length of banding around the pipe once or twice and screw both ends together to a floor joist above the pipe.

The slope requirements on vents are relatively lax: Vents just need to drain to the sewer everywhere. The code names no 1/4" per foot or similar number to target, although 1/4" per foot achieves good drainage.

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  • The slope needs to be continuous and in the correct direction so that any rain water/snow melt that gets into the vent pipe eventually runs to the house drain and doesn't settle/collect and, possibly, freeze, blocking the pipe.
    – FreeMan
    Dec 18, 2023 at 12:56
  • @FreeMan, by "no explicit slope requirements" I mean that there's no 1/4" or 1/8" per foot. What do you mean by "continous" slope? C⁰ continuity? "Continuous" seems like common sense.
    – popham
    Dec 18, 2023 at 16:07
  • Not going back up hill at any point. It does seem obvious, but not to everyone.
    – FreeMan
    Dec 18, 2023 at 16:15
  • Mathematically, "monotonic". A lack of continuity is in fact OP's entire problem. ;-)
    – Matt S
    May 16 at 20:30

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