 | Plumbing drain/wall sizing questions in US bath remodel |
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Question: I'm remodeling my bathroom here in California, and the group has been very helpful with a few questions I've asked so far. Right now I'm trying to finalize the layout, and I have a couple questions on sizing the soil stack and plumbing wall. The plumbing wall will service a water closet and lavatory on each side of the wall (back-to-back fixtures). I'm planning to locate a 3" soil stack in the wall between the two toilets and service the lavatories with a 1.5" drain/vent that revents to the soil stack in the wall (the drain will connect in the ample crawl space). So: 1) Should I use a 4" soil stack? 3" is adequate in terms of fixtures units and I don't have any problem with the aggregate vent area rule. I've also heard that 1.6 gallon closets perform better with a 3" drain line. 2) With a 3" stack, is it reasonable to frame this wall with 2x4s? My understanding is that 3" ABS is 3.5" O.D., but the stack will not intersect any studs. I assume it is OK to completely sever the top and bottom plates where the stack passes through. As for the reventing, the wall is nonbearing, so I can bore a hole up to 2" in the studs, and the O.D. of 1.5" ABS is only 1.9". Boring for a 45 degree vent run will lengthen the hole required, but the width will still be 1.9"; I assume the extra length will not be a problem.
Answer: The 1.6Gal closets should not care what the stack size is. As I mentioned earlier, you may have problems connecting 2 back-to-back closets on 3" stack if using San Cross/Dbl TEE. Better is 4 X 3 (4" stack/3" branch) and I would ask if they will even allow this in CA. Here too, I would go with 2 X 1 1/2" Dbl TEE/Cross (if allowed). The vent can reduce to 1 1/2". If you can use PVC, there is a small dimensional advantage (may not matter). I don't see any problem boring holes, although you may have to add stiffeners to the studs.
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