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I am thinking about running some plumbing through the attic. To prevent freezing, I want to run the pipes as close as possible to the ceiling drywall. I have 2x6 joists, which mean I can notch 7/8 inch to run under, unfortunately I need to run 1 inch Uponor pex-a which has outside diameter of 1-1/8 inch. The ceiling drywall is 1/2 inch.

My question is if its feasible or wise to notch 1/4 inch out of the drywall to make enough space with the 7/8 inch joist notch to run the pipe under? What other problems could I run into? What about pipe penetration protection if someone wants to hang something from the ceiling? Could I install sister joists in some fashion to increase the allowable notch depth?

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  • If at all possible would have the pipes on the warm side of the drywall instead of the cold side. It depends on what low temps you expect(20F a lot better than -20F). Drywall decent at stopping heat getting to frozen pipes. Long narrow face plates for vents would help keeping pipes from freezing.
    – crip659
    Feb 14, 2022 at 18:01
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    With or without notching the drywall, this idea has a big drawback. Someday, someone is going to hang something from the ceiling by carefully locating the joist, and drilling a hole for an anchor. The new shower will not be welcome.
    – Mark
    Feb 14, 2022 at 18:03
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    FYI, you asked an xy question here. Better to ask about your actual challenge than a proposed (and possibly faulty) solution.
    – isherwood
    Feb 14, 2022 at 18:57

1 Answer 1

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I'm no drywall expert, but I can't imagine that notching half the depth of your drywall would work very well. Aside from structural issues, it would be super easy to go a little too far and end up having to patch and paint your ceiling. Don't do that.

Plus you would have the problem that anything poking through the wrong spot will immediately hit your pipes. Normally the solution to that is a metal plate, which would be really strange to stick in there - you wouldn't even be able to attach it to the joist because it would need to be 1/4" below it.

Go with the usual - drill holes in the middle 1/3 of the joist, with 2" above and below - a 2x6 = 5.5", gives you just enough room to make that all work for a 1-1/8" hole.

And to help keep the pipes from freezing, add insulation above the pipes. Do not use loose fill insulation unless can create a tent to keep the insulation above the pipe.

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  • "Add insulation" isn't a great solution. If the water sits for a while it'll freeze anyway without a heat source. Insulating it may actually make the problem worse by isolating the pipe from the heat source.
    – isherwood
    Feb 14, 2022 at 18:59
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    @isherwood I wouldn't use loose fill - it will end up encasing the pipes. But lots of insulation above the pipes, with just minimal air space (and no insulation) between ceiling and pipes should work well. Feb 14, 2022 at 19:02
  • You should revise to make that more clear. My first impression was that you were suggesting pipe wrap. As it is your answer mostly disregards the primary motivation for the bottom notch strategy.
    – isherwood
    Feb 14, 2022 at 19:04
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    You need to make sure that the pipes are on the warm side on the attic insulation (there should be no insulation between the drywall ceiling and the pipes). This is commonly called 'tenting'. If you have blanket insulation, keep it above the pipe. If you have loose insulation, create a tent with polly over the pipe in order to keep the insulation above.
    – pdd
    Feb 14, 2022 at 19:09
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    @FreeMan Thanks for the typo fix. Feb 15, 2022 at 16:20

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