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Thread: Shower drain between, then under floor joists...

  1. #1

    Default Shower drain between, then under floor joists...

    Redoing a bathroom...here's what i want to do.

    Eventually we will be finishing the basement below the bathroom. I want to run the tub/shower drain between (parallel) the floor joists so that no part hangs down below the joists (2x10s). After about 6 ft, i want to run the drain just underneath the joists about for about 6' more until it ties in with the main stack against a wall. I want to do this so i can put the drain in a soffit with some other pipes, etc, and not have to drill a ton of holes in a ton of joists.

    How do i go about making the transition from between the joists running parallel, to under the joists running perpendicular? Do i just get a couple of long sweep 90s? Some 45s? Is this even possible?

    Thanks in advance.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Everything is "possible", but sometimes it takes more time and money to do it. The shower drain needs a vent, and until you reach the vent the drain CANNOT "drop". Once the vent is properly installed you can run the drain any way you want, or need, to. We cannot tell you whether you need, or can use, long sweeps or 45s because we cannot see your installation.

  3. #3

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    I understand what you are saying, and realize the limitations of describing this over the internet, but your response is actually helpful. All of these drain lines are run near walls, so there are plenty of places where i can tie in a vent before the drop.

    I heard the "exception" to the no santee on back rule is when it is used in a vent application - is this true? I'm in PA, so 09 UPC here i think. Also, anything run at 45 degrees between vertical and horizontal considered "vertical" for a vent application, right?

  4. #4
    In the Trades Gary Swart's Avatar
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    I know you are looking for DIY advice, but this may be a bit more than a novice should undertake. I think sometimes the best DIY advice is to hire a plumber. There are many ways to do this wrong and only about one way to do it right.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Whether you can use a sanitary tee on its back depends on your local inspectors, and whether they require any fittings below the "flood rim" of the fixture to be a "sanitary" configuration. IF they did then you could not use it.

  6. #6
    In the Trades Gary Swart's Avatar
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    It's the "little" things like HJ refers to that you can run into that you can run into that an inspector may require redone that in my opinion make hiring a plumber to be the wise route.

  7. #7

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    Well, let's see if we can get some of these other questions answered, make sure i'm on the right route here.

    The bathroom will have a tub/shower, double sink, and toilet. Where the stack goes into the basement floor it is 3".

    Here's my plan right now: 1.5" drain from tub/shower with a 1.5" vent. 1.5" drain from each sink to a double fixture fitting which has a 1.5" vent. From the bottom of the double fixture fitting 1.5" pipe until it meets up with the 1.5" drain from tub, then it will be 2" until it meets up with 3" stack. Toilet has a 2" vent. All the vents meet in attic, 2" out vent out roof. Does this sound right?

    Other question: i read you should sink fiberglass tubs in some sort of mud...what do people use? Starting from the plywood subfloor up...

    Thanks again.

  8. #8

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    Well, I think I figured out how to plumb the tub ptrap into a sanitee so its vented before the drop under the joist.

    Just need answers to my other questions now...

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