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Thread: Rough-in Plumbing Questions

  1. #1
    DIY Member tonyn1's Avatar
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    Default Rough-in Plumbing Questions

    I am trying to get an attic prepped for a later remodel. This project is not on the front burner now, but I want to have the plumbing ready to go when I'm ready to finish, as it will go through walls below, and I may have to tear into some walls to accomplish this. Anyhow, I wish to install a toilet, sink, and bathtub in the upstairs bathroom. I have 10" joists up there. I already have the main vent stack coming up in the area, which is the old iron pipe and I want to replace this with PVC anyway. The lower toilet feeds into this in the crawl space. I plan on putting the new toilet close to the stack, as I don't want to run 3" pipe through any of the joists. The problem comes with fitting all the plumbing within the joist height. If I only had a toilet, it would be easy as it could use a 45 to connect within the space, but I'll have to use a 3" T with a 2" inlet or two or similar fitting to connect everything. I think I might be able to get part of that fitting a little bit down in the wall to clear some space, but I'm not sure if I can get everything in there right and achieve the right slope as well. Any suggestions?

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Stop right there. You CANNOT connect the new bathroom to the pipe from the downstairs bathroom, so it appears your entire plan has to be revised. It does NOT sound like you have any experience in planning a DWV system, so this might NOT be a good DIY project for you.
    Licensed residential and commercial plumber

  3. #3
    Plumber jimbo's Avatar
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    As hj mentioned, the stack coming up from below is the vent. You cannot put ANY waste water in that stack. You can use it as wasted IF you open up below and take off a separate vent, or take off a separate waste pipe and send that upstairs. Where and HOW to make such tie ins requires a detailed look at your system, some photos, and knowledge of codes. We can help on here, if you provide us enough drawings and photos. A good plumber onsite would figure it out in short order.

  4. #4
    DIY Member tonyn1's Avatar
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    Quote Originally Posted by hj View Post
    Stop right there. You CANNOT connect the new bathroom to the pipe from the downstairs bathroom, so it appears your entire plan has to be revised. It does NOT sound like you have any experience in planning a DWV system, so this might NOT be a good DIY project for you.
    I've had several plumbers say I could do it that way. The toilet is not directly on top of the stack, but would be teed into it, so it would be still be vented. That's the trouble, I got no definitive answers, only different ones.

  5. #5
    Forum Admin, Expert Plumber Terry's Avatar
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    The correct answer has been given twice above here.
    No. You can't put waste down the vent stack.
    You can plumb waste from below, and then tie the vents on the upper floor back to the vent stack at 42" above the top floor.

    And please pull a plumbing permit for this.


    Last edited by Terry; 10-18-2011 at 01:27 PM.

  6. #6
    DIY Member tonyn1's Avatar
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    Thanks for the info.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    "On top of it" or "teed into it" is immaterial. You CANNOT send water DOWN that pipe if it is the vent for the downstairs bathroom, which it should be.
    Licensed residential and commercial plumber

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