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Thread: Change in DWV System shared by shower & lavatory: Is this okay?

  1. #1

    Default Change in DWV System shared by shower & lavatory: Is this okay?

    Hello. I am a newbie and find myself going crazy with a remodel of a 60 odd year old bathroom that requires major changes in a number of areas. I write now with questions regarding the best way to alter the DWV system shared by the shower and lavatory. I have included sketches of the existing system and the proposed changes I would like to make, with question as to the appropriateness of the changes. I used a simple graphics application to do the sketches, so I hope they are not confusing.

    I am motivated to make changes for six primary reasons:

    1. The existing system is constructed primarily of 1 ˝” pipe, so it is not up to code in that regard.

    2. It is constructed of soldered copper pipe, and I will need to use PVC.

    3. The original shower base was a presently unusual, shallow tub-like unit that had an overflow drain, so the p-trap came very near to the wall plumbed for the shower. The replacement shower base will have a central drain considerably closer to the main drain pipe and the vent stack.

    4. With the change in location of the shower drain, the drain pipe and p-trap come up under a pair of sistered joists as they approach the shower, so it will be difficult if not impossible to bring the vent down into the drain near the p-trap as it was in the existing system.

    5. With the required minimum grading of the drain and vent pipes, running the vent pipe to enter the shower drain near the p-trap would require a number of inconvenient cut-outs in doubled headers acting as bridging in the joist system, in order to allow the vent pipe to run from the drain to the vent stack.

    6. I would like to minimize the use of materials and simplify the project to the maximum degree possible.

    My plan is to remove the entire existing system, aside from the copper vent stack running up through walls and the major drain pipe into which this system drains, and to make a new system of 2” PVC that will tie into those two pipes with Mission couplings. For the most part, the new system will otherwise mimic the old, but my main question is how I might more conveniently tie the vent for the shower into the system.

    In review of available, related discussion here, I found the following remark (offered by Speedball 1):

    “Chapter 14, Table 1409.3 of The Stardard Plumbing Code, Titled "Distance of Trap to Vent" gives us this.

    Size of Fixture Drain Distance Trap to Vent
    In inches:
    1 1/4------------------------------------2ft.6 in
    1 1/2------------------------------------3ft.6 in
    2----------------------------------------5ft.0 in
    3----------------------------------------6ft.0 in
    4---------------------------------------10ft.0 in”.

    With my new shower base, the distance from the trap to the main vent stack is reduced to about 3 feet, and as I will be using 2” pipe and the distance is less than 5 feet, I am hopeful I can just connect the vent stack to the shower drain pipe using 90◦ bend connectors to basically make the connection in a plane perpendicular to the wall and in line with the vent stack, rather than having it run on a grade in a direction parallel to the wall. I hope my wording makes my intention clear. I have included quick sketches, but they are only in one dimension, so I hope they are not confusing.

    I also hope this is not all too obvious. I want to make sure I do this correctly, and although I think I’m likely right from things I’ve read on this site, I don’t want to take anything for granted. I will very much appreciate any helpful response.

    Rob Redden
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  2. #2
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007


    Have the sink drain and shower vent come into the shower drain with combo's or, wye and 45' your good to go here!

    Nice drawing BTW!

  3. #3


    Thanks a million. Now I can proceed with comfort! Rob Redden

    (btw, I searched this site for a drafting program I had seen someone else use here that I thought looked great. I found it and went to the site on line. It costs almost $4000 to purchase!!! I decided just to use an ordinary graphics application on my PC and took a little time to figure out the best way to get lines to look sort of like pipes. Thanks.)

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Take the old copper to the recyclers...it's around $4/pound for the scrap.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007


    I can't believe those suckers that cashed in at $3...
    I've got a garage full of gold!


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