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Thread: single vanity sink to dual

  1. #1
    DIY Junior Member bsla11's Avatar
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    Default single vanity sink to dual

    Hello all,


    I looking for advise on plumbing dual sinks for a bathroom vanity. This is a second floor bathroom with 1.5 inch wet vent pipe and 2" vent pipe. Existing wall is load bearing so I plan on framing a additional wall in front of the existing one for plumbing and build in medicine cabinets.
    I picked up a few plumbing books from the library and learned what I should't be doing but looking for advice for my particular situation. From what I have seen it's advisable to have the wet vent pipe between the sinks and install a double wye. That isn't the case in my situation.

    I included a picture of where the new sinks will be installed. They will be 45" on Center apart.

    I know I can't run both sinks off the existing p-trap because they are to far apart.

    Good advice is appreciated!
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  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    The 2" vent for the downstairs bath remains a vent. If you frame a wall in front, you can run from the left pipe over to the right of the vent. That line will be closer to the floor. Use a long turn 90 and a santee for the second lav, and continuing up, 90 back over and connect to the vent, which I'm guessing was installed at 42" from the floor.

    You should have 2" if you are using two lavs, but you don't have that. You will have to make do with the 1.5" that you have.

    You also have the option of opening the floor and running the line over to the second lav in the flooring system.

    Or you can open the floor and put the vent to the right of the new lav. Then you wouldn't need to build out the wall.

    See how fun this is? Lot's of ways to do this.
    Last edited by Terry; 09-11-2013 at 08:55 PM.

  3. #3
    DIY Junior Member bsla11's Avatar
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    OK so tap into the Wet pipe vent just below the existing connection.

    Thanks for the very quick reply!
    Last edited by bsla11; 09-11-2013 at 09:09 PM. Reason: not needed

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    Forum Admin, Expert Plumber Terry's Avatar
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    I don't know what you mean by a wet pipe vent in the previous answer.

    A vent normally is the dry pipe above the trap arm for the p-trap.

    The "waste" below that handles water.

    Therefore "waste" and "vents".

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Offset the downstairs vent so it goes around the right hand location, and then you can install the two sinks properly, but do NOT use a "double Y" OR a "sanitary cross". Both are "illegal" for your situation.
    Licensed residential and commercial plumber

  6. #6
    DIY Junior Member bsla11's Avatar
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    Appreciate the input.

    Terry, I should have said wet pipe and not wet pipe vent.

    This is what I'm thinking of doing.

    Name:  possible dual vanity v2.jpg
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  7. #7
    DIY Junior Member bsla11's Avatar
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    According to local code vent for the new sink needs to be within 3'6" of p-trap

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