Double sink vanity with 1.5 inch pipe

Discussion in 'Plumbing Code Questions' started by Robert Lehman, Aug 10, 2020.

  1. Robert Lehman

    Robert Lehman New Member

    Joined:
    Aug 10, 2020
    Location:
    Seattle, WA
    I am preparing to install an 84" vanity with dual sinks, and then I find out the sink drains are 34" apart. That would require individual p-traps. But when I opened the wall, the existing single sink vanity drains into a 1.5" vertical pipe. This is a 1928 home, with various remodels over the years, and there is no way to get a 2" pipe to the top floor master bathroom without tearing out floors and ceilings. When I proposed to the inspector the
    method I found on these forums from Terry Love, they said it violates the code.

    I don't get it. If the sinks are 30" apart, they can share a p-trap and go out the single 1.5" drain. But at 34", with a much more robust setup such as this, they say 'no'. Not only is the flow out a vanity sink small, but as anyone who has shared a bathroom with dual vanity knows, it would be rare for both sinks to be draining much water at the same time.

    I don't know what I can do.

    [​IMG]
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Yes, not code by the book, but it's as good as you can get without changing out all the pipe below to 2".

    Also, showers in the 60's and before were 1.5" and they have always worked well. That was with the old high flow shower heads too. Now the code is 2.0" for a shower with 2.5 GPM heads.

    I'm sorry it didn't work out.

    [​IMG]

    This is current code in Washington State for a double lav now. It's too bad he's not cutting you some slack for a remodel of an older home though.
     
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  4. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    UPC Table 703.2 says 1-1/2" drain is good for 2 DFUs when vertical, and 1 DFU when horizontal. So if the existing 1-1/2" is all vertical, then it should be fine to drain two lavatories into it. Unless Washington State has amended that?

    Cheers, Wayne
     
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  5. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    I like that call Wayne! and the inspector shouldn't push that even if he could second floor difficult situation I would respectfully ask him to reconsider . but you have to split them in 2 you can't wet vent 2 lavs on 1 1/2" line
     
  6. cej22

    cej22 Member

    Joined:
    Mar 18, 2009
    Location:
    SLC, UT
    Replying to an older thread in order to not create clutter. Apologies if that's bad form around here.

    For the configuration in the pic in the original post, are the dimensions between fittings relevant at all? Can you tie the second vent into the original line lower than is shown? My assumption is that you can, but I'm not a plumber.
     
  7. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    Reventing takes place six inches above the flood level of the fixtures, typically at 42".

    [​IMG]
     
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