Plumbing plan for an upstairs addition

Discussion in 'UPC Plumbing Code Questions' started by Clifford82, Aug 4, 2020.

  1. Clifford82

    Clifford82 New Member

    Aug 4, 2020
    Auburn, WA
    Long time reader, first time poster. I'm converting a small upstairs bedroom to a small bathroom. The layout is pretty standard as seen in my hand draw masterpiece below. The toilet and sink are to the right of the entry, there will be a clawfoot tub to the left.

    What makes this build unique is that this bathroom is on the second floor of an A-Frame home, so the vanity and toilet will be against a knee-wall on one sloping ceiling, and the tub will be against a knee-wall on the opposing sloping ceiling. I would like to wet vent this so I only have to drill one hole into the sloped ceiling.

    The second drawing is my rough plan; is this acceptable for wet venting? Do I need a second vent coming up from the 3" section before it connects to the vertical section going downstairs (like in the 3rd image)? Also is there anyway I could avoid drilling through my ceiling entirely with an AAV? I'm in King County Washington for reference.


  2. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013

    AFAIK, you could vent this with an AAV, even under the lavatory. This presumes there is a though-the-roof vent connected elsewhere for the house.
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  4. Clifford82

    Clifford82 New Member

    Aug 4, 2020
    Auburn, WA
    Awesome, thanks!
  5. Clifford82

    Clifford82 New Member

    Aug 4, 2020
    Auburn, WA
    After getting the flooring up and actually taking measurements I've had to reconfigure the layout of my bathroom. The room is about 9' deep and 13' wide. Can someone tell me if this looks okay? Thanks!

    In case my drawing isn't clear, here are the specifics of the system:
    • At the top of the new system there is a bathtub with a p-trap on a 2" pipe, this will travel about 3' to the knee wall, where there will either be a vent or an AAV off of a sanitary tee. This will make a 90 degree bent using two 1/8 bends.
    • Next is a sink with a p-trap and a sanitary tee on 1.5" pipe with either vent or AAV, it will make a 90 degree turn vertical to horizontal turn with two 1/8 bends, run about 11' under the floor and connect with a 2x2x1.5 combo wye + 1/8.
    • The 2" pipe will expand to 3"
    • Next is the toilet with a 4x3 closet flange, to a 3" pipe, which then connects to the 3" waste line with a 3x3x3 combo wye + 1/8
    • The 3" waste pipe will then make a 90 degree horizontal to vertical transition using two 1/8 bends, and connect to a 3" vertical pipe.
    • This vertical pipe will carry waste from upstairs, down through the main floor, to the crawl space
    • In the crawl space, the waste will make a vertical to horizontal transition with a 3x3x3 combo wye + 1/8. The other end of this wye is a cleanout
    • This will continue through a 3" pipe and connect to my existing system with a 3x3x3 wye

  6. Tuttles Revenge

    Tuttles Revenge In the Trades

    Oct 15, 2014
    The single vent at your lavatory in 2" thru the roof or equivalent sized AAV is all the venting that horizontal wet vent system needs. Additional venting can not hurt, but is not needed for it to work. AAV manufacture rules indicate where and how they're to be installed properly.
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