Wet venting bathrooms in Seattle

Discussion in 'UPC Plumbing Code Questions' started by JeffreyP, Dec 9, 2020.

  1. JeffreyP

    JeffreyP New Member

    Joined:
    Dec 9, 2020
    Location:
    Seattle
    I'm planning my drain/vent system for a remodel of my house. Since I'm in Seattle, I'm using this resource https://www.kingcounty.gov/depts/he...ocuments/plumbing/horizontal-wet-venting.ashx which calls out the Seattle specific UPC amendments and has some helpful explanation/comments.

    I'd love some feedback on my plan to confirm if I'm on the right track with my understanding the rules and with my planned design. The A/B options below are the same except for how drain lines of the two 2nd floor bathroom groups join - I'm not sure if this should be joined while still both horizontal (Option A) or if they should start dropping down and be joined when both are vertical (Option B).

    plumbing diagram.png
     
  2. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Looks OK to me. Either option is fine. Where are the kitchen sink and laundry, and how are they vented?

    BTW, what software did you use to make your diagrams?

    Cheers, Wayne
     
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  4. JeffreyP

    JeffreyP New Member

    Joined:
    Dec 9, 2020
    Location:
    Seattle
    Thanks for the feedback Wayne.

    Here is an updated version that also shows the kitchen/laundry (and a basement utility sink) that you asked about. I just used Microsoft Paint to make the diagrams. I'm sure there is a fancier way but Paint is pretty simple to use and gets the job done.

    Also, I upsized the wet vents coming from the lavs to 3" in this version, not sure if this is needed or not but figured it wouldn't hurt. I'm planning on trying to ask the local inspector as well, but figured I try to get some feedback here first to make sure I'm on the right track.

    Plumbing DWV v2.png
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Still looks good to me. I don't see any upside to upsizing the lav horizontal wet vent to 3" before it hits the toilet.

    You could downsize the kitchen sink/laundry vents to 1.5", that's good for 8 DFUs (excluding WCs).

    Cheers, Wayne
     
  6. JeffreyP

    JeffreyP New Member

    Joined:
    Dec 9, 2020
    Location:
    Seattle
    Point noted about the kitchen sink/laundry vent size - thanks!

    For the change from 2" to 3" for the wet vent, I was reading this section:
    908.2.2 Size. The wet vent shall be sized based on the fixture unit discharge into the wet vent. The wet vent shall be not less than 2 inches (50 mm) in diameter for 4 drainage fixture units (dfu) or less, and not less than 3 inches (80 mm) in diameter for 5 dfu or more.
    and then adding 1 (lav) + 2 (shower) + 3 (WC) = 6 which was making me think that I needed to upsize that first part of the wet vent.

    Perhaps I'm not understanding it correctly and the 'discharge into the wet vent' part doesn't mean for the whole wet vent but just section by section?
     
  7. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    Yes, section by section. The horizontal wet vent before the toilet comes in is only carrying 1 DFU.

    But if you had a wet vent that was lav - shower - bathtub - toilet, the section after the bathtub comes in is carrying 5 DFUs, so it would have to be 3", even before the toilet comes in.

    Cheers, Wayne
     
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