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Thread: Second story bathroom venting

  1. #1

    Default Second story bathroom venting


    I have attached a basic drawing of the bathroom drain system that I am thinking of installing, and would like some feedback on the venting. Does this look like it will work, and pass inspection?

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  2. #2

    Default That's one very wet vent

    You've got two fixtures wet vented: the toilet and the lavatory (bathroom sink). I'm not a professional plumber, but I lived in a house with an almost identical setup, and the toilet had a tendency to siphon the trap for the shower when it was flushed, especially if it had a fairly large load.

    Inspectors vary as to what they'll approve, as do plumbing codes, but I think most would not okay your bathroom as drawn. In addition to the double wet vent, if you're really proposing to put the trap for the lavatory below the floor, you'd have a sink tail piece well over 24", which is a code violation. With a tailpiece that long, the weight of a sink full of water would stand a good chance of siphoning the trap.

    If it were my bathroom, I'd install more venting. If you can't run vents from the lavatory and toilet up into the attic (assuming there's an attic above your second floor), then you might consider Studor vents (a/k/a air admittance valves), if they're legal in your area.

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default vents

    You have two different questions. Will it work? Yes to a point although the lavatory could have odor problems both caused by the long tailpiece. One, the trap could lose its seal, and two, a tailpiece that long will get "fouled" with accumulations and start giving an odor. The second question is whether it will pass inspection. Not by any inspector I have ever met.

  4. #4

    Default Add vent

    Wow, thanks for the input; I really appreiciate it!

    How about if I add a vent up from the sink? This would make only one wet vent, the toilet. The biggest problem is the window over the toilet, and a desire to not punch through the studs on either side of the window in the wall. Is there entirely another way to go about what I need to do?

    Thanks a lot,


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