Yet another question about wet venting.

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by khamilton, Apr 20, 2017.

  1. khamilton

    khamilton New Member

    Jan 7, 2011
    Nova Scotia
    Hi all,

    I've seen this image posted on the forums here multiple times, so i figure it's a good starting point for my questions.

    I'm planning (hoping) to plumb in a washing machine on the main floor (Laundry is currently on the 2nd floor and I don't like that idea) The new laundry will be directly under the second floor bathroom. I was originally thinking this configuration in it's original form would be ideal for me, until I read more on this forum, and now I don't think it is.
    1. In my house, the pipe marked A is a 4" soil stack that runs straight from the roof down to the basement where it exits out to the septic system, so it's currently used to drain the sink, toilet and tub on the 2nd floor (although the tub and sink are vented independently of this stack). If i interpret everything I've read here properly, the fact that this is the drain for the fixtures on the 2nd floor, this configuration in it's original form won't work for me - Am I correct? I think I am, but hoping i'm not.

    I think I would either need to either:
    1) make the vents join (C) at a point above the toilet upstairs or in the attic before it exits the roof (this wouldn't be impossible, but I'm trying to avoid tearing anything apart on the 2nd floor if it can be avoided)
    2) Can I just add an AAV at the top of pipe B? I know it's not ideal, but the wall cavity where this will be is an interior wall with no insulation, and it will remain accessible.
    3) The pipe I drew in with blue lines represents the 2" drain that is currently used for the upstairs laundry and it actually vents through the roof as well. the vertical piece is actually about 18 ft from where the new laundry would go, and the horizontal actually runs under the 1st floor. i don't think I can tie into this either can I? I think it would essentially be creating an S trap in order to go down through the floor.

    Thanks in advance

    KH Shot 2017-04-20 at 4.03.35 PM.png
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    The downstairs washer can tie into any line carrying waste, but not the vent.
    You could tie it into the 4" on the left, or the 2" on the right.
    The vent for the washer will need to be somewhere. The best would be to tie in above the next foor at 42" or through the roof.
    Or you could use the AAV, keeping it accessible and open to air. They do make boxes with grills for that purpose.
    Some inspectors may not like the AAV though. You do need something though.
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  4. khamilton

    khamilton New Member

    Jan 7, 2011
    Nova Scotia
    Thanks very much for the confirmation Terry! Much appreciated.
    I think it makes most sense to go with the AAV for now. I'll place it so I can easily replace the AAV with a proper vent when it comes time to re-do the bathroom and hallway upstairs in a few years and everything will be accessible.
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