AAV Placement for Basement Bath Group

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by plains2hills, Jun 28, 2014.

  1. plains2hills

    plains2hills New Member

    Messages:
    5
    Location:
    CO
    Howdy!!

    I've exhausted all other options for venting our basement bathroom group and will need to install an AAV. Below is a photo of the rough-in plumbing. I need to move the toilet back about 6 inches before installing the flange, and also re-route the drain line for the lav.

    My question is; Can I install 1 AAV in the lav cabinet as pictured? OR, do I need to tie into or also vent the tub since it connects after the sink/lav?

    BASEMENT PLUMBING.jpg
    photo 3.jpg
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,129
    Location:
    Bothell, Washington
    You can vent the tub with the lav, if you change the fitting to a wye there. The lav wyes off the tub line, which should be 2", and 2" to the lav on the wet portion. The lav trap arm can be 1.5" as can the tub trap arm.
    The AAV goes above the trap arm for the lav.
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    There is a very good chance that the tub ties in to the 3" toilet drain, not the 2" sink drain and if so the AAV will NOT protect it from siphonage.
  4. plains2hills

    plains2hills New Member

    Messages:
    5
    Location:
    CO
    hj,
    You're correct. The Tub does tie into the 3" toilet drain downline from where the sink drain attaches (below). Additionally, both the sink and the tub are 1 1/2." Would it make sense for me to cap the current sink line and then wye off of the tub drain?

    bsmt plumbing.jpg
  5. plains2hills

    plains2hills New Member

    Messages:
    5
    Location:
    CO
    Or could I put an AAV on the Tub drain just behind the toilet (leave it sticking up out of the concrete) and one in the cabinet for the sink?
  6. Terry

    Terry Administrator Staff Member

    Messages:
    15,129
    Location:
    Bothell, Washington
    You should be wying off the 3" with 2"
    From that two inch, you install a combo or wye fitting for the lav vertical that has an AAV on top, above the lav trap arm and trap
    From that combo, you extend out to the tub.
    Now the AAV vents the entire group.
  7. plains2hills

    plains2hills New Member

    Messages:
    5
    Location:
    CO
    Thanks so much for your help! It's greatly appreciated and now this makes perfect sense. Can I reduce from the 2" combo/wye to a 1 1/2" for the tub since the tub drain and trap area already laid in 1 1/2? In that case could I also reduce for the sink from the wye or would I want to keep that 2" going up to the sink and AAV?

    Thanks again for taking the time. Incredibly helpful
  8. Terry

    Terry Administrator Staff Member

    Messages:
    15,129
    Location:
    Bothell, Washington
    The 2" goes all the way to the lav santee. Sometimes I use a 2x1.5 santee, extending 2" to the AAV
    For wet venting you need to bump the wet portion to 2"

    The trap arm for the tub can be 1.5" if it's within 42"
    So you would use a 2" combo with a 2x1.5 flushbush on the end for the tub side.
    plains2hills likes this.
  9. plains2hills

    plains2hills New Member

    Messages:
    5
    Location:
    CO
    Wow. It's been a really long time since I've been able to work on this. It turns out that the AAV would be about 54" from the 1 1/2" tub trap arm. I know that out community uses IPC standards. Would it still be OK using the sink AAV for the tub if the tub drain and trap is 1 1/2" pipe from the combo at a distance of less than 5'? This would be down stream from the toilet

    Thanks again
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