I am about to fully re-do the plumbing in my bathroom and could use some advice on my current layout. I am in a UPC region.

This house has a single bath with drain lines in a crawlspace, single story flat roof overhead. The bathroom is a long rectangle in the corner of the house and the sewer main is in that corner with a cast iron vent stack penetrating the roof. Instead of adding additional roof penetrations or attempting to splice into the existing iron pipe, I would like to try and use a maximum of 2 AAVs and a horizontal wet venting layout. The fixtures I have, in order from furthest from the sewer main, are:

Front loading washing machine




I wanted to wet vent everything starting from the washer, but I didn't realize it has a 4 DFU rating, which I think would require a minimum of 3" diameter pipe for everything. Instead, I am trying to vent the washer separately and wet vent everything else from the lav with only 2" pipe.

I did a quick layout sketch (assumes 1/4 in/ft slope)


3" pipe straight run from wc to sewer main, 12ft long.

2" wet vent that starts at lav trap (using AAV in attic), ties in shower trap, ties into 3" pipe about 4ft down from wc.

2" washer trap with dry vent (another AAV), 2" drain pipe that is about 12ft long and ties into 3" pipe about 6ft down from wc.

Does this layout look acceptable? Also, I understand the wye connections of the horizontal wet vent should be flat, but what about the 3x2 wye for the washer drain connection? Should this be rolled above centerline?

  • AAVs fail, and stink. I would advise real vents, but suit yourself.
    – Ecnerwal
    Mar 4, 2021 at 16:51
  • When and if they fail it is easy to replace them. I'd rather that to a roof leak in my ceiling. Maybe when I replace the roof I will go ahead and extend the vents but not now.
    – sinthome
    Mar 4, 2021 at 17:12
  • Oops I noticed the drawing has a 90deg bend in the wet vent, but it is really supposed to have two 45s
    – sinthome
    Mar 4, 2021 at 19:30


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