Best transtion(s) from 3" waste stack to 1 1/2" vent stack

Discussion in 'UPC Plumbing Code Questions' started by homewrecker2010, Sep 3, 2012.

  1. homewrecker2010

    homewrecker2010 New Member

    Apr 20, 2010
    Saint Louis, Missouri
    First, thanks to everyone who contributes to this awesome resource!

    I'm rebuilding a very old 2" cast iron kitchen waste stack that literally disintegrated. It was vented to the roof by a 1 1/2" lead pipe. Everything below the sink trap down to the basement floor is rotten and needs to be replaced.

    Under the basement floor, the main horizontal drain for the house passes under the kitchen on it's way out to the street, and it's in good shape. There is a 3" floor drain connected to the horizontal main in this location, because there are two water heaters, a washing machine, and a boiler nearby.

    I'd like to replace the tee used to connect the floor drain to the main with a wye+45, and bring a new stack above the basement floor, installing a new floor drain of the same size and provide inlets for the fixtures mentioned above. I'm experienced with sizing drains and vents for number of fixture units, but I'm not sure what sequence of transitions here would be most proper.

    Code says the 2" is sufficient for kitchen and washer, but I've not had good luck with long runs of 2" pipe from kitchens -- I'd like to see the sink discharge into 3" if it's not "bad." I believe a 3" waste stack can be served by a 1 1/2" vent.

    What I'd like advice on is, where in the following is the best place to transition from 3" waste to 1 1/2" vent, or even something in between?

    (Starting at horizontal main and going up)
    A. Above the trap for the below-floor flood drain
    B. Above the cleanout for the new stack
    C. Above the inlet for the clothes washer
    D. Above the inlet for the kitchen sink

    My main concern is that this is an old brick home with only enough room for a 1 1/2" vent in the wall. I don't want to shoot myself in the foot by bringing a 3" stack above the basement floor that I'll be unable to vent properly.

    Diagram attached. Advice appreciated. Thanks so much!

    Last edited by a moderator: Sep 3, 2012
  2. frodo

    frodo New Member

    Jun 29, 2013
    i think this is what you want to do, the drawing you provided was not up to code, and would not drain

    the drawing is your 3" floor drain plumbed in under the slab. with a co above the floor
    3" is also brought up to above the floor behind the washer, using a 3x2 y with a 3x2 bushing in the top of it, to catch the kitchen sink
    with clean out on each drain line
    Last edited: Jul 4, 2013
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