Waste stack size

Discussion in 'Plumbing Code Questions' started by mprice214, May 13, 2014.

  1. mprice214

    mprice214 New Member

    Messages:
    1
    Location:
    VA
    Hello all,

    I am currently building a house myself and have found this site to be useful for plumbing questions I have had. I am capable of plumbing bathrooms, etc., but don't know a lot about "the big picture" ie starting from scratch for plumbing a house. Venting is one of the things that has been confusing me, especially when I begin to read the code.

    I have a 4" main drain, roughed in down in the basement. There is a 4" stub that will eventually become the waste stack. The house is two stories. I intend on bringing the 4" up the basement wall, topping it off with a double wye fitting. I would reduce the 3 upper portions of the double wye down to 3". The 2 45 deg portions will have the first floor drains running into them and the middle portion will continue up the wall to have an upstairs bathroom tie into it. Then the stack will continue up to go through the roof.

    I can't really see in the code whether or not I can do what I want to do.

    I think I'm ok necking down after the first floor because the 4" running up the wall in the basement would be considered the drain, while the 3" that I transition down to would now become the waste stack as it is now providing venting for the fixtures that attach to it within the critical distance. (confirmation here would be great :eek:)

    If that is correct, what if I take a utility sink and run it into the 4" within the critical distance so that it doesn't need to be vented? Will the 4" drain now become a waste stack above that point and therefore I have a problem necking down at the first floor to a 3" stack?

    And finally, let's say I'm reading all of this wrong and I can do the utility sink into the 4" and then neck down to a 3" up above, is there anything that prevents me from necking down to a 2" above my last drain to be able to go through the roof with just a 2"?

    I appreciate all the help in advance!
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,130
    Location:
    Bothell, Washington
    The utility sink will need a vent before entering the 4" waste stack. As long as there is waste going down the stack, it's a waste stack, not a vent.

    Most plumbing codes want to see a 4" area through the roof if you have 4" in the lower floor. That would be a single 4", or four 2" vents.
    A vent from a basement ultity sink could vent either all the way through the roof, or at six inches above the highest fiixture on the same wall. So if you have a utility sink next to a waste stack, you would run a vent alongside, go up a floor, or maybe two floors depending on where the plumbing is above, and tie in 6" above the flood level of the highest fixture. That prevents a vent from being clogged with waste.

    [​IMG]

    You can plumb a wall like this with a 2" vent, but you will need more 2" vents if you have an entire home.
    This is just a portion of the plumbing.

    4" is need for four toilets on the horizontal. On the vertical you can do four toilets on 3"
    Three toilets can be plumbed on the horizontal in 3"
  3. Reach4

    Reach4 Well-Known Member

    Messages:
    2,432
    Location:
    IL
  4. Terry

    Terry Administrator Staff Member

    Messages:
    15,130
    Location:
    Bothell, Washington
    [​IMG]

    You mean like this?
  5. Reach4

    Reach4 Well-Known Member

    Messages:
    2,432
    Location:
    IL
    Or this? huge3.jpg
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