Main Sanitary Stack Code Question

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by seaneys, Dec 15, 2007.

  1. seaneys

    seaneys New Member

    May 8, 2007
    Chicago Suburbs
    I am working on a fairly significant project (3 1/2 bathroom remodel).

    I need to move my main sanitary stack. I've eliminated all of the fixtures and branches that tied into it.

    All of my fixtures are vented individually. If I read the Illinois plumbing code correctly, I still need a main stack to my house that is at least 3" in diameter EVEN if I all of my fixtures are vented individually.

    Am I reading the code correctly? I'm wondering why I need a separate main stack if all of individual branches are and fixtures are vented separately.


  2. TMB9862

    TMB9862 New Member

    Nov 12, 2006
    Three and a half bathrooms, that's eleven fixtures right? You have to come through the roof with 3" (here you do at least). So you would have a pretty unsightly house if all eleven of those fixtures have their own 3" vent coming up from the roof. Completely legal but wrong, and ugly. You didn't replumb the whole house using AAVs did you? That's probably not going to fly with the inspector.
    The point of the stack is it's a place for the vents and/or wastes from the fixtures to dump into then come out of your roof with one 3 or 4in line instead of eleven.
    Last edited by a moderator: Dec 15, 2007
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  4. seaneys

    seaneys New Member

    May 8, 2007
    Chicago Suburbs
    I rejoin the vents in the walls / attic as much as possible. I will end up with two vents for the new bathrooms and one existing one for the kitchen. The vents are on the rear of the house. The only real limitation is the amount of plumbing I want to run in the attic. We want to use it for storage...

    The city said that they prefer 4" roof vents. I believe the code calls for 3", but I am not going to argue with them...

    As of now ALL of the vents are from fixtures. I think I blew this on the design (purely my fault). I can very easily shoot a 3" vent from the basement to the attic at this point. My plans are to combine it with one of the bathroom vents so that I do not need to add an additional whole in the roof.

    Does that seem reasonable?

  5. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    Some areas allow several smaller vents an agregate area equal to a 3" vent, while others require at least one full sized 3" vent. When I was there the requirement was a 4" vent. It is a local thing without a whole lot of logic or common sense.
  6. construct30

    construct30 New Member

    Jun 16, 2007
    NorthWest PA
    I've alway wondered what the people at the ICC were after when they came up with the IPC. I know when you have a multi story building they require a main stack and vent stack to remain the same as or bigger than the main drain, but in a house what do they really want? Is a main drain branched off and vented into smaller pipes the best or is maintaining a full size stack all the way to the open air the best? In many cases it seems you would get more vent with branches, it can be less complicated than trying to get all the pipes returned to a main stack.
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