Clarification on vertical offsets

Discussion in 'IPC Plumbing Code Questions' started by Jackmac, Jul 2, 2016.

  1. Jackmac

    Jackmac New Member

    Joined:
    Jul 2, 2016
    Location:
    Connecticut
    Hello,

    First a little background on the project. I just purchased a house what was built in 1924. All the drain piping in the house is cast iron. The house has a 4" stack running from the basement, up 2 floors, and then out the roof. We are currently renovating the kitchen, and the stack is external to the wall. The previous owners had built out a bulk head around the stack. I would prefer to reduce the size of the stack to 3 inches and sink it back into the wall between the studs.

    Currently, the 2nd floor bathroom drains from a common branch off of this main stack. The first floor bathroom and the kitchen sink currently drain into the 4" cast iron drain system after it has gone horizontal on its way out of the house and toward the septic tank.

    So the question is how do I get the waste stack pushed back into the stud bay in our kitchen in accordance with the 2003 IPC (Connecticut's current plumbing code)?

    My thought has been to rip out the cast iron and move to 3" PVC from the roof down to the basement and tie into the 4" cast iron. Due to the layout this would require an offset just before current cast iron stack goes horizontal.

    I think this falls within code, but I am confused on the waste stack vent portion of the IPC. If I put an offset in and reduce the size of the stack, am I no longer able to use the waste stack as a vent?

    Thanks
     
  2. hj

    hj Master Plumber

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    The offset is no problem, but unless you redo the entire stack, you cannot tie the upstairs 4" into a 3" going down the wall, but you can still use the 4" vent ABOVE the upper level for the vent out of the roof.
     
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  4. Jackmac

    Jackmac New Member

    Joined:
    Jul 2, 2016
    Location:
    Connecticut
    Thanks for the reply! So if I keep the vent above the upstairs bathroom 4 in, then transition to a 3" where I will tie in the upstairs bathroom and then carry the 3 " down into the basement where it will tie back into the building drain (4" cast iron) will that meet code. The way I read it, size transitions were allowed, but they must get larger in the direction of flow. The way I am seeing this, I am changing the system to a 3" drain with a 4 in vent, or is that totally off base?
     
  5. hj

    hj Master Plumber

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    The increase in the direction of flow applies to drains. Vents are the opposite, (until you realize that the air is flowing in the opposite direction).. The can get bigger as they move away from the drain.
     
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