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Thread: Soil Stack Question

  1. #1
    DIY Member pensfan84's Avatar
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    Default Soil Stack Question

    I recently tore out my old cast iron stack in my house and am in the process of replacing it with ABS. I've replaced the vent portion thus far from the basement through the roof flashing with 2" ABS. I've also connected to the main cast iron pipe in the basement floor using a 4 band fernco coupling to 4" ABS. This soil stack is used to drain 2 lavatories, 2 toilets, and one tub.

    Should I continue to use 4" ABS as the soil pipe before it is reduced to 2" for the vent stack, or should I use 3" ABS?

  2. #2
    Plumber jimbo's Avatar
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    Default

    For what you have, 3" would be adequate...but is it code? Some areas require a full size vent all the way to roof. What existed in cast iron?

  3. #3
    DIY Member pensfan84's Avatar
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    Default

    4" existed before, minimum regulation here is 1 1/2" for the vent.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default vent

    You have to differentiate between what size is required for EACH fixture, and what size, or aggregate size, is required out the roof. They are two different numbers.

  5. #5
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    Default

    One vent, 1/2 the size of the building drain is required to vent through the roof. IPC

  6. #6
    DIY Member pensfan84's Avatar
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    Default

    Right - 2" is both code and is appropriate for everything that is being vented.

    That's not my question - I am wondering if a 3" stack will work just as well as a 4" would for my scenario.

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