IPC Shower Dry Vent

Discussion in 'IPC Plumbing Code Questions' started by wwhitney, Oct 28, 2020.

  1. wwhitney

    wwhitney Well-Known Member

    Mar 17, 2019
    Berkeley, CA

    Is the only way to dry vent a shower under the IPC to have the drain line run underneath a wall within the allowable trap arm length, and takeoff the vent under the wall so it can immediately rise vertically to 6" above the shower flood rim?

    UPC 905.3 has the language "Unless prohibited by structural conditions, each vent shall rise vertically to a point not less than 6 inches (152 mm) above the flood-level rim of the fixture served before offsetting horizontally". I take that to mean it is OK under the UPC, when not practical to run the shower drain under a wall before hitting the maximum trap arm length, to take off the vent with a wye rolled up, then go horizontal under the floor, proceed to a wall, and turn up into the wall with a long turn 90.


    However, the IPC equivalent section is 905.5, which reads in the second sentence "Horizontal vent pipes forming branch vents, relief vents or loop vents shall be located not less than 6 inches (152 mm) above the flood level rim of the highest fixture served." As an individual vent is a branch vent, and this section has no language about structural conditions, does that mean an underfloor dry vent takeoff as previously described is prohibited by the IPC? You'd have to do a wet vent instead?


  2. James Henry

    James Henry In the Trades

    Jul 23, 2019
    Billings, Montana.
    Doesn't matter what anyone says, you'll just argue with them until you win or they give up
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  4. wwhitney

    wwhitney Well-Known Member

    Mar 17, 2019
    Berkeley, CA
    If I wasn't interested in others' knowledge, I wouldn't have started a thread. I'm hoping someone can explain how I'm misreading IPC 905.5, or can point to some other language in the IPC that allows a UPC-style underfloor dry-vent takeoff.

    When you and I discussed the meaning of "fixture unit discharge into the wet vent" in UPC 908.2.2, I thought I convinced you that the DFUs of the fixture being vented aren't counted. I'm always happy to learn something new, and that discussion helped me understand wet venting better.

    Cheers, Wayne
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