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Thread: A couple of DWV questions

  1. #1

    Default A couple of DWV questions

    Question fundamentally has to do with combining separate vent lines in the attic and through the roof.

    Situation: Doing a remodel, Old bathroom had a toilet and shower sharing a 2" vent through the attic and out the roof. There is a separate 1 1/2 inch vent going through the roof for the single vanity sink.

    With the remodel, I'm moving toilet, shower, and adding a vanity. So I'll have four separate vents moving through walls into the attic--a 2" toilet vent, a 1 1/2" vent for shower, and two 1 1/2" vents for the two separate vanities.

    Question--can all of these work on current vents through roof? Easiest would appear to be to combine the toilet and shower vents in the attic to the 2" exit through the roof, and combine the two vanity 1 1/2" vents to exit the 1 1/2" vent through the roof. If not, what needs to be enlarged.

    Question #2. Shower vent will need to come off 2 " drain raising at a 45 degree angle until I hit a wall and go strait up. What is the proper fitting to go off at a 45 degree vertical angle. (And in what direction is it to be oriented?)

    Thanks a lot.


  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    The size of the vent line through the roof (and internally as well) is covered by local codes. Essentially, it is figured by fixture units...add up the values for the things it is venting, and that determines the size of the vent required. In some places, they require the part going through the roof to be larger than the parts down lower to prevent the water vapor from condensing, freezing, and closing the vent off. If you made the one roof penetration large enough, you could use just one, but location in the house may make that impractical. To prevent pooling of rain or condensation, the vent needs to be sloped, just like a drain. This can make long runs impractical as well.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3



    Thanks. In San Jose, CA. Cal Building Code based on UPC.

    Not sure of fixture units and chart--gotta go look.

    And the second question?



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