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Thread: Four DWV Venting Layout questions

  1. #1
    DIY Senior Member jch's Avatar
    Join Date
    Jan 2006
    Victoria, British Columbia, Canada

    Question Four DWV Venting Layout questions

    A previous owner developed the attic in our house in 1994. This included adding a bathroom up there (clawfoot tub, lav, toilet).

    We want to replace the tub with a custom shower (center drain). The clawfoot tub is alongside an exterior wall (which makes venting tricky).

    I've been reading lots about this and was hoping to get a final opinion from you folks before I pull a permit.

    Here is a layout of the current DWV plumbing layout for that bathroom:

    1) If I move the Bathtub drain 25" to make it a center drain for a shower, I know I should make it 2" pipe (rather than the current 1-1/2"). Can I continue to use the Lav as a wet vent if I run this 2" pipe parallel to the existing 1-1/2" and tie-in via a Wye 18" downstream of where it currently connects? Or do I need to figure out how to separately vent this drain arm?

    2) The toilet clogs *much* easier than the identical model in our other bathroom (both are Toto Ultramax's). Would changing the 90 under the closet flange to a long-sweep 90 (from what appears to currently be a vent 90) improve things? If so, would the loss of headroom/slope be a problem? (Currently the 3" waste is 60" long in a 2x10 joist bay, so currently a 7" drop over 60")

    3) Currently when you drain the bathtub, it drains in a hurry (!). Problem is, it also sucks about 1" of water out of the toilet bowl. Do I need to install a separate vent upstream of where the 2" Lav/Shower line joins the WC line? If so, can the vent be a horizontally-installed wye? (very little headroom)

    4) There are a whole bunch of 45s (four of them) plus a long-sweep 90 as the 3" pipe winds its way through the joist cavities before it finally heads down to the basement. Do I need a relief vent here? Or is 3" pipe big enough to self-vent?

    Really appreciate any help you could offer

    - John

  2. #2
    Homeowner geniescience's Avatar
    Join Date
    Nov 2005
    humid summers hot, humid winters cold


    1) Yes ... continue to use the Lav as a wet vent ...
    2) I don't know what to do here
    3) No ...Do I need to install a separate vent upstream of where the 2" Lav/Shower line joins the WC line? ...
    4) No ...Do I need a relief vent here? ...

    Based on what (I think) plumbing code is in BC.



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