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    RodButler's Avatar
    RodButler Posts: 11, Reputation: 1
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    #1

    Apr 22, 2009, 02:39 PM
    Minimum vent size for flush valve water closets
    I think the code says that you need to size a vent at one half the diameter of the largest waste pipe. But I seem to recall somewhere that said a minimum vent through the roof was 3 inches.
    massplumber2008's Avatar
    massplumber2008 Posts: 12,832, Reputation: 1212
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    #2

    Apr 22, 2009, 03:12 PM
    Hi Rod...

    All houses must, at a minimum, have one 3" vent that penetrates the roof. The minimum vent through a roof, however, is 2".

    The minimum vent required for all water closets, whether 3" or 4" pipe is 2"... so here, the 1/2 diameter rule doesn't apply.

    Let me know if you have more questions...

    MARK
    RodButler's Avatar
    RodButler Posts: 11, Reputation: 1
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    #3

    Apr 22, 2009, 03:28 PM
    Quote Originally Posted by massplumber2008 View Post
    Hi Rod...

    All houses must, at a minimum, have one 3" vent that penetrates the roof. The minimum vent through a roof, however, is 2".

    The minimum vent required for all water closets, whether 3" or 4" pipe is 2"...so here, the 1/2 diameter rule doesn't apply.

    Let me know if you have more questions...

    MARK
    What about commercial installation using flush valve water closets? Same rule?
    massplumber2008's Avatar
    massplumber2008 Posts: 12,832, Reputation: 1212
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    #4

    Apr 22, 2009, 03:31 PM
    Same rule... 2" vent required for all toilets!
    RodButler's Avatar
    RodButler Posts: 11, Reputation: 1
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    #5

    Apr 22, 2009, 04:08 PM

    Awesome, thanks.
    Milo Dolezal's Avatar
    Milo Dolezal Posts: 7,192, Reputation: 523
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    #6

    Apr 22, 2009, 09:34 PM

    They may be combined... and what you see is 3" or 4" vent end piece that penetrates roof. This is more likely in warehouse-type installations where you have several toilets next to each other...
    speedball1's Avatar
    speedball1 Posts: 29,301, Reputation: 1939
    Eternal Plumber
     
    #7

    Apr 23, 2009, 04:53 AM
    Quote Originally Posted by RodButler View Post
    I think the code says that you need to size a vent at one half the diameter of the largest waste pipe. But I seem to recall somewhere that said a minimum vent thru the roof was 3 inches.
    My Code requires one thre inch vent per dwelling, (we put ours in the kitchen) and a 2" vent for every fixture that has a trap with the exception of floor drains.Regards, Tom
    PlumbRob7's Avatar
    PlumbRob7 Posts: 5, Reputation: 2
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    #8

    Feb 3, 2011, 04:26 PM
    Hi
    In British Columbia every building must have one 3" vent.. also any water closet must have min. 1.5" vent and 2" wet vent...and floor drains 3" and larger can vent themselves.

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