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Thread: Can vent go downward below the highest fixture?

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    DIY Member keano016's Avatar
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    Default Can vent go downward below the highest fixture?

    Might seem like a silly question, but please bear with me.

    I know that venting must go vertically up 6 inches above the highest fixture, which is usually the sink prior to going horizontally.

    My question is, once I go vertical, let's say 20inches above the rim of the vanity, can I go horizontal for a foot or so, then go downwards vertically for 30 inches, and connect to a vent?

  2. #2
    One who lurks Basement_Lurker's Avatar
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    No you can not.
    Broken promises don't upset me. I just think, why did they believe me? -Jack Handy


    www.blackbirdkitchenandbath.com

  3. #3
    In the Trades Tom Sawyer's Avatar
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    It will trap condensation and over time will seal off the vent.

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    Moderator & Master Plumber hj's Avatar
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    It will work because condensation will drain both ways, but I doubt that you would ever find an inspector who would approve it. They usually only know what is "in the book" and cannot visualize how anything else would work properly.

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    DIY Member keano016's Avatar
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    Here is my situation. The bathroom is in a dormer in the attic that has one wall that is an outside wall but there is a 2 feet crawl space on the bottom. So I was thinking of wenting from the sink go up then down then around to connect to the 2 inch meta venting that goes to the roof.

    What would you do?


    Last edited by keano016; 03-12-2011 at 05:29 AM.

  6. #6
    Test, Don't Guess! cacher_chick's Avatar
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    I cannot make sense of the drains in your drawing, but it appears that the lav can be vented into the 3" CI or go straight up through the roof.

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