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Thread: Common Venting

  1. #1
    DIY Member Hazel's Avatar
    Join Date
    Jan 2006

    Default Common Venting

    Hi ,
    I need some advice about venting through a new addition roof. We added a second floor and simple trussed hip roof on top of our existing house and I need to poke whatever vent holes are required through the roof prior to shingling.

    There are like 8 or more vents in various locations on the floorplan, as much as 32 feet apart, and now that there is attic space I wonder if we can combine all those vents into one or two to minimize roof holes.

    I've read that the combined vent area should be larger than the main drain and that I need min 1/4 in per foot slope on any vent. Are there any other restrictions that would disallow combining vents in the attic space?

    Thanks so much,
    Last edited by Hazel; 01-16-2006 at 02:51 PM. Reason: typo

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Bothell, Washington
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    Combing vents is ok.

    Where the horizontal is more than 1/3 the vertical, you should go up a pipe size.

    If you have 4" going out, then you will need at least
    4- 2" vents.
    1- 4" vent.


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