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Thread: Vent Stack Question

  1. #1

    Default Vent Stack Question

    Apologies in advance for the dumb question...

    We bought an old house last year that needs work. The longtime previous owner had done a lot of questionable DIY projects over the years that need to be redone right. On top of that, an interim owner who bought the house as an investment property did an extremely half-assed (pardon the expression) "renovation" that essentially covered up a lot of the problems but didn't fix them. The contractors I've had over to my house have either burst out laughing or shaken their heads in dismay when they see some of this stuff. I'll post some pictures sometime.

    Anyway, the reason I'm writing is that the plumbing stack, rather than going out my roof, terminates in the attic and is capped. My question is, how problematic is this? My upstairs bathroom sink belches some funky smelling gas when it drains (hell, who doesn't?) which I assume might be related. If this is the most catastrophic consequence, I suppose I can wait to have it fixed. Is there anything I'm missing?

    Many thanks,

    Mikael

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
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    New England
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    First, I'm not a pro, but without a proper vent, when water goes down one trap, it can suck the water out of the others. This means that there is no barrier between the sewer and the inside of your house - sewer gas is nasty stuff, and if it accumulates can reach explosive proportions (it contains methane from the rotting wastes). It can also let bugs and whatever into the house.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member Mike Swearingen's Avatar
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    Jan 2005
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    The vent stack must be vented outside through the roof.
    All fixture drains must have traps to prevent sewer gas from entering your home, and there must be a vent after each trap (toilets have built-in traps) tied into the main stack or also vented directly outside.
    If a trap isn't properly vented, every time water drains through the system, it will siphon the water out of the trap to create a "vent", allowing in sewer gas.
    Unbelieveable what those nitwits did.
    Check with your Building Inspection Department for local code and permit and inspection requirements, and do it right or your drain/waste/vent system will never perform correctly.
    Good luck!
    Mike

  4. #4

    Default Capped vent

    You said that the house is an "old" house. If it's old enough, the vent you describe may be the only vent for the entire plumbing system. You certainly need to extend the vent to the exterior through a proper roof jack flashing.

    You also want to make sure that once the vent is extended to the exterior that all the applicable clearances for the vent termination are met, i.e.,(assuming that you have a sloped roof) a minimum of six inches above the surface of the roof covering, a minimum of twelve inches from any vertical surfaces, a minimum of two feet above any building opening ten feet or closer to the vent (three feet if the Uniform Olumbing Code applies), and a minimum of four feet below any building opening ten feet or closer to the vent termination.

    Other factors may also come into play regarding the vent such as the number of fixtures that are being served by the vent and the diameter of the vent.

    Both you and the contractors that you've had look at the house already know that non-professional work has been performed. So, you'll want to make sure that all future modifications, corrective measures, or new work performed at the house conforms to all applicable industry standards and all applicable governmental codes, ordinances, and regulations.

    Hats off to you for wanting to do it right!

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