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  1. #1
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    Mar 2007
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    Washington State
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    Default AAV vent in attic

    Found this at yesterday's inspection. AAV vent terminates in attic. I have read that it's allowed in some cases. This vent is for a master bath addition, 3" drain/vent. I don't believe that it's connected to any other outside vents.

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  2. #2
    Join Date
    Mar 2012
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    Lansdale, PA
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    876

    Default Re: AAV vent in attic

    Quote Originally Posted by Trent Tarter View Post
    Found this at yesterday's inspection. AAV vent terminates in attic. I have read that it's allowed in some cases. This vent is for a master bath addition, 3" drain/vent. I don't believe that it's connected to any other outside vents.
    Depends on local codes. The IRC allows them on a waste stack that terminates in an attic, as long as the AAV is 6 inches above the insulation. There also must be a least one vent that extends to the outside. Some areas do not permit them even though they are approved per the IRC.


  3. #3
    Join Date
    Feb 2009
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    Southern Vancouver Island
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    Default Re: AAV vent in attic

    I would tell them to vent it through the roof to prevent sewer gas from making squirrels and rats go crazy and damaging the house.
    Also its a source of moisture.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  4. #4
    Join Date
    Mar 2007
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    Default Re: AAV vent in attic

    Quote Originally Posted by Mark Reinmiller View Post
    There also must be a least one vent that extends to the outside.
    That is also critical for the proper operation of the AAV.

    Quote Originally Posted by John Kogel View Post
    Also its a source of moisture.
    How so?

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  5. #5
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    Default Re: AAV vent in attic

    Quote Originally Posted by Jerry Peck View Post
    That is also critical for the proper operation of the AAV.

    "Also it is a source of moisture"

    How so?
    Warm moist air rises here in my part of the world. Steam from a shower drain, stuff like that.
    Sewer air is warmer than the attic air for some parts of the year. Don't ask me to prove it with a quote from a codebook.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  6. #6
    Join Date
    Mar 2007
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    Default Re: AAV vent in attic

    Quote Originally Posted by John Kogel View Post
    Warm moist air rises here in my part of the world. Steam from a shower drain, stuff like that.
    Sewer air is warmer than the attic air for some parts of the year. Don't ask me to prove it with a quote from a codebook.
    Warm air rises in my part of the world too, but ... ... but AAVs allow air to enter the air ADMITTANCE valve ... ... but not exit from the AAV.

    If sewer gas or air is exiting the AAV, the AAV needs to be replaced as it is defective or has 'gone bad'.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  7. #7
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    Default Re: AAV vent in attic

    Methane gas pressure will build up in the vent stack and then it will blow, as well as suck.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  8. #8
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    Mar 2007
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    Default Re: AAV vent in attic

    Quote Originally Posted by John Kogel View Post
    Methane gas pressure will build up in the vent stack and then it will blow, as well as suck.
    It is designed NOT to blow (release) gas, air, etc., not unless there is something wrong with the system.

    Now, if you mean KaBoom! when you say blow because of a build up of gas, then there is something in the vent system which created a spark ... and that something should not be in the vent system.

    AAVs are not intended for 'positive pressure' DWV systems, and a properly designed gravity draining DWV system will not have the problem you are describing.

    There is nothing wrong with having an AAV in the attic when the DWV system is a gravity (not forced) drain system and at least one vent is open to outdoor air (that keeps the system at atmospheric pressure and prevent pressure build up. If you manage to blow an AAV off the stack it is on, they you have a positive pressure forced system and should not be using the AAV anyway.

    There have been occurrences where utility companies 'blow out' the street mains with pressure and, indeed, that pressure can create quite a few problems with all the gravity drain systems connected to the street main which is being pressurized, and not just systems with AAVs. That practice has become recognized as 'not a good practice' because of the damages and messes it can make in the connected systems which were not designed for pressure. Most utilities have, I believe, stopped that practice.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  9. #9
    Join Date
    Mar 2007
    Location
    Spring Hill (Nashville), TN
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    Default Re: AAV vent in attic

    Quote Originally Posted by John Kogel View Post
    Methane gas pressure will build up in the vent stack and then it will blow, as well as suck.
    This is one of reasons that the home must have a vent to the atmosphere outside the structures envelope if it has an AAV. If the AAV is allowing sewer gas to enter, it is faulty and needs to be replaced.

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

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