AAV as a vent on a main waste stack

efsDecember 13, 2011

We have two waste stacks in our house.

One is used as a main stack for solid waste (serving two full baths and a powder room), while the other was used for kitchen sink and laundry sink.

During renovation they cut out the vent for the secondary stack (the one that serves kitchen and old laundry sink). I was told that the plumber plans to use AAV on the secondary stuck in lieu of the vent that is gone (both kitchen sinks that will drain to this stuck will also have AAV on them so there will be no traditional vent on any of the fixtures that will drain to that stack). Laundry sink had no individual vent (was utilizing the vent that was cut off). Is this OK? I am in CT.

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from CT building code:

"... 917.7 Vent required. Within each plumbing system, a minimum of one stack vent or vent stack shall extend outdoors to the open air. ..."

Do I read this correctly that when the AAV vented drains drain into my secondary stack, this stack (or at least one waste line connected to this stack) should be vented outdoors?

    Bookmark   December 13, 2011 at 11:29PM
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You don't have a plumber. You have a cheap hack. NO, it's not OK to vent a main stack with an AAV. Never has been anywhere, so it's not like this is an unsupervised apprentice going "oops, it's OK is Yokeltown so I assumed it's OK here." type of situation. A licensed plumber would know differently. A licensed GC would know differently. BIG RED FLAGS!

    Bookmark   December 14, 2011 at 11:12AM
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thanks- I am learning it the hard way.

    Bookmark   December 14, 2011 at 11:52AM
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The stack in question does not require any vent..This stack is serving only the kitchen and laundry, and they will both be fitted with AAV's, therefore the stack is now only a vertical portion of a vented branch and it does not require a vent.

    Bookmark   December 14, 2011 at 1:56PM
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the laundry sink does not have any vent at the moment.

The two kitchen sinks will have AAV vents.

    Bookmark   December 14, 2011 at 3:28PM
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the two kitchen sinks are on the first floor; the stack and laundry sink are in the basement. Is this still "vertical" portion of the vented branch?

    Bookmark   December 14, 2011 at 3:33PM
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Yes, and if the utility sink has an 1-1/2" drain and it is not more then 6ft from the trap to the stack it does not require additional venting.

    Bookmark   December 14, 2011 at 4:11PM
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AAV's are one-way valves, and therefore do not handle positive air pressure. This is why it is best practice not to rely on AAV's, in general.

A strong argument can be made that your kitchen + laundry stack (since it's vertical) might drain poorly at times depending on the activity in the vented stack, from tubs toilets and showers. More than that I cannot say.

    Bookmark   December 15, 2011 at 11:50AM
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