Air admittance values

I have an air admittance value in the crawl space with the top of the value 2" from the bottom of the floor insulation. Does anyone see an issue with that?

Russell Truluck

No. AAV’s are OK in a crawlspace or even inside a sink cabinet.

If I see more than one AAV in a home, then there are issues.


I’ve never heard of AAV’s being allowed in a crawl space. Admittedly, I don’t see many AAV’s in CA (because they’re not allowed by State Standards) but from what I know they’re required to be near or above the flood level of the fixture(s) they serve.

It seems to me that an AAV in a crawl space is just asking for trouble. . .

David - why would multiple AAV’s be a problem?

If you had an AAV below the level of the trap, what would be the point. Gases are supposed to rise through the system.

Once again we apparently do things differently down here in San Diego. I have whole subdivisions of expensive homes with multiple AAV’s in the houses: Rancho Bernardo, Scripps Ranch, 4S Ranch, Del Mar Highlands, Del Mar Heights, Rancho Penasquitos, and probably a few others. The first time I ran into them back in 2001, I called my plumber and he didn’t have a problem with them. Then I called two other plumbers and they didn’t have a problem with them either. That gave me the concensus that I was looking for.

When I find one under the kitchen sink, I know they will be in the bathrooms and the laundry, and, indeed, they area.

They make sewer stacks for that reason.

But why would multiple AAV’s be a problem?

Probably not a problem unless there is no main vent stack for the stucture.
They are not a perfect devices or without problems in the long term.

Your AHJ and codes would determine what is allowed in your area.


As with anything, though, right?

As the AHJ’s have already done here.

I find multiple AAV’s in the rich areas with McMansions. The reason is because all those ugly vents sticking up through the roof make the roof ugly. So when one has 19 bathrooms and 37 sinks, one really doesn’t want 37 doohickeys sticking up through the roof making the roof uglier than it already is.

Fewer doohickeys sticking up through the roof also make it easier for our South-of-the-Border roofing labor to install the roof. That flashing around 37 doohickeys can be soooooooo troublesome.

The CPC does not recognize AAV’s. As always, local jurisdictions vary. I’ve seen them in subdivisions as well as in manufactured homes - it usually depends on whether the area is incorporated within the county, having their own building standards. Unincorporated areas will usually be following State Codes.

In most homes (where I’ve seen AAV’s), they’ve been installed in the attic. Manufactured homes will generally have them at each fixture (that’s why I asked), but I can’t recall ever seeing one in a crawlspace. . .

I never stated that they are a problem. I stated that there will be issues with multiple AAV’s.

If construction is well planned ahead of time, and sewer stacks are considered into the plan, AAV’s are not needed because multiple fixtures can be added into a single sewer stack.

Normally I see a single AAV’s in manufactured homes (at the kitchen sink) due to the distance from the bathroom to the kitchen. I hardly ever see AAV’s in SF homes.

So I’ll repeat the question, which you quoted:

Or, in other words, what “issues” would there be with multiple AAV’s.

I’m trying to learn something here. Thanks.


Use your head for something other than a hat rack…

That’s what I thought. You can’t come up with any “issues.” That’s okay. I did learn something. :wink:

RR - AAV’s are a mechanical device and as with all mechanical devices there is the probability of failure (no matter how small). Gases that they are exposed to aren’t necessarily kind to mechanisms (springs). When they fail, and eventually they will, they erase the vent system for that area of the DWV. That is not a good thing as you know.
The next step is how many people test the AAV’s in there house to see if they are functioning properly. Do any of the HI’s in NACHI test the AAV’s they find. I don’t and I used to be a plumber. One of my pet peeves is that plumbers and code inspectors seem to think it is okay to replace a vent stack with an AAV on new construction. Not good.

BTW I’d rather see an attic filled with PVC tying all the vents together and a single 4" stack. Problem is it takes time and PVC pipe to do that, AAV much cheaper.

Think of all those soldered joints of the copper water pipes. Soldered by human beings, who are prone to make errors. Many times those joints fail, but I’m not going to call out “multiple soldered joints.”

I’ve even seen vents plugged on the roof from birds and other rodents, and everything is subject to failure. That’s a big “Duh!” as far as I’m concerned. So my question remains:

Why are multiple AAV’s a problem?

Indicate lowest bid or lazy plumber?:wink:

Here is a helpful list of state AAV approval status.

RR, I see that CA only has partial approval. Do you know what’s partial?

They are still outlawed in Minnesota because of union pressure.

Wisconsin permits them with stipulations and limited to two mfrs. only( Studor and Oatley).

RR - Tell me you don’t have pictures of some of my solder joints back when I was going to school.