It seems to be a very divisive topic among plumbers. The Air Admittance Valves vs. traditional plumbing stacks with roof penetrations. No doubt that the traditional roof vents are standard and the most reliable since there are no valves to malfunction. The cons to them are they create a hole in your roof so the potential for roof leaks and they create an energy loss in homes with a hot roof design (SIPS) since you are going through the EPS or spray foam. They also can clog with debris or rodents can find their way in and come into the home (Norway Roof Rats). I've seen them do that as they can swim and you will end up with a rat in your toilet!



In some areas code does NOT allow for one to install metal screens on top of the plumbing stack to stop roof rats/debris. The reason given is that the metal screen during winter will capture vapor due to condensation forming. The screen will get wet and ice over and block the plumbing stack from working properly.

I read that AAV or Studor vents are used a lot in Europe and especially in high rise buildings and they are very reliable when you buy the correct one (not made in China). They can last for 30 years and go through 500,000 cycles and won't emit sewer gas. Some European manufacturers claim their units are tested for up to 1.5 million cycles, or at least 80 years of use. If they fail, they can easily be replaced.

I prefer ZERO roof penetrations and will run my bathroom fan vents through an ERV setup and vent out the side wall with one hole. The only roof penetrations in my SIPs would be the bathroom plumbing stack vents but if they can be eliminated with an AAV, I would go that route.

So are quality AAV's as those found in Europe worth going that route or go with the traditional plumbing stack through the roof?

Check with your local building inspector. In my area, AAV's are not allowed based on the most recent version of the applicable code. Can't remember which code it was that disallowed them, but was likely either the 2009 IBC or 2009 UPC. They had previously been allowed, but the county adopted these new codes late last year. My plumber actually installed an AAV under my kitchen sink, trying to avoid running a vent in my ICF walls, but the inspector failed it based on the current code requirement. That might answer your question, like it or not.....

Good luck!

Plumbing has been the single-most frustrating aspect of building my house. There are at least 3 different national codes, there are regional differences within those codes, and then the local jurisdictions often have their own specific rules. Plumbing codes seem to be quite vague and arbitrary compared to the other building disciplines. To top it off, it seems to be impossible to get plumbing advice. Whenever I've asked on forums, or even asked licensed plumbers a question, I've been stonewalled at every turn. In the process of posting a picture of my under-slab work, performed by a licensed plumber, and approved by the building inspector, I learned the it will probably work, but doesn't meet code! I finally spent a lot of time learning how plumbing actually works, studied code books, and designed and installed my own DWV system. Will it pass inspection? Who knows!

OK, rant over, but my point is, you had better make sure that whatever you do will fly with your inspector. AAV's seem to be a last resort for difficult situations where a regular vent is impossible. Usually they turn up in island sinks, or a sink in front of a window. In my kitchen, the sink is in front of a large window, making it impossible to run a vent straight up. I vented the sink a bit downstream, but I'm not sure if the sink trap is protected from another sink on the same circuit. I'll ask the inspector what he thinks, but I will probably add an AAV just to be sure. Personally, I think they are OK if they are periodically inspected/replaced/cleaned, but most people aren't that diligent with home maintenance. I could see some kind of goo backing up and glueing the thing shut, rendering it inoperable. Nothing with moving parts is infallible, where an open pipe to atmosphere is about as trouble-free as it gets.

Pests can and do enter the house through vent stacks. Our old house in FL had a terrible roach problem, and a co-worker said that they enter through the vents and swim the trap. I looked into the vent at night, and there were hundreds of roaches in there! A simply screen eliminated about 90% of the roaches.

Also, I've learned the hard way that just because they sell something at the big box store doesn't mean that it is code-compliant. The associate may even tell you something is code-compliant, even of it isn't.

AAV's are allowed in my State. When it comes to plumbing it is a weird and diverse world. Plumbers either love or hate the AAVs and I don't buy the old statement that they are valves and valve can break. There are valves in toilet bowls and sinks, so what? If the valve breaks you replace it for $30. I honestly believe this is a $$$ issue because it's always more money to run a plumbing stack from each bathroom, kitchen, laundry room, etc., and then poke a hole in the roof in 7 spots. Now you have 7 protrusions in your roof, all the labor to install the pipes and the potential to have 7 area pipe flashing done wrong and cause a leak when it rains or snows.

You will notice that states with strong plumber unions will not allow AAV's but other states with very little to no union presence will allow them. So in Chicago where you pay a union plumber $100 an hour the AAV's are not allowed. More money can be spent on running PVC to the roof and for the roofers to flash and seal all those holes.

At least that's my theory...

My concern with an AAV is that if it failed to operate, how would you know? The fixtures would continue to operate, but the trap could get sucked dry (which I finally learned is what vents are for), and you could have sewer gas in the house. You can tell when other plumbing valves are faulty. You don't need all individual stacks on the roof; you can combine quite a few together, although it gets complicated, and it's easier for the plumber to just punch straight through the roof and let someone else deal with it.

if it failed to operate, how would you know? you'd smell it - pretty quickly

Some code officials will allow vent stacks to exit through a wall instead of the roof.  Wall exits may be easier to waterproof.

Posted By Bob I on 21 Jul 2013 04:43 PM
if it failed to operate, how would you know? you'd smell it - pretty quickly

Exactly. If the valve failed, the smell would let you know pretty quickly that it went bad. That or the flushing and draining of the fixture would be substantially weakened.

These valves have gone through 25+ years of in-duty use and over 500,000 cycles and have performed exceptionally. It's an easy swap when they do go bad, since by code they have to be accessible. The in-tank valves of most toilets will fail within 5-10 years of install. I've already replaced 3 flapper valves on toilets that were only 5 years old.

The "maintenance" of these valves has been completely blown out of proportion by plumbers. As I mentioned, it's about $$$ and plumbers make a lot more money running PVC up through a wall and roof rather than installing a $30 valve.

Traps prevent GASES from entering the house. Sewers stink. Methane does not. You can get one with out the other. Dry traps can let in gas without odours.
Most code require a minimum of one 3" vent to exit the house. In almost all cases, no matter what happens in the city mains, this will allow enough air to follow to prevent dry traps. Installing cheater vents instead of venting to the exterior does not usually allow that volume of air to follow. Is your families life worth that little?
In extreme cases, a gasoline leak due to an accident on the street or a natural gas leak from a ruptured line can and has found its way into houses with devastating consequences.

Posted By FBBP on 21 Jul 2013 08:56 PM
Traps prevent GASES from entering the house. Sewers stink. Methane does not. You can get one with out the other. Dry traps can let in gas without odours.
Most code require a minimum of one 3" vent to exit the house. In almost all cases, no matter what happens in the city mains, this will allow enough air to follow to prevent dry traps. Installing cheater vents instead of venting to the exterior does not usually allow that volume of air to follow. Is your families life worth that little?
In extreme cases, a gasoline leak due to an accident on the street or a natural gas leak from a ruptured line can and has found its way into houses with devastating consequences.

Here is where the engineers get angry because AAV's are not "cheater vents" as they have been disparagingly called. A "cheater vent" is some type of knockoff of what an engineered AAV actually is.
A true AAV is:
  NSF Certified,
  ASSE 1050 & 1051
· ICC ESR-1664
· NSF Standard 14
· IAPMO – Classified Mark
· ASTM D 2665/D 2661
  IPC & IRC Code Approved

If the valve has a spring in it, it is not an air admittance valve. Those devices are typically called cheater vents. An AAV does not have spring in it.

The system will be connected to a private septic tank, not the city sewer.

They have been used in Europe for decades and here in the States also for decades and I haven't heard of anyone dying from methane or natural gas leaks due to a failed AAV.

AAV's don't replace a sink or sewer trap, the traps are still installed.

AAV's have been installed in these hundred million dollar high rises, hotels, stadiums, condos, etc:

Projects: North America

If they were so problematic and dangerous, I doubt they would be installed in such high end commercial buildings.

"In extreme cases, a gasoline leak due to an accident on the street or a natural gas leak from a ruptured line can and has found its way into houses with devastating consequences"
FBBP This is a discussion about plumbing vents - if gasoline runs into a house from 'an accident on the street', or natural gas flows in "from a ruptured line", how would either material get into the plumbing system in the first place? At least in my house, it's difficult to imagine how a gas or liquid flowing into my home could "run into" my toilet!

Bob - If there is a wreck near a city sanitary manhole chances are fluids from the wreck are going to enter the manhole and from there the explosive vapours will enter into the building sewer drain from your house. The older the city, the poorer the condition of the infrastructure so to have an undetected underground natural gas leak migrate to the city sewer system is not uncommon.
A bigger concern these days with the adaptation of natural gas as the choice of heating fuels is cross connections. As most n. gas services into older areas are done by horizontal boring the is many times where the bore pierces the sewer line. No real problem until you decide to send a cutter down to clear the blockage. If it is a clear cut, it is detected right away. If it is just a scar or pinhole, it may not be detected till to late.

Bear - if you read the documentation you will find the following -

Figure 11
The IPC and the IRC both would show that Air Admittance Valves are permitted for the use of individual vents, branch vents and circuit vents. The Studor MINI- VENT or REDI-VENT may serve as the termination point for these vents " AS LONG AS THERE IS AT A MINIMUM OF ONE VENT TO OPEN ATMOSPHERE WITHIN THE BUILDING SYSTEM. " Through out the documents you will find comments to that effect. In other words they may be used as secondary or fixture venting as long as one stack vent is to atmosphere. All the approvals are for following the manufactures install instructions.
All the certifications don't mean a thing until you actually read what the are certified for. All these organizations certify many different things

Cheater vents work fine for island sinks etc. instead of bull venting them, but to use them for whole house??

If it has a spring in it, it is still an aav because it lets in air and prevents dry traps, it might not be a Studor.

Private septic systems still need air. Without proper air flow they turn anaerobic and turn into ground water polluters. Many packaged treatment plants do all their secondary treatment by way of compressed air added to the effluent but every tank and treatment field needs air. If you are required to denitrify the effluent you need to move it from aerobic to anaerobic and back again.

FBBP: good point. Most of my work occurs miles from manholes, but I can see the issue in urban areas.

Without proper air flow they turn anaerobic and turn into ground water polluters.

Conventional home septic systems are anaerobic and don't need air and don't pollute the ground water. Rarely do home sewage treatment systems use an air compressor to create an aerobic system.

I would use AAVs wherever allowed by code.

Posted By jonr on 22 Jul 2013 03:38 PM

Without proper air flow they turn anaerobic and turn into ground water polluters.

Conventional home septic systems are anaerobic and don't need air and don't pollute the ground water. Rarely do home sewage treatment systems use an air compressor to create an aerobic system.

I would use AAVs wherever allowed by code.

Jon - here is one of the primary reasons we don't do Anaerobic.
https://en.wikipedia.org/wiki/Escherichia_coli
To get a health colony of good bacteria to kill bad bacteria like e. coli. you NEED to have air in the system. While it is true that much of the settlement and clarification of sewage on its trip back to drinking water happens in an anaerobic climate in the tank, until you move it to an aerobic state, you will not treat it, only dispose of the bad guys into the ground water.
It is because people don't understand septic systems that they are being banned or needing to be installed under the care of engineers and that is why advanced treatment plants that require air are becoming a multi billion dollar industry.
In any case, the decomposition of the sewage produces gasses that need to be vented out of the tank at a safe height, both for safety and for aesthetics.

I do plan on having at least one vent through the roof for the plumbing stack but I also will utilize the AAV's where I can. I'll take 1 roof penetration over 7 of them. My local code allows for AAV as long as I install one 2"+ roof stack, I can use the AAV's elsewhere.

In regards to the septic system: My septic will be aerobic as I will have SludgeHammer system installed. It uses an air pump system that continually injects oxygen into the underground 2-chamber septic tank. This makes for a much cleaner effluent, less toxic gasses, higher waste disposal rate and a septic tank that will need less frequent pumping. From my research there is no doubt that an aerobic system is 100x better than an anaerobic. Even though my soil perk allows a conventional anaerobic system, I will step up and install the SludgeHammer unit. It's really easy to do.

I am also installing the Infiltrator system for my leach field with capped air vents at the ends. This also lets in oxygen into the leach field to help with waste breakdown. The Infiltrator setup is way better than the standard PVC pipe with holes in it.