Updated: Mar 10, 2020
Air admittance valves (AAV's) are mechanical plumbing devices that can take the place of plumbing vents. How does it work? Air admittance valves work with a sealing mechanism that is lifted to let air into the drain system when there is negative pressure and allow proper drainage. Positive pressure causes the mechanism to close so that gases cannot escape into the home. #AirAdmittanceValves are very inexpensive and easy alternative to installing traditional plumbing vents.
Current Alabama Plumbing Code
At this time Alabama currently follows the 2015 IRC (residential building code)
Basics of Air Admittance Valve codes:
AAV must be installed minimum 4 inches above drain
If AAV installed in attic, must be installed minimum 6 inches above any insulation materials
Air admittance valve must be accessible and open to air flow/be installed in location that allows air to flow through it
Within each home plumbing system, there must be at least one traditional plumbing vent stack extending to outdoors to fresh air
Without proper venting, the plumbing system cannot drain properly. Just recently at a home inspection, a couple of vent stacks on the roof had been capped off (for whatever reason..). Which resulted in poor drainage in the master bath of the sink and fixtures. A strong sign that you have a venting issue is if you here a loud an excessive "gurgling" sound when water is going down the drain. One possible issue that could cause this is if maybe a vent stack on a roof has become blocked with excessive debris or of course being capped off.
Pros of Air Admittance Valves
AAV's are really inexpensive to purchase and you also save money on the extra material and labor needed to install vent stacks in a traditional plumbing system. Most of the money coming out of your pocket would be put into labor installations. They also lower the risks of any possible roof maintenance. If you only have to run one vent stack through the roof, that means less holes in your roof that could cause possible leaks.
During home inspections, it is more common than you think to find leaks around all the vent stacks. They can be improperly installed and water can find its way under the vent stack boot flashings and make its way into the attic. Then not only do you have to fix the leak, if the situation is let go long enough it can cause more water damage and more damage to your wallets.
An AAV can take the place of a traditional plumbing vent at individual fixtures because it allows air into the drain without allowing sewer gas to enter the building. The diagram at the top of the page is a great illustration demonstrating on how the venting device works. The sealing mechanism helps keep sewer gases from entering the home.
Air admittance valves are most commonly used when island sinks are installed in the middle of a kitchen/room when you can not just run a vent stack in the open. Although there are other options such as installing loop system venting, AAV's are a very easy, simple, and inexpensive option.
Air admittance valves have a typical life expectancy of 20-30 years, so if you start to have issues with sewer gases or smells being released around your sink or in the attic-wherever installed- the air admittance valve could be faulty or failed and should be replaced as soon as possible.
You also want to make sure your AAV is installed correctly. The air admittance valve is required to be installed a minimum of 4 inches above the drain and 6 inches above any insulation material if installed in the attic. Pictured here is an air admittance valve I came across while crawling through the crawlspace. Installed lower than the drain and in the crawlspace located with limited air flow, the AAV will not work properly or efficiently as it should.