Air Admittance Valves (AAVs) are devices used in the plumbing systems of buildings, as well as ships, to address the problems associated with inadequate plumbing drainage venting.

Adequate venting of the plumbing drainage system is an essential consideration in the design, construction and renovation of any type of building. By employing a vent pipe, the problem of negative air pressure can be effectively relieved, since the pressure inside the wastewater stack can equalise with the ambient pressure. However, since the vent pipe must always vent to the atmosphere and penetrate the roof of the building, drainage venting solutions which employ venting pipes are often complex and unsightly affairs (read more about the problems associated with plumbing drainage venting).

By contrast, an Air Admittance Valve (AAV) allows air to enter the plumbing drainage system through a one-way air valve when a plumbing fixture is operated and water flows through the pipes. When the flow stops, the valve closes by gravity and prevents the escape of sewer gas from the plumbing system. Compared to a venting pipe solution, AAVs provide many advantages:

- They replace extensive vent piping, saving costs in material and installation.

- They reduce the need for fire-stopping devices by preventing the “chimney effect” in pipes, reducing the risk of fire spreading upwards between floors.

- They protect the inner mechanism against the entrance of vermin, foreign objects and materials.

- They eliminate the risk of water leakages through the roof penetration which a traditional stack pipe requires.

- They provide greater freedom of design for engineers and architects.

The problem of positive transients is somewhat more complex to resolve (read more about the problems associated with plumbing drainage venting). While AAVs only address the problem of negative air pressure, a device referred to as P.A.P.A. (Positive Air Pressure Attenuator) is increasingly used as a simple and effective solution to this problem. If used in conjunction, AAVs and P.A.P.A.s provide a perfect balance in returning the drainage system back to atmospheric pressure without the siphonage of any traps – and without the complexities and problems of traditional venting solutions.

AAVs were developed by the Swede Sture Ericson in the 1970s.