An air admittance valve is a mechanical one-way valve fitted to a soil pipe, stack or branch waste that opens to admit air during discharge but closes again to prevent drain odours escaping into the room. AAVs allow drainage systems to be ventilated without extending a vent pipe through the roof, which is particularly useful in extensions, loft conversions and refurbishment of London terraces where external pipework is restricted. UK Building Regulations Part H1 and BS EN 12380 set out the conditions under which AAVs can be used and require at least one open vent on the system overall. Valves must be installed above the highest connected fitting and accessible for inspection. Over time, the diaphragm can stiffen or stick, leading to gurgling drains and loss of trap seals.
Air admittance valve (AAV)
One-way valve allowing air into a drain system without releasing odours.
