Air Admittance Valves (AAVs) provide a sound alternative method to venting plumbing systems. First developed in Europe in the 1970s, AAVs introduced the idea of trap seal protection without the need for multiple vents through the roof. Introduced into the U.S. market in the mid 1990s, AAVs continue to grow and have eliminated the need for secondary venting. The American Society of Sanitary Engineering has developed regulatory standards relating to Air Admittance Valves performance. Model-plumbing codes have incorporated these ASSE standards allowing the use of AAVs. Air admittance valves are looked at as a way to improve plumbing systems by minimizing roof penetrations, reducing labor while increasing plumber flexibility.