Answer Hi Fred, Ultimately, this depends on what Code is in force and being followed in your area. Check with the LA County Building and Safety. Per the 2006 International Plumbing Code: Section 905 – Vent Connections 905.1 – Connection All individual, branch and circuit vents shall connect to a vent stack, stack vent, air admittance valve or extend to the open air. Section 917 – Air Admittance Valves 917.1 General Vent systems utilizing air admittance valves shall comply with this section. Individual-and-branch-type air admittance valves shall conform to ASSE 1051. 917.2 Installation The valves shall be installed in accordance with the requirements of this section and the manufacturer’s installation instructions. Air admittance valves shall be installed after the DWV testing required by Section 312.2 or 312.3 has been performed. 917.3 Where permitted. Individual, branch and circuit vents shall be permitted to terminate with a connection to an air admittance valve. The air admittance v