Air Admittance Valves

By Published On: July 28th, 2015Categories: Home Inspection Career Guide0 Comments

As technology changes and new or additions are made to building codes, inspectors will start to see new things that they maybe have not seen in the past.  Building codes vary across the country, but 49 States in the U.S. use the International Residential Code (IRC).  Your particular state may or may not allow things that are in the IRC code, so the state makes amendments to the code.  Check with your particular jurisdiction for what is accepted and what is not.  Home Inspectors are not code inspectors, but knowing if something is allowed per the building code will make you a better home inspector and help you build credibility with your referral source and the client. This article addresses Air Admittance Valves in the plumbing system.

This paragraph was taken from and explains how an AAV works:

“The membrane in the AAV will remain closed during periods of inactivity; so when you are not using the drainage system, it will remain sealed as a result of the gravity force applied on the membrane. Then, when the toilet is flushed, for example, the flow of the water causes a negative pressure within the pipework. As this happens the membrane in the valve will open, allowing fresh air to be sucked in through the valve and down into the system until pressure equalization is achieved. The equalization of pressure will bring the valve back into its closed mode, preventing the foul air from escaping and the water seals in the traps (bath, toilet and basin) from depleting.”

AAV’s are becoming more widely accepted around the country.  The 2012 IRC code does allow the use of AAV’s.  Some things to keep in mind per the code in regards to AAV’s are as follows:

  • Individual and branch-type AAV shall conform to ASSE (American Society of Sanitary Engineering) 1051.  Stack-type AAV shall conform to ASSE 1050.  The ASSE Seal gives inspectors, code officials, and customers confidence in the product’s performance via testing standards.
  • Installation: Shall be in accordance with the code as well as the manufacturer’s instructions.
  • Permitted: In individual vents, branch vents, circuit vents and stack vents with a connection to an AAV

Individual and branch type AAV shall vent only fixtures that are on the same floor level and connect to a horizontal branch drain.

  • Location: Individual and branch AAV shall be located not less than 4” above the horizontal branch drain or fixture drain being vented.  Stack-type AAV’s shall be located not less than 6” above the flood level rim of the highest fixture being vented.   The AAV shall be located within the maximum developed length permitted for the vent.  The AAV shall be installed not less than 6” above insulation materials where installed in attics.
  • Access and Ventilation: Access shall be provided to the AAV.  The valve shall be located within a ventilated space that allows air to enter.
  • Size: The AAV shall be rated for the size of the vent to which the valve is connected.
  • Vent required: Within each plumbing system, not less than one stack vent or a vent stack shall extend outdoors to the open air.
  • Prohibited installations: AAV without an engineered design shall not be used to vent sumps or tanks of any type.

Information provided by the 2012 IRC Code, Studor.n

About the Author: Kristin Warner

Kristin is the Marketing Director at AHIT. She has authored content for numerous real estate brands, and managed corporate communications for a public real estate company. She is passionate about the home inspection and real estate industries, and loves digging into research to provide insights that empower home inspectors and real estate agents in their businesses.