Vent an Island Sink…and Other Tricky Spots
A handy one-way valve eliminates most of the plumbing work.
Synopsis: Putting a sink in a kitchen island used to mean that you had to run a complicated plumbing vent loop up, down, and under the floor until you reached a wall where you could extend the vent line through the roof. Enter the air admittance valve (AAV). This handy gadget is a one-way valve that allows air to enter when the sink is drained but keeps sewer gases trapped in the vent line. Lynn Underwood, a building official in Norfolk, Virginia, gives the pros and cons of AAVs. You’ll learn where you can use them, how to install them, and how to convince your building inspector if (s)he’s dubious.
Adding a sink or a dishwasher to a kitchen island isn’t quite as simple as just tapping into the water supply and the drain line. You also need to vent the drain line (usually through the roof) to keep water in the sink trap. Without this vent, water in the trap can be siphoned out when someone flushes a toilet or drains a bathtub, allowing smelly sewer gases to seep into your house. A vent pipe is easy to install in some situations, but kitchen islands (inset drawing) and many plumbing-project remodels pose some major venting challenges.
Air-admittance valves (AAVs) solve these problems elegantly. An AAV allows air to enter the drain system through a one-way valve that then closes by gravity after the sink drains. This valve keeps the water trap sealed and sewer gases out of the house. AAVs have many other benefits, too: fewer holes to cut through framing; fewer holes to cut in your roof; and up to 75% less pipe in your house.
It’s not new, but it’s not conventional, either
Invented in Sweden nearly 30 years ago and used…