Where to Position a Drain Vent Pipe
By: Danny Lipford
My shower and washing machine drain need a vent pipe. Should I put the vent downstream from both of them or in between them? -Deb
Depending on the distance between the drain pipes for the shower and washing machine, you may be able to install a single vent at the drain further downstream to serve them both.
The maximum distance recommended between two drain pipes for them to share a vent is 3½’ for a 1½” drain and 5’ for a 2” drain pipe. If they’re further away than that, each should have their own vent, though the two vents can join together before going through the roof.
If your codes allow, you may be able to avoid running another vent stack through the roof by attaching a one way vent known as an air admittance valve on the drain line. This allows air in while preventing sewer gases from coming out.
Good luck with your project,