Taken from this thread which seems appropriate for your question.
We are cuurently doing a remidel and adding a shower. Right now the toilet is 6" from the 3" main drain and has a 3" vent pipe. I can Tee into the 3" line right under the toilet very easily then I want to run a 2" ABS line for the shower. Will the toilet vent be enough or do I still need to vent the shower as well? If so how to I add the vent in that line? Thank you.
Last edited by kingsotall; 12-10-2008 at 10:19 PM. Reason: Forgot to include pic
i understand the drawing, but my main vent pipe has the toilet 6" away from it and the shower about 5' away from it. Can't I just use that vent for the shower as well? or do I need to separately vent the shower? how about using one of those inline vents if I need to vent it? Thank you.
IPC will let you run 6' of 2" to a vent.
If I understand your question, no you cannot vent the shower with the main stack. When you flush your toilet, water flowing down the drain will (in theory) create negative pressure, and suck your shower trap dry.
You need to vent the shower drain separately.
If you want to use an air admittance valve to do so, it must be accessible, at least under the IPC. It must be installed vertically, and must be installed 4-6" above the trap weir, depending on manufacturer.
ABS is dead, use PVC.
oh no kidding, yeah dont see much of it at all up here in NH