I've been living in a fixer-upper for a while… I've been fixing a lot that was previously done wrong.
I've finally gotten around to ripping out our first floor bathroom (two full bathrooms) and I'm noticing some plumbing issues. Mainly that there's what seems to be a vent pipe terminating into my wall. So yeah, there are no proper plumbing vents in this house. Surprisingly I haven't yet had any problems, but now that I've got a bathroom torn out it seems like I should fix it correctly.
I've made a diagram of the existing… situation. The large pipe is 4" PVC, and the smaller pipes are 2" PVC — I don't have wall access into the second floor bathroom at this point, but from what I can tell by the first floor, everything is draining into a single 4" pipe.
Edit: looking at the existing work some more, it just seems better to redo the entire waste line system. Here's my plan. Any red flags here?
Best Answer
I am not a plumber but I think your plan is just fine according to these tables:
http://publicecodes.cyberregs.com/icod/ipc/2012/icod_ipc_2012_7_sec009.htm
http://publicecodes.cyberregs.com/icod/ipc/2012/icod_ipc_2012_7_sec010.htm
A 3" pipe is plenty for the number of DFU's in your stack and horizontal run. The 2" vents on the sinks are probably even oversized and so they should be plenty.
The only issue I see is you can't take sink through the roof as a 1.5". At least not here in the north where it could frost over.
Have you considered tying the kitchen vent into your main vent and avoiding another roof penetration? Just a thought.
The only time plumbers around here use 4" in a single family home is for the main sewer exit from the house, and then only a few feet of the exit itself.
Good luck!