Venting question tying into vertical stack

[ERichter]

Hi all,

I'm renovating a 2nd floor bathroom in my 1908 house, which is currently the only bathroom tied to that stack. I'm planning to add a powder room directly below this one and possibly a bathroom with shower in the 3rd floor attic, so I'm trying to make sure everything is plumbed and vented appropriately to allow for this future work. Here is the piping plan I've come up with, the bath vent will join 2" vent stack in the attic, which will then tie to the main stack just before the roof exit and in the basement. My question is primarily whether this 2" vent stack would be sufficient for supporting the fully realized bathroom plan, which would be 3 toilets, 3 lavs, 1 bath and 1 shower. I have a plumber friend who is insistent that a 2" vent can only support a single toilet on the first floor of the building, but I've looked through our local code (Allegheny County in PA) and I can't see any requirements beyond a minimum 2" vent for closets and limits on developed length and fixture units, both of which I'm well under.

 

[ERichter]

I realized that what I posted doesn't work due to the horizontal vent from the toilet so I've revised it to make it a wet vent from the sink. That's 1 1/2 in pipe from the bathtub and for the sink trap arm, then 2" for the wet vent and Vent Stack.