I am building a combo bathroom / laundry room in an existing building in a room where there was no plumbing before. I want to avoid venting directly out this roof (for reasons I can describe if you'd like), so my intention is to circuit vent the fixtures in this room back to the main stack.
My main question is: do the horizontal sections of the vent have to be sloped? And if so, with a 2" pipe, should it be 1/4" per foot or can it be less? The code book is unclear, or at least my interpretation of it is. Seems like it would vent and drain just fine if it were level, as any moisture would not have a chance to pool any more than the surface tension of water allows; it can drain to the stack or back to the branch it vents. Any slope I give it will take inches off my ceiling height. I have enough, but more is better :)
To elaborate, in case you wish to keep reading, the room will have a shower and sink vented together (2") and then a clothes washer and laundry basin vented together (2"). The two 2 inch vents will join to a 3" horizontal before joining the 3" stack.. a total horizontal distance of about 15' for either vent. There is also a toilet downstream of these two branches, but my understanding is it is not limited by any critical distance to a vent (the stack about 8 feet away will serve as it's vent).
