I have two questions regarding vent pipes as I am renovating a bathroom where the original ventilation system was non-existent. (1) I read in an article that roof vent pipes can run horizontally since gas-air pressure is drawn upward by the lower atmospheric pressure outside the house. Is there a specific length that this cannot exceed? For example, we are looking to connect to the vent in another bathroom, which is approx 40 ft away. Is this okay? (2) Is there is a specific number of bathroom/appliances that can be added to one roof vent pipe?
All plumbing waste & vent piping is to be “pitched”, slanted in the direction of flow. Waste piping is pitched downward, typically @ 1/4″/foot. Vent piping is pitched upward, as it’s drawing air from outside, & anything other than flat is acceptable, 1/8″ or even 1/16″. It’s pitched because rainwater that falls in the vent piping can cause problems. There are tables as to size & length of all piping, generally, the longer the pipe gets, the size increases. Typically, any full-size vent stack in a residence can handle any amount of fixtures you’de be able to connect to it.