I am replacing my shower/bath, including removing the wall that houses the vent pipe (the new unit is free-standing). To make the repiping easier, I want to redirect the tub vent pipe to merge with the vent stack for the double sink, which is about 7 feet away. My plan is for the tub vent pipe to start vertical, then almost immediately turn to run horizontal for that 7 feet, then vertical again (with some maneuvering) to merge into the vent stack for the sinks. I know vent pipes can be run horizontal as long as there is a slope, but is there a rule about minimum rise distance of a vent pipe before it can run horizontal?
Rule about minimum rise of a vent pipe before it can run horizontal
drain-waste-ventpipevent
Best Answer
Yes. The vent can't run horizontal until you've reached the overflow height of the attached fixtures. The idea is you don't want the water to backup into a horizontal section of venting and deposit debris in the event that the waste pipe clogs. If the waste pipe clogs then the fixture should overflow before water runs into a horizontal section of vent pipe.