I have a vent that runs from my middle floor bath to the roof. From the bathroom it runs down into the basement level garage and into the slab with a cleanout before entering the slab floor. The only items that drain into the line are a toilet and sink. The shower has its own drain and vent.

My question is does it need to be 3 inches in diameter? I am wanting to move it into a new wall, but only have room for a two inch pipe to go between two joists. I know that when it hits the roof it is only 2 inches.

I can leave it 3" as the drain, but would really love to change the vent. If so I plan on getting a plumber to do it, but I don't want to get him out until I know for sure. Otherwise, I'll just leave it where it is and just reframe a new wall around it.

Thanks in advance,
Ed

Hi Ed,
I assume this is a home and not a condo. I was sure of my answer until I read," I know that when it hits the roof it is only 2 inches."
What plumber chokes down a 3" vent to 2"? On all of our new houses we make one main 3" vent. As a rule it's the kitchen sink vent since we increased the rough in drain to 3". However, on the other hand if the vent's been choked down to 2" without affecting the system then, if local codes allow, I see no reason not to convert the vent back to 2" so it will fit through the walls. Good luck, Tom