1. The line can be reduce in size and be kept small if there are enough additional vents to give the required aggregate area out through the roof. 2. The pipe size cannot be reduced but has to be full size from the house sewer all the way to the roof.

Can you reduce a vent pipe?

If there are enough additional vents to give the required aggregate area out through the roof, then the line can be reduced in size and kept small. It is not possible to reduce the size of the pipe from the house sewer all the way to the roof. …

Can you reroute a vent stack?

You can just put an up-turned wye coupling in the existing vent stack just above the existing connections, run it through the same path you show in your diagram, and tie back in with a 90° elbow (or a couple of 45° elbows), and cap off that 2″ pipe in the wall straight above the connections to the big drain pipe.