I am designing a house to build as a homeowner builder and one question I have has to do with plumbing in load bearing walls. One of the bearing walls will have a vent stack going up through the top caps, it would be a 2X4 wall. Is there a restriction to the size hole you can cut through the topcaps and PT bottom plate to accommodate the vent stack? The only information I can find is the restriction for cutting and drilling into the vertical supporting members, nothing on the topcaps and bottom plate. I guess an option would be to build the wall out of 2X6 instead of 2X4, but that is a lot to do just for one vent stack, or run the vent up through a non bearing wall and run a 1.5" auxiliary vent up through the bearing wall and then to the main vent.

It is always good idea to build 2x6 wall if you have 3" stack going through it...

In my area, it is OK to run 3" pipe vertically through bearing wall. You can drill or cut the plates. Then, you use "L.A. Plates" or "HVAC" plate to span the cut.