I’m framing a 2-story garage that is attached to the main house via a mudroom. The plumber wants to run his waste lines through the mudroom floor system and into the house to connect to septic. Normally, I would run joists from foundation wall to foundation wall, and line up studs so they’re bearing on joists as in the first picture but this would mean joists are in the way of plumbing, and plumber can’t cut a 4″ hole in every 2×10, of course, so I would have to core through foundation wall in garage and the house foundation to run plumbing. I could have bought open web joists but I’m not sure they’re locally available and I need to keep the project moving. 

Another approach which I drew would be to run a ledger against the main house and install joists to it with hangers. This would allow plumbing run to make a straight shot through the joist cavity with only one hole in rim board in garage and another in house rim board. In this case the studs in mudroom wouldn’t be bearing directly on joists (just rim board) but blocking could be installed to help with this. I’m probably overthinking this but input would be appreciated.