I am in the process of doing a bath gut, expansion and redo. The old bath was simple with one main 4" vent stack entending into the attic and through the roof. It had connected; a lav, a shower, a toilet and a washer drain all utilizing the same vent stack with a 2" dry vent in the attic. The new layout is more expansive and connecting to the 4" main drain in the crawl space will not be an issue. I will go back with double lavs about 12' from the old 4" exit in the roof, a toilet now about 9' from the old vent stack hole, a soaking tub on an exterior wall in proximity to the old toilet location, and a shower next to the new toilet location. My initial thought was to 4" main vent the toilet and tie in the shower vent in the attic, but I am concerned about the 9' to 10' lateral run in the attic to hit the old hole in the roof. I planned on a separate 2" vent for the double sink. I was also hoping to tie the tub vent into the main stack vent in the attic. However, the more I think about it, it makes more sense and I believe would be within IPC code to run the 4" main stack vent straight up the interior wall into the attic and through the roof; tying in the adjacent shower vent(in the attic) as a dry vent. The tub could be placed on its own vent and it could exit through the old 4" vent hole. As stated the double lav would have its own new vent. It means having 2 new 2" vents and a newly located 4" vent through the roof. Is this over kill based on code requirements? Or could I connect everything to one 4" stack like before?

Thank you for your time.