Building a detached garage in Illinois near St. Louis. Outlet will run to an existing septic system. My understanding is that needs to be 4" even though the use is only a half bath and an AC condensate drain. My question is where should this transition to 3". It has been suggested to make the wet wall 2 x 6 to allow the fresh water lines pass the main stack which seems reasonable since a 3" PVC pipe has about 3.5" OD and would completely fill a 2x4 cavity. Should I bring the 4" above the floor? Or should I reduce the stack to 3" at the first turn up? As I am thinking the incoming line would come in just above or below the footing (about 36" deep) and turn up with a sweep 90. Then a T for the toilet connection. Then proceed up for the sinks (one in bath and one utility sink back to back). Then on up for elevated trap for suspended furnace/AC.
I am also a bit unclear on wet venting and what I am allowed to use for combination vent and drain line.
I plan to run my plan by the local inspector but figured I need to know a bit more first so I don't do anything too obviously wrong...
I am also a bit unclear on wet venting and what I am allowed to use for combination vent and drain line.
I plan to run my plan by the local inspector but figured I need to know a bit more first so I don't do anything too obviously wrong...