I want to move a toilet to the other side of a small second floor bathroom. It would sit next to a new shower with a new wall separating the two. The new 2” shower drain would connect into the new 3” toilet drain, which would then run across the room about 6 feet to the existing soil/vent stack. The photos below show several options for the design of the drains and vents.
I can’t run any vents up the wall behind the toilet and shower because of various obstacles, but I can run vents up the new wall between them (it will be about 8 inches wide and 32 inches deep).
The floor joists run parallel to the wall behind the toilet (perpendicular to the new drain as it runs across the room to the existing stack). The challenge is to find a drain/vent configuration that mostly fits between adjoining joists so as to comply with the notching and drilling restrictions that apply to the joists. I can replace all the joists with a variety of I-joists and oversized lumber joists (2 x 12s), spaced at irregular intervals as needed, but a number of things limit where the new joists could be located, e.g., light canisters in the suspended ceiling in the room below and various obstructions along the top plates on which the joists rest. The joist span is only 9 feet, and especially with oversized joists I see no issue as to meeting code minimum (apart from notches and holes), but I want the floor to be as sturdy as possible to avoid deflection cracks in the tile.
I’ve toyed around with several configurations shown in the photos, trying to come up with a design that would comply with code (IRC and Illinois Plumbing Code), function optimally, and allow an acceptable plan for locating and drilling the joists. The mock-ups show the basic designs, using pipe scraps that only approximate the actual lengths needed. Since the bathroom is on the second floor, I assume that no cleanouts are required.
I’d like to minimize the bends in the toilet drain. The centerline of the separating wall would be offset about 8 inches towards the toilet from the line directly across from the stack. The drain connection at the stack is low enough to allow the proper pitch in the drain lines, but it leaves only about 4 inches between the pipe and the subfloor to play around with angled vent lines. The width and depth of the separating wall give me some additional leeway as to where the vents come up through the floor.
Photo A shows a vent arrangement that I think fully complies with the plumbing requirements (spot any errors?), but it is very problematic from a joist perspective. The toilet vent is 2” and the shower vent is 1.5”, and their inverts are above the drain centerlines. The two vents would join near the ceiling.
Big question: Do I actually need a second vent for the toilet (the existing cast iron stack continues upwards as a vent)? The developed length of the toilet drain would be more than 6 feet. The IRC seems to say that no vent would be necessary in addition to what exists at the stack. The Illinois Code seems to say that I would need a vent within 6 feet of the toilet (Sections 890.1470 and 1490). The issue is very confusing.
The other photos show options that are more “joist friendly” by assuming either that no separate vent is needed for the toilet or that a 2” vent off the shower drain would satisfy what is needed for both fixtures.
Photo B is simply a 2” vent off the shower drain upstream of where it connects to the toilet drain. Photos C and D show options that might function like a wet vent (“vertical” at 45 degrees), the primary difference being whether the branch of the 2 inch wye is used for the vent or for the shower drain.
Any observations and advice would be greatly appreciated.