yet another DWV

Been lurking for a long time but now just getting around to a bathroom remodel and could use any advice before the inspector shows up and makes me redo everything. I love everyone's use of Google SketchUp. Use it its free! http://sketchup.google.com/product_suf.html
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What do you guys think of these models?

Things to note:
--My local code is IPC.
--IPC allows the double san tee for back to back water closets as long as the developed length is greater than 18 inches. I have about 3 feet on the right side and 4 feet on the left. (Model isnt to scale)
--I could vent the w.c's but best I can tell IPC allows for wet venting.
--The tub vent is 5 feet from the trap which I believe is right at the limit for the 1 1/2 pipe.
--Not shown is that I will convert to 2 inch as the lav. and shower dump in.
--The vents both are dry above and vent to the roof.

Options
#1: An easier option for me would be to drain the lav. into the vent for the tub but I am not sure if that is legal. Is it? WOuld be easier though as the wye's for the lav and shower will be in between joists and it will be a tight fit.

#2: If you guys hate the double ST with the side inlet, I may have room to drop down a little and use a double wye. The arms of the wye would extend up a bit to current level of the w.c. and then use a 45 to get back to horizontal. The other fixtures would enter the stack at the same level as shown in the model with a regular santee fitting. Guessing I would absolutely have to vent the w.c.'s then.
Thanks.


Close UP




Option #1


Option #2 (will add vents for the w.c.'s)

option 3

Option 3 would be an approved back to back fixture fitting for the two toilets and the Y connection for the others below it.

Thanks, HJ. Looks like I will have room for the Double Wye in Option #3. Though IPC does allow the santee option, finding that fitting might be different story.

One question: when adding vents to the w.c's, do they need to the typical 42 inches off the floor or can they be lower. No problem for the toilet on the left. For the toilet on the right, I will have to hide the vent under a shower seat, so I will only have about 20 inches. It will be 6 inches above the flood plane of the toilet though.