No water closet (toilet) on the 2nd floor?

Water closets require a minimum waste line at 3" in diameter. Showers a minimum of 2" waste line and tubs 1 and 1/2". ( Source: IRC 2006 Code which I believe is the plumbing code now used in California....but check to be sure)

That said, if no water closet, what you propose is fine.

If there will be a water closet, then the drain must be 3" continuous from the 2nd floor to the building sewer, but only 1 1/2" vent is required.

Thanks for the feedback.

I will actually have 2 new water closets on the second floor, however, I thought that it would be simpler to separately drain and vent all the fixtures that are on the side wall of the house (opposed to the back wall that I show above). My working plan for the side wall is this.

I was planning to use 1 1/2" pipe for all the vents except for the main stack where I was going to use 3" for the vent. I tried to annotate the picture with the size of pipes. Is 1 1/2" ok for all the vent pipes? Is 3" overkill for the main stack vent?

Any other problems that anyone sees with this plan?

Thanks for your help.