Need help with drain/venting requirements

[mjr6550]

I think that I am usually pretty good at understanding codes, but venting sometimes confuses me. I am evaluating a bathroom renovation that also included installation of a stacking washer/dryer. I know some issues are wrong, but I am unsure about venting.

The washer and bathroom basin share a common drain pipe, which drains into a stack that also is used for the toilet. IRC P3109.2 say every fixture drain shall connect separately to the waste stack and that the stack cannot receive waste from toilets. The drain pipe is also 1-1/2" and 2" is the minimum for the washer drain. So I know the installation is wrong.

Assuming that installed a separate drain (correct size) for each fixture and the traps were within the allowable distance from the stack as specified in Table P3105.1 (i.e. 1-1/2"-6 feet; 2"-8 feet) this would still be wrong because the stack is used to drain a toilet?

Would it be correct if a vent was installed in each drain line and tied back into the stack?

I am thinking about this from the standpoint that there would be another bathroom on a floor above this bathroom. In reality, the building is a multi-story condo so the IPC would really apply. I just want to wrap my head around the IRC requirements before venturing into the IPC, which usually confuses me even more.

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