I'm adding a second floor addition to my 1 story home.

The existing main floor has only a bath, toilet, and 2 sinks connected to the main 4" stack. All fixtures are very close to the stack, I can tell for sure that the toilet and bath are not vented. I don't think the sinks are either.

Isn't it true that when a fixture is close enough to the stack it doesn't need a separate vent?

If this is the case, could I then use the existing 4" stack as the drain for the second floor? or Would I still have to go into the basement and Y off a new stack for the second floor addition?

I want to plan this carefully.