Either way works. The decision is made in the field based on practicality.When you vent the fixtures on the 2nd floor of a 2 story house do they need to have there own stack or is it more common to re-vent the first story fixtures up and over the 2nd story fixtures so as to avoid wet venting.
Questions like this sort of depends on your local code. For starters- you need the combined equivalent of the area of a 4" vent. if you're doing an addition/remodel you probably have an existing 4" vent stack- so you can vent your new fixtures based on their required vent size- a bathroom usually needs a 2"When you run a secondary stack just for 2nd floor does it also need to be 3"? And should it run from the roof to the basement and then tie into the main stack from underground?
The pipe through the roof is a vent stack. The pipe through the floor is a waste/drain stack. The waste stack can tie into another drain line or stack as long as it is sized correctly. It does not have to go under slab.Ok what im asking is for second floor fixtures that need their own stack. Should that new stack that runs to the roof be only for venting or should it also be a waste stack that eventually ties into the main stack in the basement? These are just things im asking for an understanding.