Vapor retarder? Upper floor gut, main floor remains. – GreenBuildingAdvisor

Working on a 1905 residential house in Marine 4C that does not have a vapor retarder on the walls or ceiling. The upper floor is being completely gutted, with new heating and air conditioning. 

The roof will be foamed at the rafters/sheathing (I’m aware of the open/closed cell discussion and will address accordingly), but this question is for the walls. Typically we just put up PVA paint on partial remodels and call it a day, but since this is a full gut we have more options. The siding is wood lap on sheathing, so not vented. Code says we need at least class II. 

I am thinking Intello (class II) on all interior second floor walls (and ceiling if we use open cell at the roof). The question is: will this screw anything on the main floor given the old house will have a different permeability on each floor?

For the roof – do conditioned CLOSED cell attics also need dehumidification? 

TIA