Vapor retarder needed with mineral wool?
I have a small renovation project about to start where we’re replacing old fiberglass in two exterior walls of a corner room with new mineral wool (among other things). The house has 1/2″ foil faced polyiso (old late 70s vintage) on the exterior, labeled as R5 but I don’t trust it to be much better than R3. A future project will be to reside the house at which time 3″ of polyiso will be installed, but it will be a few years before that happens. This is in the northern part of zone 5. The polyiso is directly over the studs with T1-11 over that as the siding, so there is no wooden sheathing in the stud bays.
My question is will a vapor retarder be needed on the interior, or will the usual latex paint over drywall suffice? The mineral wool is the usual unfaced batt stuff.