I’m getting ready to insulate the new workshop I built for myself – 44 ft x 30 ft with 12 ft tall ceiling. The slab is insulated with 2″ XPS under the entire slab, including the edges along with a 6 mil poly vapor barrier.  The wall assembly is 2 x 6 studs, Tyvek, T1-11, Benjamin Moore latex primer, and Benjamin Moore Aura exterior paint.

The shop will be heated with a natural gas fired unit heater with a usual temp of 50 to 60 degrees in the winter, dropping down to 40 degrees when not in use for long periods of time (a week or more).  There is a good possibility I may eventually add A/C at some point in the future.  I live in SE Michigan, climate zone 5.

I will insulate the walls with 6″ of mineral wool and use the Air Tight Drywall method.  My question is when it comes to a vapor barrier should I use a vapor barrier paint or MemBrain or nothing or ?  Marty