I am in zone 3, and I was able to find the R value requirements pretty easily. However the vapor retarder part is a bit confusing. Some documents say you need it on the interior, some say exterior, some say none at all and that paper kraft or paint has the right permeability. I've even read somewhere that you can sandwich vapor barrier between 2 layers of insulation.
I am so confused. Is there a definitive answer for this?