I am at odds with the way I should add insulation to the roof of my metal pole building. The roof already has the very thin backed insulation that you see in metal buildings. I use my attic and I want to insulate between the joist bays but have heard of moisture problems when adding backed insulation to the existing thin backed insulation. I want to keep the existing backed insulation were its at. Is it best to add unbacked insulation or is there another product that I am unaware that wont cause mositure problems?
Closed-cell spray foam may indeed be your answer. If you do decide to use batts somehow, I would sure make sure there is plenty of ventilation between the batts and the roofing. And don't waste time w/ fiberglass. My 2 cents.