I have a 1966 house remodel with a cathedral ceiling that has 2 X 6 framing. I have removed the asbestos popcorn texture and sealed it with paint. The ceiling space is insulated with rock wool that was placed by the original builder. Not wishing to remove and disturb the existing drywall, my plan is to place 1 1/2 inch polyiso under the drywall existing and using 2X2 furring strips to support new drywall below that. My question and concern is condensation and whether to use the foil covered product – Rmax? The climate is that of the Seattle area. The space above the existing drywall is vented from the insulated area to the soffit with a continous eave vent on the soffit.