Placement the barrier perpendicular to heat movement with a bare minimum three/4-inch air gap for optimum functionality. For maximum performance mount the barrier on the underside of the roof rafters applying furring strips to maintain suitable spacing. Alternatively, cavity insulation, together with foam boards or spray foam, can be employed https://thejillist.com/story8758727/getting-my-how-to-isolate-roofs-to-work