In regards to the question of what about the shingles when the iceneing foam is applied directly to the bottom of the roof deck. There is only one shingle manufactor in the entire US that will offer any warrenty, that in itself must tell you something. After 40 years of building, I highly recommend having a 1" airspace under the roof deck which is easily done by using the Corwin smart ventilation system. Can be used even in a retrofit. Write to tomceejay@aol.com for more information. Web site coming soon.