We have an insulation contractor in the area that does the expanding, spray in place foam insulation. On houses with the roof system forming the ceiling in the upstairs, such as in a 1 1/2 story house, he recommends spraying the foam directly to the bottom of the roof sheathing. He claims an air gap under the shingles is not needed with his very special product. I find this hard to believe, as does our very big roofing material supply house. Any comments on this one? I say we may have some burnt up shingles in 5 years or so.