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If using sprayed-in-place polyurethane foam, be sure the AS is leveled-out well , before spraying. The foam is very rigid, and will not allow the shell to flex very much,(this is a very good thing). As to the effectivness of the foam, it is perhaps a complete order of magnitude better than almost anything else commonly available at reasonable cost. This is based on a good quality foam of around 2-2.5lbs. per cubic ft. density product. The difference between sprayed foam, and air bubbles or fibergass batting is simply amazing. If possible, run wiring inside of plastic conduit, with junction boxes at key locations, to permit later removal, or pulling-thru new wiring. The sprayed foam will also almost completly eliminate the problems of trapped condensation within the shell. Foam such as this is rated with a "K" factor, rather then "R" factors, as fiberglass is. Go for it. The foam is also FAR better as a sound barrier. It is so far ahead of anything else, there is no second place.
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