We got a few quotes to get vinyl siding placed over our existing asbestos-based shingles. All but one said we would need the siding with the foam all ready attached to it. The one who didn't says it's not needed since we are putting it over the existing asbestos-based shingles which is a good insulator and he will be putting on an insulator (with insect repellent) between the wall he is putting up and the shingles, thus we wouldn't be gaining value from the foam. To me it makes sense but my wife's view is why is everyone else selling us the foam-based and telling us it's so much better than siding without the backing. So, who's right and why?