I am considering using a product call Low-E Therma-Sheet under a composite shingle roof to be installed in a few weeks. It is installed directly under the shingles with no air space.
I’m very concerned about the claims made about this product and wonder if your organization has any reports or reservations about this product – especially used in the manner I just described.
You have good reason to wonder about this application of a reflective insulation product. The company that markets this particular product isn’t a RIMA member, but I would hope they would give you the same information we do. Reflective insulation and radiant barriers must be installed in such a manner that their reflective surface(s) face an air space. Reflection of heat does not occur unless this condition is met. When a reflective material is in contact with another surface it becomes a direct conductor of heat at all points of contact. Installing it under shingles will not provide you with any worthwhile performance.