Martin writes from Denver, Colorado: "My attic has old blown in insulation and you can see the top of almost all the rafters. My house is very cold in winter living in Colorado. I was thinking of purchasing 4x4 or 4x8 sheets of polyiso with osb and laying it over the rafters and taping the seams to help insulate my attic. Is this a proper way to install this kind of insulation? I heard the R-value was very good for this type of insulation. What do you suggest?"

Answer: Owens Corning recommends installing unfaced FIBERGLAS™ insulation perpendicular to the existing blown in material. We do not manufacture the type of insulation you describe in your message.