Dennis writes from Philadelphia, Pennsylvania: "We have a newer house with a flat roof. There is a space of about 8" between the ceiling and the roof deck that is not insulated. What is the best way to insulate this roof?"

Answer: The procedure for insulating under a flat roof is the same as a cathedral ceiling. Detailed installation instructions can be found at owenscorning.com on the project page for cathedral ceilings. You will need to maintain a 1" ventilation space between the insulation and roof deck.