Jeff writes from Grand Island, New York: "I have a cathedral ceiling, with 4 x 10" exposed beams, 2' o/c, 2 x 6 t&g sheathing with 2" of rigid insulation above the t&g. Then 1/2" plywood and fiberglass shingles. I am considering some renovations and additional insulation in the ceiling, below the deck. I am concerned about the ventilation issue. Should I be? How do I proceed?"

Answer: Ventilation is required under the plywood that the shingles are applied to on your roof. We recommend the Federal Housing Administration (FHA) standard of 1" minimum space for air flow. The formula for determining how much venting you need can be found on the Owens Corning Web site at: http://www.owenscorning.com/around/ventilation/determining.asp.