Alan writes from Sioux Falls, South Dakota: "My house has an unconditioned attached garage. The garage walls have sheetrock, then a plastic vapor barrier and insulation, but the ceiling just has sheetrock. I'd like to insulate the ceiling by adding batt insulation above it in the attic (to keep it more comfortable in the summer and winter). Should I use faced or unfaced batts? (i.e. Should an unconditioned space have a vapor barrier between the sheetrock and the insulation?)"

Answer: Sorry to disappoint you but Owens Corning does not recommend insulating an unconditioned space. Adding insulation to the attic above the garage will not make the garage cooler in the summer. In fact, it may tend to create a hot box because the insulation will help to maintain a temperature whether it be hot or cold. It will trap vehicle engine heat in the summer, for example. So the only way to benefit from adding insulation above the garage will be to condition (heat and/or cool) the space after insulating. A vapor retarder is not necessary between two conditioned or unconditioned spaces.