Terry M. writes from Gaylord, Michigan: "I would like to know how to properly insulate a knee wall that is exposed to a cold attic. The big question is should the knee wall be backed with foam board? And, if the wall is not backed, what percent of the r factor would I lose?"

Answer: Some building codes do not allow foam board to be exposed on the back side of a knee wall. If your local code allows it, I would suggest using it as a backer. It will also give you an additional R-5 per inch.

Losing R-Value will only happen if the physical characteristics of the insulation are changed. For example, if the insulation is compressed it would lose R-Value. I recommend getting a good seal with the vapor retarded and caulking all seams for air infiltration.