Brad writes from Saint Paul, Minnesota: "I currently have faced r13 on knee wall in a finished attic. How do I add more insulation to this wall? Can I place rigid foam insulation over this directly over studs? Also, if I do this, do I need to cover the foam with fire retarding material?"

Answer: Most people will add FOAMULAR® extruded polystyrene insulation to the back side of a knee wall. Check with your local building code to see if they will allow you to leave the insulation exposed. Most codes require covering the foam insulation with a 15-minute thermal barrier.