Arthur writes from Florissant, Missouri: "I have a house built in the 1950's. The outside walls have fiberglass insulation between the studs however the walls are quite cold. I would like to add insulation to these walls. The only feasible way to do so that I have come up with is to cover the existing inside drywall with 3/4" - 1" rigid foam board plus a 1/2" gypsum board for fire protection and to provide for a finished wall surface. Does this seem to be a practical method? Also if it does, would a vapor barrier be required?"

Answer: Yes, the system you describe is an acceptable method for insulating an existing wall. No, an additional vapor retarder will not be necessary and is not recommended.