Richard writes from Matthews, North Carolina: "I measured the indoor temperature inside my house at ceiling height and at the floor level and came up with a temperature differential of approx 6 degrees F. I believe that my attic insulation is adequate. There is old R-11 insulation under the floor in the crawl space that has a paper vapor barrier on the side facing the floor and a thin clear plastic covering on the side facing the crawl space. It is sagging badly and needs to be re-supported. Could this be the cause of the temperature difference? Should I replace it or just supplement the existing with additional unfaced insulation? What R-value should I use in either case? Should I use batts or continuous strips?"

Answer: Yes, sagging insulation could be the cause of heat loss through the floor. The U.S. Department of Energy recommends a minimum of R-19 be used under a floor. Unfaced insulation can be added to what is there. But if there is plastic attached to the bottom of the floor joist, remove it and use it to cover the floor if it is dirt. Putting it under the insulation may cause moisture issues.