John writes from Allison Park, Pennsylvania: "I need additional insulation in my attic however, I like the fact that the center 1/3 of my attic is covered with plywood for storage purposes. Should I only insulate the uncovered areas, or should I take up the plywood, re-insulate and cover again with plywood (compressing the insulation)?"

Answer: For the insulation to perform at its best, insulate under the area where the plywood is as well as the rest of the floor. Compressing insulation will reduce its R-value. Fiber glass insulation works on the principle of trapped air pockets. By compressing fiber glass insulation, you decrease the amount of air trapped in the material.