Julie writes from Rochester, New York: "One contractor tells me I need R 49 as a minimum in my attic and his project will give me R 56. Another tell me when he is done I will have R 80. If I need R49 why would I go with either of them if I need R49? Is going to R80 over-insulating and is that a problem?"

Answer: To maximize the energy efficiency of both new and existing homes, the U.S. Department of Energy (DOE) has published R-value recommendations based on specific heating and cooling needs and the cost of energy across the country -- Zip Code by Zip Code. The Owens Corning website has a calculator to help you determine the R-Value Recommendations for your area. The DOE recommendations are substantial so I don't see a need to exceed them. The only drawback in going beyond the recommendations is the long time it may take to save enough additional energy to pay for the extra insulation. Once you reach the recommended R-values there may be other opportunities in your home that will deliver a better energy efficiency payback.