John writes from Danville, Illinois: "Much of my attic is not floored. With that in mind, what is the proper amount roll insulation I should use?"

Answer: The amount of insulation to add depends on two factors - the amount and type of insulation already in place and the recommended R-value for your location.

You can check online for the R-value recommendations published by the U.S. Department of Energy. The 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. One source for that information is the R-Value Recommendations page of the Owens Corning Website. After entering your zip code on the site, enter your heat source - gas, oil or electric - then click the "Find R-Values" button.

DOE recommendations represent the R-values necessary to optimize your home's energy efficiency. You may find that these recommendations differ from building codes. State energy codes are generally minimum insulation requirements for new construction. You can check online or call local officials in to find out what the code is for attic insulation in your area.