Robert writes from Monument, Colorado: "Its cold and dry in co.-----i want to add insulation to the present 6 inches of faced fiberglass insulation in my attic.---which of the following do i use -- and-how much for max. energy efficiency.---encapsulated fiberglass-or, cellulose-or, unfaced fiberglass??????????"

Since you already have faced insulation, you should use unfaced insulation. You can use thermal batts or fiberglass blown insulation. Of course, I prefer PINK fiberglass insulation.

As for thickness, 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 also check online or call local officials to find out what the code is for attic insulation in your area.