One piece of the energy-efficient attic puzzle is insulation. But before installing insulation, you should first tackle some other improvements.
Properly seal any trouble spots where warm air may be leaking out in winter or into the home in summer. Look at anything that comes through the attic floor, such as recessed lights, the chimney, the attic hatch, pipes, ducts or wires. Before adding or improving the insulation, seal cracks with caulk, expanding foam or weather stripping.
Many attics are underventilated, enabling moisture and heat to build up. Moisture causes harmful mold and wood rot. A poorly ventilated attic can overheat in summer, baking shingles and shortening their life. During the winter, a warm attic can melt snow on the roof, causing it to run off into the gutters and then freeze, creating ice dams.
In proper attic ventilation, air flows from a low point to a high point. This is usually done by installing soffit vents and insulation baffles around the perimeter, plus vents near the peak of the roof. If there is no way to install enough attic ventilators, an attic fan can be installed to exhaust hot air.
Types of insulation
The three main types of insulation for attics are loose-fill, batt and rigid. Any type should provide a high enough level of insulation for your region, measured in R-value.
Batt and rigid insulation will often have the R-value printed on them. Loose-fill, which is blown in, is the most common for attic floors, and its R-value is approximately its depth in inches multiplied by 2.8.
Here in Kentucky, an attic should have a minimum grade of R-49, or about 16-18 inches of blown-in insulation. If yours is less than that, you should be able to add more on top of it as long as it is free from any asbestos (if installed before 1990), moisture, rodent, ant or termite issues. Old insulation containing asbestos will require professional removal.
Check with your electric co-op about any rebates offered as part of a weatherization program, which often includes adding insulation.