A poorly insulated attic squanders energy in both the winter and summer -- sending heat right through the roof in cold weather and serving as an enormous solar collector on hot, sunny days.

How do approach an attic insulating project depends on how you're planning to use the area. If the space will be used only for storage, insulate the floor. If it's finished or you intend on finishing it later, you need to insulate the ceiling and walls.

Either way, look first for leaks that might damage insulation. Check to make sure you have adequate ventilation, and decide if you want to cut summer heat buildup with an attic or wholehouse fan.

If your attic has a floor, you have two insulation choices: pull up sections and work the insulation under or hire a contractor to blow loose-fill through holes bored in the floor. With unfinished floors, be sure to bring up some planks or pieces of plywood so you can get around on the joists without stepping through the ceiling below.

Ceiling materials alone won't bear the weight if you made a mistake and stepped through.

Use batts, blankets, or loose-fill. If there is already a vapor barrier, use unfaced materials or slash the facing so the moisture doesn't get trapped between the two barriers. Also, it's important that you don't cover recessed light fixtures or exhaust fans; doing so could cause a fire. Instead, install baffles that keep the insulation about 3 inches away on all sides.

Caution: Some materials, such as fiberglass and mineral wool, are harmful to the lungs and skin, so be sure to wear a painter's mask, gloves, and long sleeves if you'll be working with hazardous materials.

For loose-fill, nail baffles at the eaves. Insulation should cover the wall top plate but not obstruct airflow. Pour insulation between joists, then level it with a board. Be sure you don't leave low spots or voids.

If you need a separate vapor barrier, staple 2-mil polyethylene between the joists. Seal seams with tape. When placing batts or blankets, take care not to jam them against the roof; leave space at the eaves for airflow.

When you encounter bridging or other obstacles, cut for a snug fit. Otherwise, heat will slip through the gap. When trying to achieve a high R-value with two layers of insulation, place the second layer perpendicular to the first.

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