INSULATION : Putting One More Thing in the Attic

To keep your heating costs from going through the roof, be sure that your attic is properly insulated.

There may be areas where the insulation needs to be replaced, or it may need to be upgraded overall. If the attic is unfinished and has no insulation, it’s a very cost-efficient space to insulate.

Types of Insulation

Insulation is available in several forms. Fiberglass or rock wool can be purchased in batts (pre-cut four- or eight-foot lengths) or blankets (continuous rolls). You can also buy loose fill of cellulose (paper treated with a fire retardant), rock wool, glass fiber or vermiculite.

Loose-fill insulation comes in bags that should be stamped UL and NAHB-NRC (indicating certification by Underwriters Laboratories and the National Research Center of the National Assn. of Home Builders).

Criteria

The ability to resist heat flowing outside your home is measured in R (for resistance) values. The higher the R-value the greater the insulating power. Buy insulation for the R-value, not the thickness. For the recommended R-values for your climate, check your local utility company. Generally, attic insulation should have an R-value between 30 (in the Sun Belt) and 49 (in the Snow Belt).

To determine the square footage of insulation needed for an attic floor and ceiling, multiply the floor length by the width. To prepare the attic, lay plywood or planks as temporary flooring and hang one or more work lights.

Precautions

When working with insulation, wear safety goggles, work gloves, a dual-cartridge respirator, a hard hat and long-sleeved clothing. If fiberglass particles do get on your skin, don’t scratch; shower as soon as possible.

Before installing any insulation make sure there’s a vapor retarder between the insulation and the warm interior space.

Batts or blankets are sold with or without attached vapor-retarder facings. If you use loose fill or unfaced blankets, first install a vapor retarder by laying strips of polyethylene in the spaces between the attic joists. Cut the strips three or four inches wider than the spaces, staple them to the sides of the joists, then install the insulation.

Start laying batts or blankets (vapor retarder down, if attached) at the outer edges of the attic and work toward the center. This lets you do any cutting or fitting in the area with the most headroom.

To cut, set the insulation on a board, compress it with a 2-by-4 and cut with a serrated knife. Make sure the ends of the insulation butt tightly together.

Compress insulation to fit beneath wiring. Leave a three-inch space around recessed lighting fixtures or motor-driven devices. If you have cave vents, don’t block them; there must be adequate air flow above insulation to prevent condensation.

If your attic insulation is level with the joist tops, you can increase the insulating value by installing a second layer of unfaced batts of blankets at right angles to the joists. If the second layer has a vapor retarder, slash the facing diagonally every foot or so. This prevents moisture from getting trapped between the two vapor retarders.

You can pour loose-fill insulation from the bags into the attic spaces. Or you can blow it in. Rent a blowing machine from a home center. It should have a hopper for holding the insulation, a blower motor and a hose at least 70 feet long.