All About Insulation

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Another advance in fiberglass insulation is the greater use of recycled glass. Fiberglass manufacturers typically use 30 percent to 40 percent recycled glass in their products.

Manufacturers now also produce high and medium-density fiberglass batts. In these more tightly packed batts, smaller air spaces between the fibers reduce air circulation, increasing resistance to heat flow, known as the R-value. A higher R-value means better energy efficiency. Standard medium-density fiberglass blankets for 2x4inch walls, for example, have a nominal rating of R-11, while the comparable high-density blankets are rated at R-15. Higher-density butts also are available for 2x6-inch walls and for attics.

Higher-density batts cost about 20 percent more than standard fiberglass butts, but the initial costs will be paid back in energy savings. Some builders have taken to cramming oversized standard fiberglass batts into wall and ceiling spaces. A standard R-19 butt for a 2x6-inch wall can be forced into a 2x4-inch wall, resulting in an R-14 wall with nearly as much insulation value as a high density 3.5-inch batt, says environmental building expert Alex Wilson of BuildingGreen. This approach also can be used in closed ceiling spaces, but requires vent spaces to prevent moisture from accumulating in the insulation. High-density butts do not require venting.

Fiberglass doesn't shrink, won't burn and is unappealing to insects. On the negative side, fiberglass blankets do not seal wall and ceiling cavities very tightly, and unless installers use encapsulated batts, a vapor barrier is required to protect the insulation from moisture. Fiberglass also settles, resulting in a decline in R-value over time. Like other forms of insulation, its R-value drops dramatically when it becomes moist.

Cellulose. Made from recycled newspaper and (sometimes) small amounts of cardboard shredded into a fluffy mass, cellulose is sprayed slightly damp, or blown dry, into wall and ceiling cavities, as well as attics. Loose-fill cellulose insulation is typically treated with boric acid to thwart mold, increase fire resistance and repel hungry insects. Some manufacturers add a moisture-activated acrylic binder that causes the cellulose particles to adhere better, which reduces settling.

Cellulose insulation is one of the most environmentally friendly insulation choices, and because of its economical price and availability, it easily competes with fiberglass. Fed by the massive waste of a paper-hungry society, recycled cellulose insulation manufacturing facilities are helping put mountains of discarded newspapers and cardboard to good use. Cellulose insulation is generally less expensive (up to 25 percent) than fiberglass butts, and provides more insulation per inch (R-3.2 per inch) than low-density fiberglass (R-2.2 per inch).

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