All About Insulation

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Cellulose also poses fewer health risks to installers and home owners. Although blowing or spraying cellulose into wall and ceiling cavities produces dust, there are no fibers found in cellulose that are potentially cancer-causing. A simple face mask or respirator protects installers.

Cellulose insulation does have some disadvantages. Dry-blown cellulose may settle and sag, creating air spaces. It also can absorb moisture, decreasing its R-value over time. If it remains damp for prolonged periods, cellulose can mold and rot. With its use of acrylic binders, wet-blown cellulose is supposed to solve the problems of settling and sagging. Cellulose is less expensive, but installation costs may be higher than those for fiberglass butts.

Mineral Wool. For many years, mineral wool was the most widely used insulation in the United States, Canada and Europe. Mineral wool insulation is similar to fiberglass, except the fibers in mineral wool come from stone or from iron-ore blast furnace waste. If natural stone, such as basalt or diabase, is used, the product is called rock wool. If iron-ore waste or slag is used, the finished product is known as slag wool. Roxul, a European company, produces a mineral wool insulation containing equal amounts of rock wool and slag wool. Fibrex, based in Aurora, Illinois, produces mineral wool insulation blankets, which can fit between walls, studs or ceiling rafters, made from 92 percent recycled materials.

Although mineral wool is much heavier and costs more than fiberglass and cellulose, it does offer some substantial benefits. Mineral wool is moisture-resistant and maintains its insulative properties when wet. It also is a good acoustic insulator and is more resistant to heat than fiberglass. Mineral wool insulation is noncombustible, withstanding temperatures greater than 1,800 degrees, and acts as a fire barrier, which can slow a house fire. Fiberglass insulation, in contrast, melts at slightly over 1,100 degrees, and cellulose combusts during house fires. During handling, however, small pieces can break loose from mineral wool batting, raising health concerns if the fibers are inhaled.

Rigid Foam Insulation. One form of insulation whose popularity has grown steadily in recent years is rigid foam, also called foam board. Rigid foam insulation is typically used to insulate foundations and slabs. It also is applied on exterior roofs and walls, and may substitute for loose-fill or batts in walls, roofs and floor cavities, although it must be tightly fitted to prevent air infiltration.

Rigid foam insulation has insulation values nearly twice the R-value per inch of standard fiberglass and cellulose. Some rigid foam products are ideally suited for foundation insulation because they are water resistant and can be buried in the ground on a foundation's exterior.

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