What Do You Call That Gravel-Looking Insulation in My Attic?

Installation

• Loose-fill insulation is installed in your attic with a pneumatic blower that sprays the insulation in place, leaving air pockets between the individual chunks of insulation. This property of loose-fill insulation makes it a more effective insulator than many other types of insulation. You can also blow loose-fill insulation behind walls or under attic floors to insulate areas of your home that already are finished.

Types

• Loose-fill insulation is made from three materials: fiberglass, rock wool and cellulose. Of these three types, cellulose is the strongest insulator, followed by rock wool and fiberglass. Loose fill often is marketed as environmentally friendly because it is made using recycled materials. Cellulose insulation often is made from recycled newspaper, while fiberglass insulation contains from 20 to 30 percent recycled glass and rock wool contains up to 75 percent recycled industrial waste.

Insulation Properties

• The insulating capability of insulation is measured according to its R-value per inch. The recommended R-value for the attic of homes in most areas of the United States is 30 to 40. Cellulose-based loose-fill insulation has an R-value of 3.2 to 3.8 for each inch of depth. The R-value of fiberglass insulation ranges from 2.2 to 2.7 for each inch, while rock wool is rated from 3 to 3.3 per inch. Most types of loose-fill insulation require at least a foot of insulation; however, fiberglass can require up to 17 inches.

Considerations

• Cellulose insulation is the most compact form of loose fill; however, it is susceptible to settling and moisture damage. Loose-fill insulation relies on air pockets trapped between each piece of insulation to increase its R-value. All three types of insulation settle and compact over time, decreasing their insulating capacity. Fiberglass and rock wool typically lose 2 to 4 percent of their R-value to settling, while cellulose can lose up to 20 percent of its R-value. In cold climates, the temperature difference between the attic and living areas of your home can force cold air through the air pockets in the insulation. Adding an additional layer of batt insulation over your loose-fill insulation often prevents this problem.