Insulation is a non-structural material used to reduce heat transfer. The most typical forms of insulation available are rigid sheets, flexible blankets, and loose fill. These may be composed of fiberglass or rock wool fibers, cellulose (paper) fibers, and a variety of foams. Specialized insulation, which is intended to reduce solar heat gain or air and water infiltration, is sold in plastic or metallicized-plastic sheets.
Building a Barrier
In theory, insulation is akin to the extra blanket on the bed. Bed or home, the principle is essentially the same: By trapping an unmoving layer of air next to a heat source, heat transfer is reduced and comfort is increased. Reflective insulation, as its name implies, reflects heat back to its source. Typically made of foil, treated paper or plastic film, reflective insulation becomes a radiant barrier when used alone and facing an open space. Reflective barriers can be used under roofing to prevent solar heat gains in warm climates or below floor joists to retain winter heat.
The Value of Insulation
Heat always flows from its source to surrounding cooler areas; insulation is designed to slow this heat transfer. The relative efficiency with which it does so is called the R-value, with R representing insulation's resistance to heat flow. Manufacturers are required to disclose the R-value of their insulation products, and usually provide this data on the product packaging. If it is not there, ask the seller for a fact sheet containing this information.
R-value is proportional to the insulation's thickness, and varies depending on the type of insulating material. An inch of fiberglass blanket or batt has an average R-value of 3.2, while the R-value of loose-fill cellulose is about 3.5 per inch. Sprayed-on polyurethane foam tips the scales at an average R-value of 5.9. The overall R-value of a building has a critical impact on home energy consumption. The U.S. Department of Energy reports that an average home spends up to 70 percent of its energy consumption on heating and cooling. Higher home R-values mean greater efficiency as well as comfort.
Keeping air from moving really matters, since even a small draft can reduce insulation's efficiency. DuPont claims that air infiltration can drop a wall's insulative value from an installed rating of R-13 to a performance value of R-5. Manufacturers have addressed this problem by offering air infiltration barriers, commonly referred to as house wraps or building wrap, to shield insulation from moving air. These barriers are often designed to combat water infiltration as well, a liability that can seriously impair insulation's efficiency.
Other products can team with insulation to make the entire building envelope more energy efficient and the conditioned indoor space more livable. These would include products like spray foam sealants, electrical cover plate gaskets, and hot water pipe covers. Doors and windows are obvious partners, but so are their less visible counterparts like caulking and weather-stripping. These energy-saving components can be installed over the weekend and will help boost your home's overall thermal performance immediately.
Where to Put It
Insulation is usually placed in the interior cavities or on the rough surfaces of the exterior walls, and covered with finish materials such as drywall. Certainly homeowners doing new construction and remodeling work have the greatest number of insulating options, since their buildings are wide open. There are some retrofit insulation products designed for minimal disruption to finished wall or ceiling surfaces in existing homes.