How effective is your insulation?
Of all the energy used in the average house, 50 to 70 percent goes for heating and cooling. Adding more insulation can reduce your utility bills and pay for itself in a few years-especially if your house was built before the early 70s, when building codes began to place more emphasis on energy conservation. If you question the adequacy of your insulation, call your utility company and ask about scheduling an energy audit. Most Western utilities will send a qualified auditor to inspect your house at no cost. He or she will evaluate the insulation, look for air leakage and excessive condensation, and recommend additional insulation or other ways to lower energy costs. How efficient is your insulation? The efficiency of every form of insulation is measured in terms of its resistance to heat flow, which is expressed as an R-value. The higher the R-value, the more effective the insulation. Barring moisture damage or disturbance, and depending on the kind, properly installed insulation retains a fairly predictable level of efficiency over the years. If you find you need to add insulation, the kind you get will depend on where you need it and how your house is built; the energy auditor should be able to suggest the best types. Fiberglass or rock wool batts or blankets, fitted between studs and joists, are versatile and easy to work with. Unless compressed, they retain full efficiency over the years. Loose fill insulation, whether poured or blown in, settles in time with some loss in R-value. Mineral-base loose fill retains its original loft and efficiency better than cheaper cellulose kinds. Although qualified installers anticipate and compensate for specific settling factors, mineral-base loose fill may lose 3 to 5 percent of its R-value over a 20-year period; cellulose loose fill may lose 20 percent. Rigid foam or fibrous insulation board is used to insulate exterior walls or roofs during construction or when adding siding or reroofing, and to insulate crawl space walls. The escape of gases from foam can result in a small decrease in efficiency to 10 20 percent over 20 years. Reflective insulations (foils with air pockets) generally are more effective in hot rather than cooler climates, because the foil bounces radiated heat back toward its source-heated living spaces in winter and mostly outside during the summer. Reflective insulation is installed between framing members; it works well under floors because it reduces downward heat radiation. Over a 20-year period, reflective surfaces may oxidize and gather dust, with a corresponding loss of nearly half the R-value. How much insulation do you need? The US. Department of Energy has developed an Insulation Fact Sheet you can use to figure the optimal R-values for your walls, ceilings, and floors. The recommended levels are based on the cost efficiency of the initial investment, given your climate and the kind of energy used. All DOE recommendations for additional insulation are based on the 1988 DOE insulation guidelines for existing houses and assume that no structural modifications are necessary. Because of this, in some instances the recommended R-values are apt to be lower than those for new construction. The first three digits of your zip code determine your insulation zone. With this insulation zone number you can factor in the kind of heat you use (electric, or oil or gas) to figure out the optimal R-values for ceilings, floors, crawl space walls, and exterior walls. Because many microclimates can exist within the same zip code, and because of other factors like exposure, house type, and personal temperature tolerances, you'll have to use some common sense in determining your individual needs. For a free copy of Insulation Fact Sheet (DOE/CE-0180), write to CAREIRS, Box 8900, Silver Spring, Md. 20907, or call (800) 523-2929.
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|Date:||Jan 1, 1991|
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