This article was originally published in the September/October 1997 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online September/October 1997
Instant Insulation EstimatesDo-it-yourself energy retrofitters often have to figure out whether their improvements will be cost-effective. For example, they don't want to end up spending more on insulation than the insulation will save in energy costs. A professional auditor determines life cycle cost-effectiveness by considering the type of building, the heating system, the expected purchase and installation costs of the insulation, the cost of fuel, and projected changes in the cost of fuel (see Consumer Guide to Insulation, HE Jan/Feb '92, p. 29). Most homeowners don't want to bother with all of this, so they just guess at what insulation level to use.
To help consumers make more informed insulation choices, several U.S. agencies have been busily putting together convenient insulation guides. The Energy Star Guide to Insulation, which will soon be distributed by insulation dealers, is a one-page document jointly prepared by the U.S. Environmental Protection Agency and the Department of Energy (DOE). The document provides consumers with basic facts about home insulation without a great deal of technical detail. It helps them to analyze their insulation needs based on location, fuel, and building type.
The Oak Ridge National Laboratory has also developed its own user-friendly insulation guide. This guide includes a method for prescribing insulation levels based on zip code (as a climate reference), wall assembly material, current insulation levels, heating system, and whether the insulation is in a retrofit or new construction. The guide is available as a factsheet and can also be accessed at the Oak Ridge Web site. It updates the 1988 Insulation Factsheet from the DOE.
Terese Stovall, the engineer with the Insulation Materials Group at Oak Ridge who was responsible for developing the new guide, says it was time to redo the factsheet. The old factsheet still talked about the Arab oil embargo. It didn't cover many construction [techniques] that have become common, including structural insulated panels, metal framing, insulated concrete forms, and optimum value-engineered framing. Stovall reports that many subtleties have been added. The new factsheet considers walls as an assembly, including the cavity and sheathing. The old factsheet just dealt with the cavity. The goal of the new guide is to show what insulation levels will be cost-effective for each type of home in each location.
Stovall tried to make the new guide sensitive to regional differences, including climate, fuel cost, and contractor prices. To account for local differences in climate, the guide provides different recommendations for different zip codes. To account for differences in installation cost, Stovall used the average installation cost for the country--based on national surveys. She then adjusted these costs for each state, increasing or decreasing local costs based on city factors from RS Means--an industry standard construction estimating service. RS Means provided the city factors to account for different overhead and labor costs for the construction industry in different cities. Thus a state where the cities have high labor costs will have a higher estimated installation cost, which in turn lets the guide recommend a lower level of insulation. While this method of determining local costs is imperfect, it is better than the previous methods, which depended on a 1986 survey by the National Association of Home Builders.
To use the guide, readers first determine what insulation zone they are in, using the first three digits of their zip codes. New York City zip codes, for example, start with 100. On the zone chart, the number 100 is listed as zone 9. Readers next turn to a chart of heating systems. There are two tables, one for new homes and one for retrofits. These tables place readers in an insulation group. In zone 9, a new home with electric baseboard heat falls into insulation group N7. In the same zone, an existing home heated by oil is in group E5. Generalizing many climates and home styles into insulation zones and groups could cause flaws in the analysis, so a more individualized analysis is available on the associated Web site.
The next table recommends total R-values based on insulation group. R-values provided are in industry standard increments, such as R-19, R-22, and R-30. According to the guide, a home in group E5 should have an R-38 attic, R-25 floor over unconditioned space, R-11 wall cavity, R-19 unventilated crawlspace, R-11 basement wall, R-10 insulated sheathing on uninsulated walls (if the house siding is already being replaced), and R-5 sheathing atop insulated walls.
New homes are further divided up. Each of the seven insulation groups is given cost-effective insulation levels for attics, floors, cathedral ceilings (including the cost of increased framing thickness), wall sheathing, wall cavities, band joists, crawlspace walls, slab edges, basement exteriors, and basement interiors. The wall, attic, and floor recommendations are broken up according to whether the framing is traditional wood framing, optimum-value engineered wood framing, metal framing, or masonry. The guide continues with an explanation of insulation, air leakage, and the assumptions behind the tables.
Retrofitters interested in an even more detailed analysis can use the associated Web site at http://www.cad.ornl.gov/kch/zip.html (no longer active). There the geographic database is slightly more sophisticated, providing an individual analysis for each zip code and fuel type. However, Stovall says, 98% of the attic insulation levels will be the same on the Web as on paper. Some crawlspace or wall insulation levels might be slightly different.
The factsheet is available from the Energy Efficiency and Renewable Energy Clearinghouse. Tel: (800) DOE-EREC.
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