This article was originally published in the July/August 1998 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online July/August 1998


Insulation Systems: Same Tightness

The National Association of Home Builders Research Center recently compared various wall insulation products, and found that with good air sealing, different insulation systems do not necessarily change a home's airtightness. It found that fiberglass batts were far cheaper and quicker to install than other products, but that the quality of their installation was inferior.

The experiment was carefully conducted. Four builders constructed 26 houses that were evaluated between January and late October 1997. They used different insulation systems: Blow-In-Blankets (BIBs), spray cellulose, low density polyurethane, and fiberglass batts. The nearly identical two-story colonial houses were all built with good air sealing practices--double studs and plates were caulked or glued; foundation sills were sealed; windows were chinked with fiberglass and sealed with air barrier tape.

Once air-sealing practices were accounted for, the alternative methods did not significantly reduce air leakage. In other words, if a house is correctly air sealed, it can have rocks stuffed in the walls and there won't be an increase in leakage.

The test was conducted for the U.S. Environmental Protection Agency. The goal was to compare the price as well as the performance of the various insulation products. Measurements were taken to determine house tightness, worst-case depressurization, total labor time, initial moisture content, and installed quality. Infiltration and energy savings were also estimated to calculate simple paybacks. In the end, it found that cellulose and BIB systems cost 70%-150% more and took 22 times longer to install than fiberglass batts. However, when it came to installed quality, batts didn't do so well. On a scale of 0-8, where 0 was best and 8 was unacceptable, batts averaged 6.4, spray cellulose rated 1.8, and BIBs topped the field at 0.7.

The test conclusions did not consider potential performance problems due to convection loops, settling, and poorly installed insulation. It also failed to answer a persistent question in home performance circles--how effective are different insulation products at reducing air movement in, out of, and through walls, when complete air sealing is not feasible or possible?

The full report, Field Demonstration of Alternative Wall Insulation Products is $25 from NAHB Research Center Incorporated, 400 Prince George's Blvd., Upper Marlboro, MD 20774. Tel:(301)249-4000; Fax:(301)249-3096; Web site:

--Tom Sluis and Steven Bodzin



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