Cellulose insulation has been the darling of the green building movement because of its recycled content, low embodied energy, low-tech processing, and excellent energy conservation performance. But concerns are also raised about health risks for cellulose installers and occupants of cellulose-insulated buildings. In fact, some healthy home advocates strongly discourage its use. Should we be recommending cellulose to our clients? If so, on what basis? If not, why—what are its drawbacks?
EBN took an in-depth look at these questions, and we report here on our findings.Cellulose insulation is a fairly simple material produced from one of our biggest solid-waste products: newspaper. The 70 to 80 cellulose insulation manufacturers in North America purchase old newspaper that has been collected through recycling programs. There are two stages of production, according to Doug Leuthold of Advanced Fiber Technology, a company that makes cellulose insulation manufacturing equipment. In the first, the newspaper is chopped into pieces from one to several inches in diameter. The second stage (finishing mill) differs considerably from one manufacturer to another. The oldest and most common finishing mill is a hammer mill in which swinging metal plates attached to a rotating shaft beat the newspaper in a chamber until the pieces are small enough to fall through a screen. The maximum size of cellulose particles produced in the hammer mill is typically
3⁄
8” to
1⁄
4”. Disk refiners are a little different; the chopped newspaper is shredded as it falls between two rotating plates. A third, newer, process is known as fiberization. Instead of cutting the paper, fiberization actually disaggregates it back into individual fibers. In the fiberization process developed by AFT, high-pressure air is used to “blow particles apart,” says Leuthold. “You end up with a fluffy product that looks like the padding in disposable diapers, except that it’s gray.” Fiberization produces lower-density cellulose with a number of advantages.
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