rigid foam board insulation poses few health risks, although there have been some concerns about the potential off-gassing from flame retardants and the plastic polymers.
Liquid Foam. Foamed-in-place insulation has the advantage of filling wall and ceiling cavities completely, providing high R-values (3.6 to 6.5 per inch) and blocking air leakage very effectively. Installation requires special equipment, however, and must be done by licensed contractors. Generally, liquid foam is sprayed into open wall cavities, where it rapidly expands—sometimes up to 100 times its original volume—to fill the space. Once it has dried, excess insulation is easy to trim off. Some foams can be used in closed wall cavities. These products expand more slowly, to reduce the risk of structural damage.
Most liquid or spray-foam insulation products are high-density, closed-cell polyurethanes, made from petroleum— and some of these still use the ozone-depleting HCFC-141b blowing agent. Open-cell, low-density polyurethane foams have been produced with water or carbon dioxide as the blowing agent for some time.
Compared with closed-cell polyurethane, open-cell products also use significantly less material, making them attractive from a resource standpoint. These spray-foams provide an airtight, water vapor resistant seal, and eliminate the need for vapor barriers in stick-framed homes. And most resist shrinking, settling, and sagging.
Polyurethane foams rank close to rigid foam insulations in terms of their embodied energy. To improve this energy-to-efficiency balance, some manufacturers are reducing their reliance on petroleum, replacing up to three-quarters of the petrochemical-based foam with a soy-based product.
Air Krete is one of the few nonpetroleum-based foams. Made with magnesium chloride, ceramic talc, and a proprietary foaming agent, it is sprayed into wall cavities with pressurized air. One drawback is that since it does not adhere to surfaces, material shrinkage or movement in a building may eventually cause gaps in the insulation, compromising the whole wall R-value. Air Krete offers superior fire-resistance.
Installers need to take safety precautions when working with these materials; others should not be present while polyurethane insulations are being installed. However, most indoor air quality professionals consider this product to be inert once it has cured.
Other Options: Wool & Straw. Sheep's wool has been commonly used in Australia and New Zealand for decades, but is now just starting to make its way into U.S. homes. With an insulation value higher than standard fiberglass, it also retains its value when wet and is naturally flame-resistant, although some wool insulation manufacturers add boric acid as an additional flame retardant.
Straw bales have been used as a cheap and effective building and insulation material since the nineteenth century. Oak Ridge National Laboratory determined the R-value to be R-27.5 (or R-1.45 per inch), or R-33 for three-string (23-inch-wide) bale wall systems. The California Energy Commission reports that a plastered straw bale wall has an average R-value of 30. Straw-clay, a mixture of short, chopped strands of straw and clay slip, can be packed into wall forms or ceilings to create thick, fire-resistant, and fairly mold- and mildew-resistant walls, with an estimated R-value of about R-1.6 per inch, according to research results reported by the Canadian Mortgage and Housing Corporation.
Because these materials undergo little or no processing, and can be sourced locally, their embodied energy and resulting environmental impacts are generally low. They pose no or very little health risk to installers or a home's occupants.
Integrated Insulation. Some homebuilders today opt for all-in-one construction, combining insulation within their wall and ceiling structures. Several different products are available to meet this need. Structural insulated panels (SIPs) sandwich a polystyrene, isocyanurate, or even a insulation options compressed straw core between plywood, oriented strand board, or strawboard panels. Using these large panels reduces thermal bridging and air gaps more common in conventionally insulated stick-frame homes.
Insulating concrete forms (ICFs) integrate poured concrete into interlocking foam board or hollow-core polystyrene blocks to make a complete wall or foundation system. Because of its flammability, though, ICFs exposed to occupied spaces must be covered with a fire-resistant material.
Rastra "blocks" incorporate recycled polystyrene, Portland cement, and additives into a framework, which is glued or clamped together until the concrete is poured. This lightweight, strong material can be easily worked with all woodworking tools, and carved to achieve curves. By volume, Rastra contains 85 percent recycled content. No energy is used to cure the elements, and only about 1 KWH is required to produce one Rastra element— a 10-inch-thick, 15 by 10-foot panel. This product provides high insulation values with no off-gassing, and is pest- and fire-resistant.
Claire Anderson, PO Box 520, Ashland, OR 97520 • [email protected]
Thanks to Mark Piepkorn, Associate Editor at Environmental Building News (www.buildinggreen.com), and Andre Desjarlais, Program Manager of the Building Envelopes Program at Oak Ridge National Laboratory's Buildings Technology Center, for their expert review of this article.
Rastra Corp., North American Corp. Office, 7621 E. Gray Rd., Ste. A1, Scottsdale, AZ 85260 • 877-935-3545 or 480-443-9211 • Fax: 480-443-9228 • [email protected] • www.rastra.com • Rastra insulated blocks
Online Insulation Assessment: ZIP-Code Insulation Program • www.ornl.gov/~roofs/Zip/ZipHome.html
Select Insulation Manufacturers/Distributors:
Agriboard Industries, 8301 E. 21st N., Ste. 320, Wichita, KS 67206 • 866-495-3595 or 316-630-9223 • Fax: 316-636-9255 • [email protected] • www.agriboard.com • SIPs made with a compressed wheat-straw core
Bonded Logic Inc., 411 E. Ray Rd., Chandler, AZ 85225 • 480-812-9114 • Fax: 480-812-9633 • www.bondedlogic.com Cotton insulation
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For a FREE Color Catalog call us at (800) 621 -2591 www.bioshieldpaint.com
Good Shepherd Wool Insulation, RR 3, Rocky Mountain House, AB, Canada T4T 2A3 • 403-845-6705 • Fax: 403-845-6705 • www.goodshepherdwool.com • Sheep's wool insulation
Insulating Concrete Forms • www.icfweb.com • General ICF information
Johns Manville, PO Box 5108, Denver, CO 80217 • 800-654-3103 or 303-978-2000 • www.jm.com • Formaldehyde-free fiberglass insulation
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