The pursuit of green building is characterized by widely accepted approaches such as limiting the use of raw materials, minimizing pollution, and increasing energy efficiency. However, one everyday element—insulation—is currently drawing scrutiny and disagreement within sustainable design circles. Thus far, green building methods have prioritized building operating energy with regard to the insulating capability. Generally speaking, the higher the R-value, the more energy saved (depending on the climate). However, increased focus on material performance—referring here to the intrinsic environmental properties of materials—points to two concerns in the most common insulation types: embodied energy and toxicity.
Expanded polystyrene, extruded polystyrene, and closed-cell polyurethane are petroleum derivatives that exhibit high embodied energy and include ecologically questionable ingredients, such as benzene, styrene, or chlorofluorocarbons, in their processing. Other products, like fiberglass or mineral wool batt insulation, consist primarily of nontoxic substances (glass or basalt fibers, respectively) yet still require a measurable quantity of processing, although their carbon footprint is generally lower than that of fossil fuel-based insulation.
Although strong support will undoubtedly continue for all of these materials, we should seek the highest environmental performance in both embodied and operating phases (or more holistically, all phases) of the material life cycle. Biobased materials like cellulose or wood fiber insulation can attain this standard—particularly when a large percentage of recycled content is used.
Cellulose insulation is typically composed of 80 percent post-consumer recycled newspaper, with the balance comprising fire-retardants and binders. “Based on our calculations of the most recent statistics from the American Forest and Paper Association, approximately 1,126,330 pounds of paper become waste about every 10 minutes in the United States,” said Dan Lea, executive director of the Cellulose Insulation Manufacturers Association, in a press release. “Recycled as cellulose insulation, that’s enough paper to insulate 220 energy-efficient new homes every 10 minutes.” According to Alex Wilson, founding editor of BuildingGreen, a “fiberizing” process allows cellulose insulation manufacturers to improve the thermal performance and cleanliness of the final product.
Although cellulose exhibits a lower R-value than a material like closed-cell polyurethane at the same thickness, it is essential to look at the combination of insulating value and carbon footprint. In a 2017 study published in the journal Energy Efficiency, University of Ljubljana engineer Roman Kunič compared the embodied carbon of various insulating products. He analyzed the carbon footprint of these materials based on the same insulating capacity—in other words, based on the same R-value, regardless of the amount of material required. In his study, recycled cellulose outperformed all non-biobased materials.
Another familiar product is recycled denim insulation. Chandler, Ariz.–based construction materials company Bonded Logic manufactures its UltraTouch insulation from 80 percent post-consumer recycled blue jeans by weight. Bonded Logic saturates the material fibers with borates to deliver a Class-A fire rating as well as to inhibit mildew and mold growth. The product contains no chemical irritants, such as carcinogens, as some other forms of insulation do.
Wood fibers are also used for building insulation. Gutenberg, Germany–based Gutex creates rigid fiberboards made from post-industrial recycled wood chips coming from sustainably managed forests. According to the company, its recipe of 95 percent recycled spruce/fir, 4 percent polyurethane resin, and 1 percent paraffin makes the material carbon negative. Based on its watertightness, Gutex insulation serves as both insulation and a weather-resistant barrier. According to the company, “By adding this board on the exterior, the building is clad, weather and wind protected in one step.” Kunič’s research shows similarly positive results for wood fiber insulation, with the low-density variety exhibiting the best carbon footprint per thermal insulation value of any other material in his survey.
Scientists at the University of Bath in England, the University of Brighton in England, and UniLaSalle in Rouen, France, are studying additional biobased materials for potential use in building insulation. They are assessing several feedstocks, including recycled bedding, wheat straw, and corn stalks, each of which also is a significant form of waste. According to the researchers, nearly 62,000 metric tons of duvets and pillows are discarded annually, particularly from hospitals. In the United Kingdom, the production of wheat flour results in about 7 million metric tons of straw, half of which is thrown away. “It is estimated this 'leftover' 3.8 million tons of straw could be used to build over 500,000 new homes, solving the U.K. housing shortage within five years,” the scientists claim in a University of Bath press release. Corn stalks may also be utilized more effectively, with a quantity of 420,000 metric tons of corn pith—the internal portion of the stalk—produced annually. The research team has devised a series of construction modules with these various materials and is currently testing their insulating capacity as well as how they handle moisture.
Although the market for non-biobased building insulation (derived from petroleum, glass, or minerals) is established, these alternative products invite further examination from the perspective of ecological health. According to Kunič, “Synthetic or plastic materials have poorer performance in comparison with natural materials, in view of the overall environmental impact assessment.” To be sure, insulation made from natural fibers must exhibit adequate protection against fire and resistance to pests and mold. Also, many recycled feedstocks require special preparation to ensure they perform as expected. Nevertheless, when considering material health and embodied carbon in combination with insulating value, repurposed biobased materials can’t be beat.
Blaine Brownell, AIA, is a regularly featured columnist whose stories appear on this website twice a month. His views and conclusions are not necessarily those of ARCHITECT magazine nor of The American Institute of Architects.