How green is your home insulation?

Trying to decide what type of home insulation to use? Your primary goal should be to reduce the amount of energy it takes to heat and cool your home. But did you ever stop to think about the amount of energy that goes into producing insulation itself?

Green-building experts use the term "embodied energy" to describe the energy used to make any product, bring it to market and (eventually) dispose of it. To evaluate how green an insulation material is in terms of energy usage, you must weigh its embodied energy against the energy it saves when it's insulating a home. Using materials that save considerable amounts of a home's operating energy, even if the material's embodied energy is a bit higher, is a good direction," say the editors at GreenHomeGuide.com. "Using materials that save operating energy but have a low embodied energy is even better."

Which types of insulation materials have the lowest embodied energy? 

BuildingGreen.com posts a table comparing five commonly used materials: cellulose, fiberglass, mineral wool, expanded polystyrene and polyiso (the last two are thermoplastics used to make rigid board insulation). The table shows the embodied energy in the amount of each material it would take to provide the same degree of insulation over a square foot.

Cellulose has by far the least embodied energy; mineral wool is next, followed by fiberglass, polyiso and expanded polystyrene, which has the most. According to the table, expanded polystyrene has 30 times the embodied energy of cellulose.

Of course, there are other questions to consider when assessing the environmental impact of any of these materials, including how it affects indoor air quality; does its manufacture or disposal create pollution; is it made from a rapidly renewable resource; does it contains recycled content; and whether it is recyclable itself.

As it turns out, the rankings of these five materials would be about the same with the other factors taken into account. Cellulose, for example, is made of 75 to 85 percent recycled paper fiber, typically locally sourced post-consumer waste newsprint. The rest is a non-toxic fire retardant, usually boric acid (which also prevents insect infestation). The only hazard it poses is that it's a dust nuisance, requiring that you wear a mask when installing it.

Green home insulation resources

For more information about insulation materials and products, see our buyer's guide to home insulation.

Other sources worth checking include The New York Times' Home Green Home blog and the Sierra Club. Think you know your batts from your blown-in insulation? Take National Geographic's Green Guide Insulation Quiz.