What is the Best Insulation for Your Ecological House?

Philip S. Wenz

Do you want to insulate your home to save energy and money, but you’re unsure about which insulation to use? Do you find the pros and cons of the various insulations confusing and the manufacturers’ claims contradictory? Are you concerned about health and environmental problems attributed to some insulations?

Happily, your confusion and your concerns are mostly unnecessary. When insulations are compared, cellulose fiber insulation, a gray-white powder made from shredded recycled newspaper, emerges as the overall best choice. And where cellulose won’t work, there are other good, safe, products that can fill the gaps (literally).

To understand why cellulose is the best insulation, compare it to its principal competitor, fiberglass. Cellulose and fiberglass together account for over 90 percent of insulation sales.

Both insulations cost about the same, and both cost less than all their competitors. Both are readily available and easily applied in new construction and retrofits.

Cellulose powder is normally blown into attics or sealed wall cavities (through small holes made in the wall) using special equipment. It also can be moisturized so that it sticks when sprayed onto new, open walls.

Fiberglass can be blown in, but is most commonly available in rolls or “batts” — strips of fiberglass strands, usually backed with paper — that are applied by hand (rolled out in the attic or stapled between studs). One advantage of fiberglass is that you can save a little money by installing it yourself — if you’re willing to do some relatively easy but unpleasant and, arguably, unhealthy work — whereas cellulose is normally installed by professionals.

Although the availability, cost and utility of the two types of insulation are comparable, the similarities end there. Cellulose is superior in every other way.

For example, while the average R-value (resistance to heat transfer per inch of thickness) is roughly comparable for both insulations, cellulose, because of its powdery consistency, does a much better job of filling the voids in walls — working its way around pipes and wires and into cracks and crevices. A great deal of heat escapes through voids left by fiberglass.

Cellulose is 80 percent recycled newspaper by weight, with 20 percent non-toxic borates added to resist mold, insects and fire. Fiberglass contains 20 to 25 percent recycled glass — the rest is new glass.

The estimated embodied energy of fiberglass is far higher than that of cellulose. The number of British thermal units needed to produce an “insulating unit” (square foot at equal R-value) is 600 for cellulose and a whopping 4,550 for fiberglass. This is largely because making glass is much more energy-intensive than shredding newspapers, but the relatively low recycled content of fiberglass is also an important factor.

In two critical areas of safety, fire resistance and toxicity, cellulose beats fiberglass hands down. Cellulose is dense; it packs wall cavities and attics and suffocates fire. Fluffy fiberglass offers little fire resistance.

While it’s never good to breathe a lot of dust, and both materials should be isolated from your living space, the physiochemical makeup of cellulose is far more benign than that of fiberglass, a suspected carcinogen. (Most fiberglass insulation packages are required by law to carry a cancer warning label.) Although the specific health risks of fiberglass remain undetermined, it’s best to err on the side of caution in your home.

Finally, cellulose can be easily reused by vacuuming it up and blowing it into another location. Fiberglass can also be reused, but it’s often hard to refit batts, and special machinery is needed to reprocess fiberglass that can’t be refitted.

Cellulose has some drawbacks, of course. It is impractical for insulating floors, where roll or batt insulation is far easier to install. Fortunately, one can find non-toxic, low-embodied-energy rolls and batts made from materials such as scrap denim from blue-jean factories. Such “green” insulations are more expensive than mass-produced fiberglass, but they are a good investment from an environmental perspective.

Also, cellulose has only an average R-value, and the use of more energy-efficient insulations, though more expensive and derived from fossil fuels, can be justified where space is limited — in cathedral ceilings, for example.

However, when judged by all the criteria, cellulose is clearly the overall best insulation for your ecological house.