Wool in the wall: a sweater for your home
A natural insulator that’s more effective and more environmentally friendly than fiberglass.
Insulation is typically one of the least ecofriendly materials that go into a house. Fiberglass is irritating to the skin, can be harmful to breathe, and uses large quantities of energy in its manufacture. Polystyrene foam, another common choice, has more than twice the embodied energy of fiberglass. But with increased demand for sustainable building practices, various types of natural insulation are appearing on the global housing scene. These include cotton, hemp, and sheep’s wool.
A handful of companies turn sheep’s fleeces – washed, carded, and sprayed with borax to deter pests and mold – into precut batts that home-owners such as Kathleen Sauer of Northfield, Vt., say is “a real pleasure to install.”
According to GreenSpec, which identifies green building products in Britain, sheep’s wool insulation has a long list of eco-attributes: It’s recyclable, a renewable resource, nonhazardous to install, biodegradable in landfills, and its manufacture uses little energy.
It’s also a good insulator. The US Department of Energy rates its R-value at 3.5 – about 10 percent higher than fiberglass. Proponents of the product also point out that wool can absorb up to 40 percent of its weight in moisture without becoming wet, drawing moisture away from wood framing in walls and helping to prevent condensation. It’s also naturally flame-retardant.
The use of sheep’s wool insulation began in Europe more than a decade ago. Andrew Evans of Black Mountain Insulation in Denbighshire, Wales, saw the number of visitors to his booth at the Ecobuild event in London increase four times this year over last. “It’s the only insulation product people want to touch,” he said. “They stroke it like a dog.”
The main drawback of wool insulation is that it costs about three times more than fiberglass. Also, it must be protected from water leakage, which could leach out its pest-repelling borate.
Wool insulation meshes well with the growing interest in natural products, Mr. Evans notes. “Given the choice, I think people will choose natural every day.”
In Canada, Stan Potter, a shepherd-turned-businessman, has been selling his version of the product since he saw a woman selling wool rope for insulating the spaces between logs in log homes. He started making and selling wool roping and then expanded to wool batts for insulating frame houses.
As one of his customers, Ms. Sauer used the batts in a small home she and her husband renovated. She says the material “forms very well into odd crevices. It gives you peace of mind if you’re a green thinker.”
One of the biggest obstacles to making wool insulation in the US, she says, is the lack of infrastructure. “When the price of wool bottomed out in 2000, most of the machinery in the US for processing wool was snapped up by the Chinese and Europeans. I’m not sure what’s left.”
Ms. Hagen visited France two years ago to trace the budding industry there.
“They’ve been making wool insulation for 15 years,” she says, “and they’re going gangbusters now.” She also saw the difficulties they faced, such as the need to treat the wastewater at wool-washing facilities. So far Hagen doesn’t see a clear solution for growing the industry on home turf. But, she notes, “[the industry] started out really small in France.”
If sheep’s wool insulation grows on the global market, more people may find themselves stroking their insulation like a dog – or sheep.