Cork Insulation on Our Farmhouse
Posted March 19, 2013 10:23 PM by Alex Wilson
Related Categories: Energy Solutions, GreenSpec Insights
Why we chose cork exterior insulation for our net-zero-energy house
Installing cork insulation on our farmhouse.Click to enlarge.
Photo Credit: Alex Wilson
Among the innovative—some might say weird—products we’re trying out at our Dummerston, Vermont farmhouse, none is more unusual than the expanded cork insulation we’re currently installing as a layer of exterior rigid insulation. As I mentioned in a blog last summer, cork insulation has a great story behind it.
Cork? You’ve got to be kidding!
I first learned about expanded cork insulation years ago when exploring the attic of a 1920s-era home in Brattleboro. I found a rigid boardstock insulation comprised of cork with plaster on one side. It was made by Armstrong, which was then a company making cork products but is today one of the world’s leading manufacturers of flooring and ceiling products.
It turns out that the product was invented by accident in 1893 in New York City by a boat builder, John T. Smith. The cork granules he used to fill life preservers became clogged in a large tin funnel, and that slipped into the coals of a fire used to steam oak staves. When the owner of the shop discovered the tin funnel the next morning he expected the cork to be burned up, but instead it had expanded to fill the form and solidified into a solid block.
Smith experimented with the process and patented it as Smith’s Consolidated Cork, which he licensed to Armstrong. It was used for several decades for insulating buildings—especially cold-storage buildings. The apple storage building at historic Scott Farm in Dummerston, built in the 1920s or ’30s, is insulated with this product.
Detail of the cork insulation.Click to enlarge.
Photo Credit: Alex Wilson
Why I like cork
Cork is a remarkable material. It is the outer bark of a species of oak tree (Quercus suber) native to the Western Mediterranean region. This thick, spongy bark protects the trees from fire. It can be peeled off every nine or ten years, and grows back. The bark is still harvested in Portugal, Spain, Algeria, Morocco, Tunisia, France, Italy, and a few other countries much as it was 2,000 years ago.
The primary use for cork is for wine bottles. The “corks” we all know are punched out of the bark in a really simple process. The residual cork (about 65-70% of the material) is processed into granules that are processed into a wide variety of uses.
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To make cork flooring, floor underlayment, and gaskets, the granules are glued together and sliced into thin layers. Cork makes a great flooring material, because it is soft underfoot (resilient) and it absorbs sound. You will often find it in libraries, for example, due to those acoustic properties. My aunt and uncle installed cork floors in their Connecticut house in 1951, and that flooring is holding up very well more than 60 years later.
Cork is produced from ecologically rich forests that support significant biodiversity, including the endangered European lynx.
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