Let’s talk about cork. What do you think about when you think about uses for cork?
When I think of cork, I immediately think — wine. What a wonderful material to keep delicious wine in its bottle. What could realistically top (no pun intended) keeping wine safe while letting it breathe. Sure, cork can be used in life vests, you can craft some cool stamps, pin cushions, very pinterest-ee wedding décor… okay, I suppose there is a lot you can do with it. What about cork as a construction material?
As it turns out, cork is incredibly versatile in terms of its use. For starters, it looks good, and many homes use exposed cork for it’s decorative and functional features as flooring and wall covering, not to mention on that bulletin board where you post your community message. It comes in many colors and styles, and it’s natural tones blend well with most other decorations and furniture.
But cork also fantastic for thermal and sound insulation, and was in wide use in the 1920’s as a standard material sold by Armstrong. Cork is abrasion resistant, humidity and insect resistant, vapor transmissive, long lasting, needs minimal maintenance, and is natural, renewable, recyclable, and biodegradable. It is considered a carbon negative material, even with the transportation from Europe, i.e., its use creates less greenhouse gas production. Now that artificial cork is taking over the bottle sealing business, there is plenty of cork to go around for other uses.
So, what’s not to love? We were first turned on to cork by our green building advisor, Katy Hollbacher of Beyond Efficiency. The “local” supplier is Small Planet Supply in Seattle, which sells a Portuguese product branded for the U.S. market as Thermacork. Thermacork is touted as 100% natural. The bark is harvested sustainably from cork oak trees, ground up, poured into a rectangular mold and heated in an autoclave. The heat releases a chemical which glues the particles together; no other chemicals are added. The block of cork thus created can then be carved up as needed into different sizes and thicknesses.
Thermacork has an R-value of about 3.6 per inch. On our house, we are mostly using it as a one inch thick layer of “outsolation” on the outer face of the plywood skin, where it helps dampen thermal bridging — the tendency of heat to escape through the studs which have less insulative value than the insulation. We’re also using it on the roof, where it’s location on top of the plywood roof sheathing allows us to build an unventilated roof — which makes it much simpler to air-seal the house.
While the cork will be invisible in those areas, on a portion of the lower level we are using two inch thick, ship lap edge panels as exposed siding. We’re hedging our bets here: there is a four foot wide overhang giving a lot of weather protection for the exposed cork area, but theoretically the entire house could be covered with it. Hopefully, our house will not used for target practice by the local archery society! Perhaps all this cork will protect us as we age gracefully, like a nice bordeaux…
A huge thank you to our sustainability assistant, Talia Klein, for her assistance in researching and writing this blog!
Fascinating video about the production of cork panels in Portugal