Tuesday, May 6, 2008

Cob

I've been thinking a lot about natural building lately. Here in the US, we are practically forced into occupying homes that are expensive and destructive to the environment. I met a woman last weekend who lives in a yurt and has an outdoor composting toilet. She paid $3,000 for the yurt, making it a dignified way to live on a low income. She's worried because what she's doing on her own property is illegal. She's living in a safe, efficient, inexpensive structure that is extremely light on the land, an it's illegal under her county building codes.

A conventional home that costs $200,000 may end up costing $400,000- $600,000 including interest paid to the bank and all fees. If you can save money and cut out the bank, you might be able to build your own code-compliant house for $100,000 or less, including the land. It isn't difficult to see the financial advantage of building yourself.

Conventional homes are also highly destructive to the environment, partly due to materials and partly due to inefficiency of the completed structure. As usual, I'm looking for alternatives.

One possibility that has caught my imagination is a material called cob. It's made of sand, clay and straw that's mixed together and allowed to harden into a durable monolithic structure. It's a traditional form of construction throughout the world, but the word comes from the UK, where thousands of cob buildings are still standing after up to 500 years. It's similar to adobe, except bricks are not used.

Cob uses inexpensive materials that can typically be gathered on-site or nearby, and have a low embodied energy. The straw is an agricultural waste product and is very inexpensive. Building with cob doesn't require much skill or strength. It can produce highly efficient structures in appropriate climates due to its high thermal mass. It's also extremely durable if cared for properly. Cob has all the attributes of an effective vernacular building technique.

It's also not code-compliant in most places in the US, but that may change as it becomes more familiar. That's also a reason why I'm considering alternatives like strawbale and timberframe construction. It's possible to build code-compliant cob houses in the UK.

Last weekend I went to a "Basics of Cob" workshop at the Ancient Earth school of natural building on Whidbey island. We learned how to mix cob and then we built a bench out of it. The bench will eventually be coated in a smooth earthen or lime plaster. Cob is an amazing material. It's sculptable when wet, but becomes very hard when it dries. It's compatible with a number of other natural building techniques like strawbale and light straw-clay. It really is at the intersection of construction and sculpting. When you build with cob, you aren't limited to straight lines and right angles, so you can create spaces that are highly functional and aesthetic, while also being space-efficient. Here are some photos from the workshop:




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