Kelly Hart and I have been following the The Year of Mud cob house blog for about 2-3 years. Ziggy, the builder and author of the blog, learned the hard way that cob (actually, earth building in general) is not a good choice in cold climates.
Kelly has been warning people for years at GreenHomeBuilding.com (the number one most popular site on natural building) that some earth building techniques are not appropriate for cold climates. We also want to make sure our earthbag website readers are aware of the limitations of building with earth in cold climates.
Kelly has an interesting story about this on his website. He stayed in an old adobe hotel in southern Colorado one winter. It was freezing cold inside. Despite the thermal moderating effects of earth (the flywheel effect), if there’s extended freezing cold then the inside temperature can be like living in a cave, because earth is not a very good insulator. That’s why most adobe houses are built south of the Colorado/New Mexico border. That’s the range where colder temperatures start to make adobe impractical. The same is true with earthbags, unless the structure is insulated.
You can find much more on this topic on our websites by searching for “insulation”, “insulated earthbag” and “cold climate”. The key is to either fill the bags with insulation such as scoria or add a layer of insulation on the exterior.
Please note, we love Ziggy’s blog and encourage everyone to check his site regularly. He has lots of good ideas, and his open, sharing approach is conducive to learning.