I was playing around with some vermiculite and clay for an insulating layer of the rocket stove. It was squishy and lightweight. I wondered about the possibilities of this material in a traditional cob wall… Could this added R value to a otherwise not insulative material ?

Vermiculite wall
Incorporating this mixture into a tradional cob, a mixture of local clay, sand and straw wall might increase the R-value. If one built a wall with 3 inches of cob, on the outside, then 4 inches of vermi-cob, in the center, and 3 inches of additional cob internally you might create a better R-value. I could see the process being similar to building a traditional cob. One would start with a pile of vermi-cob and two piles of regular cob. Work it all together as you go.

Using cob in a cold climate seems to me a bad idea. More and more I realize that cob should be used where and when appropriate. Some climates are perfect for cob, but if you are living in Minnesota or Wisconsin, where the median temperatures are 10 º in the winter- you won’t be impressed by the R-value of a cob wall. One needs a layer of insulation to keep the heat from escaping the building. Light clay or straw-bale might be the best option for this, as far as natural building materials are concerned. Cob could be used in combination with other more insulate materials with great success. Cob floors, cob on strawbale, internal cob or adobe walls are great uses for this low embodied material. If you were set on using cob – how can you get more insulation? Using a high straw concentration in your mix, pumice, vericulite, or a paper additive might resist heat transfer a little more.

Will the vermiculite with it’s air pockets resist heat flow? What would be the cost difference? How much of a difference would it make in terms of R-value? I don’t know… It would fun to experiment with.