From time to time we answer reader’s questions.
Jeff: We are looking at building a home on acreage in central north Michigan. It is extremely cold in the wintertime where we are looking. Would an earthbag home insulated with rice hulls (using 10″ tube sandbags on exterior of earthbag walls) be sufficient for that kind of climate? How do you protect the lower courses of rice hulls from moisture from the ground to prevent rot?
Owen: Adding 10″ of insulation on the outside of walls should be plenty. That’s more insulation than 2×4 and 2×6 walls. At R-3 per inch, that’s about R-30 walls! (It’s probably less than that because of the shape of the tube, so let’s say R-25.) This will give you a superinsulated wall with a thick layer of thermal mass covered by a thick layer of exterior insulation. That’s ideal.
To protect the rice hulls, build a footer and fill lower tubes (or bags) with scoria or something that doesn’t rot. Use rice hulls once you’re above the level where moisture can cause problems. I have several articles on the Internet about building in cold climates such as this one: Insulated Earthbag Houses