2. Cob

If you want to get up close and personal with your building material, cob might be the way to go. Cob is a combination of earth and straw that you usually mix with your feet, and then form into lumps that you mash together by hand to form the wall. Cob comes from an Old English word meaning "a lump or rounded mass" [source: Smith, Evans].

Photo courtesy www.housealive.org
It may not look like much now, but that cob wall will keep some homeowner warm.

­­­Cob lends itself easily to creative, free-form construction that includes curvy shapes and sculptural forms, and it requires minimal tools or construction experience. When the cob dries, it's like concrete, thanks to the reinforcement of the straw; however, waiting for the cob to dry is essential before placing the next layer of cob lumps. Building on top of wet lumps will cause the building to sag, so cob building is very time intensive. Cob walls also cannot be built very high, but when completed, cob walls, like all of the earthen methods on this page, provide thermal mass that cools homes in the summer and warms them in the winter. ­

You may not have heard of many of these natural building materials before reading this article. After all, how many of your neighbors live in earthbag homes? But you probably will have heard of this last one we'll discuss on the next page.