If you want to build with walls of rammed earth or adobe, the great advantage is that the material is abundant, free and doesn't have to be transported to the job site. The downside is that you'll have a hard time finding specialized craftsmen who know how to build with dirt.
Countries including China, Peru and New Zealand actually account for this type of building in their codes, but the United States has not established codes for building from the earth. The difficulty of finding craftsmen who can do the job led the National Association of Home Builders to estimate that costs for labor could run at least $80 per square foot.
Even so, researchers at the association note that earthen walls provide excellent thermal mass, and the material comes from the ultimate in renewable sources.
Check out the links on the next page for lots more information on eco-friendly building.