Thank you very much. Rammed Earth walls actually have a very low R-value. They work on a different principle than insulation. Instead, rammed earth, adobe and other mass materials work on the concept of thermal mass. (there are many articles written on the subject so I won't go into detail). Rammed earth is very labor intensive, so depending on where you are building and the cost of labor it can be expensive compared to other building materials. I hope this is helpful.

Thank you. Yes, I've been able to do quite a bit of research since posing my original question. The Thermal Mass would definitely add to an energy efficiency of the home and the up front costs would far outweigh traditional wood frame construction. Since I'll be incorporating as many energy efficient methodologies as possible for the entire project, solar, water harvesting, passive solar principles and so forth. I'm more than happy to absorb the higher costs which would result in not only a more beautiful home but contribute to its energy efficiencies as well. Any ROI doesn't need to be realized any time soon since I'm in this for the long haul which is a good thing. Ty. ~R