Rammed earth walls contain tremendous thermal mass, so rammed earth homes are highly energy efficient. Further insulation may not be necessary, depending on your climate and site orientation. The earth rammer plies his trade in an environment filled with the dust of soil and cement, and the staccato thump, thump, thump of backfill tampers. Watching soil become stone beneath your feet is like magic. When the forms are removed, the well-built wall will survive the test of centuries.
Large particles provide the bulk of the wall, while the smaller particles fill in the spaces.
With every-decreasing particle sizes, virtually all of the air space within the wall can be eliminated, resulting in the densest wall possible. Density is one of the contributors to ultimate wall strength. The Sourcebook remains the best introduction to energy-efficient technology for common folks. Great reference to start design and cost estimation from each section. One of the best features of this book is the addition of the National Electric Code for RE systems.