before you take on building your project, start by sculpting yourself a model. You can use clay soil or purchase modelling clay...it doesn't matter. Your model will represent the thick walls of whatever system you are actually building with. Make sure your model represents some sort of scale...like 1/4" for each foot of the building. This is a passive solar cob house at Earthaven Ecovillage by Steveo Brodmerkel, www.kleiwerks.org