The European method of casting straw mixed with liquid clay seemed promising. The technique allows complicated shapes to be formed with curved walls and niches, yet provides a firm substrate for internal and external render. We have now constructed 6 buildings using this method.
The thermal performance of these buildings is superb - we hoped that it would be good, but were astonished how good it actually was. With just a small amount of heat the buildings remain comfortably warm though out the winter months. They also keep warm for several days after the heating has gone off, making the buildings ideal for occasional use such as a home office or study, as well as buildings with a more continuous use such as an extension or new house.
The combination of the straw and the clay gives a large amount of insulation as well as the heat retaining quality known as thermal mass.