On BBC 4 recently, Ray Mears has been describing “How the Wild West was Won” in a three part documentary. Episode two was about the Great Plains, which included a section on how people built houses there without trees (or stone, for that matter). So what did they use ? They used earth, of course, and in particular, sods of turf from the very tough grass which did grow there. It was recognised that the sods gave very good insulation properties through their thermal mass, namely cool in the summer but warm in the winter. This was essential as much of the USA has a continental climate of extremes except along the coasts. It is estimated that there were a million such houses by 1900. Watch the programme on i-player or wait to see if it will be repeated (as many of BBC 4's programmes are).