of the waterproofing is generally sufficient. The second type of insulation is a spray on foam (e.g. polyurethane solid foam insulation). This works very well where the shape of the structure is unconventional, rounded or difficult to get to. Foam insulation requires an additional protective top coat such as foil or fleece filter to help it resist water penetration. In some low budget earth shelters, insulation may not be applied to the walls. These methods rely on the U factor or thermal heat storage capacity of the earth itself below the frost layer. These designs are the exception however and risk frost heave damage in colder climates. The theory behind no insulation designs relies on using the thermal mass of the earth to store heat, rather than relying on a heavy masonry or cement inner structures that exist in a typical passive solar house. This is the exception to the rule and cold temperatures may extend down into the earth above the frost line making insulation necessary for higher efficiencies. Backfilling After previous construction stages are complete, the earth is backfilled against the external walls to create the berm. Depending on the drainage characteristics of the earth may not be suitable to place in direct contact with the external wall. Some advise that topsoil and turf (sod) be put aside from the initial excavation and be used for the grass roof and to place as the topmost layer on the berm. Finishings In the earth houses designed by Vetsch, interior walls are furnished using loam rendering which provides superior humidity compensation. The loam rendering is finally coated with lime-white cement paint. Examples Australia Coober Pedy, South Australia. Mining town with many underground "dugouts". Lightning Ridge Switzerland Lättenstrasse estate ("Earth Homes") in Dietikon, by Peter Vetsch. United Kingdom Underhill, Holme, West Yorkshire. The first modern earth sheltered building in the UK. Hockerton Housing Project, a community of 5 homes in Nottinghamshire, England. "The Burrow" in Canterbury, UK designed by Patrick Kennedy-Sanigar. There are 2 earthships in the UK, at Fife, Scotland and the Earthship Brighton in England. "The Underground House" in Great Ormside, Cumbria. Two storey earth shelter built in a disused quarry. Malator, Pembrokeshire. Built for former Labour MP Bob Marshall-Andrews in 1998. Undermill, Bushey Heath Watford, Hertfordshire, Build 1996 modern earth sheltered building 4 bedroom 170m2 in the UK. see here https://www.rightmove.co.uk/properties/100082459#/ United States Bill Gates' house, on the