Remember that your contractor charges by the square feet he has to put a roof on. For floors, Dave encourages the use of polybutylene tubes in slab even if the homeowner can't yet afford a boiler for the hot water heat. To save heat, an air lock, such as a mudroom or coat closet, is strongly recommended. It cuts down on the heat you have to generate and it captures the sun's heat. Mass is therefore an important consideration.
Packed tires are good because they are less dense than concrete.
They heat up slower than concrete but also lose heat slower. This reduces temperature fluctuations. Vanguard Homes works with an engineer who is confident of tire walls' supportive capacity, if built in a certain way. They can have 3000-pound bearing capacity, again if done correctly. In the Salida home we went down 30 inches below frostline, so if water runs down the walls, freezing won't cause heaving.