Guest post by Paul Mittig
I built my 10 x 20 house in 2005 for about $10,000 in materials, including all furnishings. It is built on six poles set two feet into the ground, that support the floor and roof. There is no framing in the walls except at the door and the large window. The walls are rigid foam insulation, R21, covered with ½ inch sheetrock and all glued together. The ceiling has R38 fiberglass insulation, and the floor has R19 fiberglass insulation. I spend about $100 a year on propane for heating, cooking, and water heating.
The house is located in the hills of Northern California. I live in it full time. The house is set up for one person, but you could easily put a double bed by the door where the tall bookcase stands. If you did this you might want to move the window.