I found this video that shows a family that lives in an old converted street car. Over a decade, Claudine raise three boys in this tiny 400ish square foot house that was originally a 1920′s street car from Santa Cruz. Originally only having one bedroom, as the family grew, so did the house. They built a tree house and then a cob hut to allow their children to have a bit more space. It is interesting because the owner is working with the city to get her home legal. Lots of great commentary on this topic.
Even though I am busy building my own tiny house, I still find myself thinking about building other houses (is that cheating on my tiny house? lol). From time to time I have been coming back to cob houses. I have thought about building a cob house if in the future I decide I need more space (get married or just want more space etc).
Cob is basically clay, sand and usually straw mixed together to be used as a building material, kinda like bricks, but the advantage is that most of the materials can be sourced on site or purchased cheaply. The houses are very strong, good at regulating temperature, are about the lightest impact home I know. They have their own aesthetic to them which I am beginning to warm up to. Here is a great video on them