Photos: Extreme tree houses

Tree houses aren't just for kids anymore. They are used increasingly as primary residences, vacation getaways and meditation retreats.

Homes perched high in a forest canopy or woven from the very branches of trees take ecofriendly building to the extreme. Future-forward designers are concocting tree houses that live and "breathe," such as the Fab Tree Hab. It uses high-tech computer modeling and ancient techniques such as pleaching, which weaves together living branches and trunks to create walls and ceilings.

"Most folks that contact us are not looking for a product that is 'environmentally friendly,'" explained Mitchell Joachim, an architect at the Smart Cities group of the MIT Media Lab. "Instead they want a product that is the environment. "