correspondent: deborah binder manages construction for mike reynolds. recycled materials are still a key building component. >> at least, here in taos, glass bottles aren't recycled anymore. and you use less cement by using them and you end up with these really beautiful walls. correspondent: earthships' side and back walls are made from about a thousand old tires. 300 to 400 pounds of dirt are rammed by hand into each tire. the tire walls are built into a mound of earth to create an extremely dense and insulating structure. >> it's almost like if you're inside a cave. so caves usually stay at about 63, 65 degrees all year round. and so then it's a lot easier to cool and to warm up that space. correspondent: in the winter, brian and jess johnson's home is warmed up by sunlight streaming in through the southern wall of windows. in the summer, a system of tubes and vents brings cooler air in from the back of the house. >> you open that vent, the hot air rises and pulls cool air through the rest of the building as it goes out. >> we'll maintain 70 to 73°f.