One word: bamboo. As wood becomes scarce, builders are fully turning to this ancient building material. Another old favorite, adobe -- earth dried into bricks or piled in a building shape -- is making a comeback. For more insulation, look to cob, a mixture of straw and clay that was a common building material in 19th century England. Other variations on the earth house: rammed earth (think of the Great Wall of China) and poured earth. Builders in the American Southwest are also experimenting with earthbags, polypropylene bags filled with dirt, straw or crushed rock. The earthbags are formed into walls and then covered with plaster. Straw bale construction is a variation of this, as is cordwood, which looks like a woodpile. Cordwood walls have short pieces of wood that wouldn't have much value otherwise. If you're really into recycling and have a lot of documents that need shredding, make a batch of papercrete -- a mixture of repulped paper, Portland concrete and sand -- from those shreds.