structure does. Thus timber frame building can actually serve to conserve rather than exhaust wood stocks if it is used instead of conventional framing. But even here, many green builders are fabricating their posts and beams from smaller stock, or using engineered wood. Ecological timber framers who employ traditional craft techniques try to source their wood from sustainably-managed forests. Using wood sustainably is easiest for owner-builders who can harvest their own woodlots. Stone was one of the first human building materialsin the form of caves, which have been called stone buildings by subtraction. Since then, weve used stone by addition for houses, cottages, barn, churches, castles, walls, aqueducts and walkways. It is among the most durable and beautiful of materials, and has also been associated with high levels of craft (Smith, 2002b). Like wood, stone has its appropriate place in contemporary building, but other environmental considerations factor in to limit its use for building structures. Unlike wood, stone is ubiquitous. But it is heavy, and very difficult to gather and transporta limitation even in a green economy that encourages people-intensive building techniques. Even more importantly, however, stone is a poor insulator, and thus stone buildings are major energy sinks (Chiras, 2000). There are ways to add insulation to compensate, but these measures add costs and resources that might be saved by the use of another primary building form. Stone buildings also require more substantial foundations. Thus, while stone may not be scarce, its use may require unsustainable use of other scarce resources (Smith, 2002b). Despite the environmental limitations on the use of stone and timber, they must be included in any discussion of natural building because of the central role of craft and self-