There are two alternatives to using green wood: recycled timber, and kiln or radio frequency kiln dried timber. Recycled timbers have become popular for use in timber frames for environmental as well as aesthetic reasons. These timbers are salvaged from old factories, mills, and railroad trestles. They are often of very high quality and are dimensionally stable from decades of drying. Recycled timbers are the most expensive timbers available at the present time. But the look and beauty of using antique cedar, Douglas fir or yellow pine cannot be duplicated. Radio frequency (microwave) dried timbers are new timbers that have been kiln dried to eliminate the majority of shrinking and checking.