Wood is a natural organic material which has been used in a variety of forms in building for thousands of years. At present it is the only common building material which has the potential to be renewable. To some extent timber will vary in its characteristics depending on how the wood log is converted to timber so it is useful to know the basic structure of wood and the relevant terms used to describe it. It is anisotropic , its properties are different in different directions. Tensile strength is much greater along the grain than across the grain.
Wood has an excellent strength to weight ratio and stiffness to weight ratio comparable to metals.
Wood is subject to expansion and contraction and possible warping due to changes in moisture content. Wood can be a very durable material if appropriately used but moisture and biological degradation are common sources of damage. Electrical conductivity varies with moisture content. Wood is combustible, however solid timber beams burn slowly and do not rapidly lose strength and distort as steel does in a fire. However, the disadvantages associated with such variations are minimised by modern methods of stress grading timber and by the production of a wide range of reconstituted wood products, ranging from laminated beams to fibre boards.