Timber

Lumber or timber is wood that is used in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production. Timber often refers to the wood contents of standing, live trees that can be used for lumber or fiber production, although it can also be used to describe sawn lumber whose smallest dimension is not less than 5 inches (127 mm). Lumber is supplied either rough or finished. Besides pulpwood, rough lumber is the raw material for furniture-making and other items requiring additional cutting and shaping. It is available in many species, usually hardwoods. Finished lumber is supplied in standard sizes, mostly for the construction industry, primarily softwood from coniferous species including pine, fir and spruce, cedar, hemlock, but also some hardwood, for high-grade flooring.

In the United Kingdom and Australia, "timber" is a term also used for sawn wood products (that is, boards), whereas generally in the United States and Canada, the product of timber cut into boards is referred to as lumber. In the United States and Canada sawn wood products of five inches (127 mm) (nominal size) diameter or greater are sometimes called "timbers". Solid dimensional lumber typically is only available up to lengths of 24 ft, yet since builders have a need for lengths beyond that for roof construction (rafters), builders use "finger-jointed" lumber that can be up to 36 ft long in 2×6 size (see Engineered Lumber below). Finger-jointed lumber is also widely used for smaller lengths like studs, the vertical members of a framed wall. Pre-cut studs save a framer a lot of time as they are pre-cut by the manufacturer to be used in 8 ft, 9 ft & 10 ft ceiling applications, which means they have removed a few inches of the piece to allow for the sill plate and the double top plate with no additional sizing necessary by the framer.

In North America sizes for dimensional lumber made from hardwoods varies from the sizes for softwoods. Boards are usually supplied in random widths and lengths of a specified thickness, and sold by the board-foot (144 cubic inches, ¹⁄₁₂th of a cubic foot). This does not apply in all countries, for example in Australia many boards are sold to timber yards in packs with a common profile (dimensions) but not necessarily of consisting of the same length boards. Hardwoods cut for furniture are cut in the fall and winter, after the sap has stopped running in the trees. If hardwoods are cut in the spring or summer the sap ruins the natural color of the timber and deteriorates the value of the timber for furniture.

Timber or lumber may be treated with a preservative that protects it from being destroyed by insects, fungus or exposure to moisture. Generally this is applied through combined vacuum and pressure treatment. The preservatives used to pressure-treat lumber are classified as pesticides. Due to potential hazards to humans and the environment, some are being phased out. Many newer preservatives are free of metallic compounds altogether, and are instead based on biodegradable organic chemistry. Treating lumber provides long-term resistance to organisms that cause deterioration. If it is applied correctly, it extends the productive life of lumber by five to ten times. If left untreated, wood that is exposed to moisture or soil for sustained periods of time will become weakened by various types of fungi, bacteria or insects.