|
History and geography Lumber was one of the first industries in the United States. Maine and New York were early leading producers; however, later expansion led to Michigan and later Oregon, Washington, and California assuming the lead in domestic lumber production. Logging, the felling and preparation of trees for lumber was a related frontier industry; various tales of lumberjacks were a substantial portion of a certain chapter in North American folklore. Classifications Rough lumber comes from the sawmill without further cutting or shaping. It is usually sold in random lengths and widths and measured in the USA and Canada in board feet, a unit of 1 foot × 1 inch × 1 foot. It is available air-dried or kiln-dried. Air-dried lumber is carefully stacked and allowed to dry for several months, depending on thickness. It is used for some outdoor purposes, such as building sheds and fences. Kiln-dried wood is stacked and dried in moisture- and temperature-controlled kilns built for the purpose. It is then ready to be used for furniture-making or other woodworking uses. Finished lumber is usually kiln-dried, then planed and cut to predetermined sizes, primarily for use by the construction industry. When using Imperial or U.S. customary measurements, the widths given are from before planing, whereas the piece actually sold is smaller; a 2×4, for example, is actually only 1½ by 3½ inches after planing. Other stock is sized similarly. The lengths are actual sizes and are usually multiples of 2 feet. Sizes from 8 to 16 feet (8, 10, 12, 14, 16) are commonly available, and smaller sizes (4, 6, 7) are sometimes available. Larger sizes (18, 20, 22, 24) are sometimes available. When using metric measurements, lumber is measured in actual sizes. In the United States, timber is cut in the forest in 24 foot lengths. At the mill it is again cut into three 8 foot lengths, an 8 foot and a 16 foot length, a 10 foot and a 14 foot length or two 12 foot lengths. Lumber is also used to refer to plywood and other composite wood products. Dimensional Lumber Dimensional lumber is a term used in North America for lumber that is finished/planed and cut to standardized width and depth specified in inches. Softwoods Examples of common sizes are 2×4 (also two-by-four and other variants), 2×6, and 4×4. The length of a board is usually specified separately from the width and depth. It is thus possible to find 2×4s that are four, eight, or twelve feet in length. In the United States the standard lengths of lumber are 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24 feet. Solid dimensional lumber typically is only available up to lengths of 24', 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' long in 2x6 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', 9' & 10' 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 The Americas, two-bys (2×4s, 2×6s, 2×8s, 2x10s, and 2×12s) are common lumber sizes used in modern construction. They are the basic building block for such common structures as balloon-frame or platform-frame housing. Dimensional lumber made from softwood is typically used for construction, while hardwood boards are more commonly used for making cabinets or furniture. The nominal size of a board varies from the actual size of the board. This is due to planing and shrinkage as the board is dried. This results in the final lumber being slightly smaller than the nominal size. Also, if the wood is surfaced when it is green, the initial dimensions are slightly larger (e.g. 1/16″ bigger for up to 4″ nominal lumber, ⅛″ for 5″ and 6″ nominal lumber, ¼″ bigger for larger sizes). As the wood dries, it shrinks and reaches the specified actual dimensions. Non-North American sizes Outside North America sizes of timber vary slightly. Sizes are, in some cases, based on the imperial measurement and referred to as such; in other cases the sizes are too far removed from the imperial size to be referred to by imperial measurement. Lengths are sold every 300 mm (a metric approximation of 1'). Common sizes are similar to the North American equivalent; 2.4, 2.7, 3.0, 3.6, 4.2, 4.8, 5.4, 6.0. Hardwoods 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). 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. Also in North America hardwood lumber is commonly sold in a “quarter” system when referring to thickness. 4/4 (four quarters) refers to a one-inch thick board, 8/4 (eight quarters) is a two-inch thick board, etc. This system is not usually used for softwood lumber, although softwood decking is sometimes sold as 5/4 (actually one inch thick). Engineered Lumber Engineered lumber is lumber created by a manufacturer and designed for a certain structural purpose. The main categories of engineered lumber are:• Preservatives 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. 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. Timber framing Timber framing is a style of construction which uses heavier framing elements than modern stick framing, which uses dimensional lumber. The timbers originally were tree boles squared with a broadaxe or adze and joined together with joinery without nails. A modern imitation with sawn timbers is growing in popularity in the United States. Miscellaneous See also | ||||||||||
|
| |||||||||||
 |
|
| |