Lumber is wood that has been processed into uniform and useful sizes (dimensional lumber), including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing (floors, wall panels, window frames). Lumber has many uses beyond home building. Lumber is referred to as timber in the United Kingdom, Europe,[1] Australia, and New Zealand, while in other[citation needed] parts of the world (mainly the United States and Canada) the term timber refers specifically to unprocessed wood fiber, such as cut logs or standing trees that have yet to be cut.
Lumber may be supplied either rough-sawn, or surfaced on one or more of its faces. Rough lumber is the raw material for furniture-making, and manufacture of other items requiring cutting and shaping. It is available in many species, including hardwoods and softwoods, such as white pine and red pine, because of their low cost.[2]
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In contrast, in Britain, and some other Commonwealth nations and Ireland, the term timber is used in both senses. (In the UK, the word lumber is rarely used in relation to wood and has several other meanings.)
Re-manufactured lumber is the result of secondary or tertiary processing of previously milled lumber. Specifically, it refers to lumber cut for industrial or wood-packaging use. Lumber is cut by ripsaw or resaw to create dimensions that are not usually processed by a primary sawmill.
Structural lumber may also be produced from recycled plastic and new plastic stock. Its introduction has been strongly opposed by the forestry industry.[5] Blending fiberglass in plastic lumber enhances its strength, durability, and fire resistance.[6] Plastic fiberglass structural lumber can have a "class 1 flame spread rating of 25 or less, when tested in accordance with ASTM standard E 84," which means it burns more slowly than almost all treated wood lumber.[7]
The basic understanding of lumber, or "sawn planks", came about in North America in the seventeenth century.[8]Lumber is the most common and widely used method of sawing logs. Plain sawn lumber is produced by making the first cut on a tangent to the circumference of the log. Each additional cut is then made parallel to the one before. This method produces the widest possible boards with the least amount of log waste.[9]
Lumber manufacturing globally is determined by the preferred style of building; areas with a "wood building culture" (homes were built from wood rather than other materials like brick) are the countries with significant sawmilling industries. Historical wood-frame home building regions are: Europe, North America, Japan.[10] Different areas of the world are recognized as significant timber suppliers; however, these areas (Indonesia, Sarawak, New Guinea, etc.) are exporters of raw logs and do not have a significant domestic lumber producing industry.
In early periods of society, to make wood for building, the trunks of trees were split with wedges into as many and as thin pieces as possible. If it was necessary to have them still thinner, they were hewn, by some sharp instrument, on both sides, to the proper size.[12] This simple but wasteful manner of making boards is still continued in some places.
Cornelis Corneliszoon (or Krelis Lootjes) was a Dutch windmill owner from Uitgeest who invented the first mechanical sawmill, which was wind-powered, on December 15, 1593. This made the conversion of log timber into planks 30 times faster than previously.[14]
The circular saw, as used in modern sawmills, was invented by an Englishman named Miller in 1777. It was not until the nineteenth century, however, that it was generally applied, and its great work belongs to that period. The first insertable teeth for this saw were invented by W. Kendal, an American, in 1826.[15]
Logging in the American colonies began in 1607 when the Jamestown settlers cut timber to build the first settlement in the new world.[16] America's first sawmill was built at the Falls of Piscatauqua, on the line between the Province of Maine and the Province of New Hampshire, in 1634. Unauthenticated records, however, claim that as early as 1633 several mills were operating in New Netherland.[12]
The American colonies were essential to England in the role of supplier of lumber for the British fleet. By the 1790s, New England was exporting 36 million feet of pine boards and at least 300 ship masts per year to the British Empire.[16] The timber supply began to dwindle at the start of the twentieth century due to significant harvest volumes, so the logging industry was forced to seek timber elsewhere; hence, the expansion into the American West.[17]
Logs are converted into lumber by being sawn, hewn, or split. Sawing with a rip saw is the most common method, because sawing allows logs of lower quality, with irregular grain and large knots, to be used and is more economical. There are various types of sawing:
The length of a unit of dimensional lumber is limited by the height and girth of the tree it is milled from. In general the maximum length is 24 ft (7.32 m). Engineered wood products, manufactured by binding the strands, particles, fibers, or veneers of wood, together with adhesives, to form composite materials, offer more flexibility and greater structural strength than typical wood building materials.[18]
Pre-cut studs save a framer much time, because they are pre-cut by the manufacturer for use in 8-, 9-, and 10-foot ceiling applications, which means the manufacturer has removed a few inches or centimetres of the piece to allow for the sill plate and the double top plate with no additional sizing necessary.
In the Americas, two-bys (24s, 26s, 28s, 210s, and 212s), named for traditional board thickness in inches, along with the 44 (89 mm 89 mm), are common lumber sizes used in modern construction. They are the basic building blocks 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.
Individual pieces of lumber exhibit a wide range in quality and appearance with respect to knots, slope of grain, shakes and other natural characteristics. Therefore, they vary considerably in strength, utility, and value.
The move to set national standards for lumber in the United States began with the publication of the American Lumber Standard in 1924, which set specifications for lumber dimensions, grade, and moisture content; it also developed inspection and accreditation programs. These standards have changed over the years to meet the changing needs of manufacturers and distributors, with the goal of keeping lumber competitive with other construction products. Current standards are set by the American Lumber Standard Committee, appointed by the U.S. Secretary of Commerce.[21]
Design values for most species and grades of visually graded structural products are determined in accordance with ASTM standards, which consider the effect of strength reducing characteristics, load duration, safety, and other influencing factors. The applicable standards are based on results of tests conducted in cooperation with the USDA Forest Products Laboratory. Design Values for Wood Construction, which is a supplement to the ANSI/AF&PA National Design Specification for Wood Construction, provides these lumber design values, which are recognized by the model building codes.[22]
Canada has grading rules that maintain a standard among mills manufacturing similar woods to assure customers of uniform quality. Grades standardize the quality of lumber at different levels and are based on moisture content, size, and manufacture at the time of grading, shipping, and unloading by the buyer. The National Lumber Grades Authority (NLGA)[23] is responsible for writing, interpreting and maintaining Canadian lumber grading rules and standards. The Canadian Lumber Standards Accreditation Board (CLSAB)[24] monitors the quality of Canada's lumber grading and identification system.
Machine stress-rated and machine-evaluated lumber are readily available for end-uses where high strength is critical, such as trusses, rafters, laminating stock, I-beams and web joints. Machine grading measures a characteristic such as stiffness or density that correlates with the structural properties of interest, such as bending strength. The result is a more precise understanding of the strength of each piece of lumber than is possible with visually graded lumber, which allows designers to use full-design strength and avoid overbuilding.[27]
In Europe, strength grading of rectangular sawn lumber/timber (both softwood and hardwood) is done according to EN-14081[28] and commonly sorted into classes defined by EN-338. For softwoods, the common classes are (in increasing strength) C16, C18, C24, and C30. There are also classes specifically for hardwoods and those in most common use (in increasing strength) are D24, D30, D40, D50, D60, and D70. For these classes, the number refers to the required 5th percentile bending strength in newtons per square millimetre. There are other strength classes, including T-classes based on tension intended for use in glulam.
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 lumber and decreases the value of the wood for furniture.
In the United States, pilings are mainly cut from southern yellow pines and Douglas-fir. Treated pilings are available in chromated copper arsenate retentions of 0.60, 0.80 and 2.50 pounds per cubic foot (9.6, 12.8 and 40.0 kg/m3) if treatment is required.
There are two main natural forces responsible for causing defects in timber and lumber: abnormal growth and rupture of tissues. Rupture of tissue includes cracks or splits in the wood called "shakes". "Ring shake", "wind shake", or "ring failure" is when the wood grain separates around the growth rings either while standing or during felling. Shakes may reduce the strength of a timber and the appearance thus reduce lumber grade and may capture moisture, promoting decay. Eastern hemlock is known for having ring shake.[36] A "check" is a crack on the surface of the wood caused by the outside of a timber shrinking as it seasons. Checks may extend to the pith and follow the grain. Like shakes, checks can hold water promoting rot. A "split" goes all the way through a timber. Checks and splits occur more frequently at the ends of lumber because of the more rapid drying in these locations.[36] 152ee80cbc