Lumber
Lumber, also called timber or fine wood in the United Kingdom, Australia, and New Zealand, is wood that has been processed into uniform and useful sizes, including beams and planks or boards. Lumber is mainly used for construction framing, as well as finishing. Lumber has many uses beyond home building. In some parts of the world, including 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.
Finished lumber is supplied in standard sizes, mostly for the construction industry – primarily softwood, from coniferous species, including pine, fir and spruce, cedar, and hemlock, but also some hardwood, for high-grade flooring. It is more commonly made from softwood than hardwoods, and 80% of lumber comes from softwood.
Terminology
In the United States and Canada, milled boards are called lumber, while timber describes standing or felled trees.In contrast, in Britain, and some other Commonwealth nations and Ireland, the term timber is used in both senses.
Re-manufactured lumber
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.Re-sawing is the splitting of hardwood or softwood lumber into two or more thinner pieces of full-length boards. For example, splitting a 2×4 into two 2×2s of the same length is considered re-sawing.
Plastic lumber
Structural lumber may also be produced from recycled plastic and new plastic stock. Its introduction has been strongly opposed by the forestry industry. Blending fiberglass in plastic lumber enhances its strength, durability, and fire resistance. 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.Timber mark
A timber mark is a code beaten on to cut wood by a specially made hammer to show the logging licence.History
The definition of the word lumber as sawn planks of wood originated in the 17th century in North America.In 1420, the archipelago of Madeira was colonized by the Portuguese Empire. Prince Henry the Navigator sent settlers to Madeira, who cleared the huge expanses of forest to grow crops. The felled trees were processed at sawmills and shipped to the mainland.
Cornelis Corneliszoon was a Dutch windmill owner from Uitgeest who invented the first wind-powered sawmill in 1593. This made the conversion of logs into planks thirty times faster than previous manually operated sawmills.
Conversion of wood logs
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:- Plain sawn – A log sawn through without adjusting the position of the log and the grain runs across the width of the boards.
- Quarter sawn and rift sawn – These terms have been confused in history but generally mean lumber sawn so the annual rings are reasonably perpendicular to the sides of the lumber.
- Boxed heart – The pith remains within the timber, post or beam, with some allowance for exposure.
- Heart center – the center core of a log.
- Free of heart center – A side-cut timber, post or beam without any pith.
- Free of knots – No knots are present.
Dimensional lumber
North American softwoods
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. 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.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, named for traditional board thickness in inches, along with the 4×4, 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.
Lumber's nominal dimensions are larger than the actual standard dimensions of finished lumber. Historically, the nominal dimensions were the size of the green, rough boards that eventually became smaller finished lumber through drying and planing. Today, the standards specify the final finished dimensions and the mill cuts the logs to whatever size it needs to achieve those final dimensions. Typically, that rough cut is smaller than the nominal dimensions because modern technology makes it possible to use the logs more efficiently. For example, a "2×4" board historically started out as a green, rough board actually. After drying and planing, it would be smaller by a nonstandard amount. Today, a "2×4" board starts out as something smaller than 2 inches by 4 inches and not specified by standards, and after drying and planing is minimally.
As previously noted, less wood is needed to produce a given finished size than when standards called for the green lumber to be the full nominal dimension. However, even the dimensions for finished lumber of a given nominal size have changed over time. In 1910, a typical finished board was. In 1928, that was reduced by 4%, and yet again by 4% in 1956. In 1961, the Committee on Grade Simplification and Standardization agreed to what is now the current U.S. standard: in part, the dressed size of a 1-inch board was fixed at inch; while the dressed size of 2 inch lumber was reduced from inch to the current inch.
In 1964, Popular Mechanics magazine hired an independent agency to test the comparative strength of multiple samples of a full-size 2×4 inches, × inches, × inches, and × inches. With A’s compressive strength benchmarked as "100%," B-C-D were 90.7%, 82.2%, and 73.6% the strength of A’s full-size 2×4. Stated another way, the 1960s’ reduction of the smaller dimension from to inches reduced compressive strength by 10.46%.
Dimensional lumber is available in green, unfinished state, and for that kind of lumber, the nominal dimensions are the actual dimensions.
Grades and standards
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.
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.
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 is responsible for writing, interpreting and maintaining Canadian lumber grading rules and standards. The Canadian Lumber Standards Accreditation Board monitors the quality of Canada's lumber grading and identification system. Their common grade abbrievation, CLS, Canadian Lumber Standard is well utilised in the construction industry.
Attempts to maintain lumber quality over time have been challenged by historical changes in the timber resources of the United States – from the slow-growing virgin forests common over a century ago to the fast-growing plantations now common in today's commercial forests. Resulting declines in lumber quality have been of concern to both the lumber industry and consumers and have caused increased use of alternative construction products.
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.
In Europe, strength grading of rectangular sawn lumber/timber is done according to EN-14081 and commonly sorted into classes defined by EN-338. For softwoods, the common classes are C16, C18, C24, and C30. There are also classes specifically for hardwoods and those in most common use 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.
- C14, used for scaffolding and formwork
- C16 and C24, general construction
- C30, prefab roof trusses and where design requires somewhat stronger joists than C24 can offer. TR26 is also a common trussed rafter strength class in long standing use in the UK.
- C40, usually seen in glulam