Lumber (North American English) or timber (as used in other areas) is a type of wood that has been processed into beams and planks, a stage in the process of wood production. Lumber is mainly used for structural purposes but has many other uses as well.
There are two main types of lumber. It may be supplied either rough-sawmill, or surfaced on one or more of its faces. 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 ; but it is also readily available in , 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 species, including pine, fir and spruce (collectively spruce-pine-fir), Cedrus, and Tsuga, but also some hardwood, for high-grade flooring. It is more commonly made from softwood than hardwoods, and 80% of lumber comes from softwood.
In contrast, in Britain and many other Commonwealth nations, the term is used for both senses. (The word lumber is rarely used in relation to wood and has several other meanings, including unused or unwanted items.)
Resawing is the splitting of 1-inch through 12-inch hardwood or softwood lumber into two or more thinner pieces of full-length boards. For example, splitting a ten-foot 2×4 into two ten-foot 1×4s is considered resawing.
|great halls 11 or 9 bays wide|
|great halls 7 or 5 bays wide|
|great halls 5 or 3 bays wide or halls 7 or 5 bays wide|
|great halls 3 bays wide or halls 5 bays wide|
|great halls 3 small bays wide or halls 3 large bays wide|
|pagodas and small halls|
|pagodas and small great halls|
|small pagodas and ceilings|
Timber smaller than the 8th class were called "unclassed" (等外). The width of a timber is referred to as one "timber" (材), and the dimensions of other structural components were quoted in multiples of "timber"; thus, as the width of the actual timber varied, the dimensions of other components were easily calculated, without resorting to specific figures for each scale. The dimensions of timbers in similar application show a gradual diminution from the Sui Dyansty (580~618) to the modern era; a 1st class timber during the Sui was reconstructed as 15×10 (Sui Dynasty inches, or 29.4 mm).
Pre-cut studs save a framer much time, because they are pre-cut by the manufacturer for use in 8-, 9-, and 10-ft (2.44, 2.74 and 3.05 m) 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 (2×4s, 2×6s, 2×8s, 2×10s, and 2×12s), 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 framing or platform framing 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 (not dried), rough (unfinished) boards that eventually became smaller finished lumber through drying and planing (to smooth the wood). 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 reliably .
|+North American softwood dimensional lumber sizes|
|1 × 2||×||19 × 38||2 × 2||×||38 × 38|
|1 × 3||×||19 × 64||2 × 3||×||38 × 64|
|1 × 4||×||19 × 89||2 × 4||×||38 × 89||4 × 4||×||89 × 89|
|1 × 5||×||19 × 114|
|1 × 6||×||19 × 140||2 × 6||×||38 × 140||4 × 6||×||89 × 140||6 × 6||×||140 × 140|
|1 × 8||×||19 × 184||2 × 8||×||38 × 184||4 × 8||×||89 × 184||8 × 8||×||191 × 191|
|1 × 10||×||19 × 235||2 × 10||×||38 × 235|
|1 × 12||×||19 × 286||2 × 12||×||38 × 286|
As previously noted, less wood is needed to produce a given finished size than when standards called for the green lumber to be 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, at a meeting in Scottsdale, Arizona, 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 (nominal) board was fixed at inch; while the dressed size of 2 inch (nominal) lumber was reduced from inch to the current inch.
Dimensional lumber is available in green, unfinished state, and for that kind of lumber, the nominal dimensions are the actual dimensions.
The move to set national standards for lumber in the United States began with 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 (NLGA) is responsible for writing, interpreting and maintaining Canadian lumber grading rules and standards. The Canadian Lumber Standards Accreditation Board (CLSAB) monitors the quality of Canada's lumber grading and identification system.
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 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 is readily available for end-uses where high strength is critical, such as , , laminating stock, I-joist 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 timber (both softwood and hardwood) is done according to EN-14081 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.
Grading rules for African and South American sawn timber have been developed by ATIBT ATIBT according to the rules of the Sciages Avivés Tropicaux Africains (SATA) and is based on clear cuttings – established by the percentage of the clear surface.
|+ North American hardwood dimensional lumber sizes|
|1 in or in|
|in or in|
|in or in|
|2 in or in|
|3 in or in|
|4 in or in||+|
Also in North America, hardwood lumber is commonly sold in a "quarter" system, when referring to thickness; 4/4 (four quarter) refers to a board, 8/4 (eight quarter) is a board, etc. This "quarter" system is rarely used for softwood lumber; although softwood decking is sometimes sold as 5/4, even though it is actually one-inch thick (from milling off each side in a motorized thickness planer step of production). The "quarter" system of reference is a traditional North American lumber industry nomenclature used specifically to indicate the thickness of rough-sawn hardwood lumber.
In rough-sawn lumber it immediately clarifies that the lumber is not yet milled, avoiding confusion with milled dimension lumber which is measured as actual thickness after machining. Examples – -inch, 19 mm, or 1x. In recent years architects, designers, and builders have begun to use the "quarter" system in specifications as a vogue of insider knowledge, though the materials being specified are finished lumber, thus conflating the separate systems and causing confusion.
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 decreases the value of the timber for furniture.
Wood with less than 25% moisture (dry weight basis) can remain free of decay for centuries. Similarly, wood submerged in water may not be attacked by fungi if the amount of oxygen is inadequate.
Fungi timber defects:
There are four recommended methods to protect wood-frame structures against durability hazards and thus provide maximum service life for the building. All require proper design and construction:
The primary objective when addressing moisture loads is to keep water from entering the building envelope in the first place, and to balance the moisture content within the building itself. Moisture control by means of accepted design and construction details is a simple and practical method of protecting a Timber framing against decay. For applications with a high risk of staying wet, designers specify durable materials such as naturally decay-resistant species or wood that has been treated with . Cladding, shingles, and exposed timbers or glulam beams are examples of potential applications for treated wood.
• Grading the building site away from the foundation to provide proper drainage
• Covering exposed ground in any crawl spaces with 6-mil polyethylene film and maintaining at least of clearance between the ground and the bottom of framing members above (12 inches to beams or girders, 18 inches to joists or plank flooring members)
• Supporting post columns by concrete piers so that there is at least of clear space between the wood and exposed earth
• Installing wood framing and sheathing in exterior walls at least eight inches above exposed earth; locating siding at least six inches from the finished grade
• Where appropriate, ventilating crawl spaces according to local building codes
• Removing building material scraps from the job site before backfilling.
• If allowed by local regulation, treating the soil around the foundation with an approved termiticide to provide protection against subterranean termites
Wood can be treated with a preservative that improves service life under severe conditions without altering its basic characteristics. It can also be pressure-impregnated with fire-retardant chemicals that improve its performance in a fire. "Wood That Fights." Popular Sciences, March 1944, p. 59. One of the early treatments to "fireproof lumber", which retard fires, was developed in 1936 by the Protexol Corporation, in which lumber is heavily treated with salt. "Lumber is Made Fireproof by Salt Treatment" Popular Mechanics, April 1936 bottom-left p. 560 Wood does not deteriorate simply because it gets wet. When wood breaks down, it is because an organism is eating it. Preservatives work by making the food source inedible to these organisms. Properly preservative-treated wood can have 5 to 10 times the service life of untreated wood. Preserved wood is used most often for railroad ties, utility poles, marine piles, decks, fences and other outdoor applications. Various treatment methods and types of chemicals are available, depending on the attributes required in the particular application and the level of protection needed.
There are two basic methods of treating: with and without pressure. Non-pressure methods are the application of preservative by brushing, spraying or dipping the piece to be treated. Deeper, more thorough penetration is achieved by driving the preservative into the wood cells with pressure. Various combinations of pressure and vacuum are used to force adequate levels of chemical into the wood. Pressure-treating preservatives consist of chemicals carried in a solvent. Chromated copper arsenate, once the most commonly used wood preservative in North America began being phased out of most residential applications in 2004. Replacing it are amine copper quat and copper azole.
All wood preservatives used in the United States and Canada are registered and regularly re-examined for safety by the U.S. Environmental Protection Agency and Health Canada's Pest Management and Regulatory Agency, respectively.
The United Kingdom, Uzbekistan, Kazakhstan, Australia, Fiji, Madagascar, Mongolia, Russia, Denmark, Switzerland and Swaziland governments all support an increased role for energy derived from biomass, which are organic materials available on a renewable basis and include residues and/or byproducts of the logging, sawmilling and papermaking processes. In particular, they view it as a way to lower greenhouse gas emissions by reducing consumption of oil and gas while supporting the growth of forestry, agriculture and rural economies. Studies by the U.S. government have found the country's combined forest and agriculture land resources have the power to sustainably supply more than one-third of its current petroleum consumption. U.S. Department of Agriculture, U.S. Department of Energy Biomass as a Feedstock for a Bioenergy and Bioproducts Industry: The Technical Feasibility of a Billion-Ton Annual Supply, 2005 Executive Summary
Biomass is already an important source of energy for the North American forest products industry. It is common for companies to have cogeneration facilities, also known as combined heat and power, which convert some of the biomass that results from wood and paper manufacturing to electrical and thermal energy in the form of steam. The electricity is used to, among other things, dry lumber and supply heat to the dryers used in paper-making.