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|The examples and perspective in this article may not represent a worldwide view of the subject. (December 2012)|
Lumber (American English) or timber (British English, Hiberno-English, New Zealand English, and Australian English) is wood that has been processed into beams and planks, a stage in the process of wood production.
Lumber may be supplied either rough-sawn, 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 hardwoods, but it is also readily available in 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 (collectively known as Spruce-pine-fir), cedar, and hemlock, but also some hardwood, for high-grade flooring.
Lumber is mainly used for structural purposes but has many other uses as well. Lumber is classified as hardwood or softwood.
In the United Kingdom, Australia, and New Zealand, timber is a term used for sawn wood products, such as floor boards, whereas generally in the United States and Canada, it refers to standing or felled trees, before they are milled into boards referred to as lumber.
"Timber" is also used there to describe sawn lumber not less than 5 inches (127 mm) in its smallest dimension. An example of the latter is often partially finished lumber used in timber-frame construction.
In the United Kingdom, the word lumber is rarely used in relation to wood and timber is almost universally used in its place; lumber does, however, have several other meanings in the UK, including unused or unwanted items.
Remanufactured lumber refers to secondary or tertiary processing/cutting of previously milled lumber. The term specifically 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.
Resawing is the process of splitting 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 2x4 into two ten foot 1x4s is considered resawing.
Structural lumber may also be produced from recycled plastic and new plastic stock, but 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 slower than almost all treated wood lumber.
Logs are converted into timber by being sawn, hewn, or split. Sawing with a rip saw is the most common because sawing allows logs of lower quality, with irregular grain and large knots, to be used and is more economical. Types of sawing are:
|The examples and perspective in this section deal primarily with North America and do not represent a worldwide view of the subject. (October 2014)|
Dimensional lumber is a term used for lumber that is cut to standardized width and depth specified in inches. Carpenters extensively use dimensional lumber in framing wooden buildings. Examples of common sizes are 2×4 (pictured) (also two-by-four and other variants, such as four-by-two in the UK, Australia, New Zealand), 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 and Canada the standard lengths of lumber are 6 feet (1.83 meters), 8 (2.44), 10 (3.05), 12 (3.66), 14 (4.27), 16 (4.88), 18 (5.49), 20 (6.10), 22 (6.71), and 24 feet (7.32 meters). For wall framing, "stud," or "precut" sizes are available, and commonly used. For an eight, nine, or ten foot ceiling height, studs are available in 92 5⁄8 inches (235 cm), 104 5⁄8 inches (266 cm), and 116 5⁄8 inches (296 cm). The term "stud" is used inconsistently to specify length, though, so where the exact length matters, one must specify the length explicitly.
Solid dimensional lumber typically is only available up to lengths of 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.
Pre-cut studs save a framer a lot of time as they are pre-cut by the manufacturer to be used in 8, 9 and 10 ft (2.44, 2.74 and 3.05 m) ceiling applications, which means they have 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 (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.
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 and it uses the logs more efficiently. For example, a "2x4" board historically started out as a green, rough board actually 2 by 4 inches (51 mm × 102 mm). After drying and planing, it would be smaller, by a nonstandard amount. Today, a "2x4" board starts out as something smaller than 2 inches by 4 inches and not specified by standards, and after drying and planing is reliably 1 1⁄2 by 3 1⁄2 inches (38 mm × 89 mm).
|1×2||3⁄4 × 1 1⁄2 in (19 × 38 mm)||2×2||1 1⁄2 × 1 1⁄2 in (38 × 38 mm)||4×4||3 1⁄2 × 3 1⁄2 in (89 × 89 mm)|
|1×3||3⁄4 × 2 1⁄2 in (19 × 64 mm)||2×3||1 1⁄2 × 2 1⁄2 in (38 × 64 mm)||4×6||3 1⁄2 × 5 1⁄2 in (89 × 140 mm)|
|1×4||3⁄4 × 3 1⁄2 in (19 × 89 mm)||2×4||1 1⁄2 × 3 1⁄2 in (38 × 89 mm)||4×8||3 1⁄2 × 7 1⁄4 in (89 × 184 mm)|
|1×6||3⁄4 × 5 1⁄2 in (19 × 140 mm)||2×6||1 1⁄2 × 5 1⁄2 in (38 × 140 mm)||6×6||5 1⁄2 × 5 1⁄2 in (140 × 140 mm)|
|1×8||3⁄4 × 7 1⁄4 in (19 × 184 mm)||2×8||1 1⁄2 × 7 1⁄4 in (38 × 184 mm)||8×8||7 1⁄4 × 7 1⁄4 in (184 × 184 mm)|
|1×10||3⁄4 × 9 1⁄4 in (19 × 235 mm)||2×10||1 1⁄2 × 9 1⁄4 in (38 × 235 mm)|
|1×12||3⁄4 × 11 1⁄4 in (19 × 286 mm)||2×12||1 1⁄2 × 11 1⁄4 in (38 × 286 mm)|
Early standards called for green rough lumber to be of full nominal dimension when dry. However, the dimensions have diminished over time. In 1910, a typical finished 1-inch- (25 mm) board was 13⁄16 in (21 mm). 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 3⁄4 inch; while the dressed size of 2 inch (nominal) lumber was reduced from 1 5⁄8 inch to the current 1 1⁄2 inch.
Dimensional lumber is available in green, unfinished state, and for that kind of lumber, the nominal dimensions are the actual dimensions.
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 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 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. A summary of the six published design values—including bending (Fb), shear parallel to grain (Fv), compression perpendicular to grain (Fc-perp), compression parallel to grain (Fc), tension parallel to grain (Ft), and modulus of elasticity (E and Emin) can be found in Structural Properties and Performance published by WoodWorks.
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 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 is readily available for end-uses where high strength is critical, such as truss 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 sawn softwood is done according to EN-14081-1/2/3/4 and sorted into 9 classes; In increasing strength these are: C14, C16, C18, С22, С24, С27, С30, С35 and С40
Grading rules for African and South American sawn timber have been developed by 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.
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 or 2,360 cubic centimetres, 1⁄12th of 1 cubic foot or 0.028 cubic metres). 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 consisting of the same length boards.
|Nominal (rough-sawn size)||S1S (surfaced on one side)||S2S (surfaced on two sides)|
|1⁄2 in||3⁄8 in (9.5 mm)||5⁄16 in (7.9 mm)|
|5⁄8 in||1⁄2 in (13 mm)||7⁄16 in (11 mm)|
|3⁄4 in||5⁄8 in (16 mm)||9⁄16 in (14 mm)|
|1 in or 4⁄4 in||7⁄8 in (22 mm)||13⁄16 in (21 mm)|
|1 1⁄4 in or 5⁄4 in||1 1⁄8 in (29 mm)||1 1⁄16 in (27 mm)|
|1 1⁄2 in or 6⁄4 in||1 3⁄8 in (35 mm)||1 5⁄16 in (33 mm)|
|2 in or 8⁄4 in||1 13⁄16 in (46 mm)||1 3⁄4 inches (44 mm)|
|3 in or 12⁄4 in||2 13⁄16 in (71 mm)||2 3⁄4 in (70 mm)|
|4 in or 16⁄4 in||3 13⁄16 in (97 mm)||3 3⁄4 in (95 mm)|
Also in North America, hardwood lumber is commonly sold in a "quarter" system when referring to thickness. 4/4 (four quarter) refers to a 1-inch-thick (25 mm) board, 8/4 (eight quarter) is a 2-inch-thick (51 mm) 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.
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.
In the United States, pilings are mainly cut from Southern Yellow Pines (SYP) and Douglas Firs (DF). Treated pilings are available in CCA retentions of .60, .80, and 2.50 pcf (pounds per cubic foot) if treatment is required.
Defects occurring in lumber are grouped into the following four divisions:
During the process of converting timber to commercial form the following defects may occur:
Fungi attack timber when these conditions are all present:
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:
Following are the insects which are usually responsible for the decay of timber:
There are two main natural forces responsible for causing defects in timber: abnormal growth and rupture of tissues.
Under proper conditions, wood provides excellent, lasting performance. However, it also faces several potential threats to service life, including fungal activity and insect damage—which can be avoided in numerous ways. Section 2304.11 of the International Building Code (IBC) addresses protection against decay and termites. This section provides requirements for non-residential construction applications, such as wood used above ground (e.g., for framing, decks, stairs, etc.), as well as other applications.
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:
1. Control moisture using design techniques to avoid decay.
2. Provide effective control of termites and other insects.
3. Use durable materials such as pressure treated or naturally durable species of wood where appropriate.
4. Provide quality assurance during design and construction and throughout the building’s service life using appropriate maintenance practices.
Wood is a hygroscopic material, which means it naturally absorbs and releases water to balance its internal moisture content with the surrounding environment. The moisture content of wood is measured by the weight of water as a percentage of the oven-dry weight of the wood fiber. The key to controlling decay is to control moisture. Once decay fungi are established, the minimum moisture content for decay to propagate is 22 to 24 percent, so building experts recommend 19 percent as the maximum safe moisture content for untreated wood in service. Water by itself does not harm the wood, but rather, wood with consistently high moisture content enables fungal organisms to grow.
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 wood-frame building against decay. Finally, for applications with a high risk of staying wet, designers should specify durable materials such as naturally decay-resistant species or wood that’s been treated with preservatives. Cladding, shingles, sill plates and exposed timbers or glulam beams are examples of potential applications for treated wood.
For buildings in termite zones, basic protection practices addressed in current building codes include (but are not limited to) the following:
• Grade the building site away from the foundation to provide proper drainage.
• Cover exposed ground in any crawl spaces with 6-mil polyethylene film and maintain at least 12 to 18 inches 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).
• Support post columns by concrete piers so that there is at least six inches of clear space between the wood and exposed earth.
• Install wood framing and sheathing in exterior walls at least eight inches above exposed earth; locate siding at least six inches from the finished grade.
• Where appropriate and desired, ventilate crawl spaces according to local building codes.
• Remove building material scraps from the job site before backfilling. If termites are found, eliminate their nests.
• If allowed by local regulation, treat the soil around the foundation with an approved termiticide to provide protection against subterranean termites.
To avoid decay and termite infestation, it is important to separate untreated wood from the ground and other sources of moisture. These separations are required by many building codes and are considered necessary to maintain wood elements in permanent structures at a safe moisture content for decay protection. When it is not possible to separate wood from the sources of moisture, designers often rely on preservative-treated wood.
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. One of the early treatments to fireproof lumber which retard fires was developed in 1936 by Protexol Corporation in which lumber is heavily treated with salt. Wood does not deteriorate just because it gets wet. When wood breaks down, it is because an organism is eating it as food. 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 (CCA), 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 (ACQ) and copper azole (CA).
All wood preservatives used in the U.S. 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.
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. Modern timber framing has been growing in popularity in the United States since the 1970s.
Green building minimizes the impact or "environmental footprint" of a building. Wood is a major building material that is renewable and uses the sun’s energy to renew itself in a continuous sustainable cycle. Studies show manufacturing wood uses less energy and results in less air and water pollution than steel and concrete. However, demand for lumber is blamed for deforestation.
The U.K, 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.
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.
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