Lumber

"Timber" redirects here. For other uses, see Timber (disambiguation) and Lumber (disambiguation).
Timber in storage for later processing at a sawmill
Wood cut from Victorian Eucalyptus regnans
The harbor of Bellingham, Washington, filled with logs, 1972

Lumber (American English;[1] timber in Australian English, British English, Hiberno-English, and New Zealand English[2]) 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.[3] Finished lumber is supplied in standard sizes, mostly for the construction industry—primarily softwood, from coniferous species, including pine, fir and spruce (collectively 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. It is classified more commonly as a softwood than as a hardwood, because 80% of lumber comes from softwood.[4]

Terminology

In Australia, Ireland, New Zealand and Britain, the term timber describes sawn wood products, such as floor boards. In the United States and Canada, generally timber describes standing or felled trees, before they are milled into boards, which are called lumber.

Timber there also describes sawn lumber not less than 5 inches (127 mm) in its smallest dimension.[5] The latter includes the often partly 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; but lumber has several other meanings in Britain, including unused or unwanted items.

Remanufactured lumber

Remanufactured lumber is the result of secondary or tertiary processing/cutting of previously milled lumber. Specifically, it is 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 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 2x4 into two ten-foot 1x4s is considered resawing.

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.[6] Blending fiberglass in plastic lumber enhances its strength, durability, and fire resistance.[7] 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.[8]

Conversion of wood logs

Logs are converted into timber 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:

Dimensional lumber

A 2×4.

Dimensional lumber is lumber that is cut to standardized width and depth, specified in inches. Carpenters extensively use dimensional lumber in framing wooden buildings. Common sizes include 2×4 (pictured) (also two-by-four and other variants, such as four-by-two in the Australia, New Zealand, and the UK), 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, and twelve feet in length. In Canada and the United States, the standard lengths of lumber are 6, 8, 10, 12, 14, 16, 18, 20, 22 and 24 feet (1.83, 2.44, 3.05, 3.66, 4.27, 4.88, 5.49, 6.10, 6.71 and 7.32 meters). For wall framing, "stud" or "precut" sizes are available, and are 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; where the exact length matters, one must specify the length explicitly.

North American softwoods

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.[9]

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 (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).

North American softwood dimensional lumber sizes
Nominal Actual Nominal Actual Nominal Actual
in × in mm × mm in × in mm × mm in × in mm × mm
1 × 2 3⁄4 × 1 1⁄2 19 × 38 2 × 2 1 1⁄2 × 1 1⁄2 38 × 38 4 × 4 3 1⁄2 × 3 1⁄2 89 × 89
1 × 3 3⁄4 × 2 1⁄2 19 × 64 2 × 3 1 1⁄2 × 2 1⁄2 38 × 64 4 × 6 3 1⁄2 × 5 1⁄2 89 × 140
1 × 4 3⁄4 × 3 1⁄2 19 × 89 2 × 4 1 1⁄2 × 3 1⁄2 38 × 89 4 × 8 3 1⁄2 × 7 1⁄4 89 × 184
1 × 6 3⁄4 × 5 1⁄2 19 × 140 2 × 6 1 1⁄2 × 5 1⁄2 38 × 140 6 × 6 5 1⁄2 × 5 1⁄2 140 × 140
1 × 8 3⁄4 × 7 1⁄4 19 × 184 2 × 8 1 1⁄2 × 7 1⁄4 38 × 184 8 × 8 7 1⁄4 × 7 1⁄4 184 × 184
1 × 10 3⁄4 × 9 1⁄4 19 × 235 2 × 10 1 1⁄2 × 9 1⁄4 38 × 235
1 × 12 3⁄4 × 11 1⁄4 19 × 286 2 × 12 1 1⁄2 × 11 1⁄4 38 × 286

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 US 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.[10]

Dimensional lumber is available in green, unfinished state, and for that kind of lumber, the nominal dimensions are the actual dimensions.

Grades and standards

The longest board in the world (2002) is in Poland and measures 36.83 metres (about 120 ft 10 in).Long

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 U.S. Secretary of Commerce.[11]

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[12] 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)[13] is responsible for writing, interpreting and maintaining Canadian lumber grading rules and standards. The Canadian Lumber Standards Accreditation Board (CLSAB)[14] 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[15][16]

Machine stress-rated and machine-evaluated lumber is 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.[17]

In Europe, strength grading of sawn softwood is done according to EN-14081-1/2/3/4 and sorted into nine classes; in increasing strength these are: C14, C16, C18, С22, С24, С27, С30, С35 and С40[18]

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.[19]

North American hardwoods

In North America, sizes for dimensional lumber made from hardwoods varies from the sizes for softwoods. Boards are usually supplied in random widths of a specified thickness and specified length and sold by the board-foot (144 cubic inches or 2,360 cubic centimetres). 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 boards of identical lengths.

North American hardwood dimensional lumber sizes
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. The "quarter" system of reference is a traditional lumber industry nomenclature used specifically to indicate the thickness of rough sawn hardwood lumber. It immediately clarifies that the lumber is not yet milled, avoiding confusion with milled lumber which is measured as actual thickness after machining. Examples- 3/4", 19mm, 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.

Engineered lumber

Main article: Engineered lumber

Engineered lumber is lumber created by a manufacturer and designed for a certain structural purpose. The main categories of engineered lumber are:[20]

Various pieces and cuts

For more details on this topic, see Woodworking.

Timber piles

In the United States, pilings are mainly cut from southern yellow pines and Douglas firs. 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.

Defects in lumber

Defects occurring in lumber are grouped into the following four divisions:

Conversion

During the process of converting timber to commercial form the following defects may occur:

Defects due to fungi

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:

Natural forces

Main article: wood warping

There are two main natural forces responsible for causing defects in timber: 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.[21] 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.[21]

Seasoning

The seasoning of lumber is typically either kiln- or air-dried. Defects due to seasoning are the main cause of splinters and slivers.

Durability and service life

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 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:

Moisture control

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 controlling 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. 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 preservatives. Cladding, shingles, sill plates and exposed timbers or glulam beams are examples of potential applications for treated wood.

Controlling termites and other insects

For buildings in termite zones, basic protection practices addressed in current building codes include (but are not limited to) the following:

• 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 12 to 18 inches (300 to 460 mm) 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 6 inches (150 mm) 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

Preservatives

Main article: Wood preservation
Special fasteners are used with treated lumber because of the corrosive chemicals used in its preservation process

To avoid decay and termite infestation, untreated wood is separated 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.[22]

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.[23] 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.[24] 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.[25]

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 US Environmental Protection Agency and Health Canada's Pest Management and Regulatory Agency, respectively.[26]

Ancient Construction Works

Timber was used as a dominant building material in most of the ancient temples of Kerala and coastal Karnataka of India.[27]

Timber framing

Main article: 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. Modern timber framing has been growing in popularity in the United States since the 1970s.[28]

Environmental effects of lumber

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.[29] Studies show manufacturing wood uses less energy and results in less air and water pollution than steel and concrete.[30] However, demand for lumber is blamed for deforestation.[31]

Residual wood

The conversion from coal to biomass power is a growing trend in the United States.[32]

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 US 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.[33]

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.

See also

References

  1. ↑ http://www.merriam-webster.com/dictionary/lumber
  2. ↑ Oxford English Dictionary Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009.
  3. ↑ "Southern Pine Cost Estimates". patscolor.com.
  4. ↑ http://www.diffen.com/difference/Hardwood_vs_Softwood
  5. ↑ "Conceptual Reference Database for Building Envelope Research". Retrieved 2008-03-28.
  6. ↑ "Recycling and Deregulation: Opportunities for Market Development" Resource Recycling, September 1996
  7. ↑ "ASTM D6108 - 09 Standard Test Method for Compressive Properties of Plastic Lumber and Shapes" ASTM Committee D20.20 on Plastic Lumber
  8. ↑ "SAFPLANK Interlocking Decking System" Strongwell.com
  9. ↑ Naturally:wood
  10. ↑ Smith, L.W. and L.W. Wood. 1964. History of yard lumber size standards. USDA Forest Service, Forest Product Laboratory.
  11. ↑ American Lumber Standard Committee: History.
  12. ↑ WoodWorks
  13. ↑ National Lumber Grades Authority (Canada)
  14. ↑ Canadian Lumber Standards Accreditation Board
  15. ↑ Nebraska Energy Office. Factsheet: Minimizing the use of lumber products in residential construction.
  16. ↑ University of Washington, School of Forest Resources. Material substitution in the US residential construction industry.
  17. ↑ Naturally:wood
  18. ↑ http://www.plankrus.com/en338.html
  19. ↑ http://www.fordaq.com/fordaq/html/quality_africa_sata_En.htm
  20. ↑ "Austin Energy page describing engineered structural lumber". Retrieved 2006-09-10.
  21. 1 2 U. S. Department of Agriculture. "Shake", The Encyclopedia of Wood. New York: Skyhorse Pub., 2007. Print.
  22. ↑ WoodWorks Durability and Service Life
  23. ↑ "Wood That Fights." Popular Sciences, March 1944, p.59.
  24. ↑ "Lumber is Made Fireproof by Salt Treatment" Popular Mechanics, April 1936 bottom-left pg 560
  25. ↑ Canadian Wood Council About treated wood
  26. ↑ Canadian Wood Council About Treated Wood
  27. ↑ ALAYAM : The Hindu Temple;An Epitome of Hindu Culture; G.Venkataramana Reddy; Published by Adhyaksha; Sri Ramakrishna Math; ISBN 978-81-7823-542-4 ; Page 32
  28. ↑ Roy, Robert L.. Timber framing for the rest of us. Gabriola Island, BC: New Society Publishers, 2004. 6. Print. ISBN 0865715084
  29. ↑ Canadian Wood Council
  30. ↑ Lippke, B., E. Oneil, R. Harrison, K. Skog, L. Gustavsson, and R. Sathre. 2011. Life cycle impacts of forest management and wood utilization on carbon mitigation: knowns and unknowns. Carbon Management 2(3): 303-333.
  31. ↑ Peter Dauvergne and Jane Lister, Timber (Polity Press, 2011).
  32. ↑ EERE News: EERE Network News
  33. ↑ US Department of Agriculture, US 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

Further reading

External links

Look up lumber or timber in Wiktionary, the free dictionary.
Wikimedia Commons has media related to Timber.
This article is issued from Wikipedia - version of the Saturday, April 23, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.