Lumber

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Image:Timber DonnellyMills2005 SeanMcClean.jpg
Timber in storage for later processing at a sawmill

Lumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production.

Image:Logs at woodmill.jpg
Mountain ash logs at a sawmill in Australia
Image:Wood from victoria mountain ash.jpg
Wood cut from Victorian Mountain Ash

Lumber is supplied either rough or finished. 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. Finished lumber is supplied in standard sizes, mostly for the construction industry, primarily softwood from coniferous species including pine, cedar, hemlock, fir and spruce, but also some hardwood for high-grade flooring.

Contents

[edit] Dimensional lumber

Dimensional lumber is a term used in North America for lumber that is finished/planed and cut to standardized width and depth specified in inches.

[edit] Softwoods

Softwood Dimensional Lumber Sizes
Nominal Actual Nominal Actual
1 × 2 ¾″ × 1½″ (19×38 mm) 2 × 2 1½″ × 1½″ (38×38 mm)
1 × 3 ¾″ × 2½″ (19×64 mm) 2 × 3 1½″ × 2½″ (38×64 mm)
1 × 4 ¾″ × 3½″ (19×89 mm) 2 × 4 1½″ × 3½″ (38×89 mm)
1 × 6 ¾″ × 5½″ (19×140 mm) 2 × 6 1½″ × 5½″ (38×140 mm)
1 × 8 ¾″ × 7¼″ (19×184 mm) 2 × 8 1½″ × 7¼″ (38×184 mm)
1 × 10 ¾″ × 9¼″ (19×235 mm) 2 × 10 1½″ × 9¼″ (38×235 mm)
1 × 12 ¾″ × 115/8″ (19×286 mm) 2 × 12 1½″ × 11¼″ (38×286 mm)
3 × 4 2½″ × 3½″ (64×89 mm) 2 × 14 1½″ × 13¼″ (38×337 mm)
4 × 4 3½″ × 3½″ (89×89 mm) 6 × 6 5½″ × 5½″ (140×140 mm)
4 × 6 3½″ × 5½″ (89×140 mm) 8 × 8 7¼″ × 7¼″ (184×184 mm)

Examples of common sizes are 2×4 (also two-by-four and other variants such as four-b'-two in Australia), 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 the standard lengths of lumber are 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24 feet.

Solid dimensional lumber typically is only available up to lengths of 24′, yet since builders have a need for lengths beyond that for roof construction (rafters), builders use "finger-jointed" lumber that can be up to 36′ long in 2×6 size (see Engineered Lumber below). Finger-jointed lumber is also widely used for smaller lengths like studs, the vertical members of a framed wall. Pre-cut studs save a framer a lot of time as they are pre-cut by the manufacturer to be used in 8′, 9′ & 10′ ceiling applications, which means they have removed a few inches of the piece to allow for the sill plate and the double top plate with no additional sizing necessary by the framer.

In the Americas, two-bys (2×4s, 2×6s, 2×8s, 2×10s, and 2×12s) are common lumber sizes used in modern construction. They are the basic building block 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.

The nominal size of a board varies from the actual size of the board. This is due to planing and shrinkage as the board is dried. This results in the final lumber being slightly smaller than the nominal size. Also, if the wood is surfaced when it is green, the initial dimensions are slightly larger (e.g. 1/16″ bigger for up to 4″ nominal lumber, ⅛″ for 5″ and 6″ nominal lumber, ¼″ bigger for larger sizes). As the wood dries, it shrinks and reaches the specified actual dimensions.

The timber industry states that finishing and drying the lumber results in the nominal size differing from the actual size, however, you will find that many houses built more than roughly 50 years ago usually have timber where the actual size and nominal size are the same. This has allowed new construction to become less expensive without having to modify municipal, state, and national building codes.[citation needed]

[edit] Non-North American sizes

Examples of Dimensional Lumber Sizes (Softwood and Hardwood)
Inch name Sawed Swedish Australian
2 × 4 50 × 100 mm 45 × 95 mm 45 × 90 mm
1 × 3 25 × 75 mm 22 × 70 mm 19 × 70 mm
3 × 3 75 × 75 mm 70 × 70 mm
2 × 7 50 × 175 mm 45 × 170 mm Not used
2 × 3 50 × 75 mm 45 × 70 mm 45 × 70 mm
1 × 4 25 × 100 mm 22 × 95 mm 19 × 90 mm
1 × 5 25 × 125 mm 22 × 120 mm 19 × 120 mm
2 × 5 50 × 125 mm 45 × 120 mm 45 × 120 mm

Outside North America sizes of timber vary slightly. Sizes are, in some cases, based on the imperial measurement and referred to as such; in other cases the sizes are too far removed from the imperial size to be referred to by imperial measurement. Lengths are sold every 300 mm (a metric approximation of 1′). Common sizes are similar to the North American equivalent; 2.4, 2.7, 3.0, 3.6, 4.2, 4.8, 5.4, 6.0.

[edit] Hardwoods

Hardwood Dimensional Lumber Sizes
Nominal Surfaced 1 Side (S1S) Surfaced 2 sides (S2S)
½″ ⅜″ 5/16″
⅝″ ½″ 7/16″
¾″ ⅝″ 9/16″
1″ or 4/4 ⅞″ 13/16″
1¼″ or 5/4 1⅛″ 1-1/16″
1½″ or 6/4 1⅜″ 1-5/16″
2″ or 8/4 1-13/16″ 1¾″
3″ or 12/4 2-13/16″ 2¾″
4″ or 16/4 3-13/16″ 3¾″

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, 1/12th of a cubic foot). 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 of consisting of the same length boards. 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 deteriorates the value of the timber for furniture.

Also in North America hardwood lumber is commonly sold in a “quarter” system when referring to thickness. 4/4 (four quarters) refers to a one-inch thick board, 8/4 (eight quarters) is a two-inch thick board, etc. This system is not usually used for softwood lumber, although softwood decking is sometimes sold as 5/4 (actually one inch thick).

[edit] Engineered lumber

Engineered lumber is lumber created by a manufacturer and designed for a certain structural purpose. The main categories of engineered lumber are:[1]

  1. Laminated Veneer Lumber – Generally called "LVL", they come in 1-3/4″ thicknesses with depths such as 9″, 11-7/8″, 13″, 16″, 18″, 24″, and are typically doubled or tripled up. They function as beams to provide support over large spans such as removed support walls and garage door openings, places where dimensional lumber isn't structurally sound to use, and also in areas where a heavy load is bearing from a floor, wall or roof above on a somewhat short span where dimensional lumber isn't practical. This type of lumber cannot be altered by holes or notches anywhere within the span or at the ends as it compromises the integrity of the beam, but nails can be driven into it wherever necessary to anchor the beam or to add hangers for I-joists or dimensional lumber joists which terminate at an LVL.
  2. Wood I-joists – Sometimes called "TJI" or "Trus Joists", which are both brands of wood I-joists, they are used for floor joists on upper floors and also in 1st floor conventional foundation construction on piers as opposed to slab floor construction. They are engineered for long spans and are doubled up in places where a wall will be placed over them, and sometimes tripled where heavy roof-loaded support walls are placed above them. They consist of a top and bottom chord/flange made from LVL with a webbing in-between made from OSB (oriented strand board). The webbing can be removed up to certain sizes/shapes according to the manufacturers (and engineers) specifications, but for small holes, wood I-joists come with "knockouts", which are perforated, pre-cut areas where holes can be made easily typically without engineering approval. When large holes are needed, they can typically be made in the webbing only (the top & bottom chords cannot be cut) and only in the center third of the span. Sizes & shapes of the hole, and typically the placing of a hole itself, must be approved by an engineer prior to the cutting of the hole and in many areas, a sheet showing the calculations made by the engineer must be provided to the building inspection authorities before the hole will be approved. Some I-joists are made with W-style webbing like a truss to eliminate cutting and allow ductwork to pass through.
    Image:Freshlycutlogs.JPG
    Freshly cut logs showing sap running from beneath bark
  3. Finger-Jointed Lumber – Solid dimensional lumber lengths typically max out at lengths of 22′ to 24′, but is made longer by the technique of "finger-jointing" lumber by using small solid pieces, usually 18″ to 24″ long, and joining them together using finger-joints and glue to produce lengths that can be up to 36′ long in 2×6 size. Finger-jointing also is predominant in pre-cut wall studs.
  4. Glu-lam Beams – Created by taking 2×4 or 2×6 stock and glueing the faces together to create beams such as 4×12 or 6×16. LVL beams have taken their place in most home construction.
  5. Manufactured Trusses – Trusses are used in home construction as bracing to support the roof rafters in the attic space. It is seen as an easier installation and a better solution for supporting roofs as opposed to the use of dimensional lumber's struts & purlins as bracing. In the southern USA and other parts, stick-framing with dimensional lumber roof support is still predominant. The main drawback of trusses is that less attic space is usable.
  6. Oriented Strand Board – OSB is made by adhering strands of wood in a certain direction and apply glue to make the piece strong for structural purposes. OSB has replaced plywood for use as exterior wall sheathing & roof decking (both in 7/16″ thickness minimum) and in 2nd story flooring in 3/4″ thickness in a tongue-and-groove interlocking pattern, which is nailed and glued to the I-joists. OSB used in wall sheathing & roof decking will swell up if exposed to the elements for even a brief period of time and must be replaced, therefore it is covered by a weatherproof membrane such as felt to protect it, secured with plastic cap nails. House wrapping is used on areas which will be sheathed with vinyl siding. 3/4″ T&G OSB flooring has a coating on it to protect it from the elements for a short period of time until the home is "dried-in" with a roof.

[edit] Defects in lumber

Defects occurring in timber are grouped into the following five divisions:

[edit] 1. Defects due to conversion

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

  1. Chip mark
  2. Diagonal grain
  3. Torn grain
  4. Wane

[edit] 2. Defects due to fungi

Fungi attack timber only when the following two conditions are satisfied simultaneously:

  1. The moisture content of the timber is above 20%
  2. There is presence of air and warmth for the growth of fungi.

If any of the above condition is absent, decay of wood due to fungi would not occur. Hence, dry wood due having moisture content less than 20 per cent will remain sound for centuries. Similarly, wood submerged in water will not be attacked by fungi because of absence of air. Following defects are caused in timber by fungi:

  1. Blue stain
  2. Brown rot
  3. Dry rot
  4. Heart rot
  5. Sap stain
  6. Wet rot
  7. White rot

[edit] 3. Defects due to insects

Following are the insects which are usually responsible for the decay of timber:

  1. Beetles
  2. Marine borers
  3. Termites

[edit] 4. Defects due to natural forces

The main natural forces responsible for causing defects in timber are two, namely, abnormal growth and rupture of tissues.

[edit] 5. Defects due to seasoning

[edit] Preservatives

Main article: timber treatment
Image:Treated timber.JPG
Fasteners used with treated lumber require special consideration because of the corrosive chemicals used in the treatment process.
Timber or lumber may be treated with a preservative that protects it from being destroyed by insects, fungus or exposure to moisture. Generally this is applied through combined vacuum and pressure treatment. The preservatives used to pressure-treat lumber are classified as pesticides; due to potential hazards to humans and the environment, some are being phased out. Treating lumber provides long-term resistance to organisms that cause deterioration. If it is applied correctly, it extends the productive life of lumber by five to ten times. If left untreated, wood that is exposed to moisture or soil for sustained periods of time will become weakened by various types of fungi, bacteria or insects.

[edit] 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. A modern imitation with sawn timbers is growing in popularity in the United States.

[edit] Terminology

In the U.K. and Australia, "timber" is a term also used for sawn wood products (that is, boards), whereas generally in the United States and Canada, the product of timber cut into boards is referred to as lumber. In the United States and Canada sawn wood products of five inches (127 millimeters) (nominal size) diameter or greater are sometimes called "timbers".

[edit] See also

[edit] References

  1. ^ Austin Energy page describing engineered structural lumber. Retrieved on 2006-09-10.
This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (September 2006)

[edit] External links

Look up lumber, timber in Wiktionary, the free dictionary.

de:Bauholz es:Madera fr:Bois (matériau de construction) it:Legname no:Tømmer nn:Tømmer pt:Madeira ru:Бревно fi:Puutavara sv:Timmer

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