Glossary of timber terms

A

Air-dried

Dried in a natural atmosphere.

Air-dry

Having a moisture content in equilibrium with the local atmosphere. The equilibrium moisture content varies with seasons and climates.

B

Board

A piece of sawn, hewn or dressed timber of greater width than thickness.

C

Checks or splits

Separations which extend along the grain, the result of moisture loss and shrinking during drying.

Clear timber

Timber free of any imperfections.

Conifer

A tree belonging to the order Coniferales of the botanical group Gymnospermae, typically bearing cones and carrying needle-shape or scale-like leaves. Conifers are usually evergreen and produce timber known commercially as softwood.

Conventional milling

Where the log or flitch is passed over the sawbench.

Cubic metres

A measure of volume, calculated by multiplying the thickness by the width by the length of the timber, with all dimensions in metres.

Cup

A concave curvature across the width of a board, most common in back-sawn boards.

D

DAR

Dressed all round: timber that has been dressed on all four surfaces.

Decay

Decomposition of wood by fungi.

Density

One of the measures for the structural and mechanical properties of timber expressed as weight per unit volume, e.g. in kilograms per cubic metre.

Dressed timber

Timber finished to a smooth surface on one or more surfaces.

Drying

Where moisture is evaporated or extracted from timber. Rate of drying has a major effect on the quality and quantity of the timber recovered.

Durability

A standard classification for species as to the length of time the timber will last in the ground or be exposed to the weather before decay takes place and the timber loses its structural strength.

E

E/M

End matched: boards with a tongue and groove on the ends as well as the edges.

End split

A split at the end of a piece of timber or a log.

F

F grades

A stress grade of timber for which a specific set of design properties is given in Australian Standard AS 1720.1.

Face

The wide surface of a square-sawn, hewn or dressed piece of timber, veneer or plywood, on which the grade or quality is judged.

Figure

The appearance of a wood surface due to its anatomical features, such as grain or texture, or variation in colour.

Finished Size

The actual dimension of a piece of timber after it has been dressed.

FJ

Finger Jointed timber comprises lengths of timber joined end to end utilising a micro-sized finger (joint) employing an adhesive whose strength and potential overall length is increased through the gluebonds.

Flitch

A section of timber which has been sawn from a log.

Flooring

Boards prepared for use in flooring by machining to a standard thickness and usually profiling a tongue along one edge and a matching groove along the other edge.

Framing timber

Timber used to form the basic structure of a building.

G

Gauged

Timber with a smooth, even surface that has been dressed to a precise size.

Grain

The general direction of the fibres or wood elements relative to the main axis of the piece. Grain may be cross, diagonal, interlocking, spiral or straight.

Green timber

Colloquial term for timber which is newly cut and still has a high moisture content. Technically known as unseasoned timber.

Growth ring

A ring sometimes visible on the cross-section of a trunk or branch marking a (usually annual) cycle of growth. It is visible because of the conspicuous difference between its latewood portion and its earlywood portion.

Gum veins or pockets

Gum production is a natural protection response to injury especially in hardwoods and eucalyptus. The presence of pockets of gum can reduce the strength of timber.

H

Hardwood

Technically, hardwoods are woods from trees classed as flowering plants, as opposed to conifers, whose timber is known as softwood. The names don't always describe hardness: some hardwoods, such as balsa, are soft, and some softwoods, such as yew, are hard.

Heartwood

The mature inner zone of dead wood in a tree, which provides its structural support. Its cells contain tannins, phenols and other substances, many of which inhibit fungal activity and make heartwood more durable than sapwood.

I

Interlocking grain

Grain in which successive bands of fibres spiral in opposite directions, producing a striped or ribbon figure when the timber is quarter-sawn.

J

Joint group

A classification of timber species by their strength in fastened joints, used in the timber engineering standard (AS 1720.1) and the residential timber-framed construction standard (AS 1684). There are six groups, from J1 (strongest) to J6.

K

Kerf

A saw cut.

Kiln

A chamber used for drying timber, in which the temperature and humidity of the circulating air can be suitably controlled.

Kiln dried

Of timber, seasoned in a kiln usually to a specified or selected moisture content.

Knot

A section of a branch which is embedded in the wood of a tree trunk or of a large branch. It may be 'live' or 'dead'; in the latter case, it may be loose.

L

Linear metres

A measure of length that ignores the thickness and width of a piece of timber.

Lyctids

'Powderpost' beetles. The larvae of these borer beetles which attack the starch-containing sapwood of certain hardwood species, reducing it to a fine flour-like powder. They do not attack the heartwood and they cannot attack softwood timber at all. The commonest species in eastern Australia is Lyctus brunneus.

M

MGP

Machine Graded Pine: pine stress-graded by machine. Common grades are MGP10, MGP12 and MGP15.

Milled timber

Timber produced from a log which has been sawn.

Moisture content

The amount of water in a piece of timber, expressed as a percentage of its oven-dry weight. Wood generally increases in strength as it dries.

N

Nominal Size

The sawn size of a piece of timber before the timber is dressed. The nominal size is greater than the actual or finished dimension.

Q

Quarter-sawing

Where the log is turned to produce boards at a right angle to the grain. Used to produce boards of high-strength quality or where the figure is to be exposed.

R

Resin

A sticky substance produced in resin ducts, mainly in conifers, although also in some hardwood families such as the Dipterocarpaceae.

Rough sawn

Surface condition of wood as it leaves the saw.

Rougher headed

Timber that is dressed down with a fine rippled finish.

S

Sapwood

The living, immature outer wood of a tree. As its inner layers die they become heartwood.

Sawn

Timber that has not been gauged or dressed.

Scantling

Timber of small rectangular or square cross-section used in construction, such as framing.

Seasoned timber

Timber dried to a stable moisture content of 10 to 15%.

Shrinkage

The dimensional difference between green timber and timber dried to a moisture content of 12%, normally given as a percentage of shrinkage of the radial and tangential faces of a piece of timber.

Softwood

Wood from a coniferous tree, regardless of its weight or hardness.

Species

The basic unit of biological classification. With rare exceptions, a species may be defined as an interbreeding group of biological organisms, that is isolated reproductively from all other organisms.

Strength groups

A grouping of timbers by strength for engineering design. Unseasoned timber is graded S1 (strongest) to S7, and seasoned timber SD1 to SD8.

Stress grade

A grade given to timber for structural use, assessed visually or by machine. It indicates the basic working stress in bending and, by implication, the other design properties used in engineering.

Strip

A small piece of sawn or dressed timber of rectangular or square cross-section.

Structural timber

Timber selected for applications where strength is essential, such as building framing.

T

T&G

Tongue & Grooved flooring where boards are joined along the length, one with a tongue and the other with a groove.

Termites

Insects belonging to the order Isoptera; they are very active destroyers of woody material in the tropical and subtropical zones of the world.

Timber

Milled wood in a form suitable for construction or carpentry or joinery or for reconversion for manufacturing purposes.

Top nail & secret nail

Some species and board widths of T&G flooring are offered in a choice of top nail or secret nail profiles. As the name describes, top nail boards are installed with nails through the top surface, while secret nail profiles are installed with nails through the tongue, and are thus hidden by the adjoining board.

Trade name

The commercial trading name for a timber. It may or may not differ from the species' standard common name.

Truewood

Another term for heartwood.