Glossary of Timber Terms

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.

Bark: The outermost, protective layer, of a tree composed of dead cork and other elements.

Board: A piece of sawn, hewn or dressed timber of greater width than thickness. The manufactured product supplied as a rigid sheet.

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.

 

Cubic Metres: Is a measure of volume calculated by multiplying the thickness by the width by the linear length of timber. All dimension in metres.

 

Cup: Where the timber bends, most common on back-sawn boards and where a concave curvature across the grain occurs.

 

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.

 

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

 

Face: The wide surface of a square-sawn, hewn or dressed timber, veneer, 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.

 

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.

 

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

 

Girth: The distance around a tree; the circumference.

 

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.

 

Hardwood: Technically, hardwoods are woods from trees classed as ‘flowering’ plants as opposed to conifers. The timber of conifers is known as softwood. Some ‘hardwoods’ such as balsa are soft; some ‘softwoods’ such as yew are very hard.

 

Heartwood: The mature part of timber in a tree the inner zone of dead wood. It provides the structural support for the plant. Its cells contain tannins, phenols and other substances, many of which inhibit fungal activity and render heartwood more durable than sapwood.

 

Interlocking grain: In timber, where a double spiral effect is caused by the alternate bands of growth having their fibres oriented in opposite directions.

 

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.

 

Linear Metres: Is a measure of length that ignores the thickness and width of a piece of timber.

 

Lumber: Logs which have been sawn, planed, and cut to length.

 

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.

 

Milled timber: Timber produced from a log which has been sawn.

 

Moisture content: A measure of the available water in a piece of timber. Wood normally increases in strength with drying.

 

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.

 

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.

 

Resin: A sticky exudates produced in specialised microscopic structures called resin ducts in conifer timber, 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.

 

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 rafters.

 

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: A wood, regardless of weight and hardness, which comes form a coniferous tree.

 

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.

 

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.

Trade name: Commercial trading name for a specific timber. It may or may not differ from the common name used by foresters and the lay public.