Glossary of Terms


"    inches

1"    25.4 millimetres (mm)

1m    3.281 feet

1m3    35.315 cubic feet (cu.ft)

1m3    424 board feet (BF)

1MBF    2.36 cubic metres (m3)

AHEP    American Hardwood Environmental Profile. Consignment-specific shipping document providing information to demonstrate the legality and sustainability of the U.S. hardwood species contained in that shipment including quantitative data on the environmental impacts associated with delivering it anywhere in the world.

BF    Board feet

BM    Board measure

Carbon footprint    A summary of all the greenhouse gases emitted during the making process of an object and is expressed in kilograms of carbon dioxide equivalent (kg CO2 eq).

Carbon sequestration    During growth trees absorb CO2 from the atmosphere. Once trees are harvested and processed to produce sawn lumber (or any other wood product) they continue to store this CO2. This act of storing CO2 is referred to as sequestration.

Checks    Longitudinal separation of the fibres in wood that do not go through the whole cross section. Checks result from tension stresses during the drying process.

Compressive strength    The ability to resist a force tending to shorten a structural member by crushing the fibres longitudinally.

CLT    Cross laminated timber

Decay    The decomposition of wood substance by fungi (other terms: rot, dote).

Density    Weight per unit volume. Density of wood is influenced by rate of growth, percentage of late wood and in individual pieces, the proportion of the heartwood.

Dimensional stability    A term that describes whether a section of wood will resist changes in volume with variation in moisture content (other term: movement in performance).

Durability    The resistance of wood to attack by decay fungi, insects and marine borers.

FAS    The highest quality NHLA lumber grade.

FAS    Foreign Agricultural Service 

FIA    Forest Inventory and Analysis programme. The FIA tracks the growth of individual American hardwood species each year, by county, across hardwood producing states in America.

Figure    The pattern produced in a wood surface by annual growth rings, rays, knots, deviations from regular grain, such as interlocked and wavy, and irregular colouration.

Flitch    A log or part of a log trimmed and prepared for conversion into veneers, or part of a converted log suitable for further conversion.

Glulam    Glue laminated timber

Grain    The direction, size, arrangement, appearance, or quality of the fibres in sawn wood. Straight grain is used to describe lumber where the fibres and other longitudinal elements run parallel to the axis of the piece.

Gum pocket    An excessive local accumulation of resin or gum in the wood.

Hardness    The resistance of wood against indentation and abrasion. Values are given in Newtons (N) and are a measure of the load required to embed an 11.3mm ball to one half its diameter in the wood.

Hardwood    A description applied to woods from deciduous and evergreen broad-leaved trees (Angiosperms). The term has no reference to the actual hardness of the wood.

Heartwood    The inner layers of wood in growing trees that have ceased to contain living cells. Heartwood is generally darker than sapwood, but the two are not always clearly differentiated.

Kilning    The process of drying lumber artificially under scientifically controlled conditions. Kilns are the chambers used for this process.

LCA    Life cycle assessment, usually environmental. A science based measurement system involving the collection of data on all the inputs and outputs of material, energy and waste associated with a product over its entire life cycle to calculate the environmental impact.

Lumber    The American term for converted wood or sawn timber. Lumber mills and sawmills are terms used to describe the processing units that carry out this conversion.

m    metres

m2    square metres

m3    cubic metres

Material replenishment    A figure which represents the amount of time it takes for natural regrowth across the entire American hardwood forests, to replace the volume of harvested timber used in certain creative projects.

MBF    Thousand board feet

mm    millimetres

Modulus of elasticity    An imaginary stress necessary to stretch a piece of material to twice its length, compress it to half its length. Values for the individual species are given in megapascals (MPa – equivalent to N/mm2).

Modulus of rupture    The equivalent fibre stress at maximum load. A constant used in structural design and obtained by loading pieces of wood to destruction.

Moisture content (MC)    The weight of water contained in wood expressed as a percentage of the weight of the oven dry wood.

N    Newtons

NHLA    National Hardwood Lumber Association

PAR    Planed (surfaced) all round (same as S4S)

Pith flecks    Pith-like irregular discoloured streaks of tissue in wood, due to insect attack on the growing tree.

Quarter/rift sawn    Lumber that is cut from the log on or near to the radial axis to produce edge, straight or vertical grain patterns.

RWL    Random widths and lengths

S2S    Surfaced 2 sides

S4S    Surfaced (planed) four sides (same as PAR)

Sapwood    The outer zone of wood in a tree, next to the bark. Sapwood is generally lighter in colour than heartwood but lacks resistance to decay.

Shrinkage    The contraction of wood fibres caused by drying below the fibre saturation point (usually around 25-27% MC). Valves are expressed as a percentage of the dimension of the wood when green.

SM    Surface measure

Specific gravity    The relative weight of a substance compared with that of an equal volume of water. S.G. values given are based on wood volume at 12% MC and oven dry weight.

Split    Separation of the fibres in a piece of wood from face to face (other term: end-split).

Stain    A variation from the natural colour of the wood or a discoloration that may be caused by micro-organisms, metal or chemicals. The term also applies to materials used to impart colour to the wood.

Surfaced    The American term that is used to describe lumber that has been planed.

Tally    The American term for lumber measure. (Green tally refers to measurement before kilning and net tally to measurement after kilning.)

Tensile strength    The ability to resist a force acting on a member and tending to lengthen the member or pull the fibres apart lengthwise.

Texture    Determined by relative size and distribution of the wood elements. Described as coarse (large elements), fine (small elements) or even (uniform size of elements).

Warp    Distortion in lumber causing departure from its original plane, usually developed during drying. Warp includes cup, bow, crook and twist.

Weight    The weight of dry wood depends upon the cellular space, i.e. the proportion of wood substance to air space. Values are given for each species in kg/m3 at 12% MC.