Janka hardness
A measured resistance to denting: the force needed to embed an 11.28 mm steel ball to half its diameter, giving a contact area of exactly one square centimetre. Reported in lbf or Newtons.
Why it matters Predicts denting under impact and point loads, not scratch or abrasion resistance — the finish handles those. A hard floor still scratches.
EMC — equilibrium moisture content
The moisture content wood settles at and stays at, for a given temperature and relative humidity.
Why it matters Sets the target for drying and the size of seasonal movement. It says where timber ends up, not how long it takes to get there.
Fibre saturation point
The moisture content, near 28–30% for almost every species, at which the cell cavities are empty of free water but the cell walls are still saturated.
Why it matters The threshold where dimensional change begins. Above it timber dries without moving; below it every point of moisture content changes the size.
MOR — modulus of rupture
Bending strength: the stress at which a beam fails in bending, in MPa.
Why it matters Governs whether a member breaks. Most softwoods sit at 60–100 MPa, temperate hardwoods higher.
MOE — modulus of elasticity
Stiffness: how much a member deflects under load before it fails, in GPa.
Why it matters Usually decides timber sizing rather than strength, because floors and shelves are judged on how much they move, not whether they break.
Specific gravity / basic density
Oven-dry mass divided by green volume, expressed relative to water. Distinct from density at 12% moisture content, which is a higher number.
Why it matters The basis most published property data uses. Mixing the two bases over-reports weight by roughly a tenth.
Tangential and radial shrinkage
Movement measured across the growth rings (tangential) and along the rays toward the centre (radial), as a percentage from green to oven-dry.
Why it matters Tangential is roughly double radial in most species. That imbalance, not the absolute figure, is what cups a flatsawn board.
T/R ratio
Tangential shrinkage divided by radial shrinkage.
Why it matters Predicts cupping better than either figure alone. Below about 1.6 a board stays flat; above 2.0 it will cup if only one face is sealed.
Quartersawn, flatsawn and riftsawn
How a board is cut relative to the growth rings: quartersawn with rings near perpendicular to the face, flatsawn near parallel, riftsawn between.
Why it matters Decides which shrinkage rate applies across the width. Flatsawn moves at the tangential rate, quartersawn at the lower radial rate.
Heartwood and sapwood
Heartwood is the dead inner wood, often darker and containing extractives. Sapwood is the living outer wood that carried sap.
Why it matters Durability classes describe heartwood only. Sapwood of every species is non-durable, whatever the datasheet says.
EN 350 durability class
A five-class scale for heartwood resistance to fungal decay in ground contact. Class 1 very durable, Class 5 not durable.
Why it matters Decides whether a species belongs outdoors untreated. It says nothing about weathering, UV or insect attack.
Thermo-D and Thermo-S
Two ThermoWood treatment classes. Thermo-D targets durability, Thermo-S targets dimensional stability.
Why it matters Different products, not grades of one. Treatment class matters more than the base species for how the board behaves.
Mass loss
The percentage of mass lost during thermal modification.
Why it matters The accepted proxy for treatment intensity: it indicates both the durability gained and the bending strength given up.
Kerf
The width of material removed by a saw blade in a single cut.
Why it matters A 3.2 mm blade through 100 cuts removes over 300 mm of stock. It is also why a sheet never divides evenly into whole part sizes.
Hoppus measure
A round-log trade measure using quarter girth squared, dating from 1736. It deliberately deducts about 21% of true round volume.
Why it matters Approximates the squared timber a mill can recover. Buying on Hoppus and costing on true cubic metres silently moves your margin.
Board foot and CFT
A board foot is 144 cubic inches of timber. CFT is a cubic foot, the customary unit in Indian timber trade.
Why it matters One cubic metre is 35.31 CFT but 423.8 board feet. A board foot is a volume, not an area, which is why the two look unrelated.
Surface measure
Board length in feet multiplied by width in inches, divided by twelve, then rounded — the NHLA basis for grading area.
Why it matters Grade thresholds are expressed in twelfths of surface measure, so this number decides which grade a board can reach.
Clear cutting
A defect-free area of a board, measured to NHLA minimum sizes.
Why it matters NHLA grades measure clear cuttings, not appearance. A board can look poor and still grade FAS if the clear areas fall in the right sizes.
Withdrawal capacity
The axial force needed to pull a fastener out of the timber, in Newtons.
Why it matters Scales with penetration depth and density. End-grain capacity is far lower than face grain, which is why end-grain fixing is treated as temporary.
Deflection
How far a loaded member sags, usually limited as a fraction of span such as L/300 or L/360.
Why it matters Timber design is normally governed by deflection rather than strength. A joist that passes on stress can still bounce enough to be reported as a defect.
Buckling
Sideways failure of a slender compression member before the material itself crushes.
Why it matters Capacity falls roughly with the square of unrestrained length, so a mid-height restraint often beats a bigger section.
Chip load
The thickness of material removed by each cutting edge per revolution.
Why it matters The number that transfers between machines. Too low a chip load makes the cutter rub and burn instead of cut, and burnt hardwood does not sand out.
Open time
How long an adhesive stays workable after spreading, before it skins.
Why it matters Falls sharply as temperature rises. A PVA rated at 10 minutes in a cool shop can skin in four on a hot afternoon, and a skinned glue line will not bond.
Volumetric weight
A weight derived from a shipment’s dimensions using a carrier divisor, such as 1:6000 for air freight.
Why it matters Carriers charge on whichever is greater, actual or volumetric. Bulky kiln-dried timber is often billed on the volumetric figure.
Case hardening
Drying stress left in a board when the surface dries and sets before the core.
Why it matters Shows up after the board is resawn or machined, when the released stress makes it cup or pinch the blade. Caused by drying too fast at high moisture content.
A definition here is not a substitute for the standard it comes from. Where a term is defined by EN 350, EN 338 or the NHLA rules, the standard governs.
