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Timber Terminology Jargon Buster

We know that timber terminology can sometimes be testing and leave customers scratching heads, that's why here at Fulham Timber we've created the Timber Terminology Jargon Buster. Simply click the term that you'd like the definition of and there it is!

One joinery grade less than unsorted grade.

Usually in relation to Oak – left to air dry naturally – leaves moisture.

A sharp external angle of a piece of wood where two surfaces meet. An 'arris rail' is a timber product sawn into a equal right angle. When laid on one of the edges, it would create a 45 degree angle.

Square timbers cut from corner to corner to produce 2 equal pieces.

C16 graded timber allows for a number of timber defects that may reduce the overall strength of the wood, such as grain deviations and wanes, as well as superficial defects that do not affect the strength of the wood such as blue sap stains. C16 is the most commonly used timber in the UK and is strong enough to be used in most applications. It is also the most cost effective timber option.

C24 boards have fewer defects than C16 graded timber and the timber is therefore stronger and more resilient. C24 boards also tend to have a more uniformed and neat appearance as there are fewer physical imperfections.

Clear Double Vacuum low pressure treatment – primarily for internal joinery.

“Canadian Lumber Standard” – Clean C16 Graded softwood for studwork.

A mix of colour caused by fungi, chemical reaction or other causes. Timber products, being a natural product often have colour variations.

Profiled or Smooth timbers for decking.

Grade for Hardwood – “Firsts & Seconds Grade” generally the best grade.

Boards cut from corner to corner to produce 2 equal pieces.

The size of a piece of timber after machining, subject to machining tolerances. For example 20x95mm finished size softwood timber would measure to these exact sizes (within a small allowable tolerance) when putting a tape measure to the timber. Do not confuse finished sizes with the other industry term 'nominal sizes'.

A way of sorting pieces of timber into broadly similar groups, according to quality or mechanical performance, it is usually divided into structural and appearance grading. The most common gradings used in the industry are C16 and C24 which are detailed above.

Green high pressure treated – London joists are imported to this country pre-treated there are also three sub divisions for specialist treatment – for the fencing market.

Wood grain is the longitudinal arrangement of wood fibers or the pattern resulting from this.

Each piece of hardwood timber is unique – sending out hand samples to be subsequently replicated is sometimes a dangerous thing to do as each piece will vary in grain and colour.

A portion of a branch that become embedded in the wood as the tree grew around it.

Millimetres – timber trade standard for thickness & width e.g. 25x50mm.

This is the size before the timber has been planed. The finished size tends to be 4-5mm less. The term nominal would indicate that the 'finished size' would be different to the nominal size.

Size the timber starts at before Regularizing or planing.

Foftwood is supplied kiln dried for joinery and house building – House joists are kiln dried in order to kill any beetle activity in general carcassing grade softwood. Hardwoods for joinery are nearly all kiln dried.

Sawn SE (square edge) Green PT (pressure treated) Softwood.

Pinus sylvestris – European Redwood, sometimes called Deal – the industry standard for stock mouldings and PSE.

Planed All Round (also known as PAR to the trade) is also referred to as Planed Square Edge (known as PSE). This term usually refers to softwood or hardwood timber products that have been processed through a planer to create a very smooth surface, when the timber is planed on all four faces this then is called PAR or PSE.

Planed smooth Square Edge – sometimes called wrot softwood.

Slightly better than FAS Grade – Usually in European Hardwoods.

Rounded 4 edges.

Planed & rounded 4 edges.

A mixture of unsorted grade and some lesser grade joinery grades.


Rough sawn from the exporters sawmills with a square edge.

The wood from a conifer (such as pine, fir, or spruce) as distinguished from that of broad-leaved trees.

American softwood for wide joinery applications.

Where timber is produced to a square edged finish and the edges meet square, creating a right angle.

Long wedge shaped pieces of timber – taken out of treated timbers.

Slatted timber battens for roofing.

Lower grade timber usually for shuttering applications or Sleepers.

Best grade shipped in joinery softwood – timber is graded out from poorest grades first leaving only the best quality e.g. unsorted.

Sawn timber having parallel faces and with one or both edges left unsawn so that the bark or irregular surface is retained. Also called un-edged.

Abies Alba – Spruce – shipped to this country in sawfalling grade – generally of budget quality.