Timber Dictionary

At Whippletree, we understand that not everybody understands all the terms that are used by the timber industry and so we have listed below a few definitions of phrases and words that we use in our specifications which we hope will help you, please let us know if you have any other suggestions for inclusion.


We are often asked how wood grows and the answer is not easy to give in a short concise sentence. But in an attempt to give you the basics, here we go…. At the centre of the tree is the Pith. In some types of trees, it is a different colour to the heartwood that surrounds it. Heartwood is dead cells which support the tree and give it its stability. Next you find the Sapwood which has the important role of carrying the water, minerals and sugars that the tree needs to live and grow, from the roots to the leaves. In some trees, this is lighter in colour than the heartwood. Surrounding the sapwood and close to the surface is the Cambium which is a thin layer of living cells which ‘manufacture’ the wood as they develop. The cambium is protected by a layer of Bark which is the part that we are used to seeing on a growing tree. The cambium grows fast at the beginning of each season giving Springwood that is light in colour and as the growth slows down it produces Summerwood which is darker in colour. The summerwood is denser and harder that the springwood. As the winter season approaches, the cambium goes into a dormant state until the springtime when the cycle commences again. It is this cycle that produces the Growth Rings that can be seen when cutting through a section of the tree.


Air Dried Construction Oak

Is Green Oak that has been stored to naturally dry often for a period of about 1 year per inch or 25mm thickness of the timber. Often this requires 3-6 year’s storage and drying to reach a stage where it is considered good for constructional purposes as the timber will be relatively stable by this stage. The faces of Air Dried Oak take on a ‘grey’ patina as it ages which gives a distinct aged appearance but when it is cut, it displays the cut face as a new face of a clean and more modern appearance. Often in renovations projects, Air Dried Oak is selected for its stability. Timbers can be cut on all four sides for squareness if required.



This is a log sawn to a square section and can be anything in size from 25x25mm to 450x450mm


A piece of timber of greater width than thickness.

Bow or Bowing

The curvature of a piece of sawn timber in the direction of its length.

Boxed Heart

Boxed Heart is where the centre of the Oak is enclosed by the four sides of the piece along its full length leaving the heart of the wood in the centre of the piece. It is usually adopted for larger beams 150x150mm and above.



The cut away edge or corner to make a symmetrical sloping edge, this helps to prevent corner damage.

Character Oak

Used where the natural beauty of the Oak with its knots, grain, shakes and drying splits are required to give character and beauty. Character Oak includes wild grain, sound knots, pippy knots and occasional non-structural splits and is used for many applications from beams, posts, soffits, bargeboards, sarking boards, cladding, flooring etc.

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.


The process of cutting logs by sawing them into usable sections of timber such as boards, planks, beams etc.


To cut a hole that allows the head of a bolt or screw to sit flush with or lie below the level of a surface.

Cubic Metres

A measure of volume calculated by multiplying the thickness by the width by the linear length of timber. All dimension in metres.

Cup or Cupping

Where the timber bends across the grain, most common on outside boards



The lower part of an interior wall usually defined by a moulded rail known as a dado rail.


See Planks.


The mass per unit volume of a substance usually given in kilograms per cubic metre.


The change in shape of a piece of timber caused by shrinkage as the timber dries out. It includes bowing, cupping and twisting,


Round length of wood often used in framing work to join timbers together in conjunction with a physical joint and glue.

Dressed Timber

Any piece of timber that is finished to a smooth level on a single side or more.


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

Dry Rot

This usually attacks the sapwood where an environment of warm dark unventilated space is provided. It is the growth of fungi and the spores of the fungi on the decaying wood that float in the air, that spread the dry rot. It spreads rapidly when conditions are ‘favourable’ and looks like mildew on the wood and produces a really unpleasant musty smell. Dry rot continuously eats the timber which turns the timber brittle and then to powder. The spores will go through brickwork, concrete and many other materials. Moisture and a closed atmosphere is essential to the growth of dry rot and the fungus will die when exposed to fresh air. Dry rot can cause extensive damage if left undiscovered and untreated.



The edges of a roof that project beyond the walls.

End Grain

The exposed face of timber produced when it is cut across the grain.



The wide surface of a square-sawn or dressed timber on which the grade or quality is judged.

Falling Slabwood

Off cuts of scrap wood that ‘fall off’ during cutting.

Fascia Board

A length of wood that covers the ends of the rafters. The gutter is fixed to the fascia board.

Feather Edge

This is a method of shaping a board with a taper for cladding or fencing.


Patterns on the cut surface of timber which can comprise of knots, irregular grain, rays, or annual growth rings.

Finished Size

The actual dimension of a piece of timber that is required for a use.

Firring Piece

A wedge shaped in the length, pieces of wood that sits on top of a horizontal joist to give a fall to the decking on a flat roof.

Finger Joint

A joint formed where lengths of timber are shaped at the join to form ‘interlaced fingers’ which is then glued. A very strong joint.


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

Flooring - Footworn

Solid English Oak Character Grade Footworn floor boarding with guaranteed traceability and accompanied by a Certificate Of Origin. This type of flooring is used largely in renovation projects where the appearance of aged and historic Oak flooring is required. The boards are produced in three widths, 240mm 290mm and 340mm and is all a nominal 22mm thick. The flooring is hand finished and is slightly bevelled at the edges to give the footworn appearance.

Framing Timber

Timber used to form the basic structure of a building.

Free Of Sap (Sap Free)

Oak that is free from the outer layers of recently formed wood which you will find between the heartwood and the bark. Sapwood is non-durable and susceptible to insect attack as it contains starch to feed the tree.

Furring Battens

Parallel lengths of timber fixed to a wall or ceiling to form the framework for fixing boards or panels.


Glulam Beams

This is a laminated timber also known as composite beam. Glulam is formed by gluing together lengths of graded timber to produce large beams and these can be straight or curved. Glulam beams are immensely strong in comparison to a normal timber beam of the same section. They can also be kiln dried as they are made up from thinner ‘kilnerable’ sections.


The horizontal measurement of one stair tread. The horizontal measurement from the top and bottom riser of a stair case is commonly referred to as the ‘total going’.


A hugely complex subject with many different grading techniques and standards. There are large volumes of technical information available on the internet regarding grading and it is confusing and technical in its nature. Our best advice to customers to to inform your supplier of the purpose to which the Oak will be used and allow your supplier to suggest the correct grade. Sometimes beams and structural members are specified to a ‘stress grading standard’ and where this is required by the structural engineer, Whippletree will be able to help as we have ‘graders’ employed by the company who can grade and select the beams available to suit your requirements.


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 Oak

Is freshly cut Oak that has not been stored for any period of time. It is used in the manufacture of Green Oak frames for homes where the timber is expected to move, shrink and crack as it dries out, to give the familiar character that we expect of a Green Oak frame.

Green Oak Frame

A frame formed using Green Oak to construct an Oak frames building.

Green Timber

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


Hard Wood

Technically, hardwoods are woods from trees classed as Deciduous as opposed to conifers which are evergreen. The timber of conifers is known as softwood. Some 'hardwoods' such as balsa are soft; some 'softwoods' such as yew are very hard.

The top member of a wooden frame.

Head Plate

The top member of an internal or external stud partition or wall.


Heartwood is old wood that is no longer used to grow the tree. It is denser and harder and is less susceptible to fungal attack and decay.


The extended section of a window head or sill which is left in place to protect the frame until it is fitted. The horns are then trimmed off on site before fixing.


Irregular Grain

When fibres within the timber twist around knots and bulbs. This can be called ‘wild grain’.



The vertical side piece of a door frame or window frame.



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

Kiln Dried

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

Kiln Drying

The process of drying Oak where the timber is placed into a heated and ventilated chamber for forced drying usually down to a moisture content of 8-10%. This process gives stable timber that should not crack with age and is ideal for joinery purposes. The kiln drying can take from a few days to weeks depending on the thickness of the timber and the level to which the moisture content needs to be taken down to.


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


Lath - Sawn

Lath Sawn (Sawn Lath) Generally associated with ‘lath and plaster walls’, laths are the ‘slats’ of timber that are fixed to a timber frame wall onto which plaster or render is applied to give a wall finish. The word is recorded as far back as the 13th century and is cut from very straight grained knot free timber to give longer and stronger lengths to aid fixing. Sawn lath is a neater, more regular, and easier to fix product than riven lath and is a good compromise between cost and durability. Sections are 26x6mm and in lengths of 1.22 and 2.44m long with 50 lengths per bundle. 35 linear metres = 1 square meter.

Lath - Riven

Lath Riven (Riven Lath) Riven lath is hand cleft (split) from very straight grained Oak or Chestnut. As the laths are split along the grain, it gives a very strong (no short grain) and durable lath with exceptional ‘key’ and the longest lasting. Sections are approx. 32x6mm but will vary as it is hand cleft, lengths are 900-1800mm with 50 lengths per bundle. There are 30 linear metres in 1 square meter with 10mm gaps but you need to allow up to 30% waste on Riven lath

Linear Metres

A measure of length that ignores individual set lengths.



A finish applied to timber that allows the timber to dry out whilst protecting it from rainwater.


The joint in two pieces of wood that form an angle by cutting bevels of equal angles at the ends of both pieces.

Moisture Content

The percentage of water contained in the timber. In Green Oak, the moisture content when it is first cut can be as high as 80% and this will reduce as the timber is processed and stored. The shrinking process starts when the moisture content reaches about 30%. The natural Air Drying process will normally take the moisture content down to around 18-20% after 1 year per 25mm of thickness for seasoning. Kiln Drying will further reduce the moisture content even further to around 8-10% for use in joinery.


A recess or hole cut into one pieces of wood to receive a projection or tenon from the end of another piece of wood.


Level of expansion and contraction within dried wood as moisture content changes in response to humidity.


A vertical dividing member of a window frame.



The post at the bottom and top of a staircase. The newel supports the handrails.

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.


A short horizontal piece of stud fixed between two studs to provide lateral restraint.


The front edge of the tread on a staircase.



The wood that Whippletree specialise in. Oak (Quercus) has 60 distinct species, growing in Europe, America and of course the most valuable and prised England which produces the two best known species of Quercus Pedunculata and Quercus Sessiliflora. In these English species, there is little difference between the two other than small variations in leaf and fruit. The wood is very hard when dried and has fine regular grain and close texture. In its ‘green’ state when it is freshly cut, it ‘carves like butter’ The colour is light brown and is very durable either in wet or dry conditions. It is very suitable for all forms of engineering and construction work and is highly prized in joinery work and furniture making. Many of England’s most famous historic buildings and iconic landmarks many hundreds of years old, stand testimony to the durability and longevity of Oak. Much English Oak is used in the refurbishment and renovations of these buildings and new homes of distinction and quality are now seeing a resurgence in the use of Green Oak frames to provide the warmth and character so long associated with the British culture.



Finished to a smooth finish by machine or by hand plane.


Also known as medulla, is a tissue in the stems of vascular plants located in the centre of the stem. It is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the tree.

Plank or Planking

This is a term used to describe the way in which the Oak stem is converted into ‘slabs’ to facilitate the drying process. It is also used in combination with ‘waney edged’ descriptions so that you will hear ‘waney edged plank’ referring to slabs that still have the waney edge in place. Planks are parallel sided pieces of timber from 50mm to 150mm thick and 225mm or more in width. They can be from 2.4m to 5.4m long. Where the width is less than 225mm.

Post Shoe (Galvanised)

A neatly fabricated galvanised steel shoe designed to be rebated into the end of oak posts when used for timber framing. There is also an extension leg available to raise the post off the ground or to be concreted in if the frame requires erecting before the floor is cast.


A horizontal beam that provides support for rafters.


Quarter Sawn

The through and through or plain method is where the wood is cut in planks or boards. This method gives timber that is more prone to cupping but is structurally stronger when fixed correctly. It is used extensively for beams and the like where structural strength is important.



A beam that is normally part of a set of parallel beams running from the ridge to the eaves to form the main structural element of a roof.

Ray - Medullary

A narrow string of cells that store food in a tree. The rays also conduct the food throughout the tree. Rays run across the grain of the timber causing the ‘flower’ referred to in ¼ sawn Oak.


A sticky flammable organic substance, insoluble in water, exuded by some trees and other plants.


The vertical side of an opening in a wall or the vertical side of a door or window.


The vertical part of a step on steps or staircases.

Rough Sawn

Surface condition of wood as it leaves the saw.


Sanding or Sanded

A finish being smoother and finer than planing.


The fluid which circulates in the vascular system of a plant, consisting chiefly of water with dissolved sugars and mineral salts.


The soft outer layers of recently formed wood which you will find between the heartwood and the bark. The sapwood contains the functioning vascular tissue that allows the tree to grow, it is the working part of the tree that carries the sap from the roots to the growing tree, it is softer and holds starch and is therefore more susceptible to insect and fungal attack. Sapwood is removed for joinery grade timber but can be used in instances such as waney edge cladding where the sapwood forms part of the character of the wood although must be treated.


Timber that has not been gauged or dressed.

Sawn To Size (STS)

A term used to describe the process of cutting the timber from beams or planks to the customers’ requirements or cutting list.


A term used to describe the process of drying from Green, through Air Dried to kiln dried. Seasoned is also usually graded into:

  • Joinery Grade – where the grain is clear and straight with only small occasional knots, totally free of sapwood, Air dried to 18% and Kiln Dried to 10-12%
  • Character – Where the grain is wild grain, sound knots, pippy knots, and occasional non-structural splits to give the character, Air dried to 18% and Kiln Dried to 10-12%
  • Pippy - Where the grain is wild grain, sound knots, pippy knots, and occasional non-structural splits to give the pippy character, Air dried to 18% and Kiln Dried to 10-12%. Pippy is used for furniture making for its beauty.
  • B Grade – also known as Joinery ‘B’ Grade or Relocated Joinery due to its defects, generally straight grain with occasional wild grain, sound tight knots, some surface checking or occasional splits. Slight sap acceptable. Used where some character is required in the timber.


A split in wood that reveals its natural texture.

Short Grain

The term used when the grain in a piece of wood lies across the narrower section.


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.


The bottom member of a door frame or window frame.


The underside of a part of the building such as at eaves or archways.


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

Split or Shake

A separation of fibres in the direction of the length which extend to the opposite face of the timber.


The boards on the side of a staircase into which the stair treads fit. If it is against the wall it is known as a wall string and if it is the outer, then it is known as the outer string.

Structural Timber

Timber selected for applications where strength is essential, as in building construction.


Through & Through

The through and through or plain method is where the wood is cut in planks or boards one after the other right through the log which yields wider boards from the outside of the log and narrower boards through the centre because of the pith or heart running up the centre of the boards.

Tilting Fillet – Angle Fillet

A triangular shape piece of wood that sits at the edge of a flat roof against a wall to enable the flat roof covering to be taken over the fillet and up the wall at an ‘easier’ angle and avoid a 90-degree corner. Also found at the bottom of rafters against the fascia to give a ‘kick’ to the bottom row of tiles or roof covering.

Tongue & Grooved

Boards that have one edge that is grooved and the other that is machined with a projection to fit into the groove of the other.


The process of proving the origin of the Oak in terms of the place where the tree first grew. With the British Oak that Whippletree supply, the traceability is shown on a ‘Certificate Of Origin’ stating the woodland where the tree grew and the log numbers that were placed on the timbers as ‘tags’ when the tree was harvested. The ‘tags’ stay with the timber throughout its storage, drying and processing stages to ensure the continuation of the identification. Traceability is of great importance to projects of a historic nature and is used extensively on historic homes, Government buildings, palaces, listed buildings and other projects where the origin, methods of harvesting and replenishment of the trees to ensure the future of our Oak forests, is of importance.


A horizontal diving member of a window frame.


V Jointed

Often associated with tongued and grooved, it is the V shape channel that is machined into the timber to accentuate the joint or to hide slight damage.



Is the missing part of the timber from the face or edge of the timber. It is usually caused by the timber being cut to the edge of the log and may include bark.

Waney Edge

The term waney edge is used to describe planks that are converted from the trunk and stored with the bark edge mechanically removed leaving a rough splintery edge until they have been seasoned for use later on. Waney Edge is the way of cutting the timber for cladding where the boards are cut with one square edge and the other edge left with bark and sapwood left on it to give character for barn conversions and the like.


When timber has distorted or twisted.


The wood-boring larva of the furniture beetle or the damaged condition of wood resulting from infestation with woodworm.

Wrot or Wrought Timber

Timber that had been planed on one or more surfaces.

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