Oh, that’s what that word means…

Welcome to our collection of wood words and timber terms with definitions, explanations and elaborations all on the subject of wood and trees.

AD  or Air Dried

Air Dried timber is timber that has been left to season in the open air. Rule of thumb for Hardwood air drying is 1 year per inch of thickness to be fully seasoned. The reason for drying timber is to reduce the moisture content within and therefore reduce the chance of movement once in use. Air dried T&T timber is suitable for external joinery/furniture/cladding/ etc.



Horizontal load bearing timbers.



The useable (usually the lower& branchless) part of a log


BTM or Boards to make

Is a term used to refer to a way of supplying timber. ‘Boards to make’ is short for boards to make a cutting list and describes a method of supply where intact boards, waney or square edged, are selected and provided against a cutting list, rather than cut to match the cutting list nominal sizes or planed all round to match cutting list finished sizes. For experienced woodworkers it can be preferable as the choice of cut is theirs and any waste is kept but conversely it takes more work and space to store. It’s



The French term for a log butt that has been cut through and through



A method developed by Henry Ford to make a work area more organised and efficient. The five steps – which would be done in sequence – are Cleaning up | Arranging | Neatness | Discipline | Ongoing improvement.

Note: CANDO closely resembles the 5 methodology developed by Toyota which was based on Ford’s method & is often used within Lean Thinking as a business improvement technique.



This term refers literally to the ‘character’ of the timber species i.e. the typical look, feel, behaviour etc it displays.
It can also refer to a grade when talking about Oak, more than any other species, and generally means that the timber has too much ‘character’ to be able to make the plain, clear, knot free grade that some joiners and woodworkers like to use and which we call Prime. See our TIMBER GRADES page for more info



Separation of fibres along the grain forming a crack or fissure that does not extend through timber or veneer from one surface to the other



Although it is possible to obtain timber in large width dimensions for cladding there are guidelines for dimensions from TRADA that exclude large dimension widths because the shrinkage and movement that can occur will be greater in wide boards than in narrow boards and the same width long lengths tend to bend or warp very quickly, whether bowing off the saw or in storage. The resulting problems with fixing and wastage are enough for us to advise against use of timber cladding in large dimensions, width or length.

Durability of the timbers has been measured by TRADA** to a degree (we assume you are not going to bury your cladding in the ground), but the service life of your timber cladding will be largely down to the detailing and fixing methods. Water is the element most likely to cause rots and damage and is the element you are managing by purposeful design. TRADA’s book External Timber Cladding has very good information, details, photographs, advice etc.

TRADA and the BRE’s timber density figures are generally given at 12% moisture content – technically a kiln dried product – but all homegrown cladding material will be of higher moisture content than this and therefore will be heavier. As a rule of thumb F/S Oak is 1100kg/m³ at roughly 50% moisture content and A/D will fluctuate depending on the weather with an average moisture content ,once fully dried (1 yr per inch thickness for hardwoods), of around 20%.

Density of the timber is important for cladding in terms of impact resistance, durability, weight (loading), stability etc.



The colour of a timber depends on it’s species, age, the soil it was grown on, weathering and many other factors. It is probably the most important visual element in choosing a timber.


This the process of taking one raw material eg. log and converting it to another material for use eg. beam or T&T board



Forestry practice that involves the harvest of young growth of Ash, Hazel or Chestnut by cutting back stumps to ground level that quickly re-grow. The material harvested has many uses including for thatching, fence making, lath & batten making, and makes very sustainable fuel supply. We use coppice for our lime plaster laths and for fencing.


CTS  or Cut to Size

Meaning the timber is cut to a nominal width and length in a nominal thickness and sizes indicated are pre-planing dimensions



Likely to be the key factor in choice of species for cladding and external joinery work, the choice coming down to whether to use a preservative, a modified timber or rely on natural durability of a timber species and it’s ability to achieve a desired performance

Natural Durability: The inherent resistance of wood to attack by wood destroying organisms (BS EN 350.1) and in this classification relates to the resistance of the heartwood to attack by wood decaying fungi


Class 1 Very Durable
Class 2 Durable Cedar of Lebanon, Chestnut, Oak, Yew
Class 3 Moderately Durable Western Red Cedar, Walnut, Cherry
Class 4 Slightly Durable Elm, Larch (3-4), Douglas Fir (3-4), Scots Pine
Class 5 Not Durable Ash, Beech, Sycamore


External use

A few species of wood are suitable for use externally. The timber can generally can be higher in moisture content. Fresh sawn timber is fine outdoors and as air dried timber which has already lost moisture, shrunk and stabilised. Changing conditions will continue to impact timber used externally. The key is intelligent application i.e. using the right timber for the job with good detailing, good fixings and if any, good finishes.

Face dimensions

Face dimensions are the specific measurement – usually width in mm – of individual boards that are used for decking, cladding and flooring where the profile includes an overlap and the total width of the board is larger than the width of the face.


FE or Feather Edge

Feather edge is a simple 4 sided overlapping profile, usually cut from Fresh Sawn timber, for cladding and fencing use. It has one thin edge and one thicker edge, one overlaps the other.



Metals containing Iron – not many common metals are Ferrous free. For use with our timbers containing Tannin (Oak, Chestnut, Walnut, WRC) Austenitic Stainless Steel is recommended to avoid corrosion and staining issues.

Finished sizes

Finished sizes are exactly that, the sizes the piece of timber is machined to finish at. It’s used a lot in cutting list quoting where a customer provides a list of sizes of timber they require. The finished sizes have to be less (8mm) than the origin timber dimensions, what we call nominal dimensions.  So if the required finished size is 45mm thick, then the raw timber must be from 54mm thick to allow for 9mm of timber to be machined away to finish at the 45mm. It’s hard to talk about wasting so much but that’s the nature of requirements, need timber to be perfectly smooth, flat and to specific dimensions.


Fire resistance

Timber has minimal deformation during fire and it’s strength is not compromised by extreme heat, therefore risk of sudden failure is excluded. Timber will only fail mechanically after fire has eaten into the wood, which happens gradually over period of time. Steel by contrast, is affected by extreme heat and is prone to sudden failure



Also known as Woodland Management. The management of land and trees with regard to protecting the natural woodland environment whilst facilitating forestry based industries.


FS or Fresh Sawn

Fresh Sawn timber, also known as Green, is timber newly cut from the log. It is timber still in a soft state, it’s is high in moisture but evaporates most of that off as it dried,  hardening at the same time.


General Info

Descriptive. timber colour and grain pattern, whether it can be treated, painted etc and how it works. eg. prone to split when nailed etc


Timber Grade / Grading

Timber grades vary depending on the qualities within the wood and standards set for assessment for purpose. Structural timbers are graded depending on their use and fitness for purpose. Joinery (inc furniture, flooring etc) timbers are graded on their visual qualities and signs of stability. See our TIMBER GRADES page for more info. and or see Structural Grades and Joinery Grades

Grain pattern

Determined by the way a tree grows, different on every species. The main visual quality of a piece of wood is in it’s grain pattern, perhaps second only to Colour.




The inner zone of wood that, in the growing tree, has ceased to contain living cells or conduct sap.



Grown in the UK.


Internal use

Most species of wood are suitable for use internally. Wood for internal use generally requires to be kiln drying but air dried can sometimes be dried enough. Using timber internally always depends on ambient moisture content and is all about managing moisture movement.



Assembly of worked timber components and panel products other than structural timber or cladding. Generally Joinery refers to finely worked carpentry like doors, windows, frames, skirting, architrtaves and mouldings. It requires skilled wood working and a good understanding of wood. The deeper the understanding the better the joiner.


Joinery Grades

BS5756 Hardwoods
See our TIMBER GRADES page for more info


Jointed Wood

Piece of wood made up from smaller pieces joined together end to end, such as finger joint or built up with face to face or with edge to edge joints


KD or Kiln Dried

Kiln Dried timber is fully seasoned AD timber that can be further dried in the kiln. This takes the moisture level down from that achieved naturally in the open air so that the timber can be used in our very dry, centrally heated homes without risk of extreme movement.



Layer wood glued to make a solid thickness, width or length


Lean Thinking

Thinking deeply about purpose, process and people in order to maximise customer value while minimising waste.

For more information visit our Lean guru Gemma’s website SPARKimprovement



Horizontal load bearing timber supported on brick/blockwork over an aperture (window or door to you and me!)


Moisture content

All solid timber has a moisture content and this is measurable to within a few percent. Moisture meters are available in varying types and accuracies. The moisture content of a timber changes due to a natural rate of drying once sawn, the mechanical drying process and in response to atmospheric conditions.

Guidelines for levels of moisture content are given in BS 1186-3 as follows


Exterior Joinery – all 13 – 19%
Interior Joinery – Buildings with intermittent heating 13 – 17%
Interior Joinery – Buildings with continuous heating to room temperatures of 12º-19º 10 – 14%
Interior Joinery – Buildings with continuous heating to room temperatures of 20º-24º 8 – 12%


Moisture movement

Movement is the dimensional change across the width and thickness of boards when the moisture content of timber changes in response to atmospheric conditions (statement TRADA)

Moisture movement is a relative term and species have been given the broad classes of Small, Medium or Large movement

Rule of Thumb: within the moisture content range 5-30% the across the grain dimensions change by the following classes


Small 1% movement for every 5% change in moisture content
Medium 1% movement for every 4% change in moisture content
Large 1% movement for every 3% change in moisture content


to illustrate: a board of 150mm width Oak (Medium) at 25% moisture content will come down to 148.5mm at 21%, 147mm at 17%, and 145.5mm at 13%. Greater width boards are therefore more liable to larger movement.



These are the shaped profiles , often called architectural joinery, that will finish off the interior of a property. The door linings and architraves, the scotia, the picture rails, dado rails and skirting boards and any other decorative finishes that might be required.


Nominal sizes

Nominal sizes are the raw timber sizes.
When we use nominal sizes to pick on a cutting list we supply the original thicknesses – the ones we cut the logs at on the bandsaw, reduced due to shrinkage over time but pretty much predictable – and widths that allow for waste material in machining. When it comes to length we just aim for the least waste possible.

Oldest timber building

…in England, the Stave Church at Greensted in Essex, has timbers dated at 12th century. See:


Oldest timber building

…in the world is the Horiyu – ji Temple in Ikaruga, Japan has timbers dating early 7th century( built 607AD) and possibly late 6th. See:


PAR or Planed all Round

Meaning planed on each surface apart from ends (4 sides), usually to specified dimensions i.e. the required finished sizes


Peter the stockman

Peter has worked for us for over 30 years (he won’t thank me for telling you that) and knows all there is to know about the timber in the yard. He manages the stockshed and the kilns and you’ll know him by his hawaiian shirt and cheeky grin!



The occurance of Pippy knots in a timber is due to a species specific (usually Oak and Elm only) behaviour and results in a very attractive knot and grain pattern, also known as Cats Paw.



Vertical load bearing timbers


Prime Grade

Timber that is mostly knot free, clear and straight grained. See our TIMBER GRADES page for more info.



Logs are felled (generally a winter activity) and extracted (generally a summer activity) from woodlands throughout the UK and transported to our site as Round Timber (the whole log with branches cleaned off). We try to keep a stock of as many species as may be needed to cut plank and beam.

To produce Air Dried and Kiln Dried timber we saw the logs in our bandmill into planks of pre-determined thicknesses in anticipation of the future requirements of stock. These thicknesses are cut slightly larger than the required thickness to allow for shrinkage eg: to be able to supply a 25mm /1″ or nominal 27mm board we will cut a plank to 29mm and it will shrink to 27mm whilst drying. Allowances increase slightly as planks get thicker and shrinkage ratio increases.

The planks are then stacked as a whole log with small sticks of timber (usually Poplar) laid between each plank, evenly spaced to allow for constant air flow. These are then stacked in the yard and left to dry in the open air (Air Dry). The time can vary depending on thickness of board and species of timber. Some timbers are more sensitive and dry rapidly eg; Ash & Sycamore. In general hardwoods dry slowly at one year per inch of thickness. The timbers reach a level of moisture content after this time period that allows them to be kilned. Care is taken to avoid stick marks in sensitive timber species.

Beam timber is always custom cut to order so that it is in optimum condition and the customer can determine the exact size required.



The sectional outline of the timber i.e. the shape you see if you sliced across the grain. It’s mostly use to talk about machined shaped mouldings. These are the detailed, shaped profiles cut with a moulder – a machine with 6 or more heads (cutting blades) – often used in architectural joinery as part of interior finishes.



This refers to a traditional method of hand splitting wood down the grain. Used to make laths*, battens, shingles and shakes. *Hand riven laths are always the best kind as the lime plaster can grip to the roughly grooved surface of the timber easily.


RT or Round Timber

The term for trees that have been felled and are now large diameter felled logs



The outer zone of wood that, in the growing tree contains living cells and conducts sap.



Section is short for cross-section, a 90 degree slice across a width – as opposed to down a length.
Sections are the way we talk about structural timber – structural sections – because the inherent strength is a factor of the surface area of that cross section and the ratios of dimensions. Further info on STRUCTURAL TIMBER via TRADA


Service Life

The TRADA test for durability class involved timber being buried in the ground and measured the susceptibility to infestation and rot. It is not a measure of durability for typical uses eg: beams and posts, cladding, windows and doors, furniture etc. The actual service life of any species of timber may be a very long time depending on the fixing, design and detailing, orientation and prevailing weather.


Separation of fibres along the grain, irrespective of the extent of penetration, due to stresses developing in a standing tree, or in felling, or in drying of converted timber. ‘Shakes’ also refers to the riven timber tiles made for cladding.



These are WRC, Oak or Chestnut timber tiles, made by hand or machine, to clad walls and roofs



Also know as moisture movement. Can be estimated depending on species Re: Trada data.


Silver down

This is a term used to describe the way timber cladding, or any timber left unfinished externally, weathers as it dries and hardens whilst exposed to the elements. After a period, averagely 1 to 2 years, the colour will fade to a quite beautiful grey, silvery colour. To prevent this the timber must be protected with an external finish of some kind on a regular basis. To restore timber to it’s original colour would require sanding or planing work and the original colour will be revealed under the silver surface.



Where it grows/ it’s origins, inc where we source it from eg ‘SE England’ Typical growing sizes of the tree – dependent on growing conditions i.e. soil content, local climate, orientation and prevailing weather. Availability – common or rare/easy to source or not – some species are grown very low numbers, or only ornamentally and are therefore harder to source and available volumes are low and prices can reflect this.


Given as the Common Name and the Biological name of the tree



Separation of fibres along the grain forming a crack or fissure that extends through timber or veneer from one surface to the other


SE or Square Edge

Square edge, meaning the Waney edges of the boards have been cut off so that the timber is squared and usually rectangular shape rather than tapered. This is usually how imported timbers are supplied. Square edge also refers to a profile cut from Fresh Sawn timber for cladding.



Mechanical strength of timber should be assessed in relation to resistance to shock, axial compression & tension, resistance to bending and elasticity /deflection. various data sources are available for reference. Trada and BRE are good authorities on technical information on timber.


Structural Grades

BS4976 Softwoods

BS5756 Hardwoods

issues to be considered for use of structural timber : re: loading ; bending, tension, compression, shear, elasticity also :sapwood, knots, slope of grain, deflection, distortion, self-weight of frame. Further info on STRUCTURAL TIMBER via TRADA


Super Prime Grade

Super Prime grade really only applies to our Croatian Oak square edge boards that have been selected out from Prime grade stock as they achieve over and above the requirements. This grade of Oak is of a consistent pale oak colour,  it has very little variation in grain, it does include a fairly high percentage of quarter sawn boards, in appearance it is the ‘cleanest’ Oak it is possible to buy and in function it is very stable and as such is highly sought after for joinery. See our TIMBER GRADES page for more info

Tannic Acid

Some timber species contain Tannin, Quertannic acid that is corrosive to Ferrous metals, eating into the metal and leaving black blue stain on the timber but ironically (not pun intended) makes the timber species more durable.


Thermal properties

Wood is a good insulator, has good U-values, in that it does not conduct heat well. By the same token it has bad thermal mass, in that it does not store heat well.          This makes wood great as an insulator, as a barrier to stop heat getting out or cold getting in, which why it is great as flooring, external cladding and roofing. For this same reason it is not the ideal material to put over underfloor heating but if used, once the floor is up to temperature it will maintain the level of ambient heat required to heat the room but will not be able to store heat and therefore will probably use more energy than a material that has good thermal mass. It is also a good electrical insulator

T&T or Through & Through

A T&T plank is where a log has been ‘sliced’ right through the length with the bark left on. This is how we mill the majority of our logs and is always done to a specific thickness.


Timber Type

Given as Hardwood or Softwood depending on species


Timber properties

More technical info – on movement/stability, durability, strengths, density, particular values that are relevant to the appropriate uses. Fixings and metal components & tannin



The ease with which a wood can be penetrated by a liquid eg. a preservative. There are classes for which species are rated.



TRADA states that timber species rated as durability Class 3 or better can be used without treatment if non-durable sapwood is excluded (BS EN 350 Durability of Wood… statement)



This is the term we use to assess the amount timber left after conversion i.e. the ‘unusable’ timber separated from the usable timber. We have established averages for waste for the purpose of measuring and pricing, but it varies depending on species, specification and material.


WE or Waney Edge

Boards that still have the bark left on the sides, left as T&T or sometimes, e.g. for cladding, one edge is squared and one left waney. Waney edge timber is usually tapered, having the natural shape of the log i.e. the tree is wider at the base and narrows higher up



Western Red Cedar



This refers to how well a species works, whether it is easy or difficult with hand tools or machine tools, and is usually related to grain patterns, hardness, acid or resin content etc. Generally with dry hardwoods the more wavy grained and knotty they are, the more tricky they are to work. Fresh sawn timber is always softer and therefore easier to work.


Working Sawmill

We still operate as a fully functioning sawmill, sawing T&T plank through the autumn/winter season, beam, making laths, fencing and all our waste goes for firewood or sawdust for the local farm



The u-value (thermal conductivity) information for timber is very generalised and gives the value as 0.14 W/m.k .Not much data is available and what is does not go into individual species, although for construction purposes this figure seems to suffice (NB it is based on data for material 1 metre thickness) Ref.


Visual grading

Our resident Visual Strength Grader Steve (TRADA will be glad to grade your structural Oak to BS5756 if required. Call and ask him for advice on 01730 816941.



Got a question about the glossary of wood words? Get in touch…