Knowledge Base

Oh, now it makes sense…

Welcome to our knowledge base. A collection of wood words, timber terms, definitions, technical data, explanations and elaborations all on the subject of wood and trees. Come on in and grow your wood knowledge…

AD or Air Dried (seasoned)

Air dried timber has been cut (from the log, as fresh sawn) and left to dry naturally, in well ventilated spaces or in open air. The moisture held within the fibres of the wood will freely evaporate until it meets the ambient atmospheric moisture level (the same moisture content as the air around it). The moisture level reduces over time so until it reaches a level suitable for working with or for kilning. Air drying stabilises the behaviour of the wood by allowing for a slow, gentle drying process where the wood releases moisture at a natural rate. Unless handled well, mechanical drying can adversely affect the structure of the wood and reduce it’s workability and overall usefulness.

Uses for air dried wood are exterior joinery, outdoor furniture, timber cladding or decking, oak carpentry and framing for buildings.

See also ‘Seasoned’


Horizontal load bearing timbers.


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

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.


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


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.

Character Grade European Oak

Our grade specification, equivalent to the French Grades QS1/2 and QB1/2

Features Allowed in combination on the visible face:

Knots up to 40mm in a frequency of up to three per metre length.
This is qualified by the section width and thickness however, as a guide the thicker the section and the wider the width the more tolerance is permitted as the timber “holds” together.

<150mm Up to 20mm 15% of face width
160-250mm 20-40mm 20-25% of face width

Knots can be slightly open but not on edge of section
Broad Colour variation including random streaky and dark brown colour
All grain orientations, course grain and sloping grain permitted
Minor surface checks permitted especially on non visible face
Sap permitted on one face on arris edge


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
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.

Forestry Commission Bulletin No.9: Beetles Injurious to Timber by J. W. Munro

Click the document below to get a free download from website >>

Forestry Commission Bulletin No.9 Beetles Injurious to Timber by J W Munro 1928 about woodworm


Excerpt from: Introduction to Beetles Injurious to Timber:

Apart from the termites or white ants which are so destructive in tropical and sub-tropical countries, the most important enemies of timber belong to various families of the order Coleoptera of which four groups may be recognised, namely, longicom beetles (Cerambycidae), pin-hole borers (Scolytidae and Platypodidae), powder-post beetles (Bostrychidae and Lyctidae) and furniture beetles (Anobiidae)

The longicorn beetles and pin-hole borers are essentially forest insects for they attack timber just after it has been felled and abandon it when it has become dried or seasoned. The powder-post and furniture beetles on the other hand are enemies of seasoned timber, the former abounding in timber yards and the latter infesting antique furniture and the roofs of old buildings.

The destruction caused by these insects is very great and is to some extent avoidable. The object of this bulletin is therefore to describe the insects and the damage done and to make suggestions regarding preventive and remedial measures.

Read the whole document

FS or Fresh Sawn (Green)

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. Categorised as FS for the first 6 months of the air drying process.

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.

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, archittraves 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

The term ‘moisture content’ is our way of talking about the water present in wood. All solid wood has a moisture content and it’s measured by the percent of saturation. Moisture content is measurable to within a few percent using a moisture meter – a handheld electronic device with electrodes (spikes) that penetrate the surface of the wood to get an internal reading using the conductivity of the water within. Moisture meters are available in varying types and levels of accuracy.

The moisture content of a timber changes due to a natural rate of drying once sawn, Drying is the evaporation of water from wood fibres, usually a natural air drying process, a response to atmospheric conditions. Depending on use, it’s possible to mechanically dry the timber even further in a process of kilning.

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%

Read more TRADA: Moisture in Timber information sheet for more in depth information

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:

1% movement
for every 5% change in moisture content
1% movement
for every 4% change in moisture content
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

Oldest timber building in England, the Stave Church at Greensted in Essex, has timbers dated at 12th century.

See: Greensted Church.


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: worldheritage/c_6_horyu-ji.html

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.


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.

Prime Grade European Oak

Our grade specification, equivalent to the French Grades QS1 and QB1

Features allowed in combination on the visible face:

Sound Knots up to 20mm in a frequency of up to one per metre length. This is qualified by the section width and thickness however. As a guide the thicker the section and wider the width the more tolerance is permitted as the timber “holds” together.

<150mm Up to 10mm 6% of face width
160-250mm 15-20mm 6-12% of face width

Knots cannot be on edge of section
Even pale honey colour variation within a range. No distinct red/dark brown or streaky colour
Straight grain in crown, half quarter and quarter sawn grain orientation
Minor surface checks not permitted
Minor Sap on arris permitted on widths >250mm

PRODUCT INFO: Air Dried Exterior Timber Cladding

Machined, air dried cladding is a sustainable, healthy building materials achieving a weatherproof building envelope to high tolerances. Click below to download information about our air dried timber cladding machined into profiles.


PRODUCT INFO: Fresh Sawn Exterior Timber Cladding

Fresh sawn timber is freshly sawn straight from the round log. As cladding it’s a cost effective, low impact way of achieving a durable timber finish for any type of building exterior. As fresh sawn timber it’s always cut to order, to your specification, from responsibly sourced trees. Click below to download information about our fresh sawn timber cladding.



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.