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Processing & Treatment of Timber - Your Questions Answered

Timber can be a baffling product to understand and buy, the industry loves to talk in jargon and spout references to standards few people understand. To help you out we have put together this help page to bust the most common parlances and jargon helping you get to grips with the terminology and make it a little less daunting.

Strength Classes

  • C16               Timber described as C16 refers to the strength grade of the material, most frequently machine graded. C16 is a structural grade and is often used for floor joists, roofs and minor building works where the performance of the timber matters.
  • C24               Timber graded C24 offers a stronger material than traditional C16 grade and can therefore be used in more demaing circumstances and bridge wider spans.
  • TR26             TR26 is a structural timber grade used in common in the construction of UK trussed rafters. TR26 grade timber is typically in larger volumes to truss manufacturers. TR26 timber is stress graded by machine in large volumes.
  • BS 5534        BS 5534 provides the construction industry with guidance on best practice on the installation of a slate or tiled roof. Contained within this standard is a vast array of information, ranging from batten selection and fixing methods to wind uplift formulas, providing manufacturers with a means of calculating fixing specifications. It is not a legal requirement to install a roof in accordance with the British standard. However, the standard can be included within a specification, and this can be upheld in a court if necessary. If for any reason there is a legal dispute, it would detrimental to the installer’s position if the roof does not meet the standard.

Processing & Treatments

  • Tanalised               Tanalised means timber that has been preservative treated using Tanalith, this provides long term protection from decay, insect and wood borer attack.
  • Tanatone               Tanatone means timber that has been preservative treated using Tanalith with the addition of a brown colouring additive. It provides the same level of protection provided by Tanalith.
  • Dip treated               Timber is immersed in a tank of treatment then removed for drying. This process adds colour and light protection at the surface and does not penetrate deep into the timber structure, as a result it is not long lasting and is often only used for decorative purposes such a fence panels etc.
  • Pressure impregnated Vacuum pressure impregnation, is a treatment process which can provide the highest durability of timber. Timber is sealed into a chamber and a vaccum is formed, this evacuates the air from the cells of the timber making the space for the preservative, then the preservative is added under pressure forcing it deep into the cells of the timber.
  • Vac Vac                      Low pressure double vacuum impregnation process where the final stage is a vacuum to draw out excess preservative, this leaves the timber more stable and with a drier feel.
  • Incised Where the surfaces of timber posts or sleepers have been sliced or cut into superficially. This light cut to the surface does not impact the strength of the product but does allow better penetration of preservatives when pressure treatment is undertaken, this extends the effective life of the product through better preservation.
  • Regularised               Timber lightly machined to provide a consistent dimensions, semi smooth finish and rounded corners.
  • Planed                         Planed timber is where the rough sawn state has been cleaned to a smooth finish in a planer or moulder. The smooth surface of planed timber is typically used in decorative or interior applications where aesthetics are important or finishing with paint or varnish is required.
  • Sawn                            Sawn timber is where the log has been rough cut to a square section, this leaves a rough surface and is used where appearance or finishing is not important.
  • Primed                        Terminology usually referring to the first stage of finishing a product with a primer coat prior to top coat finishes such as satinwood or gloss paint etc are applied.
  • Milled                          The process of passing timber through a process in a timber milling facility.
  • Kiln Dried                   When timber is felled it contains high levels of moisture, to reduce this we cut it into sections and the kiln dry it. This heat treatment (kilning) of the timber will reduce moisture content more rapidly that simply air drying plus it provides a more consistent content level. This moisture reduction process makes timber more stable and less prone to splits, twists and dimensional instabilities making it higher performing in building applications.
  • Eased                          Eased refers to the slight rounding of edges on regularised sections, this makes them easier to handle and prevents splinters and

             

Timber Jargon

  • Batten               A flat strip of squared timber used to hold something in place or as a fastening against a wall.
  • Graded             Complies with a strength class, usually C16 or C24
  • Reversible       Used to describe where skirting boards have different profiles on the opposite face, this allows one board to provide two profile options
  • BBA                 'British Board of Agrement' - The UK's leading construction certification body, providing a symbol of quality and reassurance.
  • OSB3               Oriented Strand Board, Type 3 for use in load bearing situations in humid conditions such as house building.
  • MDF                 Medium Density Fibreboard is a product produced by breaking down timber into fibres and reforming it so it's consistent and with modified properties.
  • Composite      A material manufactured from several different substances, often with enhanced properties e.g where wood fibre has been added to plastics to manufacture decking boards.
  • EN 636            European standard for plywood for general use in load bearing applications and various climatic conditions. EN636-1 Dry conditions, EN636-2 Humid Conditions, EN636-3 Exterior Conditions
  • EN 314            European standard relating to the bond classes for plywoods. EN314-2 Class 1 Dry Conditions, EN314-2 Class 2 Humid Conditions, EN314-2 Class 3 Exterior conditions.
  • Particle board Often called chipboard, this is an engineered product produced from wood chips bound together to form a uniform and consistent panel
  • Plywood         Plywood is made up of cross laminated wood veneers bonded together to provide a very strong and stable material.
  • CLS               Canadian Lumber Standard, aka 'CLS' is used in construction of timber interior walls, framing or studwork. CLS is sold in sections 50x75 (38x63 finished), 50x100 (38x89 finished) & 50x150 (38x140 finished) but has reduced finished sizes compared to regular carcassing. Lengths are generally limited to 2.4m, 3.0m or 4.8m.
  • Long Grain    Refers to the direction of the grain of top veneer on specific plywoods such as Birch. Can also be used to describe the direction of grooves in flexible MDF. Long identifies that the direction is the parallel with the longest edge.
  • Cross Grain   Refers to the direction of the grain of top veneer on specific plywoods such as Birch. Can also be used to describe the direction of grooves in flexible MDF. Cross identifies that the direction is the perpendicular to the longest edge.
  • Carcassing    This is terminology for timber which is used for construction and primarily in structural applications, such as floors or roofing.
  • Moisture Resistant Resists the effects of moisture laden air on the product. This does not make the product waterproof or able to sustain constant wetting.
  • Softwood       Wood that has been harvested from either spruce, pine or fir species, essentially a conifer variety e.g. Scots Pine
  • Hardwood Wood that has been harvested from a broadleaved tree specie e.g. Oak
  • Joinery         Components used in housebuilding such as doors, frames, windows, staircases. Traditionally all made from wood by skilled craftsmen. Joinery can also be used to refer to specific qualities of softwood and hardwood timbers usually in their sawn (unfinished state) ready for use in a joinery shop.