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A modified timber which, due to its outstanding dimensional stability and unrivalled durability properties, is ideal for projects which require a long-lasting vacuum-coated finish.

Through the use of a non-toxic acetylation process, sustainable timber (Radiata Pine) is modified to create Accoya® wood; a uniformly attractive, consistently durable and dimensionally stable product which is fully sustainable and will last a lifetime.


It is highly recommended that Accoya wood is coated, with an opaque (solid) finish, as its outstanding dimensional stability properties ensure a clean, sound surface; the perfect coating substrate. Virtually no shelling, cracking, checking or fissuring will occur, and the paint can be expected to last at least twice as long as on unmodified woods.

In its natural form, Accoya wood is a cream/light straw colour. However, we would not recommend leaving it to weather, as the uncoated surface of Accoya wood is susceptible to blue stain mould and uneven UV weathering, which may result in an inconsistent colour when wet.

Grades and specification

Accoya wood is available in four grades (A1, A2, A3 and B). Russwood only supply the cleanest grade - A1 - to the minimum specification outlined below.

  • Grade A1 Accoya wood which has four sides primarily clear and an allowance per length of:
    • Combined total of up to three 8mm pin knots and/or bark or resin pockets (for boards less than 50mm in thickness)
    • Combined total of up to six 15mm knots and/or 10mm wide/100mm long bark or resin pockets (for boards over 50mm in thickness)
    • Three resin streaks up to 8mm wide/100mm long
    • Three surface checks, up to 1mm wide, 250mm long or equivalent
  • Uncoated surfaces are susceptible to surface mould and staining (product should always be coated)
  • Durability Class 1 (BS EN 350-2 classification)
  • Modified timber which is FSC® certified, non-toxic and fully recyclable
  • Moisture content of less than 8% ensures unrivalled dimensional stability

NBS Specification

For advice on completing the NBS H21 for Accoya wood please get in touch with our project team.


Accoya wood boasts outstanding and consistent durability properties, being categorised as Class 1 (by BS EN 350-2) – the highest possible rating for timber. After each batch of timber has been modified, its properties are analysed, ensuring that the durability at least matches, and in many cases exceeds, the performance of the world’s most naturally durable species.

Accoya wood is indigestible to a wide range of insects, including termites, and forms an effective barrier to any attack. The wood is virtually rot-proof, which helps to ensure that, when properly maintained, it can be expected to have a lifespan of over 100 years when subject to general outdoor exposure.

The way a façade is fixed and detailed can have a major effect on it’s lifespan. Our range of fixings and systems are designed by Austrian Timber Engineers to make cladding look better and last longer.


A key feature of Accoya wood, and one of the primary reasons for its popularity as a cladding material, is its outstanding dimensional stability. The benefits of this stability are:

  • Opaque coatings can last at least twice as long which reduces maintenance frequency and, consequently, maintenance costs
  • Designs which require clean, crisp lines will look fantastic, and will last for many years, as the modified wood will experience minimal swelling and shrinkage
  • It enables greater flexibility in the way in which the product is used.

These enviable stability levels are a result of the modification process, which changes the structure of the timber and results in it having an extremely low moisture content of 8%. Although Accoya wood absorbs moisture more slowly than other species, it can take longer to dry out. Consequently, extra care should be taken when storing this product, and the moisture content should be measured to the core of the boards to ensure that the reading is accurate.


In comparison to most of Russwood’s other timbers, Accoya wood is very lightweight; approximately 592kg/m3 at a moisture content of 8%. As a result of this low density, the product is easy to work with and install.

Coating suitability

By combining the impressive benefits of vacuum coating with the incredible stability and durability of Accoya wood, remarkable results can be achieved, due to the following features:

Outstanding dimensional stability

Timber swelling and shrinkage is virtually eliminated in Accoya wood, meaning that the vacuum coating is not subjected to such severe stretch and shrink cycles. This enables the coating to last for up to three times longer, thereby substantially reducing maintenance frequency and associated costs.

Exceptional durability

Accoya wood is one of the few timbers listed as durability Class 1, meaning that it is virtually rot proof. The advantages of this are that the overall lifetime value of the product is extremely high and it provides a perfect coating substrate. For further durability information, including test results, go to the download section of the Accoya website.

Accoya wood can be vacuum coated, at Russwood’s in-house state of the art vacuum coating facility, with your choice of opaque coating from our Teknos range. For information about the benefits of vacuum coating, as opposed to on-site paint application, please go to our vacuum coating page.

Accoya wood cannot currently be fire-retardant treated, although rigorous tests are ongoing to find a treatment solution.


How timber is fixed is fundamental to it’s long term performance in terms of both appearance and durability. We offer a range of fixings and systems to make cladding look better and last longer. These systems can be written into the NBS H21 specification. For more information on our recommended fixings, click here.


We can advise you on the most suitable species and profile for your project. Visit our profiles section to view some of our most popular profiles, or speak to us to discuss further options.


Accoya wood is sustainably sourced, non-toxic and can be safely re-used and recycled. Additionally, it is certified as such by the Forestry Stewardship Council® (FSC®) and the Programme for the Endorsement of Forestry Certification Schemes (PEFC). For further information on the sustainability properties of Accoya®, please visit;


We supply Accoya wood in lengths of 2.4 to 4.8m, in widths of 100 to 200mm and in sawn thicknesses of 25, 38 and 50mm. Please note that cladding is supplied as a linear meterage based on random stock lengths at time of picking order. Other sizes may be available on request.


Accoya wood is one of Russwood’s premium range products, although we recommend that it is supplied Vacuum Coated the lifetime costs are much lower than many other timbers due to the reduced requirement for maintenance and replacement. Please contact a member of our sales team for a cost estimate.

Accoya® Academy

Accsys Technologies has launched the Accoya® Academy, an easy to use, online Architects and Manufacturers educational tool. It further explains the acetylation process, the benefits of acetylated timber and also highlights certain Accoya® case studies from around the world. To visit the Accoya® Academy, click here.


  • Outstanding stability
  • Exceptional durability
  • Perfect substrate for vacuum coating
  • Flawless finish which requires minimal maintenance
  • Consistent quality and performance
  • Sustainably certified, non-toxic and 100% recyclable


Please note that we have only listed the most popular profiles for each product but there may be others available. Please speak to us to discuss the best options for your project.

LOM Architecture
Painted Accoya® profiles provided a durable and cost-effective way of bringing new life to a tired 1970s façade and creating a vibrant new public face for the school. Russwood supplied pre-coated Accoya® cladding panels, as well as thicker profiles used in the louvred sun-screen, and offered specification and detailing advice throughout the project.

Edd Rushton, LOM Architecture