Taking timber to a new level

As the construction sector’s demand for timber increases could modified wood be the answer to boosting supply?

Wood modification enhances the natural properties of timber. The process involves taking non-durable and poorer performing timber after harvesting and putting it through a cellular change to make it more durable and stable.

There are various processes but what they all have in common is that they are changing the nature of the wood itself, explained Justin Peckham, head of sales for UK & Ireland at Accsys Group, which manufactures Accoya, a high performance modified timber.

“That can be a chemical change, a physical change or a combination of both, but the important point is that the improved performance results come directly from the wood, it is not dependent on a chemical in the wood like a biocide, it is how the wood is treated. So, it is a permanent improvement in the performance of the wood,” he said.

The three main processes for modifying wood are:

  • Heat treatment – Depending on the wood species, the heat-treating process warms the wood from 185O to 212O Centigrade. Also known as thermal modification, the process makes common woods resistant to decay and heightens the natural colour to a richer hue that develops all the way through the board’s thickness.
  • Acetylation – Substances known as free hydroxyls are present in all woods, naturally releasing and absorbing water in response to changes in the weather. The process of acetylation changes the free hydroxyls into acetyl groups. In this new form, acetyl groups alter the original properties of the wood, making it more durable and dimensionally stable.
  • Polymer grafting – Polymers are formed when a single molecule called a monomer joins with at least two other monomers, a process known as polymerization. When this process is used on wood, it provides a locked in structure to the wood’s cell walls, with benefits including durability, strength, dimensional stability and resistance to the destructive effects of insects and microorganisms.

The main benefit of modified wood that it is as durable as hardwood timber species but can be made from poor performing but faster growing timber, making it much more sustainable.


Archive House © Sindre Ellingsen

“Wood is a valuable resource, but durable hardwood species take a long time to grow and reach maturity – 400 to 500 years for a teak or an oak tree to grow and that makes them not particularly environmentally sustainable,”  explained MEDITE SMARTPLY’s Peter Clifton, product manager for MEDITE TRICOYA EXTREME (MTX), an MDF manufactured from Acetylated wood elements.

“Most modified woods derive from fast growing, non-durable plantation crops which can, of course, be planted and regrown in shorter periods.”

Wood modification gives poor performing timber species all of the benefits of the best performing hardwoods with the aesthetics to match, giving architects, specifiers and developers a real alternative to non-wood materials such as plastic, compact laminates and fibre cement boards, for example.

The sustainable, durable and stable products are less likely to shrink, swell or rot than natural timbers and have a much longer shelf life, coming with guarantees of up to 50 years.

“Natural timbers have a certain amount of variability and it is often difficult to predict, when ordering wood whether it is going be at the higher end of performance for that species or the lower end and there can be quite a range. When you modify wood generally you have some quality control over that process, so you end up with a product that has a more consistent performance,” explained Peckham.

The technology used in the modification process allows wood to be taken into previously unchartered territory said Adrian Pye international sales director at Kebony.

“Increasing the lifespan of timbers normally requires a preservative, but wood modification technology does much more than that. It impregnates wood with other welcome changes such as, dimensional stability and maximum hardness,” he explained. “This gives pine, spruce and other softwood timbers the super-strength powers of traditional hardwoods like oak and maple and exotic hardwoods like teak and ipe.”

Another advantage of modified woods is that coatings such as paint tend to last a lot longer as it provides a much more stable substrate for the paint as the wood underneath isn’t shrinking or swelling as much as natural timber, so the paint is under less strain and therefore lasts longer. So much so, that some paint manufacturers give extended warranties when their products are usedon modified woods.

Modified wood is bringing wood back into focus for architects and specifiers said Clifton and there has been an increase in its use in recent years as more products come onto the market and the wider construction sector becomes more aware of its benefits and what can be achieved.

“The last decade has seen a significant increase in the demand for modified wood. Increased interest comes from the desire to increase the decay resistance and longevity of timbers from Scots pine, beech, southern yellow pine, ash, birch, alder, radiata and many others,” said Pye.

Companies in the modified wood sector are putting significant effort into marketing and promoting their products said Peckham who reported a marked increase in knowledge of the products among architects etc.

“I think there is more noise about modified wood, more people are coming up with modified wood options,” he said. “I think we will see more come to the market in future because the availability of good quality, naturally grown timber is on the decline and the construction industry needs more and more of it.”

“There will always be a place for natural timbers but to have high performance timbers in sustainable form in the quantities that is needed I think modification is an absolute must, it is a need.”

Main Picture: Archive House © Sindre Ellingsen



Accoya is manufactured by Accsys Group, which also, in conjunction with MEDITE SMARTPLY manufactures MEDITE TRICOYA EXTREME (MTX). The international company has a huge focus on research and product development work. Accoya is produced from Radiata pine at the company’s facility in Arnhem in the Netherlands, which is currently being expanded to meet demand.


Accoya is produced using a process called acetylation. This converts natural molecules in the wood called hydroxyl groups – responsible for drawing moisture into the wood from the air – into another chemical group that already exists in the wood called an acetyl group, which doesn’t draw water in from the atmosphere.

“The process makes it very difficult for water to get into the cell walls of the wood which is where it does most of its damage,” explained Justin Peckham head of sales for UK & Ireland at Accsys Group.

“It is wrong to say that you make the wood impermeable to moisture because water can still get into the capillaries between the cells, but the point is that water in the capillaries doesn’t cause rot in the wood or changes in the volume of the wood, it is water in the cell walls that does that and that is what we stop.”


Internationally Accoya’s biggest market is external joinery – windows and doors. Cladding and decking are also big markets and other uses of Accoya have included garden furniture and civil engineering projects in fresh water.


It has a 50-year guarantee above ground and 25 years in ground or freshwater, which covers rot and excessive movement. Some coatings manufacturers also give longer warranties for their products on Accoya, compared to any other timber.



Kebony is a Norwegian company operating on a global scale, with distributors in Europe, Scandinavia, Middle East, Asia-Pacific and North America. Kebony modified wood is produced from fast growing sustainable pines at the company’s production facility in Skien, south of Oslo. Due to continued capacity construction is underway on Kebony’s second European factory in Flanders.


Kebony modifies sustainably sourced softwoods by heating the wood with furfuryl alcohol – an agricultural by-product. By polymerising the wood’s cell wall, the softwoods permanently take on the attributes of tropical hardwood including high durability, hardness and dimensional stability. The process gives the wood a deep rich brown colour similar to that of a tropical hardwood which over time develops a natural silver-grey patina.


Kebony has been used internationally in commercial, public, residential and marine projects including the site of Youth Winter Olympic Games in Norway, Rochester Marina in New York and the redevelopment of Cinque Ports Street, Rye. It is suitable for a range of project types including exterior surfaces, terraces, furniture, roofing and windows.


Kebony has a 30-year guarantee and requires no maintenance beyond normal cleaning. Swelling and shrinkage are reduced by 40% to 60% when compared to the parent wood.



MEDITE TRICOYA EXTREME (MTX) is manufactured by MEDITE SMARTPLY, a manufacturer of sustainable construction panels and part of the wider Coillte Group, the state-owned Irish forestry company.

The company has two manufacturing sites in Ireland and has recently invested €59m in upgrading its OSB production facility.

All products are manufactured using FSC and PEFC sourced raw materials from the 445,000 hectares of land owned by Coillte, which is one of the few fully integrated forest companies in Europe. MTX is produced at the MEDITE factory in Clonmel from acetylated plantation softwood, which is normally a nondurable species.


MTX is made by MEDITE SMARTPLY using Tricoya technology which is owned by the Accsys Group. It is an MDF panel, made from elements modified using the same method as for Accoya wood – acetylation.


Due to the size and thickness availability of MTX panels, potential applications are quite varied and include external doors, cladding, facades, signage and landscape applications such as planters and fence screens. It has also been used in interior kitchens, garden buildings and beach huts.


Due to the enhanced performance characteristics MTX comes with a warranty of up to 50 years when it is used in exposed applications above ground and 25 years in the ground or freshwater. Some paint manufacturers provide extended warranties when their products are used on MTX.


Photo © Marcus Harvey

Kebony was chosen for the cladding at Avondale Park Primary School, North Kensington, London, which was recently extended and refurbished by ECD Architects.

Owing to a close affiliation with St Anne’s Nursery School, the extension aimed to enable the nursery division of Avondale Park to merge with St Anne’s on a single site, and comprises four new classrooms, a community hall, staff and pupil facilities, and a dedicated entrance lobby.

The joint location has enabled the two schools to retain their identity, whilst sharing resources and ultimately working together to reduce running costs.

Beyond its commitment to providing a caring and friendly environment, sustainability was a primary focus and inherent to the project brief. Several sustainable initiatives were incorporated into the design including photovoltaic panels on the roof; efficient windows, reducing the demand for heating; and good levels of natural daylight, designed with light coloured blinds to protect from glare.

Kebony was selected for the façade of the extension due to its environmentally friendly nature and strong performance characteristics.

Loreana Padron, head of sustainability at ECD Architects said: “Kebony was the ideal choice for cladding, it was easy to use and provided the same strength and durability to that of tropical hardwood. We look forward to making use of Kebony to add to the sustainable nature of our future projects.”


Photo © Kathrine Soergaard

Located in the Innovation Park (Ipark) at Ullandhaug, Stavanger, the Archive House was designed by Lund+Slaatto Architects to provide a 14,000 sqm cultural research centre, including a café, library, meeting room and exhibition area.

The building contains the most important historical sources from the Rogaland County, the city of Stavanger and the Norwegian Mission Society, with more than 70km of underground archives spanning half the site.

The building, initiated by Smedvig Property and Ipark and built by Kruse Smith Entreprenør, has four floors above ground level and three below with a central atrium exhibiting a glass roof to create a bright, open area for public functions.

Kebony was selected for the exterior cladding to create an eye-catching geometric ‘folded’ façade inspired by origami.

“From start to finish, the construction of The Archive House presented a number of challenges that required careful consideration. Kebony’s character and durability enabled us to achieve the desired origami effect,” said Pål Biørnstad, partner at Lund+Slaatto Architects.

Innovation was a primary facet of the design and the combination of unusual angles, sloping lines, and integrated window openings enables the aesthetic of the building to adapt based on the time of day, weather and the season.

Sustainability was also a focus for the building which is on track to achieve BREEAM Excellent status.



Accoya, distributed by Woodlink, was the material of choice for the vertical cladding on the Tintra pedestrian footbridge designed by Rintala Eggertsson Architects and constructed by IKM Steel & Façade.

Maintenance was an integral issue in the construction of the bridge, over the River Vosso in Vossenvangen, Norway and Accoya’s strength, durability and minimal maintenance made it a natural fit.

The project was awarded the Architizer A+ Award in the Transportation and Infrastructure category last year. The largest of their kind, they champion the very best in architectural projects from around the globe and are judged by over 400 luminaries and thought leaders, including prominent members of the architecture community and experts from the technology, art, fashion, and design industries.



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