International Timber discusses the benefits of opting for modified timber

Modified timber is quickly gaining market share. Here, John Dowd from International Timber discusses its rise to fame and everything you need to know about this popular material.



odified timber is an alternative to hardwood, which is treated in a controlled environment to improve its performance through either thermal modification or chemical processes. These modifications can completely change the structure of the timber’s cell wall components or simply concentrate on insulating the wood’s exterior.

Thermally and chemically modified wood

Thermally modified timber uses pyrolysis to thermally alter the material irreversibly. The main advantage of using thermal modification to change your softwood is that it makes it highly durable and, therefore, more sustainable.

Thermally modified wood also enjoys biological resistance against some microorganisms and insects, which is extremely useful for outside applications where normal, untreated wood may be prone to rotting.

Chemically modified wood possesses many of the same advantages. Accoya is one type of chemically modified wood that is sourced from fast-growing sustainable forests, has no toxicity and has a dimensional stability and durability that is the product of eight decades of research. Having been tested in all types of weathering conditions, both above and below the ground – as well as in water for prolonged periods of time – Accoya has been proven to withstand the harshest external environments and is better performing than even the best tropical hardwoods.

Chemically modified wood requires less maintenance than normal hardwoods and is better at holding its coatings. Test results between Accoya and unmodified wood demonstrate that coatings last up to three times as long on Accoya. The acetylation process used to make Accoya is non-toxic and doesn’t introduce chemicals not already found in the wood. The wood is modified through acetylation from the surface to the core.

Accoya is unrivalled in application where the wood may come into contact with water, i.e. for external use. For example, Accoya was recently supplied by International Timber to provide outdoor weatherproof and damage-proof seating in Manchester’s Piccadilly Gardens. The durability and design of Accoya means it has an extremely long lifespan, a key requirement for developers when considering public realm.

The process of making Accoya changes the free hydroxyl groups into acetyl groups, reducing the ability of the material to absorb water by 80%, which has a huge effect on improving the stability of the wood. The shift in cell structure also means fungi and insects do not recognise it as a wood so will not attack it nor be able to digest it. This is similar to the thermally modified option.

When choosing an outdoor wood these kinds of considerations are essential as the cost of maintaining the material should be considered as well as the original price. Another key benefit of Accoya is that it requires extremely low maintenance due to its durable properties.

Taking all these factors into account, it’s not hard to see why Accoya is a popular choice to replace high-performance materials such as tropical hardwoods and aluminium, which can lack Accoya’s green credentials.

Current demand and application

The demand for sustainably modified products continues to grow. Whether for windows, doors, decking, cladding or other joinery applications, modified timber technology is proving to be popular across all markets.

As consumers become wiser to climate change, deforestation, illegal logging and sustainable forestry, the demand for more sustainable alternatives will continue to rise. Modified timbers are ideally placed to meet this demand.

The increased availability of thermally and chemically modified woods means that where tropical timber was traditionally used, modified timbers are being substituted – for example, in the case of joinery and garden products such as decking.

The future

Modified timber is sustainable and plentiful. As well-managed plantation timber is used as the basis for the modified timber product, this timber is available in much larger dimensions than some traditional hardwoods, pushing the design boundaries and unlocking new possibilities.

Modified timber stocked by International Timber is certified, meaning it meets all the regulations in terms of both managed sustainable forestry and legal ownership.

Case study:

Cultivar uses Accoya wood to design high-end greenhouses

A top provider of high-end greenhouses has incorporated Accoya wood supplied by International Timber into its new designs for a glasshouse.

Cultivar uses Accoya wood in combination with aluminium to create stunning glasshouses for beautiful gardens. It’s praised the reliable service of International Timber, the good value for money and the expertise of employees in handling their queries. Daniel Carruthers, Director of Cultivar, said: “We have married our extensive experience in the greenhouse industry with a desire to design a beautiful glasshouse using a combination of engineered timber and aluminium.

“We needed a wood suitable for outdoor use. Whilst our greenhouses are predominantly aluminium, we recognise the aesthetic and practical advantages of wood so when designing the structure, we wanted to incorporate some.

“It’s important to educate our customer base to the merits and green credentials of Accoya. It is long-lasting, dimensionally-stable, attractive and, most importantly, environmentally and ethically-sourced.

“Our timber needs are ongoing. It’s not a one-off project and, with our eyes set on expanding the range, we can only see the relationship with International Timber growing.”

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