A Change in Timber Habits

One rapid growth area for the timber specifier are the options available in modified wood products. These have become popular across a range of construction applications ranging from cladding and decking to new joinery options.

What is wood modification? Modified wood can be defined as wood which has been treated chemically or physically to enhance its performance. The application of chemical, thermal and impregnation technologies to affect the cell structure of wood, aims to improve the performance of the wood, most notably dimensional stability and decay resistance. Additional benefits include consistency of weathering, performance of coatings and thermal efficiency. For the most part, wood modification is used to change fast grown, non-durable and unstable wood into high performing wood products that can compete with traditional old growth temperate and tropical timber species.

The market for modified timber in the UK is currently a dynamic one and currently favoured in the joinery, cladding and decking markets. Due to the loss of structural properties during modification (particularly thermal) and cost, these products are not often

being used for structural applications – although this is changing with solid glulam Accoya being increasingly seen – but the mainstays of the modified wood market include:

• Accoya – joinery and some cladding

• Kebony – decking and cladding

• Thermowood, Abodo – cladding and decking

• Brimstone, Thermory, Novawood and other thermally modified hardwoods – cladding and decking

• Lignia – yacht decking (and relatively new on the market).

There are many drivers behind the growth of modification. The increasing demand for wood has put pressure on traditional timber resources – particularly from Asia – and European chemical regulations has reduced the efficacy of chemically treated wood. Interestingly, wood modification has struggled to get a foothold in the USA where chemical regulations are well behind those in Europe. The ability to use fast growing plantation grown wood species, in the 25–50 year range, rather than a mature tree 200+ years old has created huge interest – especially in China where the main source of wood is plantation grown.

Importantly, there are large scale R&D investment opportunities to develop technologies to use homegrown wood. Brimstone was created to use locally grown British hardwoods, thermal modification developed in Scandinavia has improved the performance of locally grown pine and spruce, and Abodo was developed in New Zealand to use locally grown radiata pine. 

All of these developments tap into the desire to reduce consumption of old growth species including valuable and threatened tropical species. The future of modified wood is healthy – although not a silver bullet. In all its forms it has many advantages but there are also a few disadvantages when compared to natural timber.

In all cases it is still wood and not a plastic composite, so when used externally it will lose its colour, it may crack a bit and there will be some variation. However, the macro drivers dictate that modified wood is here to stay. Significant new technologies continue to appear, such as the new Lignia product and current technologies will be enhanced and improved.

We will undoubtedly see copy-cat technologies and maybe some new methods originating from China, followed by huge volumes of material. Technologies will be tweaked to reduce disadvantages such as brittleness and new add-on technologies will be created to further enhance performance and aesthetics. It is also likely that treatment plants of all types will continue to appear and in many cases nearer the raw material, reducing the financial and environmental impact of transportation.

To reap the full benefits of modified wood technology and boost its profile, the architectural and design community need to improve its understanding about these products and the applications to which they are best suited. Certainly the implementation of a third-party accredited testing regime to give the necessary assurances about the efficacy of different modification technologies, to underpin confidence in what are relatively new products is required – and is something the Wood Protection Association is already consulting on.





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