How to specify modified wood products

The use of so-called modified wood has significantly increased over the last few year. Known for their durability and environmental credentials these innovative products are set to conquer the market. Gordon Ewbank, Wood Protection Association, explains how to specify the right product for the right purpose.

What differentiates modified wood from other types of treated timber?

Modified wood is a generic term for timber products which have been subjected to a modification process; i.e. through the action of a chemical or physical agent. Where the modification process improves the wood durability, this does not involve the use of biocides. 

There are several different process types and therefore several different types of modified wood, each with its own distinct blend of properties. The most common characteristics of all modified wood types are enhanced durability and enhanced stability.

Where do you see the main benefits of using modified wood?

Enhanced stability of the wood provides an improved substrate for a decorative coating, so extending coating life and maintenance intervals. Enhanced durability makes most types of modified wood eminently suitable for most exterior applications above ground level. Currently only two types of modified wood (Kebony and Accoya) are suitable for ground contact applications.

Where do these benefits particularly apply?

The combination of improved stability and durability particularly adds value for exterior, decorative timber joinery products, for example windows and cladding.

What should architects be aware of when specifying modified timber products?

Because Modified Wood is a generic term and there are several different types of modified wood, each with its own distinct blend of properties, it is very important that architects specify a particular modified wood product, rather than just use the generic description. Simply stating ‘Modified Wood’ risks the wrong product being supplied and not meeting the performance expectations of either the architect or client. Full guidance on accurate specification and the different types of modified wood on the market can be obtained from the Wood Protection Association. 

What kind of maintenance do modified timber products require and what are typical lifespans of modified wood products?

The answers to both of these questions will depend on the type of modified wood specified and whether the wood is coated. Product manufacturers can provide full project specific details. As a specific example, a test evaluation conducted by Teknos UK has determined that modified wood brand Accoya significantly extends coating life and reduces maintenance requirements. As an example, after 5 years exposure Accoya® boards have remained in a fully functional condition with virtually no deterioration occurring.

Where would you recommend to go for other types of treated timber and why?

The Wood Protection Association can provide information and guidance on the accurate and appropriate specification of all wood protection systems, including wood preservation, flame retardants and modified wood. 

Can we expect more types of modified wood product to come onto the market in the next 5-10 years?

Possibly, but the growth potential of the market for modified wood products - even with the existing range of technologies - is significant. As processes are refined, production capacity and volumes grow, costs optimise and specifier and user awareness grows, the full potential of these innovative construction products will start to be realised.