Recent market research by the Wood Protection Association (WPA) and Timber Trade Federation (TTF) highlights that when it comes to buying and selling treated wood meaningless generic expressions such as ‘pressure treated’ and ‘green treated’ are common.

The inaccurate or vague description of preservative treated products inevitably increases the chance of a treated product failing prematurely in service and customer complaints. This is a particularly relevant when treated wood is for outdoor applications.

The premature failure of an outdoor wood product damages the reputation of timber as a whole and undermines the opportunities to build confidence and grow the demand for treated wood in an age where designers are increasingly turning to wood as a reliable and sustainable material. In addition, consumer and contract law require that any product offered for sale must be fit for its intended use and a wood product impregnated with preservative is no exception.

The WPA and TTF work in partnership on all wood protection matters, so both associations are now focussed on one clear priority on behalf of their members – to promote the accurate and unambiguous specification and description of treated wood products throughout the UK supply chain.

Staff turnover at some merchant outlets and the sheer range of products now handled by many merchants makes consistently enhancing product knowledge on one particular material a challenge. WPA therefore believes that the answer is to keep the message as simple as possible, communicate it through the right channels and keep reinforcing it until it becomes standard practice for both buyers and sellers. To that end, the communications partnership between TTF & WPA, which now includes the Timber Decking & Cladding Association (TDCA), is vital in order to ensure consistent messaging and maximise the target audience that can be reached.

Keeping the message simple It’s a mistake to assume that all pressure treated wood is the same. Whilst one piece of treated wood may look very much like any other, the level of preservative protection could be very different. That’s because the British Standard for wood preservation, BS 8417, requires that the loading and penetration of preservative impregnated into a timber component is tailored specifically to the service environment. Treated wood for exterior applications like fencing and landscaping are exposed to frequent wetting – the cause of fungal decay. That’s why treated wood destined for exterior applications must have higher levels of preservative protection than treated wood for internal applications where the risk of becoming wet is much lower.

BS8417 sets out the minimum levels of preservative required to protect against fungal decay by grouping the service environment and end use application for treated wood into ‘Use Classes’. Just three use classes cover the majority of interior and exterior applications where treated wood is likely to be used. Use class 2 for interior applications; use class 3u for uncoated exterior above ground applications and use class 4 which is for wood in direct ground or freshwater contact and for exterior structural applications.

The challenge for the WPA, TTF and TDCA was how best to simplify this message for buyers and sellers of treated wood without losing technical accuracy. This has resulted in the three associations agreeing two key messages which will be used by them to target specific sectors of the treated wood market.

1. For the fencing, garden and landscaping sector, the focus is on promoting the use of the term Use Class 4 for treated wood used in contact with or close to the ground, using the WPA’s ‘Make Sure it’s 4’ campaign and communications package.

2. For the broader timber supply chain, the focus of communications is on differentiating between interior and exterior applications for treated wood – using a bold, colour coded Use Class 2, 3 or 4? message and simplified product descriptions.

For those who need further guidance on what the three key use classes mean in practice, WPA and TTF have developed three new Guidance Notes: Understanding Use Class 2,3 & 4 preservative treated wood. These include a simple explanation of what national standards require for each application, what species are most suitable, what preservative penetration to expect in different treated commodities and the necessary quality control criteria.

For wood treatment companies who may need to delve even deeper, the WPA Technical Manual and website provide more extensive information.

For further information or guidance on any of the above please download the new Guidance Notes on Use Classes 2, 3 & 4 and the WPA/TTF Buyers Guide to Treated Wood from the resources page of the WPA website via, call the WPA advice line or get in touch via

Fencing News Blog