The Wood Protection Association (WPA) is urging online buyers of pre-treated timber fence posts to make sure the product they are looking at is fit for purpose before they click the ‘buy’ button.
Research by the WPA has highlighted a growing trend for offering fence posts that are only treated for external, out-of-ground- contact applications and not in compliance with British Standards – in which a higher level of treatment is essential for wood that is embedded in the ground. Online sellers claim such fence posts are ‘UC3 treated’, are ‘durable’ – meaning resistant to fungal decay – and that they will give a ‘long-term performance’, but without exception, they fail to qualify what these statements mean.
“This is grossly misleading and will only result in these posts rotting and failing after just a few years,” says WPA Chairman Steve Young, who emphasises that the actions of a few selling under-treated wood have negative consequences for the many involved in timber supply and merchanting. “While a business selling a wood product incorrectly treated for its application may profit from those sales, it is a short-sighted strategy and will only result in a loss of trust in the performance of treated wood.” He adds that the knock-on effect of this will inevitably reduce demand for every business with a commercial interest in producing and selling treated wood in the UK.
At a time when the sustainability, carbon-capture and climate-change benefits should be giving treated wood sales a boost – because while wood locks up carbon, treated wood locks it up for longer – selling products that are compliant with the British Standard specifications for preservative pre-treated wood BS 8417 is the only way to grow demand.
Research by the WPA also highlights that knowledge about how to specify and buy wood products correctly treated and fit for the purpose required is low. “Helping improve seller and buyer knowledge is a key reason behind the WPA recently joining the BMF,’ says Young. “We look forward to working with the BMF and Timber Forum team to bring this about.”
Largest ever UK field trial shows treated wood significantly outperforms untreated
Interim results of the largest independent assessment of British treated softwood ever carried out in the UK demonstrate that treated wood for ground contact applications such as fencing can be relied on to provide a long service life.
The 10-year UK field trial of hundreds of wooden fence posts and test stakes was commissioned by the WPA and carried out by the Building Research Establishment (BRE) at two test sites: at BRE Garston, Watford, and Birnie Wood, Elgin, in the north of Scotland. It shows a substantial improvement in durability and resistance to decay when compared to untreated timber products.
The majority of the untreated wood posts at the sites have now completely failed due to fungal decay, with data suggesting an average service life of less than five years. The study also notably shows that posts made from larch are failing faster than any other species. “These results clearly show that untreated wood of any kind is not fit for purpose for ground contact applications,” said WPA Director Neil Ryan. “Only wood that has been correctly treated gives the performance required to ensure long-term success. The study also dispels the myth that larch is durable and can be used in this way without a preservative treatment.”
After 10 years, the preservative-treated posts in the trial are performing well, particularly incised spruce. Some opening of incisions and elevated moisture content has been noted, but without deterioration of the wood.
Across all species and treatment types in the trial, there have been only isolated failures of treated posts. “This is not entirely unexpected after 10 years. These are clearly outliers on the bell curve of preservative performance, with others in the same species and preservative group rated zero – meaning they still have no visible decay present at all,” said Ryan.
WPA Chairman Steve Young added: “This landmark independent study demonstrates clearly that preservative treated wood works outdoors. It confirms that correctly treated wood is the only reliable choice for ground contact applications. At a time when businesses’ sustainability obligations are increasing, correct treatment allows them to use wood – the only endlessly renewable construction material – for the maximum possible time.”
The WPA set up the field trial in 2015 in partnership with BRE and a group of industry sponsors, with the goal of helping develop industry standards, including BS 8417 and the WPA Code of Practice – to support WPA Benchmark quality approval schemes for treated wood, and to build market confidence in preservative-treated British softwood species. After the completion of the initial 10-year term, the project has been extended for a further five years.
