The Wood Protection Association’s (WPA) Benchmark quality scheme provides independent confirmation that wood products have been treated correctly in accordance with BS 8417, the British Standard for preservative impregnated wood, and the WPA Code of Practice for Industrial Wood Preservation 2021.

Whilst BS 8417 specifies the minimum levels of preservative penetration and retention for every application where wood is used, it does not provide recommendations on how to achieve these critical levels of protection. In this respect it points to the WPA Code of Practice for the essential process guidance.

The WPA Benchmark quality scheme operates on the principle that wood treated in accordance with the WPA Code will achieve the minimum penetration and retention requirements for the end use and service life set in BS8417. Put simply, WPA Benchmark provides the third-party verification of compliance with BS 8417 that TTF members are seeking.

Benchmark broke new ground when it was launched 10 years ago but it is now tried and tested and we believe that the decision taken in 2020 by TTF members to require third-party verification of treated wood will be a major driver to change the way such products are marketed in the UK, building supply chain and buyer confidence and growing demand.

Feedback from wood treaters who were early adopters of the WPA Benchmark show clearly that the scheme has improved customer satisfaction regarding the performance of treated wood in service. These are exactly the commercial benefits that lay behind the decision of TTF members to make the third-party quality assurance of treated wood a key part of their drive to grow demand for treated wood that can be trusted.

WPA Benchmark verifies the quality of an individual treated wood product such as a fence post, decking joist or building component. The scheme provides independent confirmation for both sellers and buyers that a wood product is compliant with the standards set in BS 8417. For ground contact applications a key feature of the scheme is that treated wood products with both the 15 and 30 years desired service life treatment specifications can be certificated.

Wood treaters looking to join WPA Benchmark must be able to demonstrate that a consistent relationship known as the ‘Safe Relationship’ exists between penetration and retention requirements and the more easily measurable aspects of the treatment process, such as preservative concentration and pressure cycle. They must then be able to show that they can control these various aspects in subsequent treatment activities. Verification that a treatment safe relationship is in place for every product requiring WPA Benchmark certification is assessed by an independent auditor. Depending on the data provided by the treater this is carried out either remotely or at the treatment site.

Once a treater achieves accreditation the continued certification of their products is subject to an annual surveillance audit. Depending on the compliance history of a treater this too can be a remote audit.

Under the scheme, Approved Products are those lines for which the production process has been subject to audit and for which the required penetration and retention of preservative has been assured by direct testing or by safe relationship testing. Approved Products will normally be defined by end use/Use Class, species and service life as a minimum. The scope of Products approved will be recorded on a company’s Benchmark accreditation certificate and should be clearly stated in/on company marketing materials, online or in paper form.

Approved Treaters are those companies operating a treatment plant or plants that have been subject to audit and shown capable of producing Approved Products under the terms of the Benchmark scheme. Not all materials produced by an Approved Treater will necessarily be Approved Products, depending on the scope of products submitted for audit.

More details of the scheme and costs can be found in WPA/TTF Guidance Note TW07 WPA Benchmark QAS Executive Summary, available to download free of charge from the WPA website (

We have expanded our team of independent auditors to help meet demand for treaters seeking accreditation to WPA Benchmark before the deadline of July next year. The process of accreditation does not happen quickly and can take a number of weeks if the required data is not available or is incomplete, so we would encourage TTF members who have not already started the process to get in touch now and avoid an accreditation log-jam in the new year.