As stability returns to the timber industry following the turbulent trading conditions of 2021 the need to quality assure preservative-treated wood is again concentrating minds.

That’s because members of the Timber Trade Federation (TTF) decided in November 2020 to require independent verification of the impregnation process that produces the treated wood they supply and are now working to make this happen. TTF members account for over 80% of all the wood placed on the UK market. Such a market share comes with responsibilities and taking the lead on treated wood is seen as essential to their customers buying timber that can be trusted.


Until now, UK timber traders have shown little appetite to adopt schemes that independently verify treated wood processes and products. Compare that with the USA, Canada and Scandinavia where third-party quality assurance schemes for treated wood have sustained demand for decades it is no small wonder that the members of the TTF now see quality assurance as the key element in the Federation’s Action Plan to build buyer trust and loyalty and grow demand for added value treated wood products.

Other key elements of the TTF Action Plan include communication campaigns to highlight how treated wood should be specified and marketed to reflect its application, indoors or out as well as guidance on installation good practice. With these campaigns ongoing until 2023, TTF members are now increasingly focused on how they comply with their commitment to getting the treated wood they produce or source from others quality certificated by a recognised third party. For many wood treaters, the route to treatment process compliance is the WPA Benchmark quality scheme operated by the Wood Protection Association (WPA).

The WPA Benchmark QA Scheme has been operating successfully for over 10 years and includes wood treaters in the UK and overseas. Under this scheme, individual treatment plants and the products they produce are certified by a third-party verification audit as being compliant with national treatment standards. The early adopters of the scheme say that certification has dramatically improved customer satisfaction ratings and WPA reports a significant rise in applications to join the WPA Benchmark scheme from both TTF members as well as the companies that supply them. The journey to quality certification starts with understanding the principles on which the WPA Benchmark scheme is based and what’s involved in the compliance process.


The British Standard for preservative impregnated wood is BS 8417. Published as a Code of Practice this standard recommends the minimum preservative penetration and retention (‘R’ values) that must be achieved to ensure a wood product is treated correctly for its intended application to meet the 15, 30 or 60 years desired service life options set out in the standard.

Whilst BS8417 recommends the levels of preservative impregnation that must be achieved, it does not state how these critical ‘minimum requirements are to be achieved. In this respect, BS8417 points to the WPA Code of Practice: Industrial Wood Preservation for practical guidance. As such, the basic principle on which the WPA Benchmark QA Scheme operates is that wood treated consistently in accordance with the WPA Code of Practice is a durable material, resistant to biological organisms and will exhibit the minimum penetration and retention requirements set in BS8417 for a given end-use and desired service life specification.

The wood treater being audited must be able to demonstrate that a consistent relationship – known as the ‘Safe Relationship’ – exists between the penetration and retention requirements and the more easily measurable parameters of the treatment process, such as preservative concentration and pressure cycle. They must also be able to demonstrate how these parameters are controlled consistently in all subsequent treatment activities.


The WPA Benchmark scheme can be used as either an ‘Approved Products Scheme’ or an ‘Approved Treater Scheme.

Approved Products or product groups are lines for which the production process has been subject to audit and for which the required penetration and retention of preservative is verified and backed by test results. The Scope of products approved will be recorded on a company’s WPA Benchmark accreditation certificate which can then be used in sales and marketing materials aimed at buyers.

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 treated materials produced by an Approved Treater will necessarily be Approved Products, depending on the scope of products submitted for audit and the commercial objectives of the treater.

Detailed information about the WPA Benchmark and guidance on the third-party audit process and the evidence that has to be provided is available on request from the WPA.

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