Make sure it’s UC4

Make sure it’s UC4

Independent accreditation of wood treatment operations is now a requirement for Timber Development UK (TDUK) members

Nick Boulton
Head of Technical & Trade

To ensure that you buy the product that has had the right treatment, first it is important to understand which is the right treatment.


The WPA Benchmark Approval Scheme provides quality assurance for wood which has been preservative pre-treated by an industrial process.

The Wood Protection Association has published a series of guides to ensure users know the difference in timber treatments, from Use Class 2 for interior use, to Use Class 3 and Use Class 4 for exteriors.

Part of the project is to note and reference those companies that are treating their products to their respective Use Class with a “Benchmark Approved Treater” logo, as well as “Benchmark Approved Treater Product” logo to assure merchants and buyers of it having the right treatment.

The audit process focuses on establishing that an effective quality management system is in place which meets the criteria clearly set out in WPA Quality Guidance Note QGN2.

Particular emphasis will be placed on the accurate specification of treated products and description/labelling of goods, along with the provision of adequate customer/end user information and training, where appropriate, on the safe and effective use of treated products.

Approved Product accreditation can only be granted to a company already holding Approved Treater status. However, the company being audited must also be able to demonstrate that a consistent relationship exists – known as a Safe Relationship – between the penetration and retention requirements and the more easily measurable parameters of the treatment process.

For a treated product to be approved, sample analysis data must be presented to demonstrate that the penetration and retention requirements for that product have been achieved in a statistically significant number of samples.

With independent accreditation of wood treatment operations a requirement for TDUK members, promotion of treated timber products on our channels is strictly limited to those who meet the appropriate standard.


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