Preservative Treatment Approval Schemes
Find a WPA Benchmark Approved (TW) Treater
The WPA Benchmark Approved Treated Wood (TW) Scheme relates specifically to the durability of wood and wood based materials pre-treated by an industrial process.
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Approved Treater
A company operating a treatment plant or plants that have been subject to a WPA 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.
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Approved Product
Treated wood product 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 (indirect) testing*. Approved Products must comply with the requirements of BS8417 / WPA Code of Practice: Industrial Wood Preservation and 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.
(*as defined in the WPA Code of Practice)
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Whilst BS 8417 recommends the levels of preservative penetration and retention it does not provide guidance on how these critical minimum requirements are to be achieved - it points to the WPA Code of Practice: Industrial Wood Preservation to provide guidance in achieving this performance benchmark.
The WPA Benchmark Scheme therefore operates on the principle that wood consistently treated in accordance with the WPA Code of Practice is a durable material which will exhibit the minimum penetration and retention requirements for the relevant end use and service life.
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For full details refer to the Scheme document - available from the WPA.
Apply for WPA Benchmark TW accreditation
WPA TW7 summarises assessment criteria and itemises costs - including discounts for Timber Development UK (TDUK) members.
WPA Benchmark Approved Formulations (TW)
The WPA Benchmark Approved Formulation (TW) scheme provides independent verification of the efficacy of an industrially applied wood preservative, manufactured under ISO9001. Expert assessment is carried out on the laboratory and field test data used by manufacturers to give their customers guidance in the use of a preservative.
The Scheme is specifically for preservatives applied by penetrating processes, typically vacuum-pressure. Approval is based on the minimum retention to be found in the 'analytical zone' after treatment to meet BS 8417 requirements for use class 4 and service life (15 or 30 years) combinations.
The data to be supplied in support of an application is clearly defined in the Scheme Document and is submitted to the WPA for assessment.
Flame Retardant
Approval Schemes
Interlocking approval schemes cover every stage in the production of flame retardant wood based materials. In each scheme, assessments and audits are conducted by independent experts.
WPA Benchmark Approved Formulations (FR)
The WPA Benchmark Approved Formulation (FR) Scheme provides independent verification of the efficacy of a flame retardant formulation. It must be applied or added to wood based materials by a factory controlled process monitored under a recognised quality assurance scheme.
The data to be supplied in support of an application is clearly defined in a Scheme Document and is submitted to the WPA for assessment by an independent Efficacy Panel.
The assessment includes:
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examination of fire test certificates and classification reports and;
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other characteristics that affect performance in service such as wood strength and smoke emission.
WPA Benchmark Approved Treaters (FR)
The WPA Benchmark Approved Treater (FR) Scheme for wood-based materials relates to the factory process used to apply FR formulations.
Where a flame retardant is added during the manufacturing process (for example, MDF, OSB or plywood when covered by a designated (GB/NI) or harmonised (EU) CEN standard) then that process must be subject to factory production control accredited by an approved body (notified body if producing for the EU market). If the manufacturer is the person placing the product on the market, the product should carry the quality mark relevant to the intended market (GB, NI or EU) and be accompanied by a Declaration of Performance (DoP) (or a link to the DoP on a website) when it leaves the factory.
Where the product is factory FR treated after manufacture (typically solid wood and some plywood when covered by a designated (GB/NI) or harmonised (EU) CEN standard) by a service treater, that company must also operate factory production controls accredited by an approved body (notified body if producing for the EU market), alongside those of the company placing the product on the market, so as to maintain full chain of custody. If the treater is the person placing the product on the market, the product should carry the quality mark relevant to the intended market (GB, NI or EU) and be accompanied by a DoP (or a link to the DoP on a website) when it leaves the factory.
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Treaters certificated under this scheme must use a WPA Benchmark Approved Formulation (FR) and the treater must follow the manufacturer’s instructions regarding the uptake of flame retardant required to achieve the desired Euroclass.
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The scheme provides independent third-party auditing and verification that the WPA Benchmark Approved flame retardant has been correctly applied.
The WPA Benchmark Approved Distributor (FR) Scheme is for companies supplying and distributing flame retardant treated wood products which have been treated by a third party, accredited under the WPA Benchmark Approved Treater (FR) scheme and using a WPA Benchmark Approved Formulation (FR).
The Scheme provides independent third-party verification that such distributors can trace products back through their supply chain to verifiable fire test classification reports.​
WPA FR Build approved members
The FR Build scheme is operated by WPA for the Structural Timber Association (STA).
It provides third-party certification of the factory process used to apply STA approved flame retardant on timbers used in the construction phase of a building. This scheme does not confirm compliance of the chemical formulation used with STA performance requirements - that is the responsibility of the chemical manufacturer.
Modified Wood
Approval Schemes
A WPA Benchmark Approved Product (MW) Scheme for modified wood used in ground contact is available. A quality scheme covering the manufacture of modified wood is currently under development.
Apply for Scheme Approval
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If you are interested in submitting an application for a formulation, product or distribution service for any of the WPA Quality Schemes, Contact Us directly and ask for a copy of the relevant Scheme document.