Decisions about the need and level of treatment must also take into account the risk and consequences of failure.  One use class can cover a range of components yet the risk and consequences of failure can vary from one to another. 


During project specification each timber component should be assigned a service factor code to assess the need for preservative treatment. 


The most widely used process for applying preservative treatments to both solid wood components and panel products is vacuum-pressure impregnation. This is carried out by specialist companies in large pressure autoclaves under factory controlled conditions.

Industrial impregnation plants are sealed and controlled systems, there is no wastage of preservative or risk to the environment and human exposure during the process is prevented


Find out more in the Application Technologies section

WPA Industrial Wood Preservation Manual – updated version available soon!

We have covered timber preservative treatments and their specification here in brief but if you need more in-depth information, please get in touch as our manual is currently being updated.

Alternatively, visit our Resource Centre where we have a wealth of additional information, free to download.


Members who are National Highways Sector Scheme 4 certified

Every aspect of highways construction and repair is covered by a specific sector scheme. Procedures for treated wood fencing specification and procurement is covered in Sector Scheme 4 (SS4). Companies must be ISO9001 certificated as SS4 compliant before they can bid for treated wood supply contracts on highways projects.


Much of the SS4 Scheme Document published by UK Accreditation Services (UKAS) is based on and makes direct reference to WPA Quality Guidance Note 2 (QGN2) and the specifications and practices set out in the WPA Manual of Wood Preservation. 

Take a look around the

Resource Centre

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All of our resources are free to view and download. Please contact us if you have questions about any aspect of wood protection specification, quality assurance or application good practice.

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