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WPA Resources:
Preservative Treated Wood

WPA publications are free to view and download 

Buyer's Guide to Preservative treated wood

The Buyer's Guide to Preservative Treated Wood

Preservative treatment provides wood with added durability. However, it’s a mistake to assume that all pressure treated wood is the same. Whilst one piece of treated wood may look very much like any other, the level of preservative protection could be very different 

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Use Class 4 Timbers: 
specifying, buying and installing

For the fencing, garden and landscaping sector, for applications in contact with the ground, frequently wet and/or providing exterior structural support, the fitness for purpose of treated wood is crucial.

Specify Use Class 4 treatment and make sure to buy from a trusted supplier.

FAQs, Guidance Notes & Information
Codes of Practice
Training and Webinars
Research Projects
Use Class House graphic

Learn about our campaign to promote
'fit for purpose' treated timber

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FAQs - Guidance Notes & Information Sheets
Guidance for wood treaters in the Nordic region

Q. How do UK preservative treatment requirements (of BS 8417) relate to the Nordic NTR Scheme?

WPA TW1: Guidance for Wood Treaters in the NTR Region

Timber treaters in the NTR region do not normally treat spruce for external, uncoated applications. However, this is permitted by BS 8417, the relevant UK standard. This fact sheet provides guidance to NTR treaters on how the treatment of spruce to meet a BS 8417 Use Class 3 specification aligns with current NTR classes and specifications. 

Achieving quality treated wood TW2

Q. How can wood treaters assure effective quality timber treatments?

WPA TW2: Guidance on Achieving Quality Treated Wood

 In 2017 TTF & WPA collaborated on a survey to identify the strategic priorities needed in order to grow demand for preservative treated timber. Analysis of the responses identified three priority areas for action. This note concentrates on the last point: To ensure independent verification of the treatment process. 

Brexit and the BPR TW3

Q. How does Brexit and the BPR affect the treatment or supply of treated timber?

WPA TW3: Brexit and the EU Biocidal Products Regulation (BPR)

Treaters and users of treated wood (whether treated in the UK or imported treated) should, for the time being, see no impact on their practices and availability of treated wood from a regulatory viewpoint, now that the UK has left the EU. This Guidance will be updated if things change.

Indoor Air Quality and treated wood TW4

Q. What impact does treated timber have on our indoor air quality?

WPA TW4: Preservative Pre-treated wood and Indoor Air Quality

The indoor air environment is a complex subject that needs to consider the nature and source of any chemical, its ability to pass into the indoor air, its effect on humans when in the air, and the ability to remove it from the air by ventilation. 

Preventing mould growth on treated wood TW5

Q. How do you prevent mould growth on treated wood products?

WPA TW5: Preventing Mould Growth on Treated Wood Products

Mould fungi can grow in the water layer on wet and damp timber surfaces. The growth is often fluffy and may be white, green, black or coloured, depending on the species and presence of spores. 

Creosote treated wood TW6

Q. What are the current rules about creosote treated timber?

WPA TW6: Use of Creosote and Creosote-treated Wood

There are specific permitted uses for creosote in the UK under the Biocidal Products Regulation - read all the details in this publication.

WPA Benchmark Treated Wood Scheme TW7

Q. I'm a timber service treater, how do I get WPA Benchmark Approved Treater accreditation?

WPA TW7: WPA Benchmark Scheme for Preservative Treated Wood - Executive Summary 

The WPA offer two compliance routes to WPA Benchmark accreditation. This note summarises assessment criteria and itemises costs - including discounts for Timber Development UK (TDUK) members.  

WPA guidance TW8 Understanding Use Class 4

Q. How do I know if my ground contact treated timber will last and be fit for purpose?

WPA TW8: Understanding Use Class 4 - Preservative Treated Wood  

make sure its 4 logo

For wood in permanent ground or fresh water contact, or providing exterior structural support, Use Class 4 levels of protection MUST be achieved. Read why this is important and how it can be achieved through correct specification and treatment.

WPA guidance TW9 Understanding Use Class 3

Q. How do I know if my above ground treated timber will last and be fit for purpose?

WPA TW9: Understanding Use Class 3 - Preservative Treated Wood  

For outdoor wood used above the ground, such as decking or cladding boards, Use Class 3 levels of protection apply. Read why this is important and how it can be achieved through correct specification and treatment.

Understanding Use Class 2 TW10

Q. Do internal construction timbers need to be preservative treated?

WPA TW10: Understanding Use Class 2 - Preservative Treated Wood  

Where wood is used indoors, above ground and within the building envelope, but with an occasional risk of wetting (and where roof timbers are at risk from Hylotrupes beetle infestation), Use Class 2 levels of protection are required. Read why this is important and how it can be achieved through correct specification and treatment.

Understanding Use Class 3C TW11

Q. Do coated outdoor joinery timbers need to be preservative treated?

WPA TW11: Understanding Use Class 3c (coated) - Preservative Treated Wood  

For outdoor joinery wood which is coated and used above the ground, such as window frames or cladding boards, Use Class 3c levels of protection are required. Read why this is important and how it can be achieved through correct specification and treatment.

BAT and Timber Treatment Operation TW12
UK IG Note 2021

Q. What are the rules around permits for wood treatment operations in the UK?

WPA TW12: Best Available Techniques (BAT) Conclusions for Timber Treatment Operations – UK Interpretational Guidance  

Timber treatment activities with plants having a capacity of more than 75m3 per day, (excluding anti-sapstain treatment), are required to operate in accordance with a regulated permit.  In December 2020 the EU published a new reference document on how to determine permit conditions and best environmental practice: EU Best Available Techniques (BREF) conclusions for Timber Treatment Operations.


On 6th January 2021, the UK IPC Regulators Group issued interpretational guidance on the recent EU BAT conclusions document - the UK IG Note 2021. This will be used by the relevant UK regulators when determining new permit applications and reviewing existing permits.

Guidance Note TW 12 covers the background and implications of both documents and looks at the new permit process.

Installing Treated Timber Fence Posts TW13

Q. What do I need to know when installing treated timber fence posts?

WPA TW13: Installing Preservative Treated Fence Posts - Best Practice Guidance  

All pre-treated wood products are impregnated in their finished form and are designed to be installed without modification.

This Guidance Note details, with simple illustrations, everything you should consider when preparing and installing both ROUND and SQUARE sawn softwood posts, pre-treated with a preservative for fencing applications.

WPA TW 14 Classification of Wood Waste

Q. How do I dispose of treated wood waste safely?

WPA TW14: UK Guidance on the Classification of Treated Wood Waste

Guidance from the Wood Recyclers' Association to help ensure waste wood is: correctly classified at its origin; is not mis-described and is processed into appropriate end uses; can be identified as hazardous or not.

Preservation Treatment of Wood-based Sheet Materials TW15

Q. How do I specify preservative treatment for wood-based sheet materials ?

WPA TW15: Preservative Treatment of Wood-based Sheet Materials

This Guidance Note applies to the preservation of panel and engineered wood products. But is also relevant to other products such as I-beams which include either a mixture of different wood-based composite products, or a mixture of wood based composite products and solid wood.

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Q. How do I handle and store preservative treated timber?

WPA TW16: Storing and handling and preservative treated timber

Wood preservatives used in industrial treatment plants are highly regulated to ensure they are safe and effective. Equally, suppliers and end users have a duty of care to store, handle and use treated timber as advised by the supplier of the treated wood product.

TW14 Waste Wood
TW16 handling treated timber
TW 15
Quality Guidance Notes: Controlled Copies
WPA Quality Guidance Note 2

Quality Guidance Note 2 (QGN2): For use with BS EN ISO 9001:2015
Relating to the controlled preservation of wood and wood-based materials to improve their durability.

This document can be used as part of a Quality Management System audited by a Certification Body and as part of a quality plan audited under the WPA Benchmark scheme. QGN2 forms the basis of the National Highways Sector Scheme 4 for the preservative treatment of fencing and is referred to directly in Highways England quality scheme documents. QGN2 is an operating document of the WPA. It is a ‘controlled document’ in Sector Scheme 4 and is an essential part of the verification audits required by the scheme and carried out by UKAS accredited Certification Bodies.

Marked timber for construction

Q. How do I mark my treated wood product to be in line with current rules?

INFORMATION: A Guide to Marking Wood (treated with a preservative or flame retardant)

From the end of the Brexit transition period (31 December 2020) new rules apply to the marking of timber in the UK outside of N. Ireland – the area called Great Britain or GB. This Information document provides model examples of markings for treated timber products.

Marking Treated Wood information
Marking Wood
TW cop
WPA Codes of Practice
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NEW WPA Code of Practice: Standards of Training  
Timber Treatment Installations

To support employers of timber treatment plant operators, this Code of Practice provides practical guidance on the standards of training required for safe and effective wood preservation.

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4th Edition WPA Code of Practice: Industrial Wood Preservation

A valuable and current reference of standards and good practice for treaters, specifiers and users of treated wood. This publication supports the ongoing education campaign to raise awareness within the wood supply chain for the accurate specification of preservative treated wood products.

This document replaces the former WPA Manual: Industrial Wood Preservation - Specification and Practice.

WPA Code of Practice Timber Treatment Installation

6th Edition WPA Code of Practice: Timber Treatment Installations 
Design and Operation

A publication reflects changing technology and legislation and provides up-to-date practical guidance on environmental, safety and health issues relevant to all companies engaged in the activity of industrial timber treatment. 

Research Projects
Preservative Treatments for Wood: Research Projects
Treated Timber Field Trials Year 7 Summary

WPA Field Trial of Preservative Treated British Softwoods - Year 7 Observations
To assess the durability in differing test site conditions

WPA in collaboration BRE commissioned a long term controlled field trial of sawn and pressure treated British Softwood posts at two sites with differing soil conditions - here's a summary of the results so far. 

Indoor Air Quality and Treated Timber

Preservative Treated Wood and Indoor Air Quality

The WPA commissioned Building Research Establishment (BRE) to help them understand how treated timber performs in the context of air quality within buildings to actively support the continued safe and appropriate use of wood preservatives to enhance the performance of timber used in construction.

Need to get in touch?

If you cannot find the answer to your question within any of the listed publications, please get in touch.


We have knowledgable people based in the UK office as well as numerous technical consultant members we can call upon to assist you.

Go to CONTACT US page or give us a call.

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