Introduction

The British Standards for specifying preservative treated timber, BS EN 351-1 and BS EN 351-2, have been published for over four years. They require specifications to be written in terms of the results of treatment processes; not by describing the treatments, as used to be the case in the UK. A required penetration of preservative into the wood and the retention (concentration) of preservative within a defined zone of the treated timber is specified. BS EN 351-1 lists nine options that can be used to specify penetration. The retention is specified as the concentration of preservative formulation found to be effective in a series of standard biological test methods laid down in BS EN 599-1. The most significant change for the UK preservation industry is that the treater has to demonstrate to the specifier that the required level of treatment has been achieved. This can only be done by obtaining a sample of the treated timber, randomly selected according to BS 6000-1, ISO 2859-1, and analysing it for penetration and retention. BS EN 351-2 prescribes methods of obtaining the samples for analysis from the selected components.

On publication of the new European Standards, it was recognised that a document to interpret them in terms of the relevant British Standards was required. The British Standards Institution (BSI) published Draft for Development 239 (DD 239) in 1998 to fulfil this role. DD 239 was open for review over the next two years, though feedback was limited due to the lack of practical experience with results based specifications. However, now that the European Public Procurement Directive is in place, specifiers are encountering the European Standards more frequently. Since publication, the DD 239 working document has changed significantly but these changes have not appeared in the publicly available version. The reviews have occurred within British Standards Committee B/515/3 which includes representatives from industry, the British Wood Preserving and Damp-proofing Association (BWPDA) and the UK Government. The Committee has resolved text issues and points of clarity but primarily has focused on the data needed to be incorporated into information tables. During the review period a joint BRE and BWPDA workshop, ‘Specifying timber durability with confidence: the new way forward with preservatives', was organised, seeking input from users and treaters to the final stages of the review of DD 239.

This Information Paper reports on the review of DD 239 and the feedback from the workshop, with special reference to a case study for creosote treated transmission poles.