Preservative treatment for timber – a guide to specification

Preservative treatment for timber – a guide to specification

Date Published

16 August 2022

Document Type





The first decision to be made regarding preservative treatment is whether the use of a naturally durable species will satisfy the durability requirements or whether treatment is needed. This Wood Information Sheet aims to guide the specifier through the process necessary to reach a decision that will result in a timber component that is fit for purpose.

Aspects considered include service factors, desired service life, the in-service environment, natural durability and regulated products.

This Wood Information Sheet (WIS) guides the specifier through the process of:

Deciding whether a preservative treatment is required to protect a timber product
Specifying where a treatment is required
Specifying an appropriate treatment to ensure that a timber component is fit for purpose with regards to its durability

Key Information

Consider whether treatment is needed by reference to service factor and the natural durability of the heartwood provided the timber component is free of sapwood.

Where minor post-treatment cross-cutting, drilling or notching is unavoidable, this area must be re-treated by liberal brush coating of a preservative recommended by the supplier of the preservative treatment used.

Good design and a specification for maintance of wood components are also important to achieve the desired service life from a treated wood component.

Case studies

Hopkins Architects has been involved in the design of new facilities at Norwich Cathedral for 14 years; the first phase of development, the Refectory (the subject of a TRADA Case Study in 2007) forms one side of the Cloisters and the second phase, the
now-completed Hostry, runs at right angles to it.

The Wooden Annex is a single-storey, fully timber extension to a 1950s end-of-terrace house in South London. The addition of the annex accompanied a complete refurbishment of the existing house, creating increased and improved open living space for the homeowners.