2.3 Timber preservation (natural solid timber)

SCOPE

This Chapter gives guidance on meeting the Technical Requirements and recommendations for the protection of natural solid timber against fungal decay when exposed to damp conditions and against insect attack.

LIMITATIONS

This Chapter only refers to treatment of natural solid timber. It does not relate to timber products such as plywood and wood particle boards.

This Chapter only gives acceptable treatment schedules and does not cover:

• condition of the timber before treatment
• techniques of operating the treatment process, which is the responsibility of the organisation carrying out the operation.

DESIGN STANDARDS

2.3 - D1	Design standards
2.3 - D2	Statutory requirements
2.3 - D3	Durability
2.3 - D4	Method of treatment
2.3 - D5	Compatibility with metal components

Design that follows the guidance below will be acceptable for timber selection and preservation.

STATUTORY REQUIREMENTS

Design should be in accordance with relevant Building Regulations and other statutory requirements

DURABILITY

Timber and external joinery should be either:

• naturally durable and resistant to insect attack, or
• treated with preservative in accordance with this Chapter.

Appendix 2.3-A provides information to establish whether or not treatment is necessary for a particular element or timber species and also the type of treatment.

METHOD OF TREATMENT

For timber or joinery which requires treatment, it is important that it is carried out to appropriate standards which are both suitable and safe. Treatments in accordance with procedures set out in British Standards, Codes of Practice or which have been satisfactorily assessed by an independent authority, will be acceptable, unless otherwise notified in writing.

COMPATIBILITY WITH METAL COMPONENTS

Where copper/chromium containing preservatives (CC, CCP or CCB) have been used, it is important that metal fittings are not applied to the timber until the salts of the treatment have been "fixed" (7-14 days). In situations where occasional dampness is expected, metal fittings in contact with timber treated with copper containing preservatives should be galvanized. Where timber treated with copper containing preservatives is likely to become wet, fittings of austenitic stainless steel should be used.

Copper containing treatments can create a corrosive cell between mild steel and aluminium.