NHBC Standards 2011

2.3 Timber preservation (natural solid timber)


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.


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.


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

2.3 - D1
Design shall meet the Technical Requirements

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


2.3 - D2
Timber and its preservative treatment shall comply with all statutory requirements

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


2.3 - D3
Timber and joinery used in the construction of dwellings shall either have adequate natural durability or, where treatment is undertaken, receive a satisfactory preservative treatment against fungal decay and insect attack

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.


2.3 - D4
The method of treatment and treatment process shall reasonably ensure that the timber is safely and satisfactorily protected against fungal decay and insect attack

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.


2.3 - D5
Measures shall be taken to prevent adverse effects from incompatibility between metal components and treated timber

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 organic  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.