The key sources of guidance on enhancing the durability of wood are:
- BS 8417: Preservation of wood – recommendations
- Specification Manuals of the Wood Protection Association (WPA)
- Industrial Wood Preservation Code of Practive
- Modified Wood Specification Manual
BS 8417 provides broad guidance on the pre-treatment of solid timber and panels with the preservatives approved for use in the UK.
WPA is the UK authority of wood protection technology and is principal advisor on the development of wood preservation, flame retardants and modified wood technology. Its specification manual on wood preservation includes Commodity Specification codes for the most popular applications.
Care should be taken to source materials that are treated in strict compliance with BS8417. Inappropriate levels of treatment or poor site practice may result in in a treated component having lower durability than that required in Use Class 3 cladding applications.
The WPA Commodity specification code for the preservative treatment of External Timber Cladding is C6. WPA wood preservation commodity codes are also referred to and form the basis of NBS specifications (Code Z12).
TDCA recommends that preservatives be manufactured in accordance with ISO9001 quality certification and applied by treaters that are WPA Benchmark approved or approved by the preservative manufacturer. The main treatments for cladding are shown in the table below.
WPA COMMODITY CODE C6
Suitable wood preservatives to give a 30 year desired service life based on service factor C.