Selection, specification, sourcing and use

The Timber Decking and Cladding Association (TDCA) is offering a material sourcing service where it will contact potential suppliers on your behalf to generate a list of those willing and able to meet your specific needs for individual projects. This and designing for durability are common themes in the daily stream of enquiries received by the TDCA.

In response, the organisation is urging specifiers and users of timber to tighten up on specifications by detailing the durability required in line with relevant standards, particularly for support structures as these can be overlooked.

Broadly speaking you have a choice to design to 15, 30 or 60 year desired service life for external timbers; 15 being the default for decking and 30 years for cladding. The service life is achieved through good design detail coupled with selecting materials of the right quality.

Sourcing accredited materials will help in the pursuit of acquiring durable products; DeckMark^TM and CladMark^TM are the quality accreditation schemes operated by TDCA for its members.

With pressure treated timber, the TDCA stresses the importance of obtaining evidence of treatment which includes confirmation of the standard of treatment and the conferred desired service life. All too often timber is put in place without any inkling of whether or not it meets requirements. Likewise evidence to support the durability claims of any material should always be requested.

A common misunderstanding relates to natural durability; durability classes apply to heartwood only; put simply heartwood comes from the central core of the tree whilst the sapwood is from the periphery or the outer section of the tree. The sapwood of all species is non durable and should either be enhanced by a suitable means or excluded (suitable means includes pressure impregnation with preservative or wood modification).

TDCA online resources covering this and other subjects are designed to help specifiers, designers and installers alike to design for durability. There you will find technical help and publications free to download and if you can’t find what you need, you can use the association’s enquiry service.