A question of durability

A perennial weed in the flowerbed of timber specification is the question about the service life of a wood product. It depends where, what and how?

To those who understand wood, it’s a complex enough business, requiring comprehension of many standards and distillation of years of experience to provide instinctive evidence. If it’s complex for us, it’s unsurprising that the wider user community and general public struggle to understand, and that can manifest in premature failure, disappointment and a loss of confidence in wood.

Performance classification of wood in construction aims to bring together the material characteristics of a product and its exposure to weather and moisture to define a performance class. It is focused on specification of the right material for purpose. It’s key to underpinning confidence in wood; its ability to deliver service life specifications and, more importantly, to meet customer expectations of performance. It is needed for service life information in environmental product declarations, for material certification schemes and for replacement intervals in whole building assessment methods such as BREEAM.

Standards help provide vital frameworks to build on, but the mix of service classes in EN1995 Eurocode 5, use classes in EN335 and durability classes in EN350 is unclear to many. I had to re-read a passage in one standard four times before I fully understood its meaning. Standards help, of course, and the Wood Protection Association underpins its quality schemes with BS8417 and desired service lives for products of 15, 30 or 60 years. It is the first standard to mention service life aspirations for durability and helps answer the durability question in many respects, certainly for treated wood.

If we consider how steel, concrete and plastic tackle the question “How long will it last?”, they’ve developed specifier software to do just that. Some may say that’s easy for a homogenous man-made material, but it’s still complicated by exposure conditions, application, end use and design and build quality. For wood in construction we don’t have such software for specifiers, who require a product with a specific performance classification to meet their needs.

So at BRE we’ve embarked on a three-year, pan- European research project under the ForestValue funding umbrella, which aims to plug this gap.

Project CLICKdesign will develop a performance-based specification protocol to enable provision of a software tool for architects and other specifiers to embed service life performance specification for wood. This will help them deliver low carbon construction through performance-based design with wood. It will inspire new wood-based design solutions and specifications and support a new generation of ‘timber savvy’ designers by taking an important step towards knowledge digitalisation following open source standards for BIM readiness.

The project brings together researchers and industry from Finland, Sweden, Norway, France, Germany, Slovenia and the UK. BRE will co-ordinate UK workshops for industry and specifiers with the aim of ensuring this tool uses the right language, targets appropriate actions and, crucially, can answer the durability in use question to the benefit of UK business.