Performance Based Specification Of Wood

Fundamental to the continued growth of wood in construction is reliable information on the performance of wood in different end-use environments. Ed Suttie, Director at BRE outlines how Project CLICKdesign is set to kick-start a knowledge revolution.

Wood as a material for construction is hugely versatile and offers considerable opportunity to help tackle the climate emergency through afforestation and locking carbon into our buildings through the products we specify.

Improvements to accessing material characteristics is essential. Often this knowledge is locked up in standards, experts' heads, databases and previous research projects. Making it accessible would help get the right product specified for the endues application against a desired performance, from structures to cladding, windows to landscaping uses. A European consortium is working on a new ForestValue research Project called CLICKdesign to do just this by delivering fingertip knowledge to enable service-life performance specification of wood.

Project CLICKdesign started in March 2019 and will run for three years. BRE are leading a consortium of eight European organisations delivering the core research components of building physics, wood science, BIM, service life modelling, entomology and wood based construction products. Alongside a diverse pan-European Industry Group of 19 members from wood protection, architecture, specification, users will pilot and test the modelled components of performance of wood in use to develop an open source tool. Industry group members in the UK include Architype, the Wood Protection Association, Accoya and George Barnsdale windows.

Awareness of the cultural legacy of wood in construction around us are constant reminders of the enduring possibility of wood if knowledge is applied, including knowledge of species and material qualities, knowledge of design details and construction skills, knowledge of local conditions, climatic and other challenges. This knowledge is fragmented, localised and in some cases difficult to analyse and use especially by non-wood experts. The solution through CLICKdesign is to put this knowledge at the fingertips of the specifier, so more can meet their ambitions to deliver low carbon construction, through performance based design with wood.

Service-life planning and performance classification are core issues in construction underpinning product specification and use. The absence of durability performance-based specification for wood is currently a limit of opportunity. Concrete, steel and polymeric sectors deliver software to architects and students enabling performance based specification and consistent teaching of design best practice. This does not happen comprehensively in Europe for wood, though specific initiatives do exist e.g. UK Structural Timber Association guidance and the German Carpenter Association's Guideline on Building Facades, Terrace decking and Balconies. This gap and the fact that technical specifications for performance are increasingly required for use in Building Information Modelling (BIM) and life cycle analysis (LCA) service-life data has driven the development of project CLICKdesign.

Project CLICKdesign key objectives are to:

• Provide the scientific understanding of how the inherent properties of a wood and in-service environmental exposure are related to the response
(performance) linked to defined limit states for the product
• Understand and bring together the models and performance databases associated with decay and integrity, aesthetic function, insect and termite
performance to create a holistic pan-European approach
• Validate a set of models using real-case studies (buildings, structures) from across Europe in collaboration with expert witness and
engineering bureaus
• Inspire new wood-based design solutions and specifications and support a new generation of 'timber savvy' designers by taking an
important step towards digitalisation of knowledge and specification
• Deliver a software tool into pilot usage following the open source standard (IFS, ISC) for BIM readiness via consideration of information
template, databook entry and plug-ins.

The established specification of wood durability is not performance-based. Service-life is referred to as unquantified and an ambiguous way using terms such as 'reasonable working life' or 'satisfactory performance'. Timber engineers utilising Eurocode 5 find the ineffectual language doesn't stand scrutiny and is of little value. For performance modelling of wood products biological agents need to be considered with particular attention for mould, decay fungi, termites and other insects. First attempts prepared using various dosimeter models were made in previous European research projects. Good progress has been made during recent years in service-life planning and performance prediction of woodbased woodbased components and structures, but as repeatedly became evident, the complexity of performance is still not captured in these processes and it remains 'on the shelf' rather than in use. The foundation of previous work has been gathered and reviewed as first priority of the project. In addition, project CLICKdesign includes for the first time a focus on:

• Robust time forecasting of visual aesthetic changes on wood surfaces e.g. exterior cladding
• Development of a European termite and insect performance measure
• Accommodation of climate change driven changes to exposure dose e.g.the distribution and locations of wood destroying organisms which
may, for example, expand termite risk zones in Europe.

Key to the success for CLICKdesign is that the tool finds application across Europe's rich diversity of geographic, climatic and cultural regions. This will be possible by using a structured approach that enables direct localisation for the user. The team are cognisant of fostering the different traditions for the use of wood, differences in expectations on service-life and warranties, differences in cultural aspects towards product maintenance and providing language accessibility. 

The specification of performance of wood products is complex and requires use of multiple platforms of data, empirical evidence, experience, standards and national recommendations. CLICKdesign over the next three years will provide a tool that has embedded within it the decades of excellent research, the complexity of the standards specification systems and the variation of approach due to tradition, materials and culture across Europe. The tool will be accessible to professional users and will be refined with industry to ensure relevancy and accelerate uptake and use. This will increase market confidence with users for selecting wood as a reliable product and enhance an optimised performance of timber in the built environment. We are hopeful it will also inspire new wood and woodbased products using the tool and create business opportunities for the forest-based industries to innovate. 

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