Awareness of the contribution of greenhouse gas emissions to global warming has led to a variety of strategies being proposed to capture or sequester carbon dioxide in biomass, not least in the forest, and subsequently as timber in service. A wide range of other greenhouse gas abatement strategies have also been considered, including displacement of materials with high embodied carbon by those with lower embodied carbon. The embodied carbon of a material is generally due to fossil-fuel consumption in manufacture or to carbon emissions resulting from chemical reactions such as the hardening of cement. Many industries have developed decarbonisation strategies, to reduce fossil fuel consumption, increase process efficiencies, and thus reduce carbon emissions associated with manufacture. Simultaneously there has been an interest in diversifying the fuel platform from fossil based to renewable sources, leading to development of biomass energy from resources such as wood chip, short rotation coppice, miscanthus and wheat straw. This gives rise to a need to evaluate the volumes of timber available for different uses as we move towards a future where there is increased reliance on timber as a renewable structural material, and as a potential source of bio-energy.

The use of timber in the built environment offers two distinct benefits in reducing the carbon footprint of buildings. Firstly, timber can be manufactured using relatively low energy and carbon inputs, leading to a low global warming potential when evaluated by life cycle assessment (LCA). As a result, the increased use of timber in construction, either in timber framed houses, or in mass timber structures offers a displacement effect relative to traditional methods such as brick and block, or concrete or steel frames systems. Secondly, the timber within buildings offers a long term use of timber, providing a pool of sequestered carbon dioxide within the built environment, where residence time is likely to be in excess of 50 years, and in many cases is greater than 100 years. This concept has been indicated by the Read report, among others, with the indication that between 1.1 and 2.2 MtCO2e per year could be locked up in UK new housing starts, with variation resulting from different methods of estimation employed (Suttie et al. 2009, Robson et al. 2014). Within a recent project (to be reported this summer), the project team have developed this concept using model buildings to permit evaluation at a bill of quantities level for open panel timber framed systems and brick and block masonry structures of identical footprint. More recent developments such as cross laminated timber (CLT) in tall timber buildings have further expanded the potential to use timber to store sequestered carbon in structures.

Utilising these model houses, this presentation will explore the GHG abatement potential of a model new town with a variety of house types. While such a new town is a model concept, it offers insight into the potential role of timber in long term storage of carbon, and offers an opportunity to compare carbon accounting within bioenergy (short cycle) and long cycle systems. The thought experiment permits quantification of the effect of storing sequestered carbon in buildings, and allows comparison between building methods and structural forms. It is highly likely that as energy efficiency measures in the built environment take effect, the carbon intensity of the structures themselves will be increasingly relevant in balancing the nation’s carbon budgets. Therefore consideration of GWP of buildings is timely. In addition, when considering carbon storage in the built environment, the building service life and eventual reclamation and recycling of wood waste from demolition becomes relevant. This discussion of carbon accounting for timber in service, in bioenergy or in generating energy from wood waste is highly relevant to the forest and timber sectors.