First broadcast on 5 January 2021
In this episode, Tom Heap and Dr Tamsin Edwards take a look at the global possibilities of cities built of wood.
Trees soak up carbon dioxide, trees store carbon dioxide. So why not build with wood instead of concrete and steel?
The usual reason is strength, but Dr Michael Ramage at Cambridge University has what he thinks is the answer- cross-laminated timber. It's strong enough to build a skyscraper and replaces lots of that carbon from conventional building.
Listen now on BBC Radio 4
We invited Dr Harry Kennard FRGS, a Research Fellow in Energy, Climate and Health at the University College London Energy Institute, to offer some observations on the potential of cross-laminated timber beams, and the use of timber in buildings generally. His points take some of the themes of the programme a step further, and some relevant links are offered below:
When focusing on buildings, it’s important to recognise that when you take a ‘whole life-cycle’ approach to a building’s greenhouse gas (GHG) emissions, it becomes clear that most of the impacts result from their use, principally in the form of emissions arising from heating and cooling. Therefore, a focus on reducing construction emissions is most relevant in scenarios where the energy supplied to buildings is already low carbon.
In terms of replacing concrete and steel in construction, it is unlikely that cross-laminated timber (CLT) would be viable for the majority of built environment uses. Darby, Elmualim and Kelly’s case study, which investigates the life cycle carbon emissions and carbon storage capacity of a CLT multi-storey residential building, makes clear that only the building superstructure can be replaced by CLT. The fact that emissions savings are also very sensitive to the end-of-life disposal means of buildings, adds further uncertainty.
An example of a 'mature' built environment in Canterbury, UK (Image: Alyssa Bossom/Unsplash)
Replacement of steel and concrete with these timber-based technologies looks to be most impactful in low to medium-density residential contexts. Moreover, in countries such as the UK, that have ‘mature’ built environments, the vast majority of buildings that will be standing in 2050 already exist. The focus in terms of slashing emissions from the building stock should be on the improvement of energy efficiency in buildings via retrofit and the decarbonisation of the energy supply.
Globally, the fastest growing urban environments are in China, India and sub-Saharan Africa. Here, there may be more scope for CLT. However, the increased demand on the lumber industry must also be considered. Within this broad field there is also scope to consider emergent concrete technologies which hold the potential act as carbon sinks. The importance of placing these technological advances within a wider policy context must be considered.
With this in mind, it's worth reading the conclusions of the UN report on decarbonisation of buildings which emphasises the importance of building codes/regulations."
Ibn-Mohammed, T. et al. (2013), Operational vs. embodied emissions in buildings—A review of current trends, Energy and Buildings 66, pp. 232-245
Darby, H.J., Elmualim, A.A. and Kelly, F. (2013) A case study to investigate the life cycle carbon emissions and carbon storage capacity of a cross laminated timber, multi-storey residential building. In Proceedings of the Sustainable Building Conference, Munich, Germany
Ramage, M.H. et al. (2017) The wood from the trees: The use of timber in construction. Renewable and Sustainable Energy Reviews 68, pp. 333-359
Global Alliance for Buildings and Construction, International Energy Agency and the United Nations Environment Programme (2019) 2019 global status report for buildings and construction: Towards a zero-emission, efficient and resilient buildings and construction sector (pdf)
Rathi, A. (2017), The material that built the modern world is also destroying it. Here’s a fix, Quartz
39 ways to save the world is a new radio series by BBC Radio 4 developed in partnership with the Society and broadcast in 2021. It showcases 39 ideas to relieve the stress that climate change is placing on the Earth. In each 15 minute episode Tom Heap and Dr Tamsin Edwards meet the people behind a fresh and fascinating idea to cut the carbon.
Over the course of 2011, the Society will be producing events and digital content to accompany the series.
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