Structural Engineering and Carbon Footprints of CLT Buildings

The multi-disciplinary research project “Improving the competitive advantage of CLT-based building systems through engineering design and reduced carbon footprint” (Linnaeus University, 2019) is an example of effort to optimise CLT in building applications. This large project is a collaboration between the academia and industry in Sweden and addresses four major aspects of CLT in building construction (Figure 2): (i) optimized raw material utilization for CLT panels, (ii) construction and connections of CLT assemblies, (iii) risk management in building service-life, and (iv) life cycle carbon footprint of CLT buildings. A primary focus of the research is to identify the synergies between the four aspects.

The research on optimized raw material utilization concerns efficiency of raw material use and the development of appropriate grading schemes for production of strong and stiff CLT panels. The research on construction and connection focuses on the development of connectors with optimal material usage and efficiency in the assembly phase of CLT construction. The research on building risk part concerns assessment and mitigation of plausible risks during the service life of CLT buildings. Theresearch on life cycle carbon footprint explores and identifies strategies to optimise the climate impact of CLT buildings, focusing on the synergies between the structural engineering aspects and life cycle climate performance.

Synergies for reducing the carbon footprint

Ongoing research (Dodoo et al., 2021) shows that CLT-based building systems can be further optimised from a structural engineering design and climate impact point of view. For example, the thickness of CLT structural elements may be optimised to achieve a 5% average reduction of the thickness of typically designed CLT elements. Steel-based screws and fasteners for connection of CLT elements may be greatly optimised, thereby achieving about 25% reduction in the mass of the screws and fasteners without compromising the structural performance. Long-term service life monitoring facilitates prediction of potential damage and hence timely preventive actions in CLT buildings. Subsequently, damage, repairs and replacements of CLT elements are minimised with the improved service life risk management.

Analysis shows that the life cycle carbon footprint of a CLT multi-storey building may be reduced by up to 43% when considering the synergies between structural engineering solutions and LCA (Dodoo et al., 2021). Research is helping to improve the confidence in, and competitiveness of, CLT in multi-storey building construction.

References

Birgisdóttir, H. (2021). Why building regulations must incorporate embodied carbon. Commentary in: Buildings and Cities. https://bit.ly/3Bu0sMQ

Boverket. (2020). Utveckling av regler om klimatdeklaration av byggnader (In English: Development of rules on climate declaration of buildings). Karlskrona: Boverket. https://bit.ly/3nxZDhL

Dodoo, A., Truong, N.L., Dorn, M., Olsson, A., Bader, T.K. (2021). Exploring the synergy between structural engineering design solutions and life cycle carbon footprint of cross-laminated timber in multi-storey buildings. Wood Material Science & Engineering. https://doi.org/10.1080/17480272.2021.1974937

Global Alliance for Buildings and Construction, International Energy Agency. (2019). 2019 Global Status Report for Buildings and Construction: Towards a Zero-emission Efficient and Resilient Buildings and Construction Sector. https://bit.ly/3nOO2ff

Jayalath, A., Navaratnam, S., Ngo, T., Mendis, P., Hewson, N. & Aye, L. (2020). Life cycle performance of cross laminated timber mid-rise residential buildings in Australia. Energy and Buildings, 223, 110091.

Kuittinen, M. & Häkkinen, T. (2020). Reduced carbon footprints of buildings: new Finnish standards and assessments. Buildings and Cities, 1(1), 182-197. http://doi.org/10.5334/bc.30

Lehne, J. & Preston, F. (2018). Making concrete change: Innovation in low-carbon cement and concrete. London: Chatham House Report, Energy Environment and Resources Department.

Linnaeus University (2019). Improving the competitive advantage of CLT-based building systems through engineering design and reduced carbon footprint. Available at https://lnu.se/en/research/searchresearch/research-projects/project-improving-the-competitive-advantage-of-clt-based-building-systems/

Serrano, E. (2009). Uppföljnings-och dokumentationsprojektet Limnologen: Översikt och delprojektrapporter i sammanfattning. (in Swedish) [In English: Follow-up and documentation project Limnologen: Overview and sub-project reports in summary] Vaxjo, SE: Växjö University.  https://bit.ly/3Fy1M3d

Serrano, E., Enquist, B. & Vessby, J. (2014). Long term in-situ measurements of displacement, temperature and relative humidity in a multi storey residential CLT building.  Proceedings of the World Conference on Timber Engineering.  Quebec City, 10-14 August, 2014. 2459-2466. ISBN: 978-1-5108-5820-6

Tettey, U. Y. A., Dodoo, A. & Gustavsson, L. (2019). Carbon balances for a low energy apartment building with different structural frame materials. Energy Procedia, 158, 4254-4261.