Whole life cycle emissions of buildings include not only operational carbon due to their use phase, but also embodied carbon due to the rest of their life cycle: material extraction, transport to the site, construction, and demolition. With ongoing population growth and increasing urbanization, decreasing immediate and irreversible embodied carbon emissions is imperative. With feedback from a wide range of stakeholders – architects, structural engineers, policy makers, rating-scheme developers, this research presents an integrated assessment approach to compare embodied life cycle impacts of building structures. Existing literature indicates that there is an urgent need for benchmarking the embodied carbon of building structures. To remediate this, a rigorous and transparent methodology is presented on multiple scales. On the material scale, a comparative analysis defines reliable Embodied Carbon Coefficients (ECC, expressed in kgCO2e/kg) for the structural materials concrete, steel, and timber. On the structural scale, data analysis evaluates the Structural Material Quantities (SMQ, expressed in kg/m²) and the embodied carbon for existing building structures (expressed in kgCO2e/m²). An interactive database of building projects is created in close collaboration with leading structural design firms worldwide. Results show that typical buildings range between 200 and 550 kgCO2e/m² on average, but these results can vary widely dependent on structural systems, height, size, etc. On the urban scale, an urban modeling method to simulate the embodied carbon of neighborhoods is proposed and applied to a Middle Eastern case study. A series of extreme low carbon case studies are analyzed. Results demonstrate that a novel design approach can lead to buildings with an embodied carbon as low as 30 kgCO2e/m² which is an order of magnitude lower than conventional building structures today. Two pathways are implemented to lower the embodied carbon of structures: choosing low carbon materials (low ECC) and optimizing the structural efficiency of buildings (low SMQ). This research recommends new pathways for low carbon structural design, crucial for lowering carbon emissions in the built environment.
Low carbon pathways for structural design : embodied life cycle impacts of building structures
Catherine De Wolf
Massachusetts Institute of Technology