Circularity-based embodied carbon performance in building design: Index development and circular initiatives

This study introduces the Circularity-based Embodied Carbon (CiBEC) index, a comparative metric designed to assess the effects of circular actions on the embodied carbon (EC) of building projects. Built upon the conventional EC measurement, this index enhances traditional approaches by incorporating inclusive material inflow and outflow allocations, acknowledging variations in usage intensity, and factoring in potential changes to building lifespan strategies. Unlike conventional methods, it also recognises the collective efforts of all stakeholders - including third-party contributors - by fairly redistributing carbon savings across product (A) and beyond the building (D) phases of the life cycle assessment, offering a more holistic and equitable perspective. While demonstrated on a global scale, the index is applied to a real office building project to validate its practicality and demonstrate real-world applicability. Both individual and combined circular scenarios are assessed, revealing how key benefits from circular initiatives - often unaccounted for in conventional methods - are effectively captured through the CiBEC framework. The results indicate that among the eight developed circular scenarios, two - specifically, renovation and the multi-use of building spaces - are identified as EC-intensive. In contrast, the remaining scenarios achieve reductions of up to only 10 % when the conventional approach is used. However, when assessed using the CiBEC method, the “renovation” scenario notably demonstrates a 36 % reduction. Furthermore, the study shows that integrating various circular strategies through the development of seven combined scenarios can lead to substantial EC reductions, decreasing the initial EC from 629 to 191 kgCO2 eq./m2. This significant reduction is not achieved through a simple statistical aggregation but through the complex interactions among the different strategies. Therefore, it seems that while the CiBEC index is most effective during the early design stages, it also allows project stakeholders to refine and monitor EC reduction throughout the project's lifecycle.