Multi-level spatiotemporal embodied carbon analysis of high-rise buildings adopting steel modular method compared with conventional concrete construction in Hong Kong

Abstract

Embodied carbon (EC) accounts for a substantial part of greenhouse gas emissions. Steel modular construction (MC) has been promoted worldwide. However, limited research has investigated the EC of steel modular high-rises. This paper aims to systematically examine the cradle-to-end-of-construction EC of steel modular high-rise residential buildings, and identify whether and how it can achieve EC reductions compared with conventional concrete construction. A multi-level spatiotemporal EC assessment model was developed to address the EC in the temporal dimension to identify EC-intensive lifecycle stages and in the spatial dimension to examine the EC in line with the building elements at material, component, module, floor, and building levels. A 17-story steel modular building was selected for case study, and its EC results were compared with those of a baseline case with the same layout design but adopting conventional cast-in-situ construction. The cradle-to-end-of-construction EC of the case building was quantified as 609 kgCO₂e/m², of which the cradle-to-site EC contributed over 90 %. Structural steel in modules were the primary EC sources at all five spatial levels. The case building slightly increased (by 6 %) the cradle-to-end-of-construction EC, but achieved 38.9 % transportation and 56.8 % construction EC reductions, respectively, which indicates that cities will benefit from using MC by shifting the carbon emission burden from local construction sites to module manufacturing locations. The developed multi-level EC model provides a novel method for future research on EC of steel modular buildings, and the findings will shape future practices of decarbonizing modular buildings in a systematic manner.