Extended end-of-life carbon assessment and savings: A case study of steel-framed modular buildings in Hong Kong

Modular construction (MC) advances conventional approaches such as material efficiency, shorter construction time, and reduced onsite waste, leading to lower carbon emissions in some stages. However, the End-of-Life (EoL) carbon has never been made explicit, particularly for MC, and there remains a lack of evidence on how much carbon emissions are generated and reduced from the EoL stage of modular buildings. To address the gaps, the present study proposes an EoL carbon estimation model for MC based on the life cycle assessment (LCA) method. The developed model was empirically validated through a case study of a typical high-rise steel-framed modular residential building in Hong Kong. The results reveal that net carbon emissions during the EoL stage could be −764.40 kg CO₂ eq./m², presenting the great carbon savings potential of MC. Compared to those in traditional on-site construction areas, steel modular components have far greater capabilities to mitigate carbon emissions, as most of them can be reused. Nevertheless, an average of 41.56 kg CO₂ eq./m² of carbon is still released in the EoL stage, most of which is contributed by transportation, followed by waste disposal, demolition, and waste processing. This study makes an original contribution to understanding the extent of EoL carbon emissions and the potential of carbon savings in steel modular buildings. Also, these findings unveil the practical significance of reusing modules for EoL carbon mitigation and provide useful suggestions for demolition contractors and policymakers to mitigate carbon emissions to further promote the transition towards carbon neutrality.