Comparative Analysis of Embodied Carbon Emissions in Steel and Concrete Modular Buildings

Modular construction (MC) is a disruptively innovative technique for reducing embodied carbon (EC) in the built environment. However, whether MC with steel or concrete structures releases less EC has never been made explicit. To address this, this study first quantifies and compares the life cycle EC of these two modular buildings. A comparative EC estimation model was developed and then validated through two cases of typical modular buildings, designed by using steel and concrete structural systems, respectively. Results show that the cradle-to-end of construction EC of typical floor for steel modular building is 788.80 kg CO2/m2, compared to only 540.13 kg CO2/m2 for concrete one. Despite the difference in numerical values, most of them are contributed by the modularization, followed by material production, for both buildings. Nevertheless, steel modular building presents greater potential in mitigating end-of-life EC, at −630.49 kg CO2/m2, which is more than four times that of concrete one. Thus, MC with a structure in steel contributes to substantial environmental benefits on EC and its application should be promoted in the long run. These findings not only enhance our theoretical understanding of the similarities and differences in life cycle EC between steel and concrete modular buildings but also provide new insights for developers regarding how to choose modular systems when it comes to short-term or long-term EC reduction targets.