A Framework for Embodied Carbon Reduction through Systematic Material Substitution in Modular Building Systems

Sammanfattning

The construction sector is a major contributor to global greenhouse gas emissions, with material production representing an increasingly important share of total climate impact as buildings become more energy efficient. In modular building systems, reducing embodied carbon is complex because material choices are constrained by technical requirements, standardized interfaces, supplier conditions, implementation feasibility and circularity considerations. Existing research has largely focused on quantifying embodied carbon at building or system level, while providing limited guidance on how such results can be translated into structured material substitution decisions within existing modular product systems. The purpose of this study was to develop and apply a structured approach for identifying and prioritizing high-impact materials within an existing modular building system, and to evaluate how potential material alternatives can be assessed while considering embodied carbon, technical feasibility and circularity. The study was conducted as a single case study of a modular classroom system. An abductive mixed-method design was applied, combining quantitative embodied carbon assessment with qualitative interview data. The quantitative analysis was limited to life cycle modules A1–A3 and was based on company-provided climate declaration data, material quantities, emission factors and product-specific Environmental Product Declarations. A Pareto-based hotspot analysis was used to identify dominant contributors to embodied carbon. The qualitative analysis was based on semi-structured interviews and a written questionnaire with company representatives, analyzed through thematic analysis. The results show that embodied carbon within the studied module is concentrated in a limited number of materials. Facade board made of compressed insulation, fibre cement board and glass wool insulation 33 in the external wall were identified as the three dominant hotspot materials, together accounting for approximately 40 percent of total embodied carbon. The empirical findings show that material substitution decisions are shaped by system constraints, technical requirements, cost, supplier availability, implementation conditions and circularity ambitions. Based on these findings, a structured six-step framework was developed, consisting of material mapping and system understanding, embodied carbon assessment, hotspot identification, substitution feasibility screening, multi-criteria evaluation, and implementation prioritization with iterative reassessment. The study concludes that embodied carbon reduction in modular building systems can be supported by combining hotspot-based prioritization with feasibility screening and multi-criteria evaluation. This enables companies to focus substitution efforts on high-impact materials while ensuring that technical, economic, organizational and circularity-related requirements are considered.