Circularity index analysis of buildings with different structural materials: a modelling approach for sustainable construction assessment

The transition towards circular construction requires transparent methods for assessing material recirculation, future recovery potential, and building adaptability. The aim of this study was to develop and apply a quantitative building-level circularity assessment framework and to demonstrate its application using concrete, steel, and timber variants of a hypothetical office building. A BIM-Dynamo workflow was used to extract material quantities and evaluate author-defined deterministic material-sourcing and end-of-life pathway scenarios using four complementary indicators: Secondary Material Use (SMU), Material Reusability Potential (MRP), Spatial Reversibility (SR), and Sharing Space Potential (SSP). An ADP-weighted Circularity Index (CI) and a simplified mass-based Circularity Index (CIs) were calculated, and the sensitivity of CI to variations in Abiotic Depletion Potential (ADP) coefficients was analysed. The resulting value ranges were compared with published LCA-based studies of office buildings as a preliminary plausibility check of the proposed framework. Within the adopted scenario assumptions, the steel structural variant showed the highest average and most stable circularity-index values, whereas the concrete variant exhibited the greatest variability across the analysed scenarios. The CI was most sensitive to changes in the ADP coefficient for steel, indicating that the comparative results are partly influenced by the adopted resource-depletion weighting. The proposed BIM-Dynamo workflow integrates material, spatial, and resource-based indicators within a consistent framework that may support transparent comparison of structural alternatives and circular design decisions during the early design stage. The comparative results should be interpreted within the adopted reference-building geometry, system boundaries, material-sourcing and end-of-life assumptions, pathway weighting factors, spatial assumptions, and ADP coefficients, and should not be regarded as a universal ranking of structural materials.