Design-Space-Based Surrogate Modelling of Embodied Carbon and Material Cost Intensities for Early-Stage Commercial Office Design

Few early-stage building studies combine systematic design-space exploration with concurrent assessment of embodied carbon intensity (ECI) and installed material cost intensity (MCI). Evidence therefore remains limited on how design choices jointly affect these indicators and when carbon and cost priorities converge or conflict. This study addresses this gap across an Australian commercial-office design space comprising 892 quality-screened Carbon Designer 3D scenarios. The scenarios were restricted to rectangular plans and six predominantly concrete-based structural systems, with variations in recorded gross floor area (GFA), storey count and three aspect ratios. Matched comparisons examined the effects of vertical development, plan proportion and structural system on A1–A3 product-stage ECI and MCI. Both indicators increased with storey count, although proportional increases declined with increasing recorded GFA; the size of the ECI increases may partly reflect the platform’s area-normalisation convention. Aspect-ratio effects depended on structural system. The same structural system minimised ECI and MCI in 89 of 108 matched configurations (82.4%), whereas 19 exhibited cost–carbon trade-offs. Six regression algorithms were evaluated as design-space-specific surrogates using 713 training scenarios and 179 held-out scenarios. Support vector regression produced the lowest five-fold cross-validated mean absolute error and was retained as the in-domain surrogate for both targets. The principal contribution is the joint analysis of ECI and MCI across a controlled commercial-office design space; the surrogate models provide a computational basis for rapid screening and subsequent multi-objective optimisation within that same design space.