Cumulative Intervention Area and Reconfiguration Carbon Intensity: A Comparative LCA of Hybrid Dry Floor Systems in High-Churn Office Buildings

Office buildings accumulate embodied carbon not only during construction but repeatedly throughout operation, driven by tenant improvements (TI). In contexts where regulatory and supply-chain constraints limit full design-for-disassembly, this paper explores partial decoupling of a dry slab system within the high-churn zone of a Seoul office. Two area-normalised indicators are introduced—cumulative intervention area (Acum) and Reconfiguration Carbon Intensity (RCI)—defined on the structural slab/panel boundary to complement the mass-weighted Circularity Index (CI). The indicators are demonstrated on a 17-storey Seoul office over 60 years across three scenarios: a wet composite baseline (S1), full-dry CLT (S2), and a hybrid placing CLT within the high-churn zone (S3). S3 reduces RCI by approximately 45% relative to the wet baseline, capturing 71.7% of the full-decoupling benefit while converting only 11.5% of the floor area to CLT—a benefit-to-conversion ratio of 6.2×. Both shares are fixed by the floor-plate geometry, so this ratio is a consequence of the high-churn zone’s concentration rather than an independent empirical finding. A joint-uncertainty stress test confirms that S3 outcomes lie entirely below S1 across plausible parameter ranges. A placement test compares three configurations of the same floor that differ only in CLT placement location relative to the high-churn zone. Mass-weighted CI cannot distinguish these configurations, whereas RCI ranges from no reduction to the full hybrid benefit depending on placement—isolating the diagnostic value of the use-phase indicator. Hybrid zone-scale decoupling offers a feasible pathway for use-phase decarbonisation without committing to full-floor dry construction.