Timing matters: life cycle embodied GHG emissions of circular building strategies

Circular building strategies (CBS) aim to reduce greenhouse gas (GHG) emissions related to the construction, maintenance and end-of-life of buildings. However, the timing of these reductions, whether immediate or in the future, is often overlooked. Given the urgency of addressing climate change, accounting for the temporal dimension is crucial to understand accurately the decarbonisation effects of CBS. Existing life cycle assessment (LCA) studies on CBS are analysed for the timing of reported reductions and the connected temporal considerations in the model. The analysis of LCA studies (n = 42) shows consistent reduction patterns for upstream CBS (e.g. reuse of existing components), but the assessment model includes little temporal detail. The reductions are more inconclusive for downstream CBS (e.g. design for disassembly), and they highly depend on temporal modelling. The findings highlight the need for a consistent LCA framework that accounts for the timing of GHG emission reductions when applying CBS. The identification of when actual GHG reductions occur arising from different circular strategies will aid in the understanding of CBS’s role in meeting climate targets. POLICY RELEVANCE CBS do not deliver GHG emission reductions equally over time, which has direct implications for policy design and decision-making. CBS acting early in the life cycle (e.g. component reuse) consistently reduce upfront emissions, supporting near-term climate targets. However, downstream CBS (e.g. design for disassembly) produce uncertain or delayed benefits, limiting their effectiveness for urgent decarbonisation goals. Current assessment methods often overlook this temporal dimension, risking misaligned incentives. LCA frameworks should be updated to explicitly report and account for when GHG emissions occur, not just the overall reduction. Additionally, policy frameworks should differentiate between short- and long-term mitigation, aligning subsidies, GHG emission limits, and reporting standards accordingly. Recommendations are provided to support evidence-based decisions and ensure the building sector contributes effectively to near- and long-term climate targets.