Circular Building Strategies in Relation to Climate Goals: Categorisation and Temporal Analysis

Licentiate thesis, 2025

The construction industry accounts for nearly 40% of global greenhouse gas (GHG) emissions, with embodied impacts from material production and construction becoming increasingly critical as buildings become more energy efficient and energy systems decarbonise. At the same time, global climate goals defined by the Paris Agreement aim to limit warming to well below 2°C, preferably to 1.5°C, compared to pre-industrial levels. According to recent IPCC assessments, the remaining carbon budget compatible with the 1.5°C target is expected to be exhausted within the next decade, and the 2°C budget within a few decades if current emission levels persist. These findings underline the urgency of achieving substantial and immediate emission reductions across all sectors, including construction. Circular Economy (CE) strategies are discussed, both in research and practice, as a promising pathway to reduce these emissions through improving resource efficiency and minimising waste.  However, the application of Circular Building Strategies (CBS) in new construction remains fragmented, and their actual climate benefits, particularly over time, are still not well understood. This licentiate thesis lays the groundwork for examining how CBS can contribute to achieving time-bound climate goals, with a focus on embodied GHG emissions and the temporal dimensions of Life Cycle Assessment (LCA).

The research is based on two studies. The first study develops a structured classification of CBS through an integrative review and synthesis of existing literature, identifying key categories and their relationships. The second study systematically reviews existing CBS case studies regarding their reported GHG impacts across different life cycle modules, with particular attention to methodological differences and temporal assumptions in LCA. The results show significant variation in how CBS are defined, implemented, and assessed, which makes comparisons between studies difficult. These inconsistencies are reinforced by a lack of transparency and uniformity in LCA reporting, which limits the reliability of both qualitative and quantitative results. In addition, the research highlights that most LCAs treat time as a static factor, despite its importance in circular design. The timing of emission reductions plays an important role, especially for long-lived products such as buildings, where delayed benefits may not align with near-term climate targets. The absence of temporal granularity, including when a strategy is applied and when its effects occur, reduces the accuracy of climate impact assessments and limits the understanding of how circular strategies perform over time. By combining the insights from both studies, this thesis provides a conceptual and methodological foundation for assessing CBS with a temporal perspective. It emphasises the need for more comparable, transparent, and time-sensitive LCA methodologies to enable consistent evaluation and support the transition of the building sector toward meeting both near-term and long-term climate goals.