The building sector is under increasing pressure to reduce upfront embodied carbon (UEC) in order to meet climate goals. Paris Proof threshold values are becoming increasingly stringent, placing new demands on design teams to evaluate material choices not only for environmental performance but also for financial feasibility. This thesis presents the Circular-Carbon Framework (CCF), a decision-support model developed to assess circular construction strategies based on three key indicators: carbon, cost and circularity. The model addresses a gap in current practice by enabling integrated trade-off analysis during the early stages of building design. A mixed-methods approach was used, including a structured literature review, semi-structured interviews, expert validation, and a case study of a commercial office project. The scope was limited to structure and skin materials, which together account for the majority of UEC. Results indicate that circular strategies can support reductions in both UEC and cost, though outcomes vary depending on material type and project context. The CCF enables design teams to systematically explore these trade-offs and make informed decisions aligned with Paris Proof requirements. The thesis concludes with scientific, practical, and policy recommendations to advance the integration of circularity in sustainable building design.