To face to continuous and tremendous increase of material consumption and its direct results - scarcity of raw materials and pollution -, circular economy and the dynamic to create loops of use are presented as a main strategy to solve the situation. In this challenge, construction sector has an important role to play because it represents approximately a third of material flows in European countries. Circular Economy (CE) is commonly shared as one of the main strategy to reduce the flows and to create positive local externalities. Dynamics and projects are numerous. Policy makers develop plans as a framework to implement this approach in European cities. Practitioners try the experience in projects and researchers or advisors proclaim methodologies but the current macro results are far away from the ambition : important flows, only 1-2% are reused and the social externalities seem limited. 

However, current exemplary projects as Usquare present more optimistic outlook : most of the buildings can be preserved, till 10% of reuse rate and integretion of innovative approaches (fonctionality economy, design for dissambly or biosourced materials). these results are possible with a paradigm shift, an holistic understanding of CE, new tools and new collaborations (participation of the research team to advise project teams). Indeed, CE development induces new parameters in a complex public equation : the development of ambitious urban program in a local context with limited budget, existing buildings and new circular demands.

This research aims to question the material circularity on the two highest levels of waste hierarchy (preservation and reuse) in different projects developed by public stakeholders (urban planner, project manager) from urban planning to execution. By this bottom-up approach, practical limitations and opportunities can be identified in every stage of the urban projects.