End-of-life insulating glass units (IGUs) continue to follow a linear, wasteful path from renovation and demolition sites into landfills or low-value recycling. To get one step closer to the question of how to close the glass loop, this exploratory research outlines a cross-practitioners review of glass circularity in conventional Flemish and Brussels practices. A series of semi-structured interviews with network actors and an extensive literature study is conducted to identify existing and missing circular practices and to pinpoint the key barriers and opportunities. In general, the circular strategies repurpose and open-loop recycling of end-of-life IGUs are successfully applied in Flemish and Brussels construction practices. Repair, reuse, and closed-loop recycling remain unexplored. The main barriers are the lack of collaboration, logistic and labour costs to collect end-of-life IGUs, its complex disassembly, the lack of legal incentives and the conservativeness of the construction sector. Case studies, the high recycling potential and the scale of projects are found to be the main opportunities for glass circularity. The cross-practitioners’ insights in this paper contribute to close the glass loop and to further development and up-scaling of circular strategies.

Architectural flat glass is a fully recyclable material but continues to follow a linear, wasteful path from renovation and demolition sites into landfills or low-value recycling. To make the shift towards circularity, understanding the whole flat glass network is essential. Therefore, the present paper identifies constraints and leverage points for circularity from a systemic perspective. Departing from literature and in-person discussions with network actors, value network mapping is applied to conventional practices, a transition tool to define essential missing roles, relations, and transactions. First, the roles and general relations are mapped, and step-by-step the value transactions and flows are detailed. An alternative circular value network map was then developed in which systemic changes are suggested to improve reuse, repair, and recycling applications. Leverage points are identified, such as learning from best-practices, sharing knowledge between actors, creating awareness, and creating incentives for the actors. From these findings, specific interventions in the conventional value network of flat glass can be conceived and planned as a sustainable transitions experiment (e.g., in the context of a living lab project initiated by governmental or private forerunners), or as an enduring redefinition of some roles and relations in the construction sector with a systemic result.