In Europe, the building sector is responsible for almost a quarter of the total mass of generated waste and hence has a major environmental impact. To reduce that impact, the Flemish region, like others, has put forward the ambition to realise an economy of closed material loops by 2025.

Architectural flat glass is a fully recyclable material, but continues to follow a linear, wasteful path from renovation and demolition sites into landfill or low-value recycling. Yet, various niche practices illustrate that technologies and skills are at hand to repair, reuse and recycle flat glass at high value. What lacks is the proper transfer of this information into concrete guidance of practitioners.

As a response to this knowledge gap, the research aims at developing a practitioner’s road map – serving as a prototype for other waste flows – to support all practitioners of the building sector in valorising end-of-life flat glass. To achieve this, two questions are key. First, which circular strategies allow to maximise the value of flat glass in a closed material loop with a minimal environmental impact? And second, how can practitioners collectively implement those strategies in building projects?

By the involvement of practice’s stakeholders throughout the research, a road map will be developed, tested and validated to support designers, engineers and contractors in making better-informed choices, close the flat glass loop and make the transition to the circular economy happen.

This research aims to apply circular economy principles to the life-cycle of architectural flat glass, a material that is primarily used in windows of buildings.

Today, end-of-life flat glass from deconstruction and renovation sites is mainly recovered to low-grade fill applications, brought to the incinerator, or put into landfill. As an alternative for this linear ‘make, take, waste’ model, this research develops closed-loop alternatives for end-of-life flat glass that support the transition towards a circular life-cycle of flat glass. The closed-loop alternatives considered are repair, reuse, repurpose, and recycle. In this research, the environmental impact of each closed-loop is discussed and the barriers that limit them to niche markets are identified.

Repair, reuse, and repurpose consist of interventions such as replacing the seal, cleaning the glass, improving the thermal performance, and remanufacturing the glass unit for reuse or repurpose. These interventions prevent new production of flat glass by extending the service life of architectural flat glass, which in turn saves all the raw materials, energy, and CO2 associated with this process. A less significant, but still positive environmental impact is achieved with recycling flat glass. Reusing this cullet to make new flat glass products generates resource, energy and CO2 savings during the production process. Furthermore, flat glass producers are requesting party for high-quality flat glass cullet, because the energy savings lead to economic benefits.

There are three main barriers encountered in this research. The first is the technical and economic feasibility to selectively collect or reclaim flat glass due to the labour intensive deconstruction process, logistics, transport, and storage provisions. The second barrier is the inflexible standards that thermally limit the repair, reuse, and repurpose of flat glass. The last main barrier concerns the conventional design approach in which designers rely on newly manufactured products, instead of considering the products on the second-hand market.

Finally, this research concludes that the education and collaboration of all actors involved in the glass industry and the development of technologies of sorting and smarter product use and manufacture will lead to a circular life-cycle of flat glass.

This research was conducted by Esther Geboes over the course of the academic year 2019-2020 to obtain the degree of Master of Science in Architectural Engineering.