Glass recycling and reuse offer significant potential to reduce carbon emissions in buildings, but to fully harness this potential, design strategies must prioritize durability and ease of disassembly.
Building accounts for 80 percent of the glass industry’s market, with transport taking 15 percent. In the UK alone, three float glass plants produce approximately 750,000 tons annually. Across the European Union, production reaches about 10 million tons, while global output exceeds 76 million tons.
Despite glass being 100 percent recyclable and capable of being recycled indefinitely, this advantage remains underutilized. Scaling up global recycling efforts is imperative. designers play a critical role by ensuring the collection and recycling of end-of-life glass, particularly during the deconstruction phase before refurbishment.
reducing the embodied carbon of glass is achievable. Typically, virgin raw materials are heated in a batch process, releasing CO2 through decarbonation—a process responsible for up to 25 percent of the total CO2 emissions from the float process. However, these emissions can be mitigated by using cullet, which is recycled glass sourced from production-line waste or existing buildings, and has already undergone decarbonation.
Cullet melts at lower temperatures than raw materials, leading to energy savings of up to 30 percent and corresponding reductions in emissions. Thus, it is urgent to develop the cullet stream at both industrial and national levels.
For glass to achieve circularity, it should be reused or, at a minimum, recycled into material of the same quality, such as flat glass. Despite this, only 6% of flat glass is effectively recycled, with most being downcycled into lower-quality products like glass bottles and insulation.
When flat glass is recycled back into a flat glass of equivalent quality, it is crushed into a cullet and returned to the float line for remelting with other glass-making materials. Currently, most cullet used in flat glass production comes from pre-consumer waste. For example, in 2018, less than 1 percent of cullet used by Saint-Gobain came from post-consumer waste from renovation or demolition sites. However, in France, new anti-waste regulations are driving change, and by 2023, Saint-Gobain had increased its collection of post-consumer cullet to 4,107 tonnes through a network of over 40 glass waste processors.
Challenges for closed-loop recycling of flat glass include the establishment of new logistical and recycling streams to collect glass on-site. Non-glass components must be removed before cullet production to avoid contamination, which could cause issues during the float process. The intact transport of glass to off-site cullet facilities requires careful planning and budget allocation at the outset of refurbishment projects.
Closed-loop recycling offers substantial benefits. Recycling one tonne of glass can save up to 300 kg CO2e, 1.2 tonnes of raw materials, including 700 kg of sand, and 30 percent of the energy required for production.
The reuse of insulated glass units has not been widely adopted due to factors like short lifespan, rapid obsolescence, warranty requirements, and lack of standardization. However, the reuse of monolithic glass is more common, particularly for internal applications.
Both reuse and recycling of glass face challenges due to the labor-intensive nature of disassembling facade glazing, which is often a composite unit. Additionally, glass may be bonded to other parts of the facade, such as window frames, complicating the separation of elements for circular processes. To avoid repeating these challenges, new facades should be designed with demountable systems that facilitate reuse and recycling.
Designers have often sought to integrate multiple functions into insulated glazing products, such as integrated blinds and photovoltaics. While beneficial for reducing a building’s energy consumption, these elements increase embodied carbon and complicate reuse and recycling. Opting for simpler, low-tech glass solutions is often preferable.
To reduce emissions, designers and consumers must consider the quality and demands placed on glass. Moves to incorporate more reused or recycled glass may affect glass quality, potentially leading to aesthetic defects such as bubbles. Acceptance of such defects could allow for lower furnace temperatures and associated emissions.
For existing facades, extending their lifespan through refurbishment is critical. This could involve repairing or reconditioning poorly performing glass units. Identifying and addressing leaks, reinjecting gas, or even removing and remanufacturing panels could enhance their performance to current standards. However, these processes require further development in the market.
When replacement is necessary, materials and glass should be reused or recycled to avoid waste. Additionally, designs should prioritize facade longevity, incorporating timeless aesthetics, easy disassembly, and durable materials.
To ensure that products remain circular at the end of their lifecycle, future designs should account for the reuse of resources. An online database, www.glazingrecovery.org, will be launched later this year to guide glazing replacement and refurbishment, connecting providers in the sector.
Case Study: Unesco V Refurbishment Project in Paris
The Unesco V building in Paris, originally designed by Zehrfuss and Prouvé in 1970, is undergoing a circular refurbishment led by Patriarche with facade consultancy by Eckersley O’Callaghan. This project involves the reuse of cladding and the recycling of flat glass. The glass was carefully dismantled from the existing facade and sent to Ares for cullet production. After inspection, the cullet was delivered to Saint-Gobain’s float line for inclusion in its low-carbon production process. Recycling the flat glass saved approximately 30 tonnes of CO2e.
The project’s success was due in part to the original ‘kit of parts’ facade, which facilitated easy handling and deconstruction. The reused materials were integrated into a bio-based, high-performing inner skin, contributing to the project’s low-carbon design.
Gallery
