Introduction
Glass that performs. Glass that would otherwise be lost
Glass is one of the most energy-intensive materials used in construction. Producing flat glass requires temperatures of approximately 1,400–1,600°C, making glass manufacturing a continuous and energy-demanding process [1]. At the same time, large volumes of functional glass leave the built environment every year. In Denmark alone, an estimated 36,000 tonnes [2] of demolition glass waste is generated annually. Yet while glass packaging is recycled at very high rates [3], only around 5% of flat glass from construction and demolition projects is recycled [4]. Much of this glass has not failed. It has simply reached a point where it no longer fits its original application. Roof window production rejects units that do not meet strict visual requirements. Renovation projects remove facade glazing that no longer satisfies modern energy standards. In both cases, the glass often retains its structural and functional properties.
This is where a:gain works. We develop building products around existing glass resources, keeping valuable materials in use for longer, reducing the need for new glass production, and creating products with a significantly lower and documented CO₂e footprint.
Why glass matters
Most flat glass removed from buildings does not remain glass. While a high percentage of post-consumer glass packaging is recycled in Denmark, the infrastructure and legislative framework for construction glass are far less developed. As a result, only a small proportion of flat glass is recycled, and even then it is rarely recycled back into flat glass. Instead, the material is typically downcycled into products such as insulation, containers, aggregates, or sent to landfills [5] [6] [7]. Valuable material is recovered, but much of the value already embedded in the glass is lost [8]. This matters because manufacturing new flat glass is highly energy intensive. The flat glass process operates continuously at temperatures of approximately 1,400–1,600°C and contributes to an estimated 0.3% of global carbon emissions [9] [10] [11] [12]. When glass is remelted, it must once again pass through this process before it can become flat glass. By keeping glass in use at a functional level, rather than returning it to raw material form, more of the value already invested in the material can be preserved. This principle forms the foundation of both Viddø and Tystø.
Glass streams
Two glass streams. Two products
While the principle is the same, it works with two very different glass sources.
Discarded glass
Velux produces insulated glass units (IGUs) for roof windows to extremely high quality standards. Some units are rejected due to minor visual characteristics that have no impact on thermal or structural performance. The units retain their thermal transmittance, and structural integrity. They simply do not meet the optical requirements of their intended application. Together with Krone Vinduer, a:gain transforms these discarded units into Viddø, a certified facade window system. The glass units are sorted, digitally arranged, and incorporated into new window elements with wooden or wood-aluminum frames. Depending on project requirements, between 60–100% of the glass in a Viddø solution originates from these discarded units.
The result is a documented facade solution with verified thermal performance, product guarantees, and 43 % lower CO₂e compared to comparable virgin alternatives, when 70% of the glass used are discarded.
Demolition glass from renovation projects
When buildings are renovated or transformed, existing facade glazing is often removed and replaced. In many cases, the glass no longer meets current requirements for exterior applications. U-values, solar performance, and energy regulations have evolved since the glass was originally installed. But those requirements are largely irrelevant in interior applications. Rather than treating the material as a waste stream, a:gain identifies glass units that remain suitable for continued use. The glass is assessed based on condition, dimensions, and usability. Each unit is individually tagged and registered to ensure full traceability throughout the process.
Together with DEKO, a:gain transforms this glass into Tystø, a modular interior partition system with a verified EPD, documented performance, and up to 73 % lower CO₂e compared to conventional partition systems. Each glass unit can be traced back to its building of origin, providing transparency around both material provenance and environmental impact.
What the numbers show
Keeping glass in use is not just a material story. It delivers measurable results
Tystø is made from used thermo glass units and discarded pine wood
Reduction in CO₂e compared to similar products
Waste saved per m²
CO₂e per m²
*CO₂e footprint is based on Tystø EPD including phases A1–A3 and C1–C4. Phase B and D excluded. Comparison is based on average available EPD data on virgin glass partitions as of May 2025. Declared unit for all compared EPDs: 1 m² of partition wall. The glass in the virgin walls has a thickness of 12–12.8 mm and hence a similar dB reduction. The discarded glass used for the Tystø wall will have a varying thickness depending on the input source, which means that the Tystø wall will have a different dB reduction from case to case. For more info, confer ‘Explainer_Tystø_EPD_Comparison’ in our download centre.
Viddø is made from discarded glass IGU’s
Reduction in CO₂e compared to similar products
Waste saved per m²
CO₂e per m²
*CO2e footprint and comparison are based on available EPD data including phases A1–A3 and C1–C4. For more info see our sustainability page.
For architects, developers, and contractors, these CO2e reductions are fully documented through Environmental Product Declarations (EPDs) and can be incorporated directly into the building LCA, DGNB submissions, and sustainability reporting. The exact reduction varies by product and application, but the principle remains the same: extending the useful life of existing glass reduces both material waste and the need for new glass production.
Designed for disassembly
Glass is one of the few construction materials capable of retaining its value through multiple applications
a:gain products are designed for disassembly, allowing glass and frame components to be separated and recovered at end-of-life. Through our take-back systems, materials can re-enter the material cycle and continue delivering value in new applications. The goal is simple: keep high-value materials in use for as long as possible before energy-intensive reprocessing becomes necessary.
Learn about our wood streams
Learn about our plastic streams
