Innovative project gives old windows a second life
Glass from old windows could be recycled just like glass bottles. At present, however, the additional effort and cost involved make this economically unviable. A ZHAW project aims to change that.
Ninety per cent of glass bottles are recycled, but more than 80 per cent of window glass ends up in landfills. Only a small proportion is melted down and used to manufacture new bottles, which effectively constitutes downcycling. In Switzerland, around 500,000 tonnes of flat glass are discarded annually, including windowpanes from demolished buildings and windows that are replaced because of poor thermal insulation.
“Unfortunately, it is cheaper to dispose of flat glass in landfills than to bear the cost of separating old windows from their frames and recycling the glass,” says Michelle Schneider from the Institute of Constructive Design at the ZHAW School of Architecture, Design and Civil Engineering. According to the researcher, this results in a significant loss of grey energy, and new landfill sites have to be created continually. Schneider previously devoted her Master’s thesis at the ZHAW to the reuse of windows, with the aim of advancing the circular economy. This led to the launch of the pilot project Windows of Opportunities.
Avoiding contamination
When she learned that a building near the School of Architecture, Design and Civil Engineering was due to be demolished, Schneider worked with industry partners to salvage 375 window sashes. The recovered glass was melted down and used to produce new windowpanes. Recycling glass requires significantly lower temperatures than producing new glass and therefore generates less CO₂. However, adhesives, dust and plaster residue on the glass surface pose a challenge. Such contamination can be avoided if glass is collected separately rather than disposed of in a skip with other construction waste. “In future, recycling should be considered from the very beginning when building components are designed and manufactured,” says Andri Gerber, head of the Institute of Constructive Design.