Retrofitting European Office Building stock: combining principles of bio-economy and circular economy for context-based, adaptable facade solutions

Energy retrofitting is central to achieving Europe's goal of carbon neutrality by 2050 and office buildings, responsible for 40% of the energy consumption of the entire construction sector, offer great potential in this respect. Their building envelopes, are associated with 50-60% of total heat losses and are essential for improving energy efficiency. Since the 1970s, glazed curtain walls have become central for office buildings, contributing to high energy dissipation, while adding significant Embodied Carbon (EC) due to glass disposal at the End of Life (EoL). Considering that curtain wall systems have a lifespan of 30 years and represent around 36% of total office building envelopes, (with glass at 60% per module), there is the need for improved EoL solutions and for integrating more opaque and massive façade components to enhance energy performance, without raising buildings' EC. Utilising local bio-residues, absorbing carbon over their growth, offers an alternative for curtain wall insulation due to their lower EC, - going from, for instance, 0.9-3.3 MJ/kg for cellulose compared to 105-127 MJ/kg for Polyurethane (PU). Along with reusing glass elements, this strategy has the potential to significantly reduce EC and resource consumption, resulting in approximately 500 million kg of CO2-eq emissions avoided. This paper explores the systemic interconnections between regions, crops, bio-based building materials, facade products, and building renovation through a methodology illustrated by a decision-making map, to support more sustainable future retrofitting practices. It investigates a retrofitting strategy that integrates bio-economy and circular economy principles, for two practical scenarios: (1) repurposing dismantled glass for a new spandrel component combined with bio-based insulation; (2) reusing existing glass by adding bio-insulation indoors to reduce the façade's transparency or accommodate functional changes. The study systematically analyses European office building stock data, highlighting the potential of available materials from disassembly strategies; provides the geography of agricultural and forestry residues for construction applications; and informs over possible manufacturing processes for bio-insulation. By doing so, the paper identifies possible context-based strategies, their potentials and limits, and sets the groundwork for further research.