Decarbonizing curtain wall facades: a life cycle approach to embodied and operational carbon

The building sector is responsible for one third of global energy-related CO2 emissions, deriving both from operational energy use and the embodied carbon associated with extraction, manufacture, and assembly of materials. As energy efficiency and renewable technologies can reduce operational emissions, embodied carbon has become a main contributor to the environmental footprint of buildings. Within this context, the thesis explores the challenge of decarbonizing curtain wall facades through an integrated Life Cycle Assessment (LCA) approach that considers both embodied and operational carbon impacts. Glazing facades are one of the most carbon-intensive facade systems due to their reliance on energy-demanding materials such as glass and aluminium, both characterized by high emission factors and relatively short service lives. This research adopts the ISO 14040 and ISO 14044 standards for LCA and quantifies the carbon performance of different curtain wall facade configurations through the stages of production (A1-A3), replacement (B4) and use. Embodied carbon is calculated starting from the emission factors derived from the ICE database, while operational carbon is estimated through COMFEN5 simulations that account for energy demand. The study systematically varies parameters such as window to wall ratio (WWR), bay dimensions, wind load magnitudes and material alternatives for frame, glass, and opaque components to identify configurations that minimize total life-cycle emissions. The results highlight that glass and aluminium dominate embodied carbon, contributing together to more than 70% of facade-related emissions. Substituting virgin aluminium with recycled aluminium, GFRP, or laminated timber, embodied carbon can be reduced up to 50%, while the use of low-carbon glass achieves reductions of about 25%. Opaque materials such as natural stone panels show lower emissions compared to GRC panels and aluminium sheets, offering additional pathways for mitigation. The analysis of replacement scenarios reveals that insulated glass units require substitution after approximately 25 years, contributing significantly to life-cycle emissions. Extending IGU service life or improving durability therefore becomes a crucial decarbonization strategy. Operational simulations show that facade configurations with lower WWR can decrease energy-related emissions by 20-30% compared to fully glazed facades due to improved thermal performance and reduced cooling loads. However, this reduction must be balanced with daylighting needs and architectural requirements, demonstrating the inherent trade-off between embodied and operational carbon. Moreover, operational carbon plays a key role in the emissions of a building especially when built due to today’s CO2 factors, but through the decarbonization of the grid, its impact can decrease over the building service life. By combining all life-cycle phases, the study identifies that adopting low-carbon materials, optimized facade geometry and durable components can cut total facade-related emissions by 30-45% without compromising comfort, aesthetic or structural integrity. The findings underline the importance of integrating life-cycle thinking into facade design from the earliest design stages and provide quantitative guidelines to decrease emissions. Finally, the thesis demonstrates that the decarbonization of curtain wall facades is achievable through comprehensive LCA based framework that merges material effieciency with operational energy optimization.