A recent study by ETH Zurich highlights how vertical extensions—adding extra storeys to existing buildings—are emerging as a key tool for sustainable urban redevelopment in Switzerland. The research, commissioned by the Federal Office for Housing, compares building trends and displacement rates in Switzerland’s five largest urban areas: Basel, Bern, Geneva, Lausanne and Zurich.

The findings reveal a clear shift toward densifying cities within their current settlement boundaries. In contrast to demolishing older structures and replacing them with new buildings, which often results in higher rents and resident displacement, vertical extensions offer a more environmentally and socially sustainable approach. This strategy preserves existing buildings, reduces demolition waste, and helps maintain socio-economic diversity in city centres.

The Material Opportunity in Vertical Growth

For architects and designers, vertical extensions represent a significant material challenge—and opportunity. They demand lightweight, high-performance materials that minimise structural load while maximising thermal performance, circularity, and design adaptability. Timber-based systems, bio-composites, and modular prefabricated elements are particularly well-suited to this application, supporting both speed and environmental goals.

Additionally, integrating vertical additions into heritage or mid-century residential architecture requires sensitive material transitions and facade innovations. Interior designers may also encounter unique spatial constraints that call for creative layout and acoustic solutions, especially in vertically layered housing typologies.

Industrial Conversion and Material Reuse

The research also underscores the growing role of repurposed industrial and commercial sites. From 2000 to 2023, the proportion of new residential construction in former industrial zones grew significantly, reaching up to 63% in Zurich. These sites are often well-suited for high-density developments that incorporate recycled building materials and support modular, prefabricated design systems.

While land availability in such zones is diminishing, they remain critical nodes for sustainable, material-efficient urban expansion. Adaptive reuse in these areas can support innovative facade and interior material applications, including reclaimed concrete, low-carbon cement, and circular insulation strategies.

Policy Drives Design Potential

Interestingly, French-speaking regions like Geneva and Lausanne have demonstrated that dense construction can occur with minimal displacement, thanks to stronger tenant protections and policies encouraging vertical extensions. Geneva’s laws, for instance, limit rent increases after renovation and actively promote building upwards rather than rebuilding from scratch.

These regional contrasts highlight the role of legal frameworks in shaping material choices and architectural strategies. For practitioners across Europe, the Swiss example presents a compelling case for integrating sustainability, circular construction, and social equity into urban housing design.

Source: ETH Zurich
Photo: Andrea Helbling / Keystone