To densify or not to densify? That is the question

A central tenet of sustainable urban planning since the 1950s has been to densify already built-up areas so as to prevent excessive land use and urban sprawl. This concept is still widely accepted, as demonstrated by the latest recommendations from the Intergovernmental Panel on Climate Change, which point to higher residential and job densities as a wayto reduce greenhouse gas emissions. Densification is also a central paradigm of the revised Swiss Federal Spatial Planning Act. In 2014, the Swiss government decided to put the brakes on urban sprawl, and Swiss cantons and municipalities are now implementing densification targets to protect natural and agricultural land.

The benefits of urban densification are indeed numerous. Higher densities are associated with greater economic productivity, increased proximity among individuals and firms, lower transport-related energy use, lower anthropogenic emissions and a smaller urban-footprint requirement to support a given population. However, the densification paradigm still faces challenges related to environmental quality and it is at odds with the growing need to green and de-seal urban surfaces.

The densification paradigm still faces challenges related to environmental quality.

Making space for nature

The preservation and equitable distribution of urban green spaces is particularly important for providing services that can directly improve health and well-being, such as for air purification, noise reduction, urban cooling and runoff mitigation. The efficient management of urban green spaces can have important economic implications too. Annual losses due to flooding in Europe are in the billions of euros and, according to a 2020 report by CE Delft, the mortality burden of air pollution costs Europeans €1,276 per capita every year, or €385 million per city on average. Similarly, our research has shown that urban-induced warming can cause an increase in heat-mortality risk, with an estimated average economic impact of €192 per European adult resident per year. Hence, it is now clear that by investing in urban greening projects, cities can also indirectly invest in public health.

A major research topic

So should city planners densify or de-densify urban spaces? The answer is not as straightforward as one would like, owing to the trade-offs between the costs and benefits of urban densification. At present, city planners around the world have little concrete guidance in deciding which is the appropriate goal for their city. At our lab and, in general, within the urban science community, this is now a major research topic, and we will soon have more robust scientific findings to inform urban planning and decision-making.

Gabriele Manoli, tenure-track assistant professor, head of the Laboratory of Urban and Environmental Systems, EPFL

• This article was published in August 2024 in three local dailies – La Côte (Vaud Canton), Le Nouvelliste (Valais Canton) and Arcinfo (Neuchâtel Canton) – under a joint initiative between EPFL and ESH Médias to showcase the R&D being carried out at EPFL on advanced construction techniques.