Today, densification is a principle of urban development. Nevertheless, it repeatedly encounters local resistance. ETH spatial scientists: inside have now systematically investigated in six world cities and in the canton of Zurich how the acceptance of densification can be explained among the population. Affordable housing plays a key role.
The fact that cities are better off developing within existing settlement areas than growing further and further out into the landscape is now recognized as a principle of urban development in democratic countries far beyond planning circles. After all, dense and compact cities have a number of ecological, economic and social advantages - such as less urban sprawl, protection of the undeveloped landscape, shorter traffic routes, lower greenhouse gas emissions, and a wide variety of work, cultural and residential opportunities.
Nevertheless, urban densification projects regularly meet with local resistance. The reasons for this are numerous and typically include aspects such as traffic, noise or changes in neighborhood character and loss of green space: "Lack of acceptance among the population is one of the main reasons in democratic states that can slow down or even block the densification of cities and metropolitan regions," says David Kaufmann, professor of spatial development and urban policy at ETH Zurich.
The closer to the project, the less acceptance
A key factor in urban densification is housing, as densification projects can change the value of homes and residential property as well as the rents and population composition of a neighborhood. "Housing is one of the big areas of tension in densification today," says David Kaufmann, "and we see that the acceptance of densification both in Zurich and in global metropolises is closely linked to the provision of affordable housing."
Kaufmann’s research group has therefore systematically investigated for six world cities and for the canton of Zurich why the population in large cities accepts or does not accept densification projects. Using a novel combination of survey methods, the group determines the population’s attitude toward densification and concludes which project-related factors and urban planning measures can increase the acceptance of residential densification projects and cushion the effects of densification that are perceived as negative.
For the international comparative study, which has now been published in the renowned scientific journal PNAS, the researchers surveyed over 12,400 participants: inside Berlin, Paris, London, New York, Chicago and Los Angeles. The results show that in all six metropolises, the proximity of those affected to a planned densification project has a decisive influence on acceptance: the closer someone lives to the future construction project, the lower the acceptance of densification. Acceptance increases for densification projects that are not planned in one’s own neighborhood, but in another part of the city.
"Residential densification projects that provide affordable housing in cities are more widely accepted because they help mitigate the perceived negative consequences of densification."
The researchers also refer to this as "NIMBY behavior." NIMBY stands for English "not in my backyard" or, mutatis mutandis in German, "not in my neighborhood" or "not on my doorstep." This discrepancy also exists in the canton of Zurich, as the researchers found in a study they published earlier this year in the planning journal Landscape and Urban Planning. Based on a study with an external site sample of about 3,000 respondents collected by the canton of Zurich and the research firm Anovum in 2013 , the following picture emerges: While 57.5 percent of respondents support densification as an overarching planning strategy in principle, only 11.9 percent accept it in their own neighborhoods. At the same time, it is evident in the canton of Zurich that most people who reject a specific densification project in their neighborhood nevertheless support densification as an overriding goal of urban development.
In cities, housing costs are decisive
For the canton of Zurich, the researchers have shown that the acceptance of residential densification projects differs depending on the type of residential area and the neighborhood: in areas on the outskirts of agglomerations and in single-family home neighborhoods, acceptance of residential densification is generally lower than in urban neighborhoods because those affected often expect negative effects on the value of residential property, privacy and green spaces. In urban neighborhoods, acceptance of densification is generally higher. Here, attitudes depend more on the level of housing costs and rents. Another factor is that densification often takes place in neighborhoods where older residential buildings and low-cost housing are located, and where the population wonders whether rental costs will rise above the current level in the future.
The ETH researchers have now extended the Zurich results in the international city comparison between Berlin, Paris, London, New York, Chicago and Los Angeles. In this study, they concentrated on the urban population and, for this purpose, more strongly identified which measures at the project level and in the planning instruments can increase acceptance.
In this context, the key role of affordable housing on the acceptance of densification and the implementation of urban development projects becomes apparent: "Acceptance increases if a project provides for mixed use with housing and commerce and is climate-neutral," Kaufmann explains, "Conversely, projects with purely profit-oriented investors meet with more resistance." In addition, Kaufmann’s team systematically studied - for the first time in urban development research - the effect of three planning tools used in residential densification projects:
- percentage of affordable housing in a densification project,
- rent control or limitation (in Berlin called "rent cap") and
- participatory planning and involvement of the local population.
In all six metropolitan areas, it is found that a fixed proportion of affordable housing - for lower incomes - rent control ("tenant protection") and participation increase acceptance: "Residential densification projects that provide affordable housing in cities are more widely accepted because they help mitigate the perceived negative consequences of densification," Kaufmann says. It is particularly interesting to note that both rent control, which could well have self-serving reasons, and the fixed share of affordable housing for low-income individuals have an acceptance-enhancing effect. It can be concluded from this that low-cost housing is important for shaping public opinion, regardless of whether anyone benefits directly from it or not.
Berlin and London most skeptical about densification
In the more market than regulation-oriented US cities of New York, Chicago and Los Angeles, acceptance of densification is higher than in Paris, London and Berlin. Accordingly, accompanying measures such as affordable housing influence the population less in U.S. cities. Densification is least accepted in Berlin and London, which in the German capital may have something to do with the "rent cap" debate. In England’s capital, the debate is probably more about which population groups the international investments in the housing market actually benefit.
In the next steps, David Kaufmann’s research group will investigate the acceptance of densification throughout Switzerland in the project "Densifying Switzerland," which is supported by the Swiss National Science Foundation SNSF. Among other things, they will evaluate the development of rents and all local spatial planning votes of the last 20 years in order to distill how economic, social and political factors influence the acceptance of densification.
Wicki M, Hofer K, David K. Planning instruments enhance the acceptance of urban densification. In: Proceedings of the National Academy of Sciences (PNAS) 119 (38) e2201780119, September 12, 2022. doi: external page 10.1073/pnas.2201780119.
Wicki M, Kaufmann, D. Accepting and resisting densification: The importance of project-related factors and the contextualizing role of neighborhoods. In: Landscape and Urban Planning, Volume 220, April 2022, 104350, doi: external page 10.1016/j.landurbplan.2021.104350.