Urban planners and architects have long debated the optimal height for buildings in cities. Some argue that taller buildings are more efficient and sustainable, while others claim that lower buildings are more human and livable. A new study published in the journal NPJ Urban Sustainability challenges the common urbanist belief that the ideal building height is about five stories maximum.
The Myth of Five Stories
The notion that buildings should be no more than five stories high is largely inspired by the work of Danish designer and architect Jan Gehl, who wrote in his landmark text Cities for People that taller buildings are out of scale with the human experience. He argued that human interaction is only possible below 25 meters and that beyond that, the contact interface changes to “views, clouds, and airplanes.”.
Gehl’s influential ideas have shaped many urban design guidelines and policies around the world, such as the Plan for Paris, which limits the height of new buildings to 37 meters. However, the study’s authors contend that this universal “optimal” or “ideal” building height is not based on any objective measure of what urban planners should be aiming for but rather on a subjective preference and a cultural bias.
The Reality of Urban Sustainability
The study, conducted by researchers from the University of Colorado, Edinburgh Napier University, and the University of Cambridge, analyzed the life cycle greenhouse gas emissions (LCGEs) of different urban environments, which include both embodied and operational emissions. They used an algorithm to simulate 5,000 urban scenarios with varying heights and density and compare their environmental impacts.
The results showed that taller urban environments significantly increase LCGEs (+154%), while low-density urban environments significantly increase land use (+142%). The researchers concluded that dense environments of approximately 6 to 10 stories in height offer the most environmentally friendly balance, emitting about 365 tons of carbon dioxide per person less than high-density high-rise alternatives.
The study also found that the increased land needed to construct 10-story buildings is offset by the savings in materials needed to construct tall buildings, which often require disproportionately large foundations and structural support. Moreover, the study revealed that the density of buildings has little impact on LCGEs, meaning that low and high-density typologies resulted in similar LCGE results, regardless of height.
The Implications for Urban Design
The study’s findings suggest that low-rise, high-density cities such as Paris, with predominately 5- to 6-story buildings, offer a more environmentally friendly model for urban development than high-rise, high-density cities such as New York City or Hong Kong. However, the authors also acknowledge that other factors influence the sustainability and livability of cities, such as transportation, social equity, and cultural diversity.
The study’s lead author, Francesco Pomponi, a professor at Edinburgh Napier University, said that the study’s aim was not to prescribe a specific building height for all cities but rather to challenge the myth of five stories and encourage a more holistic and evidence-based approach to urban design. He said, “We’ve always been looking at this problem from a building perspective. But when you start looking at the bigger picture, you realize you cannot put two high-rise buildings as close as you can two low-rise buildings.”
The study also calls for more research and data on the environmental impacts of different urban forms, as well as more collaboration and communication between urban planners, architects, engineers, and policymakers. The authors hope that their study will spark a constructive and informed debate on how to design cities for people and the planet.
