Sa'ad Ahmed, Pernille Krogh Ohms
June 9, 2025
How to reduce the environmental impact of urban development
More than half the world’s population lives in cities, and this is set to rise to 6 billion by 2041. A landmark study supported by The Ramboll Foundation provides lessons in sustainable urban development.
By 2050, two thirds of people will live in urban areas, according to the United Nations – 2.5 billion more than current numbers. This ever-increasing growth necessitates a sustainable approach to urban development which does not jeopardise agreed climate targets.
A study from Technical University of Denmark (DTU) explores how to mitigate the environmental impact of urban growth. Supported by The Ramboll Foundation in partnership with the Danish Innovation Fund and Realdania, Pernille Krogh Ohms, Sustainability Specialist at Ramboll, and her co-researchers used DTU’s 110-hectare Lyngby campus – with its diverse building mix of 11 different archetypes – to explore how to reduce greenhouse gas emissions whilst expanding development.
Currently, cities consume over two-thirds of the world’s energy and emit more than 60% of greenhouse gas emissions; a more sustainable approach to cities will also enhance liveability. Here are the key recommendations for urban decisionmakers.
- Reduce operational energy use
- Reduce new floor area
- Decarbonise the energy supply
- Reduce embodied carbon
- Improve heat efficiency
Reduce operational energy use
A major source of greenhouse gas emissions in cities is the operational energy use of buildings. The researchers found that reducing the operational energy demand of existing buildings will have the largest reduction in all impact categories.
In 2022, Ramboll worked with the European Environment Agency (EEA) to reduce operational carbon through renovations targeted to improving energy efficiency. The EU building stock was found to account for 36% of total greenhouse gas emissions in the EU, and Ramboll’s work improved on the policy framework. Ramboll analysed the impact of existing buildings and provide recommendations for boosting energy efficiency, including its uptake in residential projects, a continuing source of demand as urban development continues.
Reduce new floor area
The United Nations found that to cope with demand, 230 bn m2 in floor area – the size of Japan – will be built each year to 2060. Adaptive reuse, renovation, and refurbishment can revive older buildings, leading to a 10% reduction in new floor area. Using biogenic materials for extensions and retrofitting can further reduce carbon impact.
A second study by Pernille Krogh Ohms and others found that buildings are often demolished before the end of their service life. Demolishing a building and replacing it with a new one of comparable size can produce 35% higher CO2 emissions than renovation. Adapting building layouts to accommodate more users – such as shrinking the size of hallways – can reduce the environmental impact of increased demands for space.
Renovation can also be up to 45% more cost effective; over 50 years, it is twice as expensive to build new. Where increased construction cannot be avoided, building vertically can make it more sustainable, avoiding increased floor area and resulting reduction in land availability.
Decarbonise the energy supply
Researchers found that overall decarbonisation would reduce damage on ecosystems by 24.5% from 2023 to 2035. However, this would not be sufficient on its own. The study found that for building stocks to align with 1.5°C, heat and electricity supply must be completely decarbonised – but urban decisionmakers can’t simply expect society to solve this issue.
“Decarbonising is not enough on its own to align with the 1.5°C, target. The owners of the building stock need to take further action to align and cannot just rely on technology development in the surrounding society.”
Planners must balance demand for increased building with environmental impact, using renewable energy at every step of the process to reduce the per unit environmental impact of additional development. As city growth continues, focusing on sustainability and decarbonisation is vital.
Reduce embodied carbon
Decarbonising the construction process is crucial for reducing upfront or embedded carbon. Techniques like using prefabricated components reduce emissions and air pollution significantly compared to traditional on-site construction. Additionally, employing low-emission vehicles for transporting materials to construction sites also helps decarbonise the process.
Using biogenic materials, such as timber, is another way to reduce embodied carbon due to lower carbon footprints compared to conventional building materials. Reducing embodied carbon through sustainable construction practices contributes significantly to lowering the overall environmental impact, complementing other efforts.
Improve heat efficiency
Buildings with little insulation – measured at less than 3kg per square metre – tend to have a higher heating demand. If these buildings are targeted for energy efficiency focused renovation, they will require less heating and thereby have lower environmental impact.
Decarbonising the heat mix for buildings also helps, reducing damage on ecosystems by 27.5% by 2035. Better insulated buildings will mitigate the increase in heat demand relative to business-as-usual construction and heat mix. Using certain building materials, such as timber, can boost the thermal efficiency of a building, leading to a more environmentally friendly outcome.
Is it worth mentioning district heating in this section? It may be that the report does not refer to it and therefore it’s not appropriate to include.
“I believe our findings that combining multiple mitigation strategies is important would also apply to other building stocks. Our study is a demonstration of how we can combine different strategies to achieve the targets we need to reach”
Sustainable urban development is possible
As demand for urban spaces increases, overshooting the Paris target is not inevitable. Urban decisionmakers should consider these recommendations to reduce the environmental impact of accommodating a rapid rise in city-dwellers. “Although our findings are specific to this particular building stock, I am confident that we would find some of the same trends for other building stocks,” Pernille Krogh Ohms continues.
Urban growth and a sustainable future are not mutually exclusive. Through combining these mitigation strategies, urban planners can promote sustainable growth that adheres to climate goals and makes societies more resilient and liveable.
Want to know more about the role of building transformation in decarbonising buildings? Discover Ramboll’s sustainable renovation guide
Want to know more?
Pernille Krogh Ohms
Sustainability Specialist
+45 60 36 12 97