Densification is hailed as the key to the sustainable transformation of our cities. However, its implementation through the pursuit of “building new and better” is actually hurting the environment more. Our latest study reveals flaws in the sustainability of modern, densely constructed buildings. While new high-rises offer operational efficiency, they often result in higher total carbon emissions. This post advocates for a crucial paradigm shift from efficiency to sufficiency in the way we build. It presents planners with one possible alternative for densification: using existing buildings rather than demolishing them. For energy practitioners, these insights are essential for implementing truly effective energy transition measures in cities.
Densification has long been a byword for urban planners on how to sustainably transform our cities. Building within a city’s perimeter has been shown to reduce transportation emissions, land consumption, and utility costs, among other benefits. Based on these benefits, policymakers began promoting increasing density of the built environment, with Switzerland passing the Federal Spatial Planning Act in 2014 in favour of an inward development-only strategy. However, the implementation of this idea has not been complemented with careful consideration of how we build. The results reveal numerous challenges exacerbated by the mirage of sustainability in newly constructed, energy-efficient buildings.
From necessity to gentrification
Back in the 1970s, the oil crisis forced a realisation among governments and architects alike: our buildings consumed far too much energy. Building energy codes subsequently emerged as a response to this, championing superinsulation. By the 1990s, the emergence of global environmentalism had brought the concept of sustainable architecture to prominence. Since then, building energy performance has been synonymous with ultra-high efficiency, characterised by low heating or cooling demands. This formed the common belief that old buildings are inherently inferior to new buildings in terms of energy. The construction and real estate industries have leaned on this narrative to justify a “demolish and rebuild” strategy, which inevitably fuels waves of new-build gentrification. But this raises a critical question about whether they are truly sustainable.
A study on future scenarios
Our study, presented at CISBAT 2025, sheds some light on whether building denser is indeed more sustainable. We examined how various future building block typologies affect carbon emissions. To project realistic future development, four plausible futures are constructed based on the world’s two megatrends: the degree of demographic shift to an ageing society and the degree of urban spread. We model an ageing society by the degree of inhabitants spending time at home versus work, and future population growth, while urban spread is determined by the mixture of building uses in the neighbourhood. Subsequently, these occupancy and use characteristics determine the building demand loads. The study is demonstrated in a Swiss context at a neighbourhood in Altstetten Nord with existing old residential buildings and an empty plot for new development. Figure 1A summarises the six building block typologies simulated. The typologies range from the typical Swiss ones, such as row houses and blockrands, to more radical ones, such as towers, slabs, and skyscrapers. The radical typologies are also often associated with newer constructions, with a greater emphasis on higher growth possibilities and compactness through a larger floor area ratio (FAR). The simulations parameterise new building construction, occupancy, and functions, as well as the existing building level of retrofitting, resulting in a total of 2,208 simulations.
The results in Figure 1B confirm that futures with more compact typologies result in lower total energy demand . However, the results also reveal a paradox: higher efficiency does not necessarily translate to lower total carbon emissions. More radical typologies, such as skyscrapers, produce more total emissions, even though their total energy demands are smaller. The adverse impacts of highly carbon-intensive materials needed for more radical typologies outweigh the ecological benefits gained from energy savings. In the scenarios with an ageing society, the results indicate that new developments with higher FARs are not considered due to the lack of demand resulting from lower population growth. Therefore, retrofitting existing buildings with appropriate new developments, such as blockrand rather than skyscrapers, may be the best option for reducing emissions.
Shifting the paradigm: efficiency to sufficiency
The findings call for a paradigm shift in the energy transition of our built environment from efficiency to sufficiency. While the prevailing efficiency-driven strategies indeed result in lower energy demands, they are often achieved through more resource-intensive construction typologies. They are, therefore, counterproductive in our efforts to reduce carbon emissions. Instead, under the sufficiency framework, energy transition can prioritise settlement densification strategies that meet actual demographic demand rather than relying on infinite growth projections. By putting more weight on the embodied carbon emissions associated with our new developments, practitioners and planners should realise that sustainable construction and densification are no longer only a discussion of “building new and better” but also “building less excessively”.
Social and environmental sustainability go hand in hand
Our study, however, has not integrated the social and environmental sustainability in depth, despite these dimensions being intrinsically linked within the sufficiency paradigm. As mentioned, the pursuit of energy efficiency in our buildings has the negative side effect of new-build gentrification. A study conducted by the Chair of Spatial Development and Urban Policy (SPUR) at ETH concluded that new housing developments, and even renovated buildings, primarily affect vulnerable groups through displacement. Former residents are subsequently unable to return to a similar neighbourhood due to the higher rent, explained partially by the larger living space per person in the new builds. This situation brings us back to environmental sustainability: a decrease in occupancy density means that the common total area normalisation is misleading since we are accommodating fewer people. The new buildings that appear more efficient per area might not be so per capita. As the housing shortage persists, the cycle continues, generating more demand for new construction and the embodied carbon that comes with it. The environmental and social dimensions are, therefore, intertwined in the energy transition of our cities.
What’s next? Utilise our existing buildings!
So, how can energy and urban planners move forward with this? The immediate step is to overhaul the presumption that suggests “only new is better”. We may then ask how we can densify without constructing new buildings. One possible answer lies not far away from what has been there in our cities: utilise our existing buildings with potential for densification. Existing buildings with the right characteristics can be extended vertically or horizontally, infilled in underutilised land, subdivided to accommodate more families, and reused, when abandoned, for affordable housing. In short, we should aim to avoid “demolition and rebuild” whenever possible. These strategies can help prevent emitting more embodied emissions than are strictly necessary. Ultimately, we must move beyond the efficiency-first status quo and commit to a paradigm of sufficiency that treats our existing urban fabric as a potential for sustainable densification.
