🏗️ Do cities really need more buildings? My conversation with Francesco Pomponi

Hey folks! In our Urbi Atlas interview, Francesco Pomponi, a professor at the University of York, explained why true sustainability in cities means rethinking whether we build at all.

What inspired you to focus on sustainability and the built environment?

It’s been a natural journey. My family has always been environmentally conscious—not activists, just as a way of living. My father grows fruit as a hobby and refuses to discard even partly spoiled pieces, carving out the bad bits to save the rest. My sister took me to beach clean-ups as a kid, so I grew up with a strong sense of responsibility for the planet.

Later, studying engineering and seeing the waste in construction pushed me to find better solutions. Doing a PhD felt like a natural step—it seemed almost unbelievable that someone would pay me to learn new things. That’s how I became an academic: someone paying me to learn and explore felt like the best job in the world.

In your opinion, what defines a truly sustainable city or neighbourhood?

There are several aspects to consider. First, understanding the local context is essential. Cities must support their inhabitants, considering who lives there, their needs, the population’s age, and the climate. Too often, we apply a one-size-fits-all approach.

If you look at modern architecture worldwide, there’s not much diversity. Yet, traditional or vernacular architecture is adapted to suit the local environment, using materials, window sizes, wall thicknesses, and roof designs tailored to the specific climate. We’ve moved away from this. For me, sustainability begins with understanding the place where you’re building. We should also question whether we need to build at all, considering we’ve already constructed so much. Global statistics may indicate demand for new floor area, but this varies by region. Some areas genuinely need new construction, while others could repurpose existing structures.

For example, I’m from Italy. Even though it’s very hot, my parents live in a house without air conditioning, and it works fine. Yet, modern Italian buildings treat air conditioning as essential. We could address this with better education, climate-responsive design, and passive strategies. We also need to think about future climate shifts.

In developed economies, we’ve built extensively. Instead of adding more, we should consider reconfiguring what we already have. For instance, remote work has changed transportation needs and reshaped what we expect from our neighbourhoods. The concept of the 15-minute city, reducing commutes and improving quality of life, is gaining traction. These ideas should guide master planning and policymaking.

What were the most surprising findings from your research on building height, density, and greenhouse gas emissions?

It was surprising to realise that the data doesn't fully support what many people assume about taller buildings. The mainstream narrative suggests that adding height is inherently more efficient—you take one storey, then stack another on top, and you get twice the floor area with the same building footprint. Up to a certain height, maybe around six storeys, that can work. But when you go taller, new challenges emerge.

To maintain ventilation, privacy, and access to daylight, taller buildings need to be spaced further apart. Structurally, it’s necessary to give them bigger foundations. And there’s a visual trick—when you look at two tall buildings, they seem close together, but if you measure the distance, you’ll find they’re much further apart than mid-rise buildings.

When we scaled this up to larger urban areas, we found something counterintuitive. A single tall building might have more floor area for the same footprint, but at the urban level, the land use is almost the same as with less tall, denser buildings. So, in our study, we decoupled density from height for the first time. We found that density is great—you can achieve high density through clustering without relying on extreme building heights. And taller buildings come with additional carbon costs that aren’t always necessary.

Is there a way to make high-rise buildings more sustainable?

It depends on the technology we can master, the scientific evidence to support it and the regulations in place. For example, in the UK, we’re starting to see high-rise timber buildings, and this trend is growing in places like Canada, Scandinavia, and Germany. Using timber as a structural material can reduce the embodied carbon of tall buildings. However, we must ensure structural stability and fire safety. Timber has been used for thousands of years, but not in 25-storey buildings. That’s a modern challenge. Research is crucial to understanding how this reliable, traditional material can work in a contemporary context.

There's also room for improvement in conventional materials like steel and reinforced concrete. One way is material efficiency—using the right amount of material without overdesigning. With today’s tools, we can model structures precisely, ensuring materials are only placed where they’re truly needed for load-bearing. For instance, lower floors require more support than higher ones, but the same column sizes are often used throughout a building. Optimising this can make a big difference.

Another factor is the design itself. Sometimes, we aim for large spans—nine or twelve metres—for aesthetic reasons or to create open, flexible spaces. While that flexibility might add resilience, span length is only one of many factors guiding the decision to retain a building rather than demolishing it. If a building needs saving, or if we truly want to save it, it will be saved regardless of its span size. By being less extravagant in our designs, we can reduce material use and carbon emissions.

We’re also developing new technology to reuse existing buildings. This involves creativity and ingenuity in structural engineering to offer the space and functionality we need without tearing buildings down and starting from scratch.

Read the full interview in Urbi Atlas, and check out my feature on urban planning for a sustainable future.

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Elia Kabanov is a science writer covering the past, present and future of technology (@metkere)

Illustration: Elia Kabanov feat. DALL-E.