"Summer comfort has become an issue of public health and urban resilience"

Over the past decades, the real estate sector has concentrated its efforts on insulating buildings against the winter cold. But in a Switzerland that is warming faster than the global average — with a rise in temperatures of +2.9 °C compared to the pre-industrial era, versus +1.3 °C globally — the issue is changing profoundly.

By threatening the comfort, even the habitability, of many buildings during summer, this change becomes a major challenge for the entire real estate sector. For this third part of our interview series, we discuss the issues related to property development with Emanuel von Graffenried, director & partner at Bernard Nicod Conseils SA.

Has the problem of warming urban centers been underestimated by the authorities for too long?

Yes, clearly. For decades, Switzerland designed its building stock almost exclusively to protect against the cold, which was historically justified. Standards, construction culture and investments favored winter insulation, building compactness and airtightness, often to the detriment of summer comfort.

However, the scientific findings are now unequivocal: in Swiss urban centers, nighttime temperatures can remain up to 6 °C higher than in the outskirts during heatwave episodes. This situation prevents buildings from thermally “discharging” at night. The FOEN and the NCCS now explicitly warn that a significant portion of the existing building stock could become uncomfortable, even uninhabitable in summer without adaptation measures.

But this is not a mistake by our sector, rather a delay. And that delay is now becoming visible.

What about today? Is this aspect taken into account for all new developments?

Increasingly, yes, but still unevenly. The most advanced recent projects, notably those led by responsible institutional investors, now integrate summer comfort from the design phase.

Labels and regulatory frameworks are also evolving, notably through Minergie, SIA standards or the new requirements linked to the climate transition, which progressively require designing buildings with both seasons in mind.

That said, new construction remains marginal. The real challenge lies elsewhere: adapting the existing stock, which represents the bulk of Switzerland’s building stock.

Do you observe concrete consequences on the value of a property poorly protected against heat?

Yes, and the phenomenon is accelerating. We already observe a decline in rental attractiveness of dwellings subject to summer overheating, an increase in complaints in dense areas, as well as the first signs of a climate-related discount on certain properties.

Studies show that dwellings lacking solar protections or effective ventilation systems are those where summer discomfort is most strongly felt. In time, the market will explicitly incorporate these criteria, as it already has for energy-inefficient dwellings in winter.

A Wüest Partner study estimates the cost of a comprehensive energy retrofit of the Swiss building stock by 2050 at about 228 billion francs.

Between so‑called “active” or “passive” cooling, what concrete solutions exist to reduce the effects of warming urban centers on buildings?

There is no single solution, but a clear hierarchy of responses to prioritize. Passive cooling should remain the priority. It relies on a coherent set of measures — external solar protections, nighttime natural ventilation, controlled thermal inertia, green roofs and façades, light and permeable materials, appropriate siting and morphology, etc. — which, when intelligently combined, make it possible to sustainably limit overheating without resorting to energy‑intensive solutions. These approaches, both frugal and robust, are generally the most effective in the long term.

Active cooling, such as free cooling, geocooling or properly sized reversible heat pumps, complements passive measures when they are no longer sufficient, and should not be used as a substitute. The challenge is to avoid a generalization of air conditioning, which is both energy‑hungry and counterproductive at the urban scale.

Is it ultimately more difficult to reduce nuisances related to heatwaves than those associated with severe cold?

Yes, without hesitation. The Swiss building stock has historically been designed to retain heat, not to evacuate it. During prolonged heatwaves, this quality becomes a flaw. Adapting a building to combat overheating is often more complex than insulating it against the cold. One can thus say that yesterday’s thermal leaks become today’s “boilers.”

How do you assess the financial needs to renovate the existing stock, and should we fear that these needs will contribute to increasing rents already unaffordable in some Swiss cities?

The amounts at stake are considerable. A Wüest Partner study estimates the cost of a comprehensive energy retrofit of the Swiss building stock by 2050 at about 228 billion francs.

These investments create real pressure and raise a genuine social risk. On one hand, there is the urgency to adapt the building stock for health, climate and environmental reasons; on the other, the risk of increased pressure on rents in already tight markets.

The response therefore cannot be left solely to the market. It will require targeted public subsidies, phased planning, and a long‑term asset management approach. When well executed, these adaptations not only improve occupant comfort but also stabilize operating costs and preserve property value, without mechanically causing rent increases.

Summer comfort is no longer a secondary issue. It has now become a matter of value, public health and urban resilience. Those who anticipate today are not only making an environmental choice: they are sustainably protecting their assets as well as their tenants.

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