Europe spent decades designing buildings to survive winter. As temperatures rise, the continent is discovering that energy efficiency alone does not guarantee summer comfort.

Nearly half of Europeans believe their homes are not equipped to cope with extreme heat.

A 2026 survey published by the Buildings Performance Institute Europe found that 45% of respondents considered their homes unprepared for high temperatures. By comparison, 25% believed their homes could not adequately cope with cold conditions. The result marks an important shift in how Europe must think about building performance.

For decades, the central objective of European construction policy was clear: reduce heat loss during winter. Buildings became more insulated, windows became more airtight and renovation programmes focused on lowering heating demand. That strategy remains essential. But it is no longer sufficient. A building can perform well during winter and still become dangerously uncomfortable during summer.

Europe’s buildings were designed for a different climate

Around 85% of buildings in the European Union were constructed before 2000, while approximately 75% are considered to have poor energy performance.

Much of this stock was designed when prolonged periods of extreme heat were less frequent. Summer comfort was rarely treated as a primary performance criterion, particularly in central and northern Europe. Architecture was shaped around retaining warmth. Today, the same characteristics that reduce winter heat loss can intensify overheating when solar gains, ventilation and shading are poorly controlled.

Highly insulated and airtight buildings may retain unwanted heat long after external temperatures begin to fall. Large glazed surfaces can increase solar gains, while apartments with only one orientation may offer limited possibilities for cross-ventilation. Dense urban development adds another layer of risk. Roads, roofs and façades absorb heat throughout the day and release it slowly at night, preventing buildings and cities from cooling effectively.

The result is not simply discomfort. Excessive indoor temperatures can affect sleep, concentration, productivity and health, with older people, young children and those with existing medical conditions facing the greatest risk.

The problem is not glass. It is glass without strategy

Modern architecture increasingly favours transparency, natural light and visual connection with the exterior. Large windows and glazed façades can create exceptional spaces. But their performance depends on how the entire envelope is designed. Orientation, glazing specification, opening possibilities, external shading and façade geometry must operate as part of one system.

Solar-control glass can reduce unwanted heat gains. External shutters, screens, awnings and adjustable louvres can intercept solar radiation before it reaches the glazing. Opening windows can support natural and night-time ventilation when outdoor conditions permit. Architectural overhangs, vegetation, thermal mass and reflective surfaces can also contribute to controlling indoor temperatures. Individually, none of these measures solves every problem. Together, they can dramatically reduce the need for mechanical cooling.

Air conditioning cannot be Europe’s only answer

As heatwaves intensify, demand for air conditioning is expected to grow. For some buildings, particularly hospitals, care facilities and other critical environments, active cooling will remain necessary. But attempting to cool Europe’s entire building stock mechanically would create new challenges. Electricity consumption would rise precisely during periods of peak demand. Operating costs would place additional pressure on vulnerable households, and cooling equipment would release more heat into already overheated urban areas.

This could create a cycle in which cities use increasing amounts of energy to manage a problem partly intensified by the cooling systems themselves. The better approach is to reduce cooling demand before adding cooling capacity. Passive measures should therefore become the first layer of protection, supported by efficient mechanical systems where required.

Renovation must stop being a winter-only conversation

Europe’s renovation policies have traditionally focused on insulation, heating systems and carbon emissions. These remain indispensable priorities. Buildings account for roughly 40% of EU energy consumption, and the renovation rate remains too slow to meet the continent’s climate objectives.

But renovation strategies must now address two seasons equally.

Every major project should answer:

• How will the building retain heat during winter?
• How will it prevent and release heat during summer?

Adding insulation without assessing overheating risk can produce unintended consequences. Replacing windows with highly airtight units without considering ventilation can improve winter performance while reducing the building’s ability to cool naturally.

Renovation must therefore become more integrated.

Windows, glazing, external shading, ventilation, insulation and automated controls should no longer be selected independently. They must be designed as components of a single climate-responsive envelope.

Summer comfort is becoming a measure of building quality

Until recently, indoor comfort during heatwaves was often treated as a luxury or a problem limited to southern Europe. That assumption is disappearing.

The BPIE survey found no clear north-south divide in how Europeans perceive the ability of their homes to cope with extreme temperatures. Overheating is increasingly affecting countries whose housing, infrastructure and lifestyles were never designed around sustained heat. This changes the market for architects, developers and manufacturers. Thermal performance can no longer be communicated only through insulation values and winter energy savings. Customers will increasingly ask whether their homes can remain comfortable during periods of extreme heat.

That will place greater importance on external shading, dynamic façades, intelligent ventilation, solar-control glazing and building automation. The window and façade industries are not peripheral to Europe’s adaptation challenge. They are central to it.

From energy-efficient to climate-ready

Europe does not need to abandon its focus on energy efficiency. It needs to expand its definition. A truly efficient building should remain comfortable with minimal energy consumption in both winter and summer. It should capture solar energy when beneficial and block it when excessive. It should retain warmth without becoming a thermal trap. It should allow occupants to ventilate safely and should use mechanical cooling only after passive measures have been exhausted.

The fact that 45% of Europeans believe their homes are unprepared for extreme heat should be read as more than a survey result. It is a warning from inside the buildings themselves. Europe’s next renovation wave must not only reduce energy bills and carbon emissions.

It must prepare millions of homes for a climate they were never designed to withstand.