In mid-June, the German Weather Service (DWD) described the record-breaking heat in Germany and Europe as “a heat wave for the history books.”
The 40-degree-Celsius mark (104 degrees Fahrenheit) was surpassed at 46 weather stations in 11 German states, the highest temperatures ever in the month of June.
Eleven hot days and nights heated up many people’s homes so much that cooling off and getting a good night’s sleep were out of the question. Sustained lack of rest can have serious health consequences and can even be fatal.
Extreme heat waves appear to be getting more common across Europe and elsewhere. On July 7, 2026, the World Health Organization warned that “the next heatwave is already building over the Atlantic. Portugal and southern Spain are forecast to reach 43 C this week. France and the Benelux are bracing for another heat surge. Parts of Central Asia are baking under 40 C heat.”
It is high time for homeowners and local governments to rethink their approach to housing, says Thomas Auer, professor of building technology and climate-friendly construction at the Technical University of Munich.
“If you don’t think about cooling in the summer when you’re building, that’s a big mistake,” Auer told DW.
Windows: Lots of light, lots of sun, lots of heat
Direct sunlight is the number one source of heat. So, Auer says it’s important to have an “appropriate proportion of window area” — that is, a number and size of windows that provide enough light without creating a greenhouse-like atmosphere in the apartment.
In many rental apartments, there aren’t enough options for shading with roller shutters or blinds, he said.
Shading is particularly problematic in attic apartments, where heat accumulates.
“A skylight is exposed to the sun much more than a vertical window,” said Auer. “And [the requisite] shading devices are harder to manufacture.”
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Concrete, wood, clay, brick — what materials are heat-resistant?
From the floors to the walls and ceilings, most houses in Germany are made of concrete.
When it comes to regulating heat (a.k.a. thermoregulation), concrete is not such a bad idea at first glance. The material has a high thermal mass, meaning it can absorb large amounts of heat and release it gradually over time.
Concrete acts as a climate buffer. For this to work, however, it’s necessary for nights to be cool so that the concrete can release the heat it’s absorbed during the day. But if temperatures fail to drop below 20 degrees Celsius at night, the walls stay warm.
Another problem with concrete is that the cement used to make it produces high CO2 emissions, a cause of climate change.
Auer says we need a “sensible combination of mineral materials [such as concrete] and natural materials such as wood” when building a house.
“A traditional construction method in Germany was half-timbered framing filled with clay,” said Auer, who advocates a return to that method. Clay, he says, regulates room temperature and humidity.
By using so-called “activated clay building panels”, existing apartments could be made more heat-resistant. The panels are equipped with a system of pipes through which water flows.
“This would be an excellent way to regulate the climate in the apartment,” said Auer, in summer and winter alike.
Heat pumps offer another way to cool buildings. The Fraunhofer Institute for Building Physics has a webpage that explains how a heat pump can be used to cool. Heat pumps are typically installed as a heating system, but they can also be used for cooling when operated in reverse mode.
Houses with courtyards provide a better indoor climate
Auer takes inspiration from countries and regions that have long had to adapt to heat, such as Andalusia in Spain. There are many courtyard houses there — buildings arranged in such a way that a courtyard is formed in the center.
Trees and roof overhangs often provide shade in these courtyards; sometimes there’s a fountain or other kind of water source.
“This creates a pleasant microclimate and allows for cross-ventilation,” said Auer.
Air conditioning in extreme heat
Since not all existing buildings can be converted into courtyard houses, buying an air conditioner may seem like a good alternative.
But Auer says air conditioning is short-sighted, and, in some cases, could even be detrimental.
Air conditioners cause extreme temperature differences between indoors and outdoors. They remove moisture from the air, making it dry. And that can contribute to respiratory conditions and allergies, as a study based in India showed.
In addition, an earlier study in China suggested that spending prolonged periods of time in air-conditioned rooms reduces the body’s natural ability to adapt to heat.
Germany’s Federal Environment Agency also warns that air conditioners increase CO2 emissions due to their energy consumption. The greenhouse-gas-emitting refrigerants contained in some AC systems can harm the climate.
It is possible to cool buildings and protect people against extreme heat without further increasing greenhouse gas emissions.
Auer says we need to combine natural and mineral materials, with minimal use of glass and ample shading options, where technology merely complements traditional construction methods.
That said, Auer is not averse to technology like air conditioning. He’s just bought a ceiling fan for the bedroom and says, “It’s really saved us this year.”
This article was originally published in German on July 6, 2026.
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