When your apartment turns into a sauna: What really helps against heat in buildings
Summers are getting hotter, and many apartments, houses and offices are heating up more and more. But you do not always need an air conditioner right away. Building expert Stefan Mösl explains which measures help immediately — and how buildings can be better protected against heat in the future.
It is a situation many people are familiar with right now: outside, temperatures rise well above 30 degrees; inside, it becomes more uncomfortable day by day. The air is stagnant, rooms hardly cool down anymore, and restful sleep is often out of the question. Attic apartments in particular, large glazed areas, poorly shaded rooms and modern buildings with lots of windows quickly reach their limits during heatwaves.
„Viele Menschen glauben, dass ein Gebäude einfach heiß wird, weil es draußen heiß ist. In Wahrheit entscheidet aber sehr oft die Bauweise, die Verschattung und die Nutzung darüber, wie stark sich Räume aufheizen“, sagt Bausachverständiger Stefan Mösl.
The most important principle sounds simple, but is often underestimated in practice: the best cooling is the heat that never enters the building in the first place.
“What comes into the room through the glass panes has to be cooled back out later. That costs energy, technology and often a lot of money,” explains Mösl. Direct sunlight through windows is particularly critical, he says. Large glazed areas bring light and quality of living, but in summer they can become a heat trap if they are not adequately protected.
Immediate measures: What already helps today!
If you are sitting in an overheated apartment, there are still a few things you can do in the short term. Above all, the right timing for ventilation is crucial.
“At night and early in the morning, you should deliberately bring the cooler air into the building. This works best with cross-ventilation, i.e., when windows can be opened on opposite sides,” says Mösl.
It is even more effective if cool air can flow in at the bottom and warm air can escape at the top. Because warm air rises. If openings are created in the lower and upper parts of a building, a natural draft can develop.
During the day, however, the opposite usually applies.
“In the heat, many people open the windows because they feel they need to ventilate. But if it is 32 or 35 degrees outside, you are bringing exactly that heat into the building,” says Mösl. His advice: as soon as it is noticeably warmer outside than inside, keep windows and doors closed.
Solar shading should also be activated as early as possible. Roller shutters, external venetian blinds, awnings or curtains help most when they are used before the sun has already heated up the room. External solar shading is even better, because then the heat does not build up at the pane in the first place.
Solar shading is more than a comfort issue
For the next heatwaves, it is worth taking a closer look at the building envelope. Window areas in particular are crucial. Where external solar shading is missing or cannot be retrofitted, reflective films can be an option. They reduce part of the solar radiation and can help to reduce overheating.
“Not every measure suits every building. But almost every building has potential. The important thing is to first understand where the heat is really coming in,” says Mösl.
In addition to classic shading systems, photovoltaic surfaces are also becoming increasingly important. PV systems on the roof not only generate electricity, they also shade roof surfaces at the same time. Partially transparent PV elements on façades or over glazed areas could also play a greater role in the future.
“Photovoltaics can have a double effect: it protects building components from direct sunlight and converts part of the solar energy directly into electricity. That turns a burden into a benefit,” explains Mösl.
Greening, cooling and smart retrofitting
Façade greening, trees and natural shading can also relieve buildings. Plants not only cool through shade, they also improve the microclimate around the building. This can make a noticeable difference, especially on heavily sun-exposed façades.
For larger buildings, offices or residential complexes, technical solutions can also make sense. Ceiling cooling, thermally activated building systems or water-based systems can temper rooms without replicating the effect of a classic air-conditioning system. In some cases, even existing heating systems, such as underfloor heating, can be used for gentle cooling with cool water. However, a professional assessment is required.
“You must not simply repurpose existing systems. A technical assessment is needed so that no moisture damage, condensation issues or comfort problems arise,” emphasizes Mösl.
This is precisely where the expert sees a major task for owners, property managers, planners and the construction industry in the coming years. Many buildings were designed for earlier summers. However, the requirements are changing.
Not only build new, but improve existing buildings
A large part of the challenge lies not in new construction, but in existing buildings. Apartments, single-family homes, schools, offices, care facilities and commercial properties increasingly need to be prepared for heatwaves.
“We must not only preserve buildings, but further develop them. Heat protection will become a quality feature of real estate,” says Mösl.
This is not about installing air-conditioning systems everywhere immediately. Much more important is a coordinated concept: where does the heat come in? Which window areas are critical? Is shading possible? Can PV surfaces be integrated sensibly? Are there options for façade greening? Can existing systems contribute to tempering? And which measures make economic sense?
“The future does not lie in a single solution, but in the interplay of building physics, planning, building services engineering and practical experience,” says Mösl.
“And the better product is not created by the price, but by the attitude behind it.”
The most important tips at a glance
During an acute heatwave:
Ventilate thoroughly at night and early in the morning.
If possible, use cross-ventilation.
During the day, keep windows and doors closed as soon as it is hotter outside than inside.
Close solar shading early, not only when the room has already heated up.
Avoid direct sunlight on glazed areas.
For the next heatwaves:
Check solar shading and shading options.
Consider reflective window films or suitable glazing.
Factor in PV systems on the roof or façades as shading and an energy source.
Check façade greening and natural shading.
Have ceiling cooling or existing water-based systems professionally assessed.
Plan and maintain buildings not only for winter, but also for summer.
Mösl’s conclusion is clear:
“The best air conditioner is the heat that never enters the building in the first place. Anyone who wants to make buildings future-proof must factor in summer heat protection from the outset — in new construction just as much as in refurbishment.”
m3 Ziviltechniker GmbH
Farchen 26, 5342 Abersee
www.m3-zt.at
office@m3-zt.at
