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The future of building

[Translate to Englisch:] Ob mit recycelten Materialien, grünen Dächern oder Solarfassaden - das Bauen muss nachhaltiger werden um zukunftstauglich zu sein. Bild: Zac Wolff/Unsplash

High-rise buildings made of mushrooms, with cooling facades and vegetable gardens on the roof: Architecture must change to become more sustainable and climate-friendly, and solutions are coming from science.

The facade? Composed of wood from deconstructed barns. The kitchen counter? Made of recycled yogurt cups. And the windows? They come from a bank building in Basel. For their roof construction in Wuppertal, students from the Karlsruhe Institute of Technology (KIT) are relying entirely on the principle of circularity. They have designed RoofKIT, an addition to the "Café Ada" cultural center, a two-story Gründerzeit building in the old town using almost exclusively reused or recycled materials.

With this approach, the team won first place at the Solar Decathlon Europe a few weeks ago, the world's largest university competition for sustainable building. However, the award is not only a "nice success" for the research university of the Helmholtz Association, says KIT Professor Dirk Hebel, architect and one of the supervisors of the project. But it also underlines the radical rethinking taking place in the construction industry: "The new generation of female architects and urban planners takes principles such as circular justice and CO2 emissions into account in the design from the very beginning." The expert said about 90 percent of master's theses in the Department of Architecture now address issues related to the conversion of existing buildings.

That's because the construction inustryneeds to reinvent itself: Modern urban construction still gobbles up too many valuable raw materials such as copper and aluminum, steel and plastic, sand and wood. The Federal Environment Agency estimates that in Germany alone, a mass of 50 billion tons is used, with only a fraction being recycled after use. At the same time, the construction sector emits a particularly large amount of harmful gases: The UN has calculated that it accounts for almost 40 percent of global CO2 emissions.

In order to make the architecture of the future more sustainable, buildings must be planned and constructed differently, adopting innovative concepts and materials from the world of science. KIT Professor Hebel, for example, is designing buildings that can be completely deconstructed and do not produce any waste at the end of their life, and serve as material storage for future generations. For this purpose, the components are not glued, but inserted, clamped, or screwed into each other, meaning that all materials can be completely reused after use. At the same time, the researcher is developing CO2-absorbing building materials, such as building blocks made from the roots of mushrooms.

His colleague Frank Dehn, head of the KIT Institute, wants to improve the most important construction material of all: Concrete. The material will continue to be indispensable in the future, but its carbon footprint must be radically reduced as it is a major driver of global warming. Its production generates 2.8 billion metric tons of CO2 a year, around eight percent of total global emissions.

"Next to water, concrete is the most consumed material in the world, so there is a societal expectation to use it as responsibly as possible," says Frank Dehn. Photo: Regina Link

The main reason for the high emissions is the cement used as a binder in concrete. Dehn, a civil engineer, is researching climate-friendly alternatives, for example, from blast furnace slag, ash from coal-fired power plants, and raw clay. If concrete is produced using these materials, the production process releases significantly less CO2: Dehn believes a halving of the values is possible. Unlike conventional concrete, his material is also virtually calcium-free, making it more resistant to heat, moisture and chemicals. "This makes it particularly interesting for industrial applications." The first pilot plants producing the new concrete are currently being implemented together with industry.

The smallest particles from old concrete should be able to be used again as a binder for fresh building material through special processes. Image: Shutterstock/Nordroden

But building materials expert Dehn is thinking even further: As the energy transition progresses, there will eventually be fewer and fewer ashes and slags that are suitable as cement substitutes. The engineer therefore also wants to use old concrete: Up to now, it has mostly been crushed into coarse gravel. What remains unused, however, is the so-called crushed sand, a fine granulate that is produced during the demolition of houses and the further processing of construction waste. Dehn uses this "concrete dust" as the basic material for a new type of binder: It is mixed with certain bacteria whose highly active enzymes bind CO2, and in experiments this has already been successful.  "This would further improve the carbon footprint of concrete, but our research here is still in its infancy," explains Dehn.

According to Daniela Thrän, bioenergy expert at the Helmholtz Centre for Environmental Research (UFZ), The architecture of the future will include groundbreaking developments such as the use of old concrete that can be reused as concrete again, and even swallow harmful gases in the process. That's because they strengthen the local circular economy. Thrän has been analyzing biobased material cycles for years, and still keeps discovering untapped potential: Cities, for example, could make even better use of their waste and wastewater if they set up small refineries. These would not only produce biogas for local consumption, but also valuable raw materials for industry, including nitrogen for fertilizers, for example. Initial tests are underway at a wastewater treatment plant in Stuttgart with the participation of KIT.

The sponge city concept relies on infrastructures that store precipitation water close to the site and release it when needed - like a sponge. Graphic: UFZ

But Thrän sees cities not only as consumers of valuable resources, but also as overlooked producers. Food, for example: The first supermarkets are setting up facilities on their roofs to breed fish, and right next to the vats are small greenhouses where fresh fruit, vegetables and herbs grow.

In the future, private houses could also be planned and built in such a way that their roofs and facades bear fruit, says the environmental engineer, enabling a move towards self-sufficiency among tenants. The principle is already being implemented in some cities in Latin America, Asia and Africa.

Such small-scale green spaces offer even more advantages such as helping to mitigate the impact of extreme weather. In hot weather, they cool their immediate surroundings, andduring heavy rainfall, they absorb some of the water,  thus reducing the risk of flooding. More and more municipalities are having to prepare for such scenarios in terms of urban planning, explains Bruno Merz, hydrologist at Helmholtz-Zentrum Potsdam (GFZ). That's because climate change is increasing the number of extreme weather events. "Today, floods also threaten settlements that are not located on a river or sea," says the expert.

The type of building that has been common up to now has even encouraged this negative trend: Many communities have sealed their surfaces in order to drain water quickly. "We need to turn this basic idea on its head and rebuild our cities and villages to retain water for as long as possible in the future," says Merz. Parks, rooftop gardens and green spaces soak up water like a sponge when it rains. Excess water is then transferred to hidden tanks from which the green spaces can later be supplied in times of drought. At the same time, these planted areas increase the biodiversity of urban spaces.

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The elegant blue façade of the Helmholtz-Zentrum Berlin's new research building generates up to 50 kilowatts of electricity and serves as a real laboratory for photovoltaic research. Image: HZB / M. Setzpfandt

The type of building that has been common up to now has even encouraged this negative trend: Many communities have sealed their surfaces in order to drain water quickly. "We need to turn this basic idea on its head and rebuild our cities and villages to retain water for as long as possible in the future," says Merz. Parks, rooftop gardens and green spaces soak up water like a sponge when it rains. Excess water is then transferred to hidden tanks from which the green spaces can later be supplied in times of drought. At the same time, these planted areas increase the biodiversity of urban spaces.

However, there is still a lack of experience and knowledge about the optimal use of photovoltaics in the building envelope, according to Rau. HZB has therefore built a real laboratory for building-integrated photovoltaics: One of the center's research buildings in Berlin-Adlershof bears bright blue façade panels of solar modules. Rau's team wants to use them to test, for example, how robust the elements prove to be in continuous use and how much electricity they supply over the course of the year.

Houses that produce their own electricity, supply fresh food and cool themselves are among the ideas that could radically change the way we build in the future because they would mean that our housing developments would no longer be mere consumers of resources such as electricity, water or building materials. They would also be producers of valuable raw materials and energy, and thus more future-proof, sustainable and climate-friendly.

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