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Urban Mining: How Sustainable Cities Are Recycling Buildings Down To The Bone

As material costs skyrocket, an old practice is becoming popular again: reusing building materials. In Germany, the first projects are already underway – and so far, results are promising as a model for sustainable cities.

Image of scaffoldings on a construction site.

View of Havel Quartier Potsdam near the main train station in Brandenburg, Germany.

Jan Schulte

BERLIN — At first glance, Huthmacher Haus at Number 2 Hardenbergplatz in Berlin is nothing special: a large white concrete block.

The 60-meter-tall building opposite the Zoologischer Garten train station is rather inelegant – perhaps an acquired taste for lovers of post-War architecture. Having been built in 1957, non-architecture buffs might be more interested in the iconic yellow giraffe painted on the façade, a reference to the zoo around the corner.

Three years ago, investor Newport Holding wanted to tear the building down and replace it with a 95-meter-tall office complex. But the German historic monuments commission was against the idea – and suddenly, what was considered a useless concrete building became an example of a sustainable approach to using building materials.

The current owners, Bavarian company Bayerische Hausbau, want to renovate the building, preserving as much as possible and laying the groundwork for the materials to be reused in the future – an approach called urban mining.

The German Federal Environment Agency defines urban mining as “managing anthropogenic sites with the aim of obtaining durable goods and stores of secondary raw materials.” Or, in simpler terms: before a partial renovation begins, the construction company checks which raw materials in the building could be reused. That information is recorded for future generations, and as much material as possible is reused.

With the ongoing energy and supply chain crisis, concrete, bricks and metal have become scarce and expensive. The construction industry uses a lot of resources and creates a huge amount of waste. Urban mining could be an important source of raw materials for future construction needs.

Step one: inventory

Huthmacher Haus is still in the early stages of the process. The first step is to identify materials used in the building's 16 storeys. Then, the company can evaluate whether these can be reused, and create a digital model of the results and estimate the materials’ carbon footprint.

This report is called a “Building Circularity Passport.” Future owners will know exactly how Huthmacher Haus was made and which elements of the building could be reused. If the building is eventually torn down, this approach should cut material waste in half.

“It’s a pilot project for us,” explains Hannes Giese, who is responsible for the renovation of the building at Bayerische Hausbau. One of the challenges, he says, is dealing with old documents from the 1950s, some of which are hand-written. The building has already been renovated a number of times, and not all of the changes were noted in the plans.

If we want construction to continue at this rate in the future, we will have to reuse building materials

“To get a clearer overview, we removed some materials from the third floor," he says. Preliminary results showed that heating pipes could easily be reused. Giese is convinced that in future this approach will save money and effort. Alloys in these pipes, for example, will not have to be created again from scratch. “Although we haven’t yet completed the project, all the signs suggest that having a precise summary of the materials used is worth it financially," he says.

Identifying all of the materials used sounds simple, but it is not an easy task, as Matthias Heinrich knows. He is a team leader at the Environmental Protection Encouragement Agency (EPEA), part of the international construction consultancy Drees & Sommer.

“Often, the relevant data exists, but it is difficult to bring it all together. The specialists can’t always examine everything in detail on site. Often they have to randomly drill a hole into the wall to check what is behind it,” Heinrich explains.

That raises the question of whether it is even worth it. “We don’t have any other choice,” says Heinrich. “If we want construction to continue at this rate in the future, we will have to reuse building materials as much as possible.”

Image of a yellow construction machine operating between mountains of sand at a construction site in the city.

An excavator operating between mountains of sand at the Molkenmarkt construction site in Berlin, Germany.

Soeren Stache/dpa via Zuma

Materials in a usable state

Germany and the European Union are seeing a shortage of raw materials, including sand and gravel. Authoritarian states like China are unreliable suppliers. “Urban mining will help us to become more independent,” says Heinrich. “What’s more, the materials are in a much more usable state. I don’t have to process the ore from a mine. I can use it as it is to make a steel beam.”

Even if the cost saving isn’t enough of a motivation, sooner or later, planned regulations in Germany and the EU more widely will force the construction industry to start recycling materials. The German government wants to introduce a “digital resources passport” for every newbuild project.

“In the future, we will be able to see the whole life cycle of buildings,” says Housing Minister Klara Geywitz (SPD). What Bayerische Hausbau is doing in Berlin is not yet obligatory for newbuilds. There is still no date for when this legislation will come into force, but all construction companies applying for an Efficiency House 40 standard on newbuild projects already have to go through a preliminary phase, the “seal of quality for sustainable buildings”.

The idea of reusing building materials isn't new. In the past, whole castles were dismantled stone by stone so that villagers could build new houses. Heinrich believes the reason why so many construction companies are nervous about urban mining lies in a widespread myth: “There is still a common misconception that used materials are lower quality,” he says.

So far, there are hardly any companies in Germany using the method. “Urban mining is still quite a niche practice,” Heinrich admits. One of the few examples is in the town of Neustadt in Schleswig-Holstein.

The wooden façade was made from old oak beams.

Architect Ute Dechantsreiter, who specializes in using recycled building materials, working on the plans for a new office block for the municipal department of works. She used 300-meter high dividing walls taken from an old tower block in Hamburg. The wooden façade was made from old oak beams. The carpets were made from another recycled material – old fishing nets from the region.

“Not only did we avoid creating 8 tons of waste, and using 60,000 kilowatt-hours of energy to construct new dividing walls, but we also significantly reduced the costs for the newbuild project,” wrote Dechantsreiter in an article for the industry magazine Deutsche Bauzeitung.

Heidelberg thinking bigger

One German city that is thinking bigger is Heidelberg, in Western Germany. “By 2050, at the latest, we want to be environmentally neutral and reduce the municipality’s energy use by half,” Mayor Jürgen Odszuck said last summer. “We will only achieve that if we now address the huge amount of energy and resources used in the construction sector.”

Heidelberg plans to start with the Patrick Henry Village, a former housing estate for American soldiers. In the long term, the plan is to create homes for 10,000 people and offices for around 5,000 employees. At the moment there are still 325 buildings to renovate or tear down.

Seen through the lens of urban mining, the site is not a rubbish heap, but a gigantic store of raw materials. “We have already completed the evaluation,” explains EPEA expert Heinrich. The village contains around 465,884 tons of material. Around half of this is concrete, a fifth is bricks and five per cent is metals.

According to Heinrich, reprocessing projects show that the loss rate in metals is between five and 10%. “For concrete, it’s around 20%, depending on its composition and pollution level,” he says.

“Over the next ten to fifteen years, the shortage of raw materials in Germany will not improve. Prices will rise rather than fall,” he says. Heinrich is convinced that urban mining will become more widely practiced: “As soon as people see that this approach is worth it financially, that will happen automatically.”

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Migrant Lives

They Migrated From Chiapas When Opportunities Dried Up, Orchids Brought Them Home

An orchid rehabilitation project is turning a small Mexican community into a tourist magnet — and attracting far-flung locals back to their hometown.

They Migrated From Chiapas When Opportunities Dried Up, Orchids Brought Them Home

Marcos Aguilar Pérez takes care of orchids rescued from the rainforest in his backyard in Santa Rita Las Flores, Mapastepec, Chiapas, Mexico.

Adriana Alcázar González/GPJ Mexico
Adriana Alcázar González

MAPASTEPEC — Sweat cascades down Candelaria Salas Gómez’s forehead as she separates the bulbs of one of the orchids she and the other members of the Santa Rita Las Flores Community Ecotourism group have rescued from the rainforest. The group houses and protects over 1,000 orchids recovered from El Triunfo Biosphere Reserve, in the southeastern Mexican state of Chiapas, after powerful storms.

“When the storms and heavy rains end, we climb to the vicinity of the mountains and collect the orchids that have fallen from the trees. We bring them to Santa Rita, care for them, and build their strength to reintegrate them into the reserve later,” says Salas Gómez, 32, as she attaches an orchid to a clay base to help it recover.

Like magnets, the orchids of Santa Rita have exerted a pull on those who have migrated from the area due to lack of opportunity. After years away from home, Salas Gómez was one of those who returned, attracted by the community venture to rescue these flowers and exhibit them as a tourist attraction, which provides residents with an adequate income.

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