Instead of buying new materials, companies can reuse old building parts to slash emissions.
One Broadgate, in London’s financial district, was a classic 1980s-style office block, with an exterior facade made up of panels of reflective, dark-tinted glass and strips of obsidian black and burnt terracotta. It served as the headquarters for TP Icap, the world’s largest interdealer broker. No longer fit for purpose, its dismantling and demolishment began in late 2021.
But instead of the building’s steel frame being shipped overseas to smelt down for recycling, emitting thousands of tons of CO2 in the process, 140 tons of it were bought by Fabrix, a property developer, to reuse in two projects in southeast London. One is a former Victorian warehouse on Great Suffolk Street, and the other is Roots in the Sky, a redevelopment of Blackfriars Crown Court.
This process—which has been dubbed "urban mining"—could help one of the world’s most polluting industries dramatically slash its emissions. It’s a lucrative opportunity that may add as much as £100 billion ($125.8 million) to the UK economy over the next decade. Analysts at sustainability consultancy Metabolic found that from 2021 to 2030, 2 million tons of building materials will become available during demolition of buildings in the Northern Dutch provinces of Groningen, Drenthe and Friesland. If the materials can be reused, they could reach 136 million euros ($145.2 million) in value, with a 4-million euro ($3.4 million) reduction in environmental costs.
Recycling steel “is going around the houses, but it’s more sustainable than digging raw material out of the ground,” explains Tom Webster, a director at building services engineering design practice Webb Yates Engineers. The alternative Fabrix is adopting is markedly less harmful than either creating new steelwork or recycling it. Factoring in a small amount of carbon for cleaning, transporting and refabricating, Webster estimates that steel reuse would generate less than 50 kilos of carbon per metric ton reused, which is 7 percent of the recycled content approach. “It cuts emissions to almost nothing,” he says.
“We’re accustomed to repurposing existing buildings, but with a building made from scratch the mentality is that everything must be brand-new,” says Clive Nichol, Fabrix’s CEO. “There’s a tunnel vision toward mining fresh materials.” For every metric ton of steel manufactured in an oxygen furnace, which is the more traditional method, 2,710 kilos of carbon is released into the atmosphere, according to Webster’s calculations—the same output as a one-way flight from London to Sydney.
With older office buildings increasingly scrutinized under more stringent legislation, older premises are becoming getting less desirable. Some 10 percent of office stock in London, equating to 20 million square feet, is not compliant with new energy-efficiency rules and therefore risk total obsolescence. Tech and new workplace practices are shortening the lifespan of office buildings too—a tension that began long before the pandemic. According to CBRE’s Spring 2022 Occupier Sentiment Survey, 52 percent of US office-based companies are planning to reduce space over the next three years, mostly due to remote work and space efficiency. With the hybrid model still in flux, the future of existing office buildings is precarious.
The next-best alternative is to recycle used steel and reform it into a new usable shape. According to the American Iron and Steel Institute, steel is the most recycled material on the planet. But this also comes at a cost: For every metric ton of steel recycled, approximately 800 kilos of carbon are released into the atmosphere.
Amid uncertain global supply chains and increased scrutiny on embodied carbon—the amount emitted during construction—urban mining could emerge as not only a nice-to-have but a need-to-have. In the UK, the construction sector contributes some 40 percent of the country’s carbon emissions, according to the Royal Academy of Engineering. Globally, the sector is responsible for 11 percent of carbon emissions, which is more than India, in figures of the total share by country. “The reuse of metals and steel is a really obvious place to start,” says Nichol.
To scale up the concept, an EU research project in 2020 called BAMB proposed that the industry move toward recognizing buildings as material banks. BAMB says that buildings could function as banks of valuable materials—slowing down resource usage to a rate that meets the capacity of the planet, as well as increasing the potential value of said materials. In theory, each building will be issued a “material passport,” or cloud-enabled data set that describes the defining characteristics of its materials.
“Another barrier is building methods. Until now, we’ve been buying the cheapest material possible and gluing it together,” says Rachel Hoolahan, sustainability lead at the architecture firm Orms. “At the end of its lifecycle, there’s not much else to do but smash it up and send it to recycling.” To enable more sustainable deconstruction, how we install materials in buildings must transition away from chemical means toward mechanical methods, such as screwing, bolting, and clipping. Hoolahan hopes the advent of urban mining will encourage designers and clients to invest wisely in better quality materials and how they’re affixed.
Hoolahan, who has been developing an approach for creating material passports, likens the materials in existing buildings to Lego bricks that could be organized and tagged, with industry players keeping what they want to make use of and selling the rest. Eventually, any component in a structure could be tagged with a QR code containing all the necessary technical details, which the client would update throughout a building’s lifetime.
Besides metals, glass, wood and concrete—the production of which follows closely behind steel in carbon emissions—are all valuable finished products that can be part of the urban mining movement. “The infrastructure is not there yet, but urban mining has to be about small, incremental changes that make a big impact over time,” explains Webster.
The database could even be open sourced for access by the industry, constituting a centralized platform for metals which would help predict material availability and assist with the development of a material resale market. According to the UK’s Circular Metals project, a secondary metals industry focused on reuse is set to generate £20 billion ($25.3 billion) a year by 2030.
“Right now, if you take steel out of a building, you pay to store it somewhere,” says Hoolahan. “Instead of a Depop model, where the seller hangs onto something until it’s been bought, I’m imagining more of an ASOS Marketplace, where you sell directly to an organization and they’re the retailer from then onwards.” Engaging local authorities to make this a reality is key, as they may be able to host one-stop spaces and facilities for storage, checking, testing, and refurbishing.
Material passports offer up considerable possibility if combined with the use of digital twins: virtual replicas for buildings that can be used for anything from turning lights off in rooms to checking how solar panels might improve a building’s energy performance. “These digital twins could cover the whole city,” says Nichol. “One could identify the buildings set for demolition, where the materials are, who certified them, and their strengths, and create a local supply chain.”
Plenty needs to happen before urban mining goes mainstream, namely the growth of an established marketplace and infrastructures to support the practice. Offering steel for reuse that’s cheaper than a new equivalent will also be imperative, helping to smooth the process of other materials to follow, namely concrete, which is the second biggest pollutant. Architects would have to change the way they design in the world of reuse, and loosen their process so as to shop from current market availability rather than trying to serve a particular model.
For this to work, developers, managers, and renovators will have to work together. “Lots of people have been advocates of urban mining for many years,” says Nichol. “But it’s those controlling the development who must make the decision and take the perceived risk. It took us a lot of work—not everyone is interested in doing that.”
Enshrining low-carbon building practices, including urban mining, in law is another missing piece in the puzzle. “As a structural engineer, there is nothing in regulation, code, or law forcing me to invest in circular economies—it is a moral choice,” says Webster. Developers might have net-zero carbon pledges to meet, but this only covers the carbon used for operation, not the embodied carbon.
“People are smarter than just accepting net-zero carbon claims, so if it’s highly polluting but just offset they’ll see through that, particularly young people going into big organizations who demand that level of depth and authenticity,” says Nichol. The chance to cut carbon emissions by such large quantities, whether or not it’s to appeal to the moral compass of modern-day office workers, should not be ignored. As global temperatures teeter closer to 1.5 degrees Celsius above pre-industrial levels, the argument for urban mining feels more urgent than ever.