The term urban mining refers to the process of recovering and reusing materials from a city, which may come from buildings, infrastructure, or consumer products that have become obsolete. In fact, when the functional life cycle of an object is over, the constituent materials of the object itself become available for re-entry into the market. Urban mining is not new; metals from automobiles and electronics are often recycled, but the magnitude of the climate crisis demands that it be applied more ambitiously and proactively, potentially treating the entire city as a "mine" and actively searching for materials to ensure that most of their value is retained. Construction waste accounts for by far the largest amount, crediting architecture with the opportunity to contribute more to achieving a more sustainable future in the pursuit of a circular economy.

The numbers speak for themselves, buildings are responsible for 39% of global carbon emissions: 28% from operational emissions and 11% from materials and construction.

In fact, the peak emission in a building's construction process comes mainly from the production and transportation of materials. Taking into consideration that between now and 2060 the volume of cities built will double, producing 230 gigatons of embodied carbon from building materials, urban mining can and should play an important role in cities, becoming the most effective tool to move closer to the goal set by the European Union: a zero-carbon building stock by 2050.

To achieve this important milestone, the International Energy Agency (IEA) estimates that direct CO2 emissions from buildings will need to decrease by 50 percent by 2030, and indirect emissions from the building sector by 60 percent. This equates to a decrease in construction world emissions of about 6 percent per year until 2030.

To get as close as possible to this result, there are many advantages to reusing tons of materials in new projects. Not only the concrete or steel that reinforces our contemporary buildings, but also the wood, glass, copper, aluminum facades, tiles, bricks, and even the iron railings on our balconies; all of these are valuable finished products that have already gone through a long supply chain. By being present in cities, long supply chains would not be needed, thus increasing the availability and consequently the resilience of local areas.

With the intent of adopting a circular economy strategy, urban mining would allow the maximum value of the material to be maintained for as long as possible.

After all, why mine, produce, and transport these materials several times, from mines around the world, when there are abundant sources all over the place?

If they can be reused, these materials represent great value. First, in economic terms: in fact, we are talking about hundreds of millions of euros in value saved, a portion of which relates to the reduction of so-called environmental costs. But beyond environmental costs, the second benefit of urban mining concerns the reduction of environmental impacts. Indeed, the use of reclaimed materials eliminates some of the emissions associated with the production and transportation of new construction materials.

Considering that the construction sector is responsible for the extraction of 50 percent of raw materials if we can reuse as much as possible of the products currently found in our cities, then it will be possible to create fewer components from scratch and extract fewer materials, emitting less carbon dioxide and greenhouse gases responsible for ongoing climate change.

Indeed, at each stage of the construction process there are production, transportation, and labor costs, which require time, energy, effort, and emissions and thus have a large environmental impact. Each stage of production, from extraction to manufacturing and assembly, thus adds value to a construction product. This added value is accumulated in the products found in a building at the end of its life cycle, and can be retained if we plan for the disassembly of buildings and reuse the products for their original purpose (or for an even higher value, according to the principle of upcycling); alternatively, by performing selective demolition, these products can be recycled: in this case we speak of downcycling, since there is a loss of value of the original component.

Currently, the construction industry is not yet oriented toward the use of secondary materials for the construction and maintenance of the built environment. The barriers to widespread urban mining have to do with logistics, demand for reused materials, perceived performance, bureaucracy, and regulations. The biggest hurdle to overcome is the lack of information about the extractable materials present and their reuse value. In addition, deconstructing a building can be more expensive than demolishing it, although selling some of the recovered material can offset some of the cost.

It is therefore essential to build a model that predicts the value and reuse possibilities of materials and products by investigating the amount of secondary raw materials that will be available because of building demolitions in each time frame, possibly extending the concept of urban mining beyond metropolitan boundaries. While the future supply of secondary raw materials can be predicted from partial or total demolition projects within the area, the potential demand lies in the forecast of new construction and renovation projects. These analyses would provide detailed information that can create concrete opportunities for matching supply and demand. Once this information becomes more widely available in cities around the world, interested stakeholders - developers, architects, contractors, and governments - can then mobilize to try to maximize the effects and benefits of urban mining.

The identification of usable materials and products, and thus their financial and environmental value, is an essential sine qua non to help industries have a reliable supply of high-quality secondary materials.

The vast need for construction soon presents a great opportunity to plan for the urban mine of the future by facilitating the future reuse and recycling of urban materials, pursuing strategies aimed in the direction of circular architecture: for example, designing new buildings by assembly/disassembly (Design for Disassembly) and implementing the spread of so-called material passports.

Since the 1970s, builders tended to overuse materials that made selective demolition of buildings more difficult, such as glues, spray sealants, and other adhesives, leading to their loss of value as they deteriorated and lost their original performance. Allowing them to be deconstructed, on the other hand, is an environmentally friendly alternative, allowing up to 85 percent less material to be sent to landfills.

Even today, most buildings are statically welded, glued, and fused. Designing "dry" buildings of the future could prove to be more flexible and would allow buildings to be conceived of as true material banks. This would require a better system for keeping track of what is inside a building so that it can be easily and selectively dismantled when its life cycle ends.

A materials passport would provide all relevant information about any product or component that is intended for reuse within a building, thus designating a precise link between information and the item, rather than a collection of information about an item.

From a bureaucratic perspective, to make these strategies materialize it will be necessary to update local building codes to allow contractors to build with reclaimed materials. In addition, it is expected that the cost of deconstruction will decrease as regulations come into effect that will incentivize these practices to the detriment of traditional demolition, allowing the proliferation of specialized companies because of emerging market opportunities and new business models.

The founding concept of urban mining has always existed; the word waste has appeared relatively recently in our vocabulary, as in the past we valued everything that could be reused.

The postwar economic boom was responsible for a way of life that forgot that for most of our existence we knew how to give objects a second or third life. Perhaps therefore, since the mid-century, resource scarcity has become one of the issues to which most attention should be paid.

Today our climate is changing, supply chains need to be more resilient, and waste-intensive patterns need to be minimized to operate within more sustainable boundaries. The construction world has the potential to become much more resilient. The good news is that this is already beginning to happen: as governments and businesses adopt higher sustainability standards and goals, bidding requirements, purchasing guidelines, and consumer demands are following suit. An important step will be taken as all valuable materials in the local area are mapped and incentives are created to facilitate more reuse and recycling in the local area.

Ultimately, a paradigm shift is needed that comes as close as possible to the principles of the circular economy, where the word waste is forbidden and indicates a design error. Today's waste is only called that because we lack the tools to understand it as materials. Urban mining is the best tool to remind us of this, and it is already in our hands: all we must do is dig in.

A research by: Daniele Ferrari, Martha Serra