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According to the Circularity Gap Report 2025 (CGR®), a staggering 38% of all materials we consume annually end up in long-lasting, human-made structures, often referred to as ‘stocks’. Every year, more and more materials are extracted, refined and fed into our homes, transportation networks, cars, and appliances. These materials will remain locked there for decades, but not forever—roughly a third of materials in stocks are demolished or discarded every year. With this in mind, how we design, build, and use these assets today will determine whether they become tomorrow’s waste or stand the test of time.
The report also highlights that the growth of these stocks has increased 23-fold over the 20th century, roughly doubling every two decades. By 2020, the mass of human-made things surpassed that of all living beings on Earth. This trend is largely driven by urbanisation, with city populations projected to climb from 56% in 2021 to 68% by 2050. Rising living standards play a role, too, with higher incomes fueling demand for bigger houses, better cars, and new appliances.
As a result, stock build-up is not only inevitable but also encouraged in lower- and middle-income countries where there is still a need for adequate housing and infrastructure. However, this growth comes with two major challenges.
The first is the environmental impact of large-scale construction. Construction and demolition waste is estimated to comprise around a third of global waste. Moreover, extracting, processing, and using materials—especially in concrete production—generate significant carbon emissions. Housing alone is the second-largest source of carbon emissions, contributing 13.5 billion tonnes, surpassed only by transportation at 17.1 billion tonnes. Additionally, extraction activities contribute to biodiversity loss, pollution, and water scarcity.
The second challenge is resource depletion. According to CGR 2025, 10% of all materials locked in stocks are metals—a key concern as demand for critical raw materials continues to rise. The recent surge in laws aimed at securing these resources shows just how seriously governments are taking this issue. Every year, building new stocks—after accounting for what gets torn down—uses 38% of global raw materials. When we include the materials needed to maintain and operate existing structures, such as fossil fuels for heating, this figure rises to 70%.
That’s a huge strain on global resources—and it doesn’t stop there. Materials locked in stocks will remain unavailable for recycling for decades. As more and more structures are added to these stocks, fewer materials will be available to support future growth. That’s why it’s crucial to build stocks that last, use resources efficiently, and are designed so their materials can be recovered and reused at the end of life.
Given current trends, it’s not hard to imagine a point when critical materials stored in human-made structures will outnumber those available in economically extractable deposits. For example, copper is projected to reach this threshold by the end of the 21st century, making it more abundant in buildings and infrastructure than in the Earth’s reserves. Even today, existing stocks could supply a substantial portion of the materials required to satisfy societal needs. For instance, studies show that one kilogram of discarded smartphones contains more gold than what is found in typical gold ores. This illustrates the huge potential of urban mining that has yet to be realised.
Construction and demolition waste is the largest waste stream by weight, but only 22% of it is recycled. Even then, much of it ends up in low-value applications like backfilling rather than being reused in new construction. One reason for this is that older buildings weren’t designed with recycling in mind and may contain hazardous materials like asbestos. It’s often more cost-effective to demolish a building than to carefully dismantle it, and the lack of established markets and regulations for secondary materials makes reuse even harder. What’s more, new materials are typically cheaper and come with guaranteed performance, making recycled materials less competitive in cost and quality.
Despite these barriers, solutions do exist. Developing insurance schemes, certifications, and quality standards for recycled materials can build trust in their performance, while government subsidies, incentives, and urban planning can enhance cost competitiveness.
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These recycling challenges also highlight the importance of keeping existing buildings in use for as long as possible. We can extend their lifespans by removing outdated infrastructure and components containing valuable materials and upgrading basic elements like windows and insulation. These improvements can boost energy efficiency and functionality, reduce the need for new construction, and create a steady stream of secondary materials.
Yet the greatest opportunity lies in designing future buildings and products with circularity in mind. Modular buildings and appliances, for example, can be easily repaired, upgraded, or disassembled for reuse. Using renewable, lower-impact materials like timber can reduce their environmental impact. Equipping buildings with energy-efficient technologies like solar panels and heat pumps can also decrease energy consumption, lowering the ‘material cost’ of maintaining them over time.
Governments around the world are beginning to take action. In 2021, Shanghai launched a three-year action plan to reduce the construction sector’s environmental impact by increasing recycling capacity and cutting down on waste from renovations and demolitions. Meanwhile, Amsterdam’s Circular Strategy 2020-2025 aims to reduce the use of virgin materials and resources, with a specific focus on the built environment.
These strategies reflect a growing awareness that the way we build and manage our infrastructure has major implications—not just for material use and waste but also for the energy transition. Renewable technologies like wind turbines, batteries, and solar panels rely on critical raw materials. While they’re often the focus of circular policy discussions, they represent only a small slice of global material stocks. The built environment, by contrast, accounts for a much larger share. Applying circular principles—like design for reuse, material efficiency, and longevity—to buildings and infrastructure could ease pressure on critical resources, reduce emissions, and unlock far greater environmental and social benefits.
Architecture carries an almost eerie sense of permanence. The structures we build today will shape—or scar—our cities for decades, if not centuries. The cost of mistakes is high. While our predecessors were unaware of the long-term health risks and environmental consequences of their actions, today, ignorance is no longer an excuse. Thanks to an ever-growing body of research, we have a clear picture of both the benefits of circular buildings and infrastructure and the costs of continuing down the same path. The decisions we make today will either create opportunities for future generations or pass on yet another problem for them to solve.
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