Dirk Hebel speaks plainly: we already have effective solutions to avert environmental disasters, but implementation might be “too little, too late”. He sees there’s no time to continue discussing symptoms – we must set our priorities straight and tackle the causes. Circularity must underpin every step of the construction process and “sprinkling a bit of sustainability sugar on top of a project is no longer good enough”, he warns.

Circular construction needs new business models

One way of accelerating this critical shift from a take-make-throw to a take-make-repeat economy is to cocreate new systems that will enable urban mining and sustainable use of natural resources. As Dean of Architecture and Professor of Sustainable Construction at Germany’s Karlsruhe Institute of Technology, Dirk Hebel champions the concept of “mine the city” and is a member of the Academic Committee of the Holcim Foundation for Sustainable Construction that supports defining the strategies implemented by the Foundation to encourage innovative approaches to sustainable construction.

Inspired by his work in Ethiopia as Director of the Ethiopian Institute of Architecture, Building Construction and City Development (EiABC) from 2009 to 2012, he is convinced that the construction industry should do more to reuse materials through harvesting existing buildings. Copper is the prime example of a resource now more present in the built environment than in the earth’s crust.

Using cities as valuable quarries for construction materials could help with the looming resource scarcity crisis which we’re accelerating towards due to the rate of raw material extraction. According to the Vienna University of Economics and Business (WU Vienna), the total amount of raw material extracted from the earth has more than tripled in just fifty years, from around 30 billion tonnes in 1970 to over 90 billion tonnes in 2017 . Nevertheless, sifting through demolition sites to select materials to successfully repurpose is an inefficient and costly endeavour in a system still overwhelmingly geared towards extracting then discarding resources. Many materials are currently impossible to recycle due to standard assembly processes: glass that has been fused to steel or wood that has been protected with chemical layers are difficult to reuse and hazardous to dispose of. For urban mining to become widespread and effective, new practices and business models must emerge.

Sustainable design means planning for disassembly and circular flows in the future

Architects need to design for disassembly, ensuring valuable components are snapped into place rather than glued or wet-sealed. Green design and green architecture must incorporate the enabling of future use of precious natural resources. Dirk Hebel along with pioneers in environmentally sustainable and self-sufficient prototypes Werner Sobek and Felix Heisel tested the feasibility of such techniques with their Urban Mining and Recycling Unit (UMAR) in 2018. The project, built on the Swiss Federal Laboratories for Materials Science (Empa) campus near Zurich, and using exclusively recycled, repurposed, or organically grown materials, exemplifies how components can be tucked, folded, or screwed together rather than glued together. If buildings were designed for disassembly, cities could become material depots where resources circulate from one application phase to the next in closed regenerative loops.

Business models must change to make this possible. A new economy based on the lease, storage and tracking of materials, rather than on the sale and demolition of structures must evolve out of current practices. For Dirk Hebel, the digital era offers opportunities in this respect. It would now be technically possible for manufacturers to feed information into huge data banks for future referencing and reuse, and to shift their focus from merely selling products to offering a range of services. Attaching a digital passport to each manufactured item would be one way of enabling circular flows of materials over long periods of time.

“Society has to be on board for such radical change to come about”, Dirk Hebel adds, stressing the crucial role researchers and teachers play in ensuring these ideas permeate culture. A generation ago, architects were trained without being taught to think about what would happen to their projects once they were built. Young architects today can embody the promise of a more responsible long-term approach if their mentors help pave the way towards new design philosophies. Academics also have the responsibility to prove to businesses and to policy makers that the technology for circular construction not only exists but is also financially viable.

Urban mining is a stepping-stone towards a 4th industrial revolution

With these objectives in mind, urban mining should be viewed as a transitional model while more effective circular practices are developed. Mining the city will not be enough to meet increasing demand for construction materials, even if it were the most desirable way to access resources. According to Dirk Hebel nothing short of a 4th industrial revolution should take over from urban mining, in the shape of new biologically driven and digitally supported processes. In other words, it is time to “harness the sun’s energy and grow future cities”, he says. If all parties involved decided to make the shift, a new circular metabolism could arise from the simple yet powerful principle of using solar energy as the most natural and widely available fuel to produce renewable building materials like bamboo and hemp.

Still too often dismissed as a “vernacular” building material, bamboo is particularly promising – thanks to its extremely strong fibres – and could become the basis of new industrialized production methods. Dirk Hebel and his associates also advocate large-scale use of mycelium hyphae (mushroom roots) that can be activated as natural glue in biological composite foams and performance plastics. The advantage of using mushroom-based products, grown from a process of decomposition and fermentation of organic waste, is that they are fast-growing and require far less energy to manufacture whilst offering new recycling solutions. Such techniques could also allow newly industrialised areas of the planet to participate more easily in the revolution.

Multidisciplinary and collaborative future of constructing

For this future to materialise, lawmakers must tighten current regulation and facilitate the transformation of the building industry. “We urgently need to prohibit anything that runs counter to the logic of circularity”, Dirk Hebel insists. “We also have to question everything we do – especially what feels comfortable.” Achieving this conversion will require the contribution of multiple actors, from teachers and researchers to civil engineers, material scientists, biochemists, urban planners, and policy makers. The way Dirk Hebel sees it, the days where the fate of construction was in the hands of a closed triad of investors, architects and building professionals, are over. The future is multidisciplinary and collaborative.

More about Dirk Hebel

Dirk E Hebel is Dean of the Faculty of Architecture (2019–) and Professor of Sustainable Construction (2017–) at the Karlsruher Institut für Technologie (KIT) in Karlsruhe, Germany. He is also a member of the Academic Committee of the Holcim Foundation (2017–). His research is focussed on rethinking the construction industry and its bound building materials as a raw materials warehouse to preserve the earth’s resources and about the paradigm change in future architectural planning and construction.

He was a workshop moderator for “Changing paradigms: Materials for a world not yet built” at the 6th International Holcim Forum for Sustainable Construction held in Cairo, Egypt in April 2019, and was a member of the Holcim Awards jury for region Europe in 2020.