
A System for Circularity in Steel
In Summer 2024 METROPOLIS brought together visionaries from across the building industry for its Circular Future Hackathon, aimed at reimagining how we design and construct in a way that aligns with circular design principles. Representatives and sustainability experts across global firms, manufacturers, and industry organizations joined forces to tackle the building sector’s greatest circularity obstacles. Following the virtual workshops, METROPOLIS shaped these concepts into comprehensive seven forward-thinking solutions.
Shown here is A System for Circularity in Steel developed by hackathon participants Emily Borchardt, Perkins&Will; Nuala Brennan, Valerio Dewalt Train; Leo Bushell, Momentum; Alison Fidler, ZGF; Paul Fogg, Andreu World; Emily Gross, MSR Design; Yarden Harari, Arcadis; Shefali Sanghvi, Dattner Architects; Ana Sotelo, Snøhetta; and Avinash Rajagopal, editor in chief, METROPOLIS.
Steel is one of the most recycled materials in the built environment—according to the American Institute of Steel Construction, 98 percent of structural steel is recovered for recycling at the end of its life, and, in turn, structural steel being used in building projects today has 93 percent recycled content. But here’s the catch: It takes energy to recycle steel.
A 2023 paper published in the International Journal of Steel Structures estimates that reused steel has 90 percent lower embodied carbon emissions compared to recycled steel, and 75 percent lower embodied carbon emissions compared to renewable energy–powered recycled steel. If we want to slash the embodied carbon footprint of the built environment, reusing steel could have an enormous impact.
But many challenges stand in the way, and they are all interlinked. We need more steel material available for reuse, and this means we need to disassemble buildings very carefully at the end of their lives. Moreover, there are currently no established standards for engineers and contractors to assess and reuse structural steel elements. Overall, many different stakeholders in the built environment need to come together in order to increase the reuse of structural steel.
Types of structural steel on a project:
- raw steel
- painted steel
- intumescent steel
Potential Savings:
- Virgin material, untouched
- Lightly touched material, mechanically fastened
- Mixed incompatible materials, mechanically fastened
- Diverse incompatible materials with permanent connections
PATHWAYS FOR STEEL
This diagram maps out those stakeholders and highlights how they might be engaged to explore diverse pathways for used steel, including recycling mills. If this vision becomes a reality, not every ounce of steel needs to be melted down, and our buildings can leave a much lighter footprint on the planet.
