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Urban Sequoia: Thinking beyond the high-rise to decarbonise the built environment

By Mina Hasman, Sustainability Director, SOM


Last October, I traveled to Glasgow for COP26 to present Urban Sequoia, a concept to address the climate crisis by designing buildings to act like urban trees – capturing carbon, purifying the air, and regenerating our cities. Together with my colleagues at SOM, we illustrated how “forests” of buildings at different scales could be deployed in cities around the world.


The tree/forest metaphor resonated in the press stories that followed, some of which focused on the apparent paradox of a radically sustainable skyscraper. One headline asked: “Can high-rise buildings be carbon negative?” While our answer to this question is an emphatic “yes!”, a more detailed understanding of Urban Sequoia is needed. What we developed is not just a concept for tall buildings. Urban Sequoia is a systems approach, a philosophy – it is a way of thinking about cities as ecologies, as living and breathing systems that can be reconfigured to achieve dramatic reductions in whole life carbon, reframing the built environment as a solution for the climate crisis.


We tackled high-rise buildings first because they are the most challenging to design sustainably – with large amounts of structural materials, seismic concerns, complex building systems, and multiple entry points – but also because we know that we will need to find new solutions to live densely as our population continues to grow. The key to our Urban Sequoia concept is that it is scalable: Our goal was to develop a concept that can be easily implemented across all types of buildings, new and existing, large and small, in any city around the world. A single building will not make the difference in reaching our climate goals, but if we’re able to apply these principles at the scale of an entire city, we can truly achieve meaningful reductions in carbon.


It’s also important to understand that this is not a theoretical solution; Urban Sequoia brings together cutting-edge technologies and off-the-shelf systems, elegantly combined for maximum performance. For instance, the use of bio-based materials and an algae-based facade to reduce embodied carbon is at the forefront of innovation in the building sector. Together with technologies like direct air capture, this holistic design approach can turn buildings into a vehicle to sequester carbon. Other principles are tried-and-true and are simply good design: maximising passive design strategies, optimising building systems, and economising on construction materials. As an integrated architecture and engineering firm, this is where SOM excels: combining multiple solutions into a clearly resolved design.


No single strategy is enough to meet our goals – we need all of these approaches together. For a 60-storey building, we can reduce whole life carbon by 15 percent by optimising the building structure; another 15 percent by using modular and prefab elements; and another 30 percent by integrating active and passive design strategies – resulting in a combined 60 percent reduction over a 60-year lifespan. The cumulative impact of these strategies – which can only be achieved through close collaboration across the built environment value chain – allows us to deliver buildings and cities that go beyond net zero to become carbon negative.


By sharing our ideas so freely, we hope to encourage our fellow architects, engineers, designers and city planners to build on this thinking. It’s also essential that we continue to collaborate with experts outside our industry in pursuit of innovative solutions. Carbon capture is a good example: this technology has been implemented in rural areas and in oceans, but never before has it been integrated into buildings in the way that we propose for Urban Sequoia. The urgency of the climate crisis demands that we move beyond established ways of designing and building – toward a future where cities with “forests” of buildings that are just as restorative as trees will be seen not as a far-fetched concept, but as a new standard to which architects, planners, and city leaders should aspire.