A buildable prototype for a carbon-free future

At COP26, the 2021 UN Climate Change Conference in Glasgow, SOM unveiled Urban Sequoia —a concept for buildings and their urban context to absorb carbon at an unprecedented rate. SOM has developed the first step toward achieving this goal on a broad scale, with a prototype for a high-rise building that can be built today.

The need to transform the built environment is clear. The building sector generates nearly 40 percent of all global carbon emissions. As urban populations continue to grow in the coming decades, studies have predicted that another 230 billion square meters of new building stock will be needed by 2060.

The central proposition of Urban Sequoia is that the built environment can absorb carbon. SOM’s proposal transforms buildings into solutions—radically rethinking how buildings and cities are designed and constructed. It is a viable solution that could have a far-reaching impact, with the potential to create a circular economy that absorbs carbon.

Beyond net zero: Toward a carbon-removal economy

Urban Sequoia brings together different strands of sustainable design thinking, the latest innovations, and emerging technologies and reimagines them at the scale of a building. By holistically optimizing building design, minimizing materials, integrating biomaterials, advanced biomass, and carbon capture technologies, Urban Sequoia achieves substantially more significant carbon reductions than has been achieved by applying these techniques separately.

These strategies can be applied to buildings of all sizes and types. For cities, SOM’s prototype design is a high-rise building that can sequester as much as 1,000 tons of carbon per year, equivalent to 48,500 trees. The design incorporates nature-based solutions and materials that use far less carbon than conventional options and absorb carbon over time. Materials like bio-brick, hempcrete, timber, and biocrete reduce the carbon impact of construction by 50 percent compared to concrete and steel. A progressive approach could reduce construction emissions by 95 percent.

This solution allows us to move beyond net zero to deliver carbon-absorbing buildings, increasing the amount of carbon removed from the atmosphere over time. After 60 years, the prototype would absorb up to 400 percent more carbon than it could have emitted during construction. The captured carbon can be put to use in various industrial applications, completing the carbon cycle and forming the basis of a new carbon-removal economy. With integrated biomass and algae, the facades could turn the building into a biofuel source that powers heating systems, cars, and airplanes; and a bioprotein source usable in many industries.

Beyond the building: Making cities part of the solution

On an even broader scale, the byproducts of building an Urban Sequoia will help revolutionize the way we design and maintain infrastructure. Captured carbon and biomass can be used to produce biomaterials for roads, pavement, and pipes. By converting urban hardscapes into gardens, designing intense carbon-absorbing landscapes, and retrofitting streets with additional carbon-capturing technology, former grey infrastructure can sequester up to 120 tons of carbon per square kilometer. When replicating these strategies in parks and other green spaces, we can save up to 300 tons per square kilometer of carbon annually.

If every city around the world built Urban Sequoias, the built environment could remove up to 1.6 billion tons of carbon from the atmosphere every year. With immediate focus and investment in our prototype, we can start this process now and build the first Urban Sequoia.