Architecture and the built environment have received scant attention in the coverage of COP26, the UN Climate Change Conference. It’s an obvious blind spot given that the building sector currently generates 40 per cent of all global carbon emissions and that massive population growth and increased urbanisation mean there’s a lot more building to be done. It is predicted that another 230 billion square metres of new building stock will be needed by 2060. Of course, many architects have developed innovative ways to reduce that carbon debt, both in construction and during a building’s lifetime, through sustainable architecture. Now one of the industry’s giants, Skidmore, Owings & Merrill (SOM), is unveiling a model for carbon-negative architecture – meet the ‘Urban Sequoia’.

SOM unveils carbon-capturing Urban Sequoia at COP26

render overview of city using the urban sequoia building model by SOM, unveiled at COP26

SOM’s Urban Sequoia is a vision for cities that suck in more carbon emissions than they create. And the practice is launching the proposal with the design of a prototype high-rise that could be built today and, SOM suggests, would be the tallest tree in a ‘forest’ and undergrowth of carbon-capturing buildings and infrastructure.

The concept doesn’t suggest one big fix but demonstrates how a number of strategies and emerging technologies – from biomaterials and biomass to carbon-capture technologies – can be optimised and work together and at scale. 

The use of bio-brick, hempcrete, timber and bio-crete reduce the carbon impact of the concept building’s construction by 50 per cent compared to concrete and steel, says SOM. The building also includes materials and nature-based solutions and technologies that absorb carbon over time. 

section explaining how the urban sequoia building model by SOM works, unveiled at COP26

‘The power of this idea is how achievable it is,’ argues Yasemin Kologlu, principal at SOM. ‘Our proposal brings together new design ideas with nature-based solutions, emerging and current carbon absorption technologies, and integrates them in a way not done before in the built environment.’

SOM says ultimately the concept building could sequester up to 1,000 tons of carbon a year, equivalent to 48,500 trees. And after 60 years, the building would absorb 400 per cent more back carbon than was emitted during its construction.

SOM imagines the building as the hub of a number of virtuous circles and value chains, the focus of a new economy for carbon and biomaterials. Biomass and algae on its façade could turn the building into a source of biofuel that powers heating systems and even cars and aeroplanes. It would also be a source of bioprotein. Captured carbon could also be used in various industrial processes.

render of green city using the urban sequoia building model by SOM

To be truly effective, though, Urban Sequoia will have to seed new carbon-munching neighbourhoods. ‘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 kilometre,’ says SOM. ‘When replicating these strategies in parks and other greenspaces, we can save up to 300 tons per square kilometre of carbon annually.’

‘The time has passed to talk about neutrality,’ insists SOM partner Chris Copper, advocating for the firm’s innovative carbon-negative architecture model. ‘Our proposal for Urban Sequoia – and ultimately entire “forests” of Sequoias – makes buildings, and therefore our cities, part of the solution by designing them to sequester carbon, effectively changing the course of climate change.’ §

diagram showing the urban sequoia building model by SOM