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SOM unveils Urban Sequoia, a plan for carbon-consuming cities

Words:
Stephen Cousins

Buildings that absorb greenhouse gases and produce biomaterials for production would be part of a carbon-removal economy

The Urban Sequoia tower, looking up
The Urban Sequoia tower, looking up Credit: SOM

The Urban Sequoia concept was created by a global interdisciplinary team at SOM, with input from industry experts, as a radical response to the climate crisis and the fact the building sector generates almost 40% of global carbon emissions.

It proposes to transform urban centres into networks of buildings that sequester carbon ‘at an unprecedented rate’, using air carbon capture technology, and produce biomass that can be made into biomaterials for various industrial applications, such as roads, pavement, and pipes.

A prototype for a high-rise building, unveiled at COP26, was calculated to absorb up to 400% more carbon than was emitted during its construction, after 60 years.

The integration of ‘natural’ materials into the structure, like bio-brick, hempcrete, timber, and biocrete, would reduce the carbon impact of construction by 50% compared to concrete and steel, said SOM.

Urban Sequoia takes its key inspiration from natural processes, said Mina Hasman, senior associate principal and sustainability lead at SOM: ‘Our inspiration came from understanding the natural carbon cycle and how nature, especially forests, continually absorbs carbon and how activities in the construction sector throw the earth’s core systems out of balance. The built environment sector currently emits far more carbon than nature can absorb. We must reverse this.’

  • Tower detail section
    Tower detail section Credit: SOM
  • Section diagram
    Section diagram Credit: SOM
  • Section through tower
    Section through tower Credit: SOM
  • Urban section diagram
    Urban section diagram Credit: SOM
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SOM plans to apply the concept to a real-life project in the near future. However the fledgling status of some of the technologies involved places a question mark over the potential for quick and widespread decarbonisation.

For example, direct air capture, a chemical process used to remove CO2 from the air, has not been used in the building sector before and large-scale demonstrators already under way need refinement to improve the technology and reduce capture costs. Bio-bricks, made from urine, loose sand and bacteria, and algae facades have never been used at scale.

According to Hasman, the prototype showcases how new technologies can be transformed, scaled, and made far more impactful by being integrated into buildings, which it’s hoped could accelerate interest and investment.

‘There are important parallels between what we’re proposing to do with Urban Sequoia and the transformation of the modern solar panel industry,’ said Hasman. ‘The use of houses and buildings as armatures for solar panels led to an explosion in solar power generation technologies, as well as major shifts in how utilities across the country operate as they accommodate solar energy generation.’

The adaptable system can be applied to any building type and scale, with solutions developed to be specific to each context, including the local climate and locally available resources.

Urban Sequoia as part of the city landscape
Urban Sequoia as part of the city landscape Credit: SOM

Parts of the world where carbon capture and storage technologies do not reach the mainstream would need to capitalise on local biomaterials, such as bio brick or hempcrete, and nature-based solutions to deliver a carbon negative built environment, said Hasman.

Byproducts from Urban Sequoia’s algae facade could be fed back into a district or city-wide network as new ‘resources’ that are shared and exchanged between buildings and industries.

‘Algae is already used in some aviation biofuels,’ said Hasman. ‘There is potential for much wider use of byproducts from an algae facade such as food supplements and/or pharmaceutical products or for fertilizers or cleaning products.’

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