In the US, buildings are responsible for approximately 40% of all carbon emissions. Such building-related CO2 emissions can be reduced in numerous ways -- from installing more energy-efficient appliances to powering the buildings with renewable energy sources. But buildings may also provide an opportunity to remove carbon dioxide from the atmosphere. Such building-related CDR approaches might include:
1. Green walls. Walls that are covered in plants could increase the overall stocks of biomass, and thus the proportion of of carbon stored in terrestrial ecosystems compared to in the atmosphere. Such green walls wouldn't permanently sequester carbon, but as long as we expect to build and maintain green walls on new buildings, this could be one avenue for CDR.
above: ivy covering a building in Paris
above: a green wall in London
2. Using building materials that sequester CO2 in the building itself. For example, carbon negative cements could be made using CO2 from direct air capture devices or from sustainable bio-energy facilities. Also, buildings made with lumber that is sustainably harvested will sequester the CO2 the trees removed from the atmosphere.
3. Building roofs or other building facades with minerals that bind to and sequester atmospheric CO2. Such CO2 sequestering roofs have been installed in places like the UK.
The potential for CO2 removal in the built environment is probably relatively small compared to overall CO2 emissions attributable to the buildings. In the US, there are approximately 128MM residential buildings and 5MM commercial buildings -- numbers that at first glance seem incredibly large. But even if we were to build green walls on all available building facades, we would likely only sequester CO2 on the order of magnitude of 100MM tons -- or approximately 5% of building-related emissions.*
So while CDR in the built environment will not substitute for carbon-emission-reduction measures in buildings, designing building codes and sustainability standards like the LEED certification in ways to that encourage CDR could provide a good complement to help buildings have as positive an impact on the environment as possible.
*assuming that, on average, residential buildings have 100 m^2 of facade space and commercial buildings 1000m^2 of facade, vertical gardens weigh 30 kg/m^2 of which 10% is actual carbon.