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Urban space as carbon sink

Did you know that you can reduce carbon emissions as early as during the building process? This can be achieved by using carbon-negative material that also significantly improves soil conditions for the vegetation. Biochar is what makes it possible.

By using biochar as a material for the construction process we can contribute to reduction of carbon emissions.

It is commonly known that plants take in carbon dioxide as a part of a process called photosynthesis. During decay or when plants are burned this carbon is then released back into the atmosphere and that contributes to climate change. This is where pyrolysis comes in. Instead of letting organic waste to pile up and left in the field to rot and emit emissions, this material is diverted into an oxygen-free chamber. Here, through the application of high heat, complex molecules present in the biomass are broken down and are used for heating building infrastructure. The end product from this process is biochar.

This is how biochar looks like.

Biochar can be applied as a part of the substrate mixes for vegetation. With its microscopic pores it can hold water and nutrients, which are essential elements for vegetation to develop. Its half-life – the time required for a quantity to reduce to half of its initial value – is more than 1000 years. Other alternatives like turf or compost have half-life only around two years and then it needs to be added again. Besides that, biochar can also clean polluted stormwater and it provides great habitat for microbial life that contributes to the cleansing of water as well.

At Edge we are passionate about reducing the carbon footprint in our projects, and therefore we would like to show you two different urban typologies where we have performed theoretical calculations of possible carbon removal. Take a look at our examples here:

An example of a shared-space street. The blue colour symbolises an open subbase layer combined with biochar as a soil substrate for vegetated areas such as tree pits, rain beds, plant beds, etc.

Local street (width 10 m, one line of open subbase layer):
• 10 ton biochar per 100 m of street which corresponds to 20-30 ton CO2
• 20-30 kg CO2e / m2 of streetscape area
Shared street (width 12 m, one line of open subbase layer):
• 10 ton biochar per 100 m of street which corresponds to 20-30 ton CO2
• 16,5-25 kg CO2e / m2 of streetscape area
Secondary street (width 22 m, two lines of open subbase layer)
• 20 ton biochar per 100 lenght of street which corresponds to 40-60 ton CO2
• 18-27 kg CO2e / m2 of streetscape area
Main street (width 29 m, two lines of open subbase layer):
• 20 ton biochar per 100 lenght of street which corresponds to 40-60 ton CO2
• 13-21 kg CO2e / m2 of streetscape area

Another urban typology is a courtyard. As a reference we have used two courtyards designed by Edge. It includes biodiverse vegetated surfaces with biochar such as green roofs, meadows, plant beds and lawns.

The courtyard Koggen in Västra hamnen is partly constructed with biochar and acts as carbon sink. The courtyard was designed in collaboration with MKB Fastighets AB and PEAB Anläggning AB.

Kv Koggen:

  • 30-46 kg CO2e / m2 of the courtyard area (1376 m2)*
  • 13-20 kg CO2 / m2 of the property area (3450 m2; including green roofs)*
  • total 46,6-70 ton of CO2e reduced during construction (3450 m2)*

* theoretical calculations of possible carbon removal

Illustration plan for Kv Najaden. The courtyard was designed in collaboration with Slättö Förvaltning AB.

Kv Najaden:

  • 33-49 kg CO2e / m2 of the courtyard area (2225 m2)*
  • 17-25 kg CO2e / m2 of the property area (4373 m2; including green roofs)*
  • total 72,6 – 109 ton of CO2e reduced during construction (4373 m2)*

* theoretical calculations of possible carbon removal

Don’t hesitate to contact us so we can tell you more about our work!