Assessing biogenic carbon storage at urban scale through urban building energy modelling

• Envelope retrofits present an opportunity to use buildings as carbon sinks. • CityEnergyAnalyst facilitates carbon emission and storage assessments in districts. • The potential for carbon storage in districts heavily depends on the retrofit rate. • Full decarbonization of the grid with biochar material ensures net-zero emissions. • Cellulose has the lowest impact, while biochar stores more in high-rate retrofit. Curbing embodied emissions is essential for reducing greenhouse gas emissions. In the building construction sector, bio-based materials have shown promising solutions in reducing embodied emissions while offering carbon storage potential. This study presents a framework to assess the potential of biogenic carbon storage at the urban scale. A district in Zurich, Switzerland, is selected as the case study, incorporating Swiss-based life cycle data for building construction along with current and projected grid carbon intensities. Our work expands the CityEnergyAnalyst tool to include biogenic carbon data in building archetypes. The effects of retrofit on operational and embodied emissions are evaluated using three representative scenarios: low, intermediate, and intensive retrofit rates. The embodied emissions and the potential for carbon storage are assessed by comparing conventional, low-carbon, and carbon-negative materials. The temporal patterns of emissions show that grid decarbonization and building electrification are essential for reaching net-zero emissions by 2060. Furthermore, increasing the retrofit rate notably curbs operational emissions regardless of the grid decarbonization scenario. For instance, increasing the retrofit rate from 1.0 % to 1.9 % could reduce operational emissions by 16 %. Retrofitting the walls alone could store up to 360 ktCO 2 eq. in a district of approximately 2200 buildings. The study underlines that the properties of a carbon-negative material—such as its conductivity and density—play a significant role in biogenic carbon storage capabilities. The findings indicate that a carbon-negative material could boost biogenic carbon storage six-fold compared to low-carbon alternatives.