Zero-carbon balance: The case of HouseZero

Abstract In response to the need to establish net zero carbon emissions buildings and make transparent the method used for calculating the embodied CO2e emissions of these projects, this paper presents a case study of one project. The paper first outlines the life cycle assessment methods used, including system boundaries, data availability, scenarios, assumptions, and uncertainties. Whole building life cycle impact assessment results are reporting showing a normalized functional unit of 488 kg CO2e/m2. When system boundaries are aligned to current benchmarking studies, this value is 233 kg CO2e/m2. When considering the system boundary, the results showed that upwards of 42% of the project's CO2e emissions were generated by technical systems beyond those accounted for in contemporary life cycle assessment system boundaries. Further, the study provided a method to calculate the building's carbon balance over its 100-year service life based on multiple future CO2e grid scenarios. The results show that the building can achieve carbon balance under conservative scenarios when a zero-carbon emission grid is not achieved by 2050. The results illustrate the importance of transparency when declaring a zero-carbon balance in a project. The uncertainties of such a declaration are also discussed, along with relationship of building's operational vs. embodied carbon emissions.