Reuse and Retrofitting Strategies for a Net Zero Carbon Building in Milan: An Analytic Evaluation

The building sector accounts for 38% of carbon emissions, the principal cause of climate change. To meet the targets set by the Paris Agreement, including zero net emissions by 2050, it is necessary that governments develop a culture of sustainability. Whole Life Carbon Assessment of a building, comprehensive of operational and embodied carbon (EC), is described by EN15978:2011. Net Zero Carbon Buildings (NZCB) achieve a balance of zero emissions during their life cycle, promoting both reduction and compensation by adopting many strategies (e.g., reuse of existing structures, design for adaptability and disassembly, circular economy principles). Choosing bio-based materials is also helpful to compensate for EC, thanks to the biogenic carbon stored during their growth. The aim of this research is to find out which strategies are relevant to meet NZCB target, in order to apply them to a case study of reuse of an abandoned building in Milan, highlighting the design process. Material quantities were extracted from the BIM model and imported in OneClick LCA to assess embodied carbon emissions (A1–A5 modules, material production and supply, transport, construction). The final design stage achieved a reduction of 91% in EC compared to a standard new construction, while the bio-based materials compensated for the rest. Further research can improve the Environmental Product Declaration (EPD) of materials and assess the entire building life cycle.