This study critically examined the carbon accounting method designers use when considering how to interact with New Zealand's existing commercial buildings as they end their design life. A comparative carbon analysis was carried out using Life Cycle Assessments (LCA) of a commercial scale case study. This study aimed to establish the efficacy of refurbishing a commercial building at the end of its design life. The overarching question sought to identify whether a low-carbon new building would be more sustainable than increasing the design life of existing high-carbon commercial-scale buildings