Retrofitting existing buildings to improve energy efficiency and reduce greenhouse gas emissions is crucial to meet climate change mitigation goals globally. However, the adoption rate of building retrofits remains low due to various barriers such as high upfront costs, disruption to occupants, uncertainty about benefits, and lack of knowledge and easy-to-use tools to identify and assess retrofit options. There is a need for continued improvement of retrofitting tools to systematically address these barriers through integrating real building project data and user feedback. The findings are based on extensive case studies conducted on a diverse portfolio of buildings across different climatic zones, construction typologies, and usage profiles. The results are discussed in the context of the research objectives, highlighting advancements in retrofit modeling techniques, energy savings calculations, and the identification of optimal retrofit strategies.