Increasing concern about abandoned historical buildings has driven architects and heritage researchers to explore sustainable practices in adaptive reuse. The energy efficiency of these buildings is a critical aspect of this issue, especially in preserving their cultural and architectural value. This research estimates that integrating energy considerations into adaptive reuse can improve the sustainability of historical buildings and Ex-Mercati Generali Torino is selected as a case study. The way adaptive reuse is used to promote sustainability in architecture and reduce waste while conserving resources and extending the lifecycle of existing structures is examined in this study. The energy performance of Ex-Moi Generali Mercati will be evaluated and compared across three different periods—1933, the Olympic 2006 renovation phase, and the future design proposal—by analyzing metrics such as insulation quality with U-values and R-values and thermal conductivity along with the effect of architectural modifications on energy efficiency throughout these time frames.