This session will present two complementary case studies on the decarbonization of existing municipal buildings. The first examines a portfolio-based approach implemented by the City of Laval, covering multiple facilities and demonstrating how decarbonization strategies can be planned, prioritized, and scaled across a municipal asset base. The second focuses on Montréal City Hall, highlighting the decarbonization strategy developed for a large heritage building currently pursuing LEED® Gold certification for an Existing Building. The session will address key questions such as how municipalities structure decarbonization plans, sequence interventions, and translate policy objectives into technical execution. Presenters will share new insights drawn from real projects, including a practical roadmap that other cities can adapt, as well as early results from buildings that have achieved decarbonization. Attendees will gain transferable strategies and a clear framework applicable to municipal building portfolios.