The heating energy represents 35% of total energy consumption in Switzerland, and private households 60% of this consumption. The retrofit of residential buildings is a fundamental component of local energy policies. However, questions remain unresolved for many Swiss cities such as: How to know the potential in terms of retrofit of the territory? What are the priority buildings and why? What strategy to implement to achieve the objectives and what impacts on energy, costs and climate? Based on regional data, calculation with the Swiss norm SIA 380/1 per building enriched with data from our own database, the CREM has developed a semi-automatized tool to define a strategy for renovation of housing buildings on any Swiss territory. The method implemented into the tool prioritizes the buildings for retrofit based on potential energy, monetary and greenhouse gas (GHG) savings. The detailed methodology is presented here.