"About 40% of overall energy consumption in Europe is related to the building sector and over 50% of all materials extracted from earth are transformed into construction materials and products. With more than 70% of the building stock built before the first energy crisis (1970’s), energy retrofitting of buildings is envisaged as the most promising strategy to reach EU’s “20-20-20” targets. However, the traditional approach to the building energy efficient retrofitting brings poor results in relation to the urban sustainability, resource efficiency and economic return. Although the district retrofitting approach is frequently the most sustainable and cost-effective, the complexity of decision making grows exponentially when the intervention targets larger scale, even more when considering the fragmentation of the construction sector (many stakeholders, most of them SMEs). Furthermore, to support the necessary building-retrofitting market mobilization in Europe to fulfill EU-targets in 2020 and 2050, new business models and financial supporting tools need to be developed. FASUDIR will provide an Integrated Decision Support Tool (IDST) based on a new methodology supported by a software tool that will help decision makers to select the best energy retrofitting strategy to increase the sustainability of the whole district. FASUDIR’s IDST will incorporate key actors and relevant networks at the district scale and the entire value chain, and will ensure that new technologies for energy and resource efficient retrofitting are incorporated, especially those emerging from SMEs. FASUDIR takes advantage of the economies of scales and the variety of stakeholders when scaling up to the district, giving more opportunities for the development of new business and financial models with high impact in the economy. The developed methodology and software tool will be validated in three diverse urban areas, including a variety of historical periods."