The increasing availability of large-scale repositories of energy performance certificates offers the opportunity to interlink them with other data sources (cadastre, geographical data, weather data, building regulations, catalogues of refurbishment measures) and to derive innovative services that use the integrated data in conjunction with various tools (energy performance simulation, environmental impact). In the ENERSI project, two applications have been developed to make it easier for building owners and planners to take informed decisions to improve building energy performance in their properties and in their municipalities. These applications, named ENERHAT and ENERPAT, are based on the integration of building data from multiple sources and domains (energy performance certificates, cadastre, geographic information, and census), building refurbishment policies and assessment tools. Data integration has been performed using Semantic Web technologies. A user-friendly interface enables end-users of these on-line applications to obtain information about the current building status of properties, the measures which could be undertaken to improve them, the energy savings achieved and their respective costs.