Three European capital cities - Amsterdam, Budapest and Sofia - have joined forces for the Sustainable Technologies And Combined Community Approaches Take Off (STACCATO) project in order to demonstrate sustainable energy concepts in residential areas. The project uses the unique opportunity of complete renovation of residential areas to implement energy efficiency measures and renewable energy sources. The STACCATO project is expected to result in more than 50% energy savings compared to standard renovation projects. Complete and complex renovation will take place in 1000's of apartments in socialist-era blocks of flats in Budapest and Sofia, and in social housing of Amsterdam. The technological and non-technological potentials for renewable energy sources and energy efficiency will be assessed.