EE SUN aims at aiding block-of-flat houses of the CBC region by involving 24 pilot buildings (12 HU, 12 CR) into joint Energy Efficiency analyses. The conclusions are embedded into a joint CBC methodology disseminated in the whole CBC region. The general objective is the promotion of sustainable development of the border area by fostering thematic cooperation between bodies engaged in management and development of residential block buildings for the sake of reducing CO2 emission.