The building sector has a remarkable importance on the overall EU final energy consumption and CO2 emissions (with a share of 40% and 36% respectively), with about a third of the buildings constructed more than 50 years ago, meaning low energy efficiency and little or no renewable energy sources exploited. Simultaneously, EU has set challenging goals to achieve by 2030: curtailment of greenhouse gas emissions by, at least, 40% (with respect to 1990 levels), growth of the renewable energy share to 32%, improvement in energy efficiency by 32.5%. In order to improve the actual situation moving towards the targets set by EU, RE-COGNITION, a Horizon 2020 project, presents a solution which aims at employing on a large-scale Renewable Energy Sources (RES) in buildings, reaching zero-energy, or even energy positive buildings.