As clearly declared by the European Union (EU) in the framework of the EU climate actions and of the long-term strategies up to 2050, the building sector has an essential role in achieving the advocated energy transition. In order to achieve the energy and emission reductions goals, actions are needed to increase energy savings and efficiency at building and system level, as well as to improve occupants’ wellbeing and satisfaction. To do this, a new multi-disciplinary paradigm is essential, able to tackle all the building-system-occupant challenges and interactions. The objective of the work is to explore different levels of knowledge and detail of a building, in order to better identify its points of strength and weakness, but also to compare the instruments used to measure the buildings performance and the performance itself.