In order to reduce the energy gap originated by the difference between existing tools estimations and real energy consumption, HIT2GAP European H2020 project aims at advancing on building control tools by providing a newer decision-making technology. Technically, HIT2GAP offers a platform inspired by previous reference architectures (e.g., Haystack) and complements them through a knowledge-based model, called OntoH2G, to store building information under a common vocabulary and consequently to enable fine-grained vision of the building with its equipment and occupants. OntoH2G advances over existing models on two main aspects: (i) being compliant with well-known ontologies in different domains in order to cover all energy building concepts, and (ii) its ability to represent user/occupant behavior, preferences, and interactions. In this paper, we present the main features of OntoH2G and describe how the well-known ontologies have been aligned in OntoH2G.