At the design phase, architects use CAD systems, now enhanced with energy‐efficiency tools. Ideally, they should be integrated with airflow and lighting, acoustic tools, their energy modelling data should be exported to the Building Energy Management Systems that optimize energy consumption at the operational stage on building, as well as on district and city level. In turn, these systems need to obtain data from sensor clouds and energy metres, and be able to command intelligent white goods and HVAC systems. To facilitate an incremental investment of consumers in energy management appliances, a strong plug and play principle is needed and embedded in reliable cost estimation. In short time, micro and mini renewable sources will be common at every building and need to be integrated into the building systems as well. Consumers, having renewable installations, will trade with the Smart Grid their energy consumption or sales using a language that needs to be independent of the energy provider. The requirements of interoperability between all needed IT tools are therefore high. However, current developments are obliterated by the rivalry of competing low level protocols for the Home Area Network. Above these protocols, the main condition for Interoperability is to agree on the high level data models and vocabularies, where the semantics of the building systems can be captured and operably forwarded to the processing tools. Especially ontologies can play a major role here, paving the waytowards achievement of ICT standardisation in due time. However, a too early standardization can constrain innovation. Advanced research in the area is therefore highly important.