The Sustainable Intelligent Building (SIB) arises with an outstanding role in terms of efficiency and environmentally aware practices, and hence as the key enabler of the sustainability of the building itself, and thus, of the city as a whole. This Recommendation sets the minimal requirements for an efficient and sustainable management of the building as a unit. The sustainability of human activities in urban areas cannot be addressed without taking into consideration the building, which is the most basic unit that cities are composed of. This Recommendation also defines the services enabled by the SIB concept, the way it contributes to the aforementioned goals of sustainability, its features, its different possible functioning modes, or its internal architecture and requirements with the IoT node at its core. Interoperability deserves a special mention among these requirements and specifications, as most of the added-value that the SIB provides comes into action when it interacts with other parts of the building, other buildings, city elements, or the city itself. Protocols, semantics, and normalization are key as a part of this interaction, and the SIB with its IoT node is required to be compliant with all of them. Extensibility is another key feature for the SIB and the IoT node. The technology behind smart and sustainable cities is currently evolving very quickly, as it is a state-of-the-art technological arena. That is the reason why one of the most important architectural patterns to take into consideration is to design a SIB and an IoT node that support not only upgrading, but also the capacity to accommodate new technologies, protocols, services and applications that may be relevant for the industry in the future. In addition to these clear advantages for the technical durability of the SIB infrastructure, this will enable as well the creation of an open "smart ecosystem", with third parties being able to integrate their own developments, expanding the capacities of the SIB, and ultimately contributing to improve the quality of life of citizens.