The intelligent building, a major smart city research and development domain, has grown beyond the scope of automation, currently focusing on the occupant centered approaches and the ancillary services offered to the power grid. The Internet of Things (IoT) introduced in the recent years are enabling those prospects. However, due to numerous legacy automation systems already in the construction market, the IoT based intelligent building approach is frequently challenged. This paper assesses the opportunities along with the criticism for a fully IoT enabled and controllable intelligent building against the well established, legacy automation systems in a fair and transparent approach. In the second part, it proposes an interoperable intelligent building design for the creation of advanced building managements schemes, by integrating the assets of current automation tools and the emerging innovations. This unification and the progressive phasing out of legacy technologies, would catalyze the market of intelligent buildings in the context of smart cities by not limiting their potential solely on new constructions and by mitigating the investment if legacy systems are already installed. (C) 2016 Elsevier Ltd. All rights reserved.