A smart building is an intelligent structure equipped with advanced technologies that enable optimized management of its infrastructures, such as energy, lighting, security, and IT networks, through the integration of automated and interconnected systems. These buildings represent a system of systems with complex interactions, where the failure of one system can impact other interconnected systems. In this paper, we present a modeling of the IT, Network, and Lighting systems of the smart building using fault trees. We also introduce a new type of event called a connection event to model the interactions between these systems. These connection events illustrate how a failure in one system can trigger a cascade of effects in other interconnected systems, thereby enhancing our understanding and ability to manage these complex interactions in smart buildings.