Office buildings contain large sensor network deployments to monitor and maintain their internal environment. They also consume a significant amount of energy. This paper proposes the use of the use of horizontal layering, rather than the current vertical-solution approach, to expose the building data plane and enable interoporable software services and applications that monitor and control the building environment. We present our instantiation of this approach, which includes a data plane (sMAP) and storage service (IS4). Furthermore, we describe a set of applications built in this ecosystem.