There is enormous potential for building-focused applications to improve operation and sustainability, both for classical uses like modeling or fault detection as well as innovative ones like occupant-driven control or grid-aware energy management. We show that a building application stack – that addresses shortcomings of existing antiquated architectures by democratizing sensor data, constructing a framework for reliable and fault-tolerant operation of concurrent applications, and establishing an application programming interface to promote portability throughout the building stock – enables development of advanced applications. We observe the growing importance of applications that integrate sensors and actuators from the building infrastructure with those from “add-on” networks, and show how this design pattern is further empowered by the architecture. To prove the efficacy of the approach, we implement two advanced environmental conditioning applications on a large, commercial building that was not designed for either of them: a demand-controlled ventilation (DCV) system for balancing air quality considerations and energy use in conference and class room settings and a demand-controlled filtration (DCF) system for conserving recirculating fan energy in an intermittently occupied cleanroom setting. The DCV application is able to reduce air quality threshold violations by over 95% and concurrently reduce ventilation energy consumption by over 80%, while the DCF application can reduce recirculating fan power consumption by half with no repercussions on air quality when the room is occupied. Further, the portability of these applications highlights the potential of the architecture to enable widespread and rapid application development throughout the building stock.