Most of the existing sensor network deployments are convergecast data collection applications that transmit data from multiple sources to a sink. In this paper, we present CoReDac, a self-organizing, collision-free convergecast protocol. In contrast to previous solutions, CoReDac consists not only of a data collection phase but also an efficient and collision-free command phase. This way, the protocol can be used below the application layer for wireless versions of building automation protocols such as BACnet that require both efficient response and command phases. We present experiments that show that CoReDac works as expected and demonstrate its energy-efficiency for low duty cycle command-response applications by comparing it to X-MAC.