||We present the software architecture and a prototypical implementation of a dynamic building model service system. The primary purpose of this model service is to support (simulation-assisted) indoor-environmental control operations in buildings. However, as a comprehensive, structured, sensor-based, and self-updating information resource, the model can support other building tasks such as those concerned with building logistics and management. At the core of our model service design, an object tree continuously updated from sensor data reflects the current state of the building, concurrently accessible to multiple clients and backed by persistent storage. The service is embedded in a distributed infrastructure based on tuple spaces for transparent object-based communication between system components. The preliminary evaluation of the model service system suggests that the proposed design is feasible and appropriate for further testing in realistic (large-scale) settings.