Recent research and standardization in the domain of the Internet of Things aims at providing IPv6 and Web services on the most constrained devices. The constrained application protocol (CoAP) allows the deployment of RESTful Web services on limited devices by offering a protocol similar to HTTP that uses UDP as transport layer instead of TCP. This enables more efficient communication if non-reliable, asynchronous or group communication is required. Existing and mature home and building automation technologies like KNX, BACnet or ZigBee are based on non-IP communication and define a complete custom protocol stack. State of the art integration approaches usually offer a centralized Web service interface based on oBIX, OPC UA or BACnet/WS based on SOAP or RESTful Web services. This paper presents the concept of a gateway that allows the integration of building automation systems into constrained RESTful environments by an IPv6 per-device interface based on oBIX using a novel constrained application protocol binding with efficient XML interchange message encoding. This integration approach provides a service-oriented architecture with uniform interfaces for control scenarios that span heterogeneous technologies. The evaluation results show the efficiency of novel protocol bindings compared to state of the art protocol bindings and message encodings. Performance evaluation results prove that even interactive user control scenarios can be based on these Web service interfaces.