This work presents a framework for applying QoS in a network of a Smart Building environment, exploiting Software Defined Networks (SDN) and Usage Control (UCON) policy enforcement. The proposed framework will be presented in a plausible use case of a Smart Building where the available Internet connection provided by an Internet Service Provider will be distributed both to tenants and the devices responsible for the management and the safety of the building, taking into account different levels of QoS. Network traffic and bandwidth are thus managed by dynamically exploiting Usage Control framework to enforce a set of management, security and safety policies, aimed at ensuring the appropriate QoS for the provided services according to both tenants Service Level Agreements (SLAs) and current context. A set of performance experiments is reported to demonstrate the viability of the proposed approach.