This paper presents a novel type of composite floor system using cellular beams. A major benefit of the system is the integrated installation floor, providing additional value to the floor. The system is based on half cellular beams made of existing hot-rolled sections. The openings in the cellular beams allow placing installations in all directions, thus providing excellent flexibility to the user when maintaining or changing installations. The paper first presents the general design and details of the construction of the novel floor system. Then the results of tests on the dynamic behaviour and the load-carrying capacity are presented and compared to common calculation models for composite slabs. Finally, the paper presents an example of a first building where this type of floor system will be used.