Virtual reality (VR) is becoming common in the AEC/FM industry, closely linked to BIM implementation. VR tools can be used to anticipate operational issues, simulating them in a virtual prototype since early design. The paper investigates such a topic in relation to access, space and use performance of an existing hospital facility. A case study has been developed considering a pavilion where both medical and food spaces are located, causing a clash between flows of end-users in critical time-slots. Crowd simulations and immersive virtual environments have been tested as occupancy evaluation tools. Post-occupancy evaluation (POE) data have been translated into a dynamic simulation of the existing occupancy conditions within the BIModel of the pavilion and considering various profiles of end-users. Subsequently, both the BIModel and the crowd simulation have been imported into a game engine to be visualised and experienced in a VR-headset, switching from the analysis of flows to the perspective of end-users (i.e. able-bodied users, person in a wheelchair, visually-impaired person). The use of VR enables a clear visualisation and communication of the existing conditions. Moreover, POE data translated into a dynamic simulation of the building use scenario could be applied for the pre-occupancy evaluation of internal layout reconfigurations. Finally, the combined use of crowd simulation and immersive VR enables the users to perceive crowding in the occupancy evaluation and add s the user experience as design input, representing an innovative approach that goes beyond tradition al resources such as personal experience and regulations.