The Covid-19 pandemic challenges healthcare organizations with respect to the provision of care, but also regarding the built environment. Hospitals were forced to rethink the use and organization of their buildings on very short notice in order to separate Covid from non-Covid patients. How hospital buildings were adapted in six general hospitals in Flanders, was investigated based on interviews (in July 2020) with representatives responsible for infrastructural adaptations. Interviewees illustrated changes made with building plans, photos and other supportive material. Hospitals were adapted in various ways depending on the available infrastructure, local organization, and the moment during the crisis. Interventions focused mostly on providing separate tracks and spaces for Covid and non-Covid patients. From the emergency department to patient rooms, guaranteeing the division between both groups was a key concern. The separation strategies employed varied between incorporating new infrastructure and creatively dealing with existing spaces. Despite efforts to strictly divide Covid and non-Covid zones, in reality people, materials, and air cross the borders between both. Staff enter and leave the hospital regularly, waste from Covid wards is processed elsewhere, and airflows are not necessarily stopped by spatial divisions. In-between zones, like exchange zones, elevators and air shafts, are challenging, and require combining strategies to guarantee a safe environment. At the same time, interventions in these zones bring existing rules such as fire regulations to a head. Interventions made in the crisis situation foreground how adaptations to the built environment potentially challenge and are challenged by existing practices.