Purpose: Global megatrends such as urbanization and ageing of the population result in fast-paced demographic changes, which pose different types of challenges for different regions. While many rural municipalities bear the burden of under-used buildings, cities are in a hurry to develop new ones to meet new space demands. The purpose of this paper is to assess the potential of relocatable modular buildings to address these challenges, following the principles of circular economy, while at the same time offering usability. Design/methodology/approach: This multiple case study explores existing relocatable modular health-care buildings in Finland. The case buildings host hospital support functions, imaging services, a health-care centre and a care home. The primary data comprise 21 semi-structured interviews and observation during factory and site visits. Findings: Based on the findings, relocatable modular buildings have many benefits and provide a viable option for cities and municipalities struggling to meet their fluctuating space demands. Some challenges were also identified, mainly derived from the dimensional restrictions of the modules. Originality/value: This research contributes to the emerging body of knowledge on circular economy in the built environment. More specifically, the research provides a very concrete example of circularity and details a framework for usable and relocatable modular buildings. In conclusion, relocatable modular buildings could solve the challenges posed by quickly changing demographics in different types of regions and deliver both usability and circularity.