Researches in the field of ambient assisted living (AAL) have increased in the last ten years, and the paradigms of the smart home have widely spread. Smart homes must consider the health-related issues and the real needs deriving from the ageing of their dwellers. In the smart home, appliances are expected to provide support to the residents, especially when they are characterized by disabilities and/or impairments related to ageing. While most of the AAL solutions presented in literature rely on complex systems and architectures, residents affected by mild or moderate disabilities can take advantage of just a simpler reconfiguration of living environments, i.e., the replacement of certain appliances with others that are able to help them in coping with their limitations. This paper proposes a semantic-based decision support system (DSS), which relies on ontological models, to assist designers in domestic environments’ reconfiguration. The ontology leverages semantic representations of dwellers and domestic environments’ domains of knowledge to foster the adoption of appliances able to help the residents to live independently. The development process of the ontology is presented in detail together with the results deriving from reasoning processes. To ease the reconfiguration of domestic environments, a prototypical application taking advantage of the DSS is presented.