Nearly thirty new cellular prisons were built in Belgium between 1850 and the First World War. The design of these prisons was strongly influenced by the Anglo-saxon model of the star-shaped prison with radiating cell wings from a central observation point (e.g. Eastern Penitentiary in Cherry Hill, Philadelphia and Pentonville prison, London). The extent of the building campaign as well as the rigorous implementation of the cellular regime this new prison infrastructure was specifically designed for, granted the country a solid penitentiary reputation abroad. The Belgian prison system has been studied in particular from a legal-historical point of view. However, the penal concept of solitary confinement is only one aspect of the cellular prison design. An increased concern for health throughout the nineteenth century made hygienist requirements equally important aspects in the prison design program. Therefore great attention was given to building services, in particular heating, lighting, ventilation and sanitary installations. This paper presents an overview of the heating, lighting, ventilation and sanitary systems in Belgium’s prison patrimony during the heydays of the cellular regime. These developments are contextualised within the historical development of environmental techniques, as well as within the discourse on health and hygiene in reformed penal design. Sources include contemporary publications, official prison construction programmes, circulars, measuring states and correspondence of the Ministry of Justice.