Different forms of representation are ubiquitous in building design processes, circulating across and between various actors. They are mediators in the development of design. The mobilization of multiple forms of representations and visualizations suggest that design materialization might have several important roles to play in negotiating the building design and project, including in the exposition and resolution of controversy in the design process. This paper describes and discusses two cases of design activity around single bed rooms in hospitals in Denmark and UK. Across many national healthcare systems, single bed rooms are being seen as the preferred alternative to more traditional ward-style accommodation, as it has advantages for privacy and dignity for patients, less disruption to other patients and better control of hospital acquired infections. But fundamentally, single rooms mean less hospital beds in the same building envelope – hence size of these rooms becomes a critical issue. The two cases document debates over whether the single rooms in a design scheme were big enough to allow necessary clinical activities to take place within them. The two cases both involve the use of different representations and visualizations – economic calculations, drawings, and virtual and physical models. We use these cases to discuss the roles of different sorts of representations and visualizations in design process, in terms of opening up and settling controversies (such as room size), in terms of the way they differently represent and visualize ‘space’ within the design, and in terms of the kinds of materiality and collaboration they perform.