Purpose This paper aims to discuss the nexus between two societal (sub) systems of housing and energy supply to shed new light on the key institutional barriers to socio-technical energy transition in the built environment. The key research question is to explore if and how key patterns of institutional elements associated with energy retrofit and energy supply are combined, co-evolved and played out in the housing system, leading to an alternative energy transition pathway in the built environment. Design/methodology/approach A comparative case study of residential buildings in the Swiss cities of Basel and Sion is conducted to map retrofitting policies and practices in a wide range of buildings (e.g. multi-family and single family) that each requires a particular constellation of institutions, actors and artefacts. Findings The key finding is that the regulative institutions support energy transition in each urban form/housing type. However, the co-evolution with normative and cultural-cognitive institutions does not play out very clearly in the housing system. One reason is that the norms and cultures are deeply rooted in the practices exercised by business community and households and therefore they need a longer time frame to adapt to a new regulation. Research limitations/implications -The policies and actions to increase the rate of housing retrofit are discussed in the specific socio-political context of Switzerland. Therefore, the results of this study might not be applied in other contexts with different conditions, limiting the possibility for analytical generalization. The case study can generate only context-specific knowledge, which might be valuable only to cities with similar conditions. This paper addresses theoretical, methodological and policy challenges in scaling-up retrofit projects by taking a holistic and integrated approach to the systems of housing and energy supply. Practical implications -It would have been necessary to find out how the introduction and enforcement of new energy policies and regulations (regulative institutions) have changed the norms and building practices (normative institutions) used by actors from housing industry and the attitudes and energy consumption behaviour of the households (cultural-cognitive institutions). Nevertheless, information about normative and cultural-cognitive institutions require more primary data in the form of interviews with organizations and households, respectively, which goes beyond the scope and resources of this study. Originality/value Insights from different strands of literature (institutions and sustainability transition) are combined to understand if and how retrofitting practices go along with other elements of urban sustainability including architectural, technical, socio-cultural and economic factors.