As a ubiquitous form of urban infrastructure, the built environment is critical to any urban-led response to climate change. In cities across the world, the promotion of retrofit of the built environment is emerging as a major area of interest in urban governance and planning. In the Australian context, however, current practices of residential retrofitting remain fragmented. My concern, in this paper, then, is to outline a theoretical approach to explore the interactions between wider systems (eg governance frameworks, regulations), actors (eg tradespeople, residential retrofitters) and everyday residential retrofit practices. Bringing together perspectives from assemblage theory and social practice theory, the project seeks to emphasise the socio-technical, material and practice-based nature of residential retrofitting. Adopting the focussed entry point of heating and cooling retrofit through which to explore residential retrofitting, residential heating and cooling retrofit is conceptualised as a socio-technical assemblage shaped by, and through, a range of actors, relations, scales and practices. This paper suggests that using an assemblage and social practice theoretical perspective allows us to consider a wider range of practices, including residential retrofit, that can usefully broaden how and what we conceptualise urban regeneration to be.