In the UK, a large proportion of future emissions are embedded in existing cities, given that more than 80% of buildings that will be occupied by 2050 have been built. This suggests that a critical part of the low-carbon transition shall address existing urban systems and actually existing unsustainability.

Yet research shows low-carbon transition has been slow, fragmented and controversial – often framed as an ‘implementation gap’. We argue that it reflects a deeper disjunct: the planning and development systems that produced carbon-intensive urban environments remain organised around land release and new development rather than repairing and adapting existing built environments. Furthermore, despite strong policy ambitions and broader agreement on characteristics of sustainable cities, there remains considerable uncertainty about how sustainable futures can be achieved in practice.

In response, we propose urban retrofit as a way to capture the problem space around the disjunct. It helps us to understand the climate politics of the ‘existing city’ in two ways. First, it shifts attention from future sustainable visions to actually existing unsustainability embedded in inherited urban systems. Second, it shifts attention from new development and climate projects to the urban processes through which carbon-intensive environments are continually (re)produced through the planning and development systems. Urban retrofit foregrounds a politics around urban repair, reframing low-carbon transition as a challenge of reworking the existing city both materially and institutionally.

The paper concludes by outlining five approaches to urban retrofit, demonstrating a heterogenous and contested field through which different actors pursue different low-carbon futures.