Systems integration is a trend in the quest for increased environmental performance in urban districts, yet its implications are not yet fully known. Hammarby Sjöstad is a district in Stockholm, Sweden, designed with high environmental ambitions. These ambitions were later expressed in the Hammarby Model, an integrated infrastructural system aiming to minimize the metabolic flows of the district by closing its material and energy flows. Various integrated systems were already present in Stockholm when discussions began around the development of the Hammarby Model. Using a conceptual framework inspired by transition theory, this paper analyses the process of designing and building the Hammarby Model. Our aim is to create a better understanding of the implications of systems integration at the urban district level. The findings of the study show that systems integration may both enable and constrain further innovation. On one hand, integration facilitates the implementation of technologies that are add-ons or that solve a reverse salient experienced by the integrated system. On the other hand, technologies that are perceived to threaten the integrated system are locked out, prohibiting further optimization of the system.