The adoption of solar energy is lagging behind in urban areas worldwide. Although the literature on energy transition is abundant, it has been focused mostly at the systems level. Few studies have addressed on-the-ground implementation. This paper examines a specific but prominent example of such on-the-ground practice: decision-making processes in strata buildings whose owners are organized in a (home) owners’ association. These buildings constitute a significant proportion of the housing stock in European cities, and hence their role in energy transition cannot be underestimated. In strata buildings, homeowners have to reach an agreement before renewable energy measures can be implemented. These related group decision-making processes are still a black box, however. We constructed a tentative framework based on a review of group decision-making and applied literature, which we validated and refined using a survey and in-depth interviews with (home) owners’ associations in Amsterdam, the Netherlands. Our study aimed to explore what the stimuli and barriers for the adoption of renewable energy measures in group settings are. Our empirical findings suggest that leadership and information processing are key factors that explain the outcomes of group decision-making processes. Whereas many are convinced that energy transitions are technically possible, their day-to-day implementation has proven to be complicated. For energy transitions to succeed, the recognition of key factors that explain the outcomes of group decision-making needs to be taken into account.