Residential energy use accounts for a quarter of energy-related CO2 emissions in Ireland. Household emissions per capita are significantly above the European average, and need to dramatically reduce if Ireland is to meet its climate change targets set out under the Paris Agreement. This paper introduces an initial database of 55 initiatives based in Ireland that aim to reduce household energy use. Selected initiatives were discussed with three groups of experienced practitioners working in the area of community energy, with a view to gauging their perceived effectiveness in reducing energy use for specific target groups. Two cases are then selected for in-depth analysis – one that aims to reduce energy use through material and technological changes, and another that addresses changes in social practices. By combining learning across these different initiatives, it is possible to demonstrate how more integrated approaches that consider building type, as well as occupant behaviour, can lead to greater and more sustained reductions in household energy use. Lessons for upscaling and diffusion of good practice are also discussed, including the importance of formal and informal community networks. A key finding is the role of energy champions, who in one instance were recruited specifically for this purpose, but who were also found to emerge through less structured and unexpected avenues. Overall, the findings provide recommendations for practitioners and policy makers for designing and implementing community-based sustainable energy initiatives.