Community-led approaches have emerged in the UK as an alternative route for realizing reductions in domestic energy demand through changes in homeowners' understanding and behaviours when coupled with physical retrofitting. A socio-technical approach is used to develop and apply a monitoring and evaluation framework. This framework comprises assessment of longitudinal energy use, in-situ monitoring and qualitative social science surveys in order to evaluate the impacts (on changing individual and household energy behaviours) and effectiveness (on achieving real savings in energy use and carbon emissions) of energy retrofits of 27 owner-occupied homes across six low carbon communities (LCCs). Results indicate that the energy retrofits have been reasonably effective in terms of reducing energy use in dwellings (75% of homes experienced reductions in gas and/or electricity use). The research also reveals wider impacts of retrofits on indoor environmental conditions and behaviours of the occupants. Such impacts, intended or otherwise, may not be always positive; however, the LCCs appear particularly successful in facilitating the households, through increased motivations, capability, awareness and knowledge relating to energy use and behaviours. Insights from the study can help to inform future strategy implementation for reducing energy demand from existing housing to meet national CO2 targets.