This paper presents an empirical study to assess the occurrence and possible causes of summertime overheating in three occupied and two unoccupied low energy dwellings in the UK. All five dwellings are identical in terms of construction and location, but have different occupancy profiles and household compositions in the three occupied dwellings. An interdisciplinary approach is adopted, drawing from building science and social science methods, including monitoring of interior environmental conditions, thermal comfort diaries and interviews with residents. Temperature data from bedrooms and living rooms from the case study homes were analysed for overheating using both static and adaptive thermal comfort analyses methods. The findings suggest that summertime overheating is prevalent across both occupied and unoccupied case study dwellings, although overheating assessment using static criteria found a much higher proportion of the rooms to be overheated than the adaptive criteria. In the dwellings a common finding was that bedrooms were found to be more prone to overheating than living rooms. Since it is likely that methods used to assess overheating will be incorporated into regulations in future affecting the design of housing, it is necessary to deploy passive design strategies to prevent the overheating risk in low energy homes.