The indoor environmental quality in energy efficient dwellings is a significantly important yet under-researched area, particularly in bedrooms where people spend much of their time and adaptive ventilation behaviour is restricted. This paper presents the results of an indoor environmental assessment of four new build energy efficient social housing projects; focusing specifically on bedroom conditions. The study involved monitoring of bedroom temperature, relative humidity and carbon dioxide levels during summer and winter seasons, the use of an occupant diary to record conditions during the monitoring period in conjunction with occupant interviews to examine perception of the indoor environment and occupant behaviour in the dwellings. The findings indicate significant issues with night time ventilation; which suggests inadequate ventilation strategies in the case study dwellings. In addition, temperature and relative humidity levels regularly exceeded recommended levels for comfort and health. The findings demonstrate a potential negative effect of contemporary energy efficient housing design strategies on bedroom environmental conditions; highlighting a possible risk to occupant health and wellbeing.