In assessing the energy efficiency of a house design, particularly methods incorporating building performance simulation, assumptions are made about how the occupants operate the building. Often these assumptions are standardised to simplify the assessment process with the intention of enabling a straight forward comparison between designs. Assessment of performance using standardised operations may pose a disadvantage to house designs that are intended for households who are likely to operate the house outside of the assumed norm. This paper examines occupant behaviour in low energy houses in the context of the Australian regulatory house energy rating scheme and, using simulation, demonstrates the impact of alternative occupancy settings on the validity of the predicted house energy rating. The results clearly show that current occupant assumptions within the scheme fail to adequately reflect actual heating and cooling practices in low energy dwellings and, as such, overestimate energy consumption within these households. Based on these results it is suggested that, for equitable assessment of these households, settings within the simulation engine used for assessment must be modified to align with actual user behaviour. (C) 2014 Elsevier B.V. All rights reserved.