Much focus is given to the energy efficiency of dwellings, in policy and regulation, in pursuance of reduced CO2 emissions for sustainability. This article examines a terrace of 6 similar, passive solar dwellings with sunspaces and the effects that occupants' behaviours have on their energy efficiency. It was found that average annual space heating demand was less than expected, indicating potential benefits from measuring passive solar gains as a form of renewable energy. Space heating demand per person varied by a factor of up to 14 between dwellings dependent on occupant behaviour. Further evidence showed a factor of 45 possible. Significant behaviours in this dwelling type were identified. A second study used 31 personal ecological footprint (PEF) accounts to assess the significance of dwelling energy efficiency in terms of environmental sustainability. A comparison was made between residents of contemporary eco-homes and practising permaculturists occupying a range of traditional house types. It was found that the PEF of the average eco-home dweller was 1.6 times higher than that of the permaculturists. It is argued that improved education for sustainability would be a more efficient way to reduce domestic energy demand than currently recognised.