Residential buildings have continuously improved in energy efficiency, partly as a consequence of the introduction of energy regulations in many countries. Although better thermal properties and systems efficiency have lowered energy consumption for space heating in recent decades, substantial differences in energy consumption in similar dwellings are still being observed. These differences in consumption are thought to be caused by differences in occupancy patterns, by quality of construction and by rebound effects. This research addresses the effect of energy performance regulations and occupant behavior on energy consumption for space and water heating in dwellings built after the introduction of the energy performance regulations in the Netherlands. The results of this research show that improving the energy efficiency of buildings alone is not enough to decrease that energy consumption. The large differences found in the use of dwellings indicate that, especially in energy efficient houses, occupant behavior provides an opportunity for further reductions in the energy consumption for space heating which could boost the efforts to conserve energy worldwide.