The existing housing stock plays a major role in the realization of the energy efficiency targets set in EU member states such as the Netherlands. The non-profit housing sector in this country dominates the housing market as it represents 31% of the total housing stock. The focus of this paper is to examine the energy efficiency measures that are currently applied in this sector and their effects on the energy performance. The data necessary for the research are drawn from a monitoring system that contains data about the energy performance of more than half of all dwellings in the sector. The method followed is based on quantitative data analysis of physical properties regarding energy efficiency, general dwellings’ characteristics and estimated energy consumption of the households. The outcomes of this research provide insight in the energy efficiency measures applied to the existing residential stock. In addition, the impact of these measures on the energy performance is discussed, along with indications about the energy renovation practices in the non-profit housing sector.