Retrofitting existing buildings to Nearly Zero Energy Buildings (NZEBs) can significantly reduce their energy consumption and environmental impact. However, practitioners and policymakers still face the challenge of providing effective and economic energy efficiency measures (EEMs) to interested parties, due to the limited data on the actual performance of available EEMs. This study addresses the data deficiency by analyzing the actual energy and cost performance of a retrofitted single-family house towards a NZEB. Itemized electricity consumptions, including power consumption of heat pump, water pump, fan, and other accessories, as well as whole building usage, are measured before and after the renovation. New metrics are devised for effectiveness assessment – estimating energy savings upon degree day, cost and change in envelope thermal resistance R-value. The contribution of each EEM to the achieved energy savings is identified and compared. For energy consumption of air-water source heat pump, exterior wall retrofit yields the greatest savings: 1.02 kWh/dd (22.2 %) in winter and 0.64 kWh/dd (33.1 %) in summer, followed by roof retrofit. When the savings are analyzed in terms of per unit increment of R-value, windows/doors retrofit demonstrates the highest priority: 1.66 kWh/dd per unit increment of R-value in winter and 0.62 kWh/dd per unit increment of R-value in summer. Considering costs and energy saving contribution together, the optimal retrofit measure is roof retrofit. This study also contributes to the topic by adding new data to the field and extending retrofit practices to locations outside of North America and Europe.