This study assesses the energy savings and cost-effectiveness of individual retrofit options and packages of measures in single-family buildings, based on analysis of metered energy consumption and actual installation costs. We present results for 14 individual shell, heating system, and water heating measures, as well as 21 electric utility weatherization programs. The data on individual retrofit measures represent 32 retrofit projects, ranging in size from three to 30 000 houses. Most of the retrofitted homes are located in cold climates in the United States and use natural gas for space heating. Installation of additional ceiling and wall insulation was quite cost-effective, with normalized annual consumption (NAC) savings ranging between 12–21% in 10 retrofit projects, and average cost of conserved energy (CCE) values between $1.60–6.50/ GJ. Retrofit technique (interior vs. exterior insulation) and basement condition (unconditioned vs. conditioned) strongly influenced the level of energy savings in homes that installed foundation insulation, although payback times were generally quite long. Window replacements were found to have small NAC savings (2–5%) and were not cost-effective (CCE > $15/GJ). Flame retention burners for oil furnaces produced significant savings (19–34 GJ/year for the three studies in our data base) and had CCEs of less than $2.70/GJ. Several retrofit strategies that improve the efficiency of gas furnaces produced annual savings of 7–20 GJ/year (4–14% of the NAC), with CCEs that were comparable to current gas prices ($5–7GJ). Condensing furnace replacements saved 31–41 GJ/year in the three US studies and appear to be marginally cost-effective, even if a worst-case analysis is used that attributes the entire cost of the retrofit to energy efficiency. Data on packages of weatherization measures are drawn from 21 Pacific Northwest electric utility programs. The principal retrofit measures were various types of insulation and water heating retrofits. Median electricity savings were 4020 kWh per year (16% NA savings) with a median CCE of 5.4∉/kWh.