This report addresses the opportunities available to make multifamily housing more affordable by using energy efficiency practices in housing rehabiiitation. Use of the energy conservation measures discussed in this report enables developers of multifamily housing to substantially reduce annual energy costs. The reduction in natural gas usage was found to be approximately 10 Btu per square foot per heating degree-day. For an average Chicago heating season with 6,455 heating degree-days, an apartment of 1,100 f? would save about 71 0 therms of natural gas and lower its gas energy costs by approximately $355. This dollar savings exceeds the costs of one month of affordable housing for a family earning $14,000 per year. The energy conservation measures also improve the typical net cash available per dwelling unit to the owner of the building by more than $250 per year after debt service. The study focuses on a number of Chicago multifamily buildings. The buildings were examined to compare energy efficiency measures that are commonly found in multifamily building rehabilitation with the high-energy-efficiency (HE) techniques that are currently available to community developers but are often unused. The HE measures include R-43 insulation in attics, R-19 insulation in exterior walls, lowemissivity coatings on windows, air infiltration sealing, and HE heating systems. The report describes the HE features and their potential benefits for making housing more affordable. It also describes the factors influencing acceptance. This report makes recommendations for expanding cost-effective energy conservation in the multifamily building sector. Among the recommendations are: Expand HE rehab and retrofit techniques to multifamily building rehabs in which demolition of the interior structures is not required (moderate rehabs) or buildings are not vacant (e.g., weatherization upgrades); and Expand research into the special opportunities for incorporating energy conservation in low-income communities.