The Natural Resources Defense Council (NRDC), National Housing Trust (NHT), Energy Foundation, Elevate Energy, and New Ecology are conducting a multistate and multiyear Energy Efficiency for All affordable multifamily housing efficiency project with the goal of cost effectively reducing energy consumption as a means of maintaining housing affordability, creating healthier and more comfortable living environments for moderate- and low-income families, and reducing pollution. The project aim is to encourage electric and gas utilities to spearhead programs designed to capture all cost-effective energy efficiency within the affordable multifamily housing sector, significantly benefiting low income families and building owners as well as utilities. NRDC and the project partners commissioned this study to estimate the potential energy savings from the implementation of efficiency measures in affordable multifamily housing in nine states — Georgia, Illinois, Maryland, Michigan, Missouri, New York, North Carolina, Pennsylvania, and Virginia. For this study, affordable multifamily housing is defined as households in buildings with five or more units occupied by people with household incomes at or below 80% of the area median income. The study compared outputs from the different potential scenarios and sensitivity analyses assessed in the study. This study analyzed two levels of potential: 1. Economic potential — savings that can be realized if all cost-effective efficiency measures are implemented 2. Maximum achievable potential — savings that can be realized if all cost-effective efficiency measures are implemented given existing market barriers The study found that the total benefits to society, as defined by the Total Resource Cost test, from pursing energy efficiency substantially exceed the costs.