Retrofitting Affordability analyzes newly available data in the New York City multifamily building sector to identify which buildings, and which energy efficiency retrofit measures, have the greatest potential for carbon reduction, and how these benefits relate to affordability and the City’s climate action plan. Due to a very low vacancy rate and a high cost of maintenance, building owners are primarily focused on the day to day concerns of operating their buildings, and energy efficiency has not been a high priority. As a result, these buildings represent a significant opportunity to save energy, cut costs, reduce carbon emissions, improve comfort, and make a meaningful contribution to a healthier, more resilient, and equitable community. Recently, this report was updated to reflect an expanded 2013 data set. The most up-to-date results are below.