This study reported herein assesses the health benefits attributable to weatherizing affordable multifamily buildings in the United States. Weatherization is a term used to describe programs that install comprehensive sets of energy efficiency measures into low-income homes and affordable multifamily buildings, such as air sealing, insulation, and heating system repair and replacement. Using a convenience sampling approach, 382 multifamily buildings located in the Northeast and Midwest regions were recruited for this study that fell into three samples: an already weatherized group: a treatment group; and a control group. Households in these buildings were surveyed to collect data about the quality of their dwellings (i.e., apartments), health, and demographic characteristics. The survey was 1) administered twice to the treatment group, once pre-weatherization and once one-year post-weatherization, 2) twice to the control group, also one year apart, and 3) once to the comparison group during the first phase of the survey administration. The survey results suggest that many dwelling conditions improved after weatherization, including improvements in thermal performance and reductions in noise, dust and drafts. Respondents reported improvements in mental health and sleep quality and less need of medical interventions for arthritis and being too cold in their homes. Frequency of headaches decreased. There were no impacts upon respiratory conditions such as asthma and COPD.