In this project, the NorthernSTAR Building America Partnership team studied the effectiveness of the External Thermal Moisture Management System (ETMMS) as a solution for improving airtightness in a roof-only application (versus the whole-house application used in deep energy retrofits). An independent contractor provided airtightness data from two 1½-story homes that used the roof-only ETMMS process. The team analyzed and compared these data to ancillary data from market-rate utility and weatherization programs for more than 250 roof-only, interior-applied energy retrofits on 1½-story homes.