This document summarizes a project that investigated air leakage in large buildings in Minnesota. Air leakage tests were conducted on 6 buildings before and after air sealing. On average, air sealing reduced leakage by 10%. Tests found that buildings were 84% tighter than average US buildings, possibly due to the cold climate. Pressurization tests found greater air leakage than depressurization by 22% on average. Mechanical systems were found to increase total building leakage by 15-119% and have a significant effect on building pressure. Future work will model these effects and develop methods to estimate pressure effects and air sealing savings.