As cities densify, multi-unit residential buildings (MURBs) are becoming an integral part of the world's housing stock. In Toronto, Canada's largest city, MURBs comprise approximately 47% of the total housing stock. 1 In London and New York City, MURBs account for approximately 51% and 82% of the total housing stock, respectively. 2,3 As a building class, MURBs are incredibly diverse. They can be an apartment-style building, where there is a common entrance and the building is divided into suites. MURBs can also comprise of townhouse or row-house dwellings, where each suite/unit has its own entrance. They can range in height from two storeys to upwards of 70 storeys. The one constant is that there are multiple households sharing common structural and/or building systems. In recent years, there has been a lot of attention to the effects of air infiltration on building performance-particularly related to