A study of multifamily buildings that produced valuable data on inter-unit air flows. From the website: "This project included in-depth owner interviews, a survey of a large sample of renters, legal research and measurements of the movement of PFTs and SHS tracers between units in apartment buildings before and after air sealing and ventilation treatments. The project produced some of the most extensive multiple fan measurements of inter-apartment air leakage and multiple tracer gas measurements of inter-apartment air transfer. It also developed a new metric of 'effective contaminant transfer' which is used to define the magnitude of the transfer of a contaminant source to the monitored location."