The paper outlines specific aspects of the rehabilitation of a 25 year old wood frame, residential complex in the Lower Mainland of British Columbia, which experienced areas of building envelope failure directly related to air leakage. The observed problems were unexpected, as the source of the majority of envelope failures on past rehabilitation projects have been attributed to exterior moisture ingress. The paper presents the approach taken by the design team to address the issue of air leakage on this project and discusses the challenges and limitations that were encountered. The age of the building, configuration of the wall framing and basic building science principles (air barrier and stack effect) are factors that will also be discussed. A description of the building’s architectural features and the original construction practices that contributed to the air leakage problems will be provided focusing on the elements where deterioration and mold growth were observed. The extent of damage related to air leakage will be reviewed, as will the suspected modes of failure.

The potential problems caused by air leakage are not new to building designers, however air leakage can sometimes be overlooked as being a significant source of envelope failure. The information gained from this project serves to remind designers of the potential impact of air leakage on today’s lowrise residential buildings.