Reusing existing and historic buildings while also making them more efficient, healthier and comfortable is of growing importance in the housing industry – for both student and affordable housing. Air sealing the building envelope and improving the performance of existing ductwork can play critical roles in these buildings’ retrofits, but many times aren’t considered due to perceived complexity and cost. This session will delve into two case studies of air sealing in historic and older housing facilities. The building envelope and compartmentalization air sealing for a 100 year old student dormitory and duct leakage sealing for a 49 year old affordable senior housing complex will be presented, including M&V data and lessons learned.