Toronto’s Multi-Unit Residential Buildings (MURBs) account for over 2.5 million tonnes of annual greenhouse gas (GHG) emissions. This multi-phase study analyzes MURB energy-use based on a representative sample of buildings in Toronto to better understand the energy use of the city’s building stock and support policy interventions that can reduce GHG emissions. Phase I analyzes a database of 108 MURBs representing nearly 2% of the overall MURB population. Phase II analyzes a refined data set of 40 MURBs for which better quality data was available. Phase III undertakes detailed energy modelling on four archetypal buildings from the data set to explore the comparative impacts of various energy retrofit measures.