Tracking Toronto’s 'missing middle' housing options through data visualization

School of Cities researchers Remus Herteg, Jeff Allen and Ahmad Al-Musa used building permit application data to track ‘reno-ductions’ across the city of Toronto. The phenomenon decreases housing density by transforming multi-unit dwellings into single-family homes. (Image: Herteg, Allen and Al-Musa, posted in GitHub)

A team of researchers from U of T's School of Cities is using building permit data to track the impact of recent policy changes on housing density in Toronto. Transforming the data into public-facing interactive maps and data visualizations, they aim to create new modes for understanding important urban issues, including among policymakers and urban planners.

The researchers looked at the ‘missing middle,’ a range of housing types that fall between single-family homes and high-rise apartments. Some recent changes to housing policy in Toronto aim to encourage the creation of secondary suites or laneway suites, while others allow up to four units per lot in residential zones.

To track the impact of these policies, research associates from the School of Cities — Jeff Allen, Lead, Data Visualization and Ahmad Al-Musa, Projects Coordinator & Researcher — analyzed building permit application data over the past ten years. They found that while the construction of secondary suites hovered between 100 and 130 per year from 2015 up until 2019, it has since increased to 243 units in 2023. Laneway and garden suites were legalized in 2018, and while uptake was slow initially, it has since increased to 102 units in 2023. While positive, this growth is unlikely to make much of a dent in the urgent need for housing in Toronto, which is expected to grow by half a million residents by 2030.

Together with school of cities research assistant Remus Herteg, Allen and Al-Musa also tracked processes that decrease housing density, such as ‘reno-duction.’ This occurs when small multi-family structures such as duplexes and triplexes get purchased, renovated and turned into single-family homes. The team showed that the City of Toronto lost at least 200 units due to such conversions from 2017 to 2023, an average of 28 units per year. In the past two years, the number of these conversions nearly doubled, from just 22 in 2021 to 43 in 2023.

The project and its rich data visualization demonstrate how the School of Cities fosters opportunity, collaboration, insight, and knowledge exchange to address urgent urban challenges.