University of Toronto's School of Cities Visualization of Gentle Density

Swaths of Toronto consists of land only zoned for low-density single family homes (often called the Yellowbelt). There has been a big push among housing advocates, academics, and planners to increase housing supply in these neighbourhoods via building missing middle housing (a range of housing types that fall between single-family homes and high-rise apartments), in aims to provide more housing options and to make our urban areas more affordable, inclusive, and sustainable. Around 2018-2019, the City of Toronto started taking accelerating actions to increase missing middle housing supply, in what is now the Expanding Housing Options program.

At the smaller-scale of the missing middle are gentle density (or "missing little") strategies, which refers to owner-led efforts to build additional dwellings within their existing parcel of land as citizen developers. These can increase property value and provide supplementary income, but importantly, in aggregate, can incrementally scale up the density of a neighbourhood, allow for intergenerational living, and provide needed housing, particularly for those unable to afford larger homes. Relative to larger developments (e.g. larger multi-unit apartments and condominiums), gentle density is more compatible with the scale and character of existing neighbourhoods. Gentle density development is thus often seen as an approach to increase the housing supply in a way that is less disruptive to existing communities but can still help create more walkable, liveable neighbourhoods, that use existing infrastructure and services, which can save tax payers' money and reduce harmful urban sprawl.

But what is the recent uptake in gentle density housing in the City of Toronto?

To answer this, we've looked at 10 years of building permit data in the City of Toronto (from 01/2013 to 12/2022) to see how and where forms of gentle density have (or have not) been built across the city during this period. At any point in time, building permits can either be active (i.e. building in progress), cancelled, or closed. Those that are closed, we can assume construction has finished. We first counted building permits by the year they were closed for the following two types of gentle density construction, to then chart their trends over time.

Secondary Suites

Sub-dividing an existing residential structure creating one or more additional dwelling units. The most common form is converting a basement into a separate apartment, but this can include other types of conversions as well (e.g. converting from a duplex to a triplex). These conversions may or may not include building additions (i.e. expanding the volume) of the structure. They have been permitted since 2000 city-wide, with some restrictions.


Rear-Yard Suites

Building a small detached dwelling unit that is located on the same property as a single-family home. They are sometimes called Accessory Dwelling Units (ADUs), Garden Suites, or Laneway Houses. Toronto legalized rear yard suites that abut laneways in 06/2018, called Laneway Suites in city bylaws (these are often garage conversions), and then legalized them in all other residential zones in 02/2022 without the need to abut a laneway. The latter are often called Garden Suites.


Closed "Second Suite (New)"Building Permits by Year432013201388201420141272015201511720162016104201720171172018201811720192019169202020201972021202120320222022050100150200

Closed "New Laneway / Rear YardSuite" Building Permits by Yearundefined20132013undefined20142014undefined20152015undefined20162016undefined20172017undefined20182018undefined20192019102020202035202120214520222022050

The construction of secondary suites hovered between 100 and 120 per year up until 2019. It has since increased, in 2022 to just over 200. While laneway suites were legalized in 2018, none were completed according to building permit data until 2020, and only a few dozen since then. Almost all of these are concentrated in pre-war Toronto, where most of the laneways in the city are located (post-war neighbourhoods tend to not have laneways with garages facing the street).

Overall, the completion of secondary suites and rear-yard suites are quite lacklustre given the need for housing in Toronto, where the expected population growth is about 500,000 from 2023 to 2030. Summing the bars above, only 1,282 secondary suites and 90 rear-yard suites have been built in Toronto between 2013 and 2022.

Despite this sluggish uptake to date in Toronto, there are an increasing number of ongoing projects. As of January 1, 2023 there were 575 secondary suite and 458 rear-yard suite building permits that were open and ongoing. These totals are based on counting building permits with unique addresses and an initial or revised application date from the five-year period from 2018 to 2022. However, these numbers are still quite low compared to uptake in other cities like Los Angeles, where the number of issued ADU permits from 2017 to 2021 was over 25,000.

To explore further, we have also mapped below where secondary suites and rear-yard suites have been built in the city from 2013 to 2022, as well as the location of active building permits.

These highlight clustering of development in pre-war neighbourhoods just east and particularly west of the downtown core. All completed rear-yard suites cluster in these neighbourhoods since these are where the majority of the City's laneways are located since post-war development focused garage construction towards the street rather than to a back laneway like pre-war housing. Looking at the active permits, there are now several popping up elsewhere in more suburban neighbourhoods.

One notable pattern is that there is far less gentle density construction in and around North Toronto, despite this area mostly consisting of single-detached homes. This area is home to some of the city's wealthiest neighbourhoods (toggle on the income layer to check this out). Downtown Toronto also only has a few projects, but this is because it is mostly zoned for higher density development.

Location of rear-yard and secondary suite building permits in Toronto:


© Mapbox © OpenStreetMap Improve this map

Closed (i.e. Cleared) Building Permits:

 Rear-Yard Suites

 Secondary Suites


Open (i.e. Active) Building Permits:

xRearYard Rear-Yard Suites

xSecondary Secondary Suites

Residential Zoning:

 Single-Detached Only

 Other Low-Density

Reference Layers:


 Income: Low , Medium , High 

According to the estimated number of properties within Toronto that could add internal or external ADUs range between 370,000 to 390,000 lots. This emphasizes the fact that with the current uptake of a humble 1372, Toronto is barely scratching the surface of hidden housing supply within its existing neighbourhoods. Practical steps need to be taken by all stakeholders to remove the various barriers and to find solutions to make best use of this opportunity to easily provide much-needed dwelling units during the current housing crisis.

Data & Code

Data on the location, type, and status of building permits are from the City of Toronto's Open Data portal.

The residential zoning layer is also from the City's Open Data portal. The single-detached only zones are those classified as [RD] while the other low-density zones are classified as [R, RM, RS, RT]. The latter also include semi-detached, townhouses, and smaller multi-unit dwellings, depending on the zone classification.

The location of laneways is also from the City of Toronto's Open Data portal. It was filtered and extracted from the City's Centreline dataset.

The income data is from the 2021 Canadian census. The low category are census tracts with a median after-tax household income of less then $75,000, the medium range is between $75,000 and $100,000, and the high is above $100,000.

All code used to analyze this data and make this website and its graphics are on GitHub. It was built with the help of Python (pandas, geopandas), Svelte, Mapbox, and D3.