Using the model of a Just City the goal of this paper is to contribute to the discussion of additional dwelling units (ADUs) by connecting disparate literature on ADUs in North America to the body of spatial justice and posit a way forward that recognizes the drawbacks of a system of individual property ownership, while hypothesizing that more equitable outcomes could be achieved through the inclusion of ADUs within the private market system through government regulation. This paper argues that through the lens of equity, democracy, and diversity, ADUs have the potential to lead to more just outcomes within a privatized market housing system, where homeownership is both the dominant tenure and ideology. Accounting for the inequities of informal ADUs and the contradictions within a capitalist, financialised housing system, new pathways are conceived to both encourage and regulate the ADUs to ensure security of tenure and protection against market pressures.

This paper analyzes the spatial potential of detached additional dwelling units (ADUs) in Windsor, Ontario. A new GIS model, which integrates various geoprocessing commands in ArcGIS 10.8.1, is developed to calculate whether the minimum allowable size of a detached ADU can fit within the total buildable area of a residential property, based on the setbacks, the lot coverage requirements, and other factors (such as parking and flood plain areas). The model uses publicly sourced data that were obtained from the City of Windsor's Open Data Portal. More specifically, individual residential parcels and associated building footprints along with street centerlines are used as inputs to the model. The outputs are then categorized into three types (suitable, potentially suitable, and not suitable) to demonstrate where detached ADUs can be built in compliance with the local zoning bylaws, on both an individual lot basis and at an aggregate level. The conducted analysis reveals the potential of existing residential neighbourhoods in a mid‐size city, and has many implications for homeowners, policymakers, and researchers with respect to increasing housing supply within current Canadian municipalities.