Mississauga uses “additional residential unit” (ARU) for a self-contained second or third unit on a residential property. The City’s current guide says owners of detached, semi-detached, or town homes may build up to two ARUs, but unit form and townhouse ownership type affect the zoning screen.
Distinguish attached units from a garden suite
The City’s guide describes attached ARUs within the primary home and detached ARUs in a separate building called a garden suite. Only one garden suite is permitted on a single lot. A garden suite may be subject to location, access, height, size, setback, service, and other requirements; a broad ARU count does not show that a detached unit fits a particular parcel.
Check townhouse and condominium status
The City’s page says attached ARUs and garden suites are allowed in freehold or street townhouses on a public road in the RM5 zone and common-element condominiums in the RM6 zone. For those townhouse contexts, garden suites are limited to corner or through lots. The page states that standard condominium townhouses do not permit attached units or garden suites under the described rule. Where zoning does allow a unit, a condominium owner may still need board approval under the governing documents.
The City says it is reviewing standards to safely permit ARUs in all types of townhouse developments. Treat the online guidance as current only after checking the applicable by-law and property record, especially if the dwelling is a condominium or a rule is under review.
Check heritage and other approvals
For a designated or listed heritage property, the City says Heritage Advisory Committee review may be needed before the building-permit application or construction. A building permit and Ontario Building Code review remain separate from zoning permission. Use the City’s property information tool and confirm lot type, zone, heritage status, and condominium documents before relying on the screen.