Accessory Dwelling Units in Mississauga - Design, Permits, Construction

Mississauga's ARU by-law caps accessory structures at 10% rear-yard coverage, which on a typical Erin Mills lot works out to roughly 645 sq ft - enough for a two-bedroom garden suite but not for the three-bedroom units clients often ask about first. We size the concept to that percentage before drawing anything. Mississauga permits additional residential units under its 2022 ARU by-law - up to two units in the main dwelling plus one in an accessory structure, subject to a maximum 10% rear-yard coverage.

Large 1970s-90s subdivision lots with attached garages; garage conversions and rear coach houses are both common outcomes.

Four physical forms are available on a Mississauga lot - detached garden suite or laneway house, an internal basement or upper-floor suite, a garage conversion, and a factory-built module - and the lot itself, not preference, usually decides which two are realistic. We run a feasibility overlay on the parcel first - zoning envelope, servicing capacity, rear-yard access - and only then price the two forms that survive it. Bill 23 permits up to three residential units as-of-right on most serviced Mississauga lots, which removes the rezoning application from the default path.