Ontario does not provide one blanket development-charge exemption for every accessory dwelling unit (ADU). The Development Charges Act, 1997 sets configuration-based tests for certain additional residential units and a separate exemption for qualifying affordable units. The statute uses “residential unit” and building-configuration terms; a local label such as ADU, garden suite, or secondary suite does not by itself establish that a project qualifies.

Configuration-based exemptions

For specified existing and new detached houses, semi-detached houses, and rowhouses, the Act describes exemptions for a second or third residential unit in the principal building, or one residential unit in an ancillary building. In outline, the tests include:

  • A second unit in the principal building where residential use other than ancillary residential use is permitted on the parcel and the ancillary buildings contain no more than one residential unit in total under the applicable existing- or new-building rule.
  • A third unit in the principal building where that non-ancillary residential use is permitted and no ancillary building or structure contains a residential unit.
  • One unit in an ancillary building where the principal building contains no more than two residential units and no other ancillary building contains a residential unit.

The Act states separate provisions for existing houses and new houses. The exact unit count, parcel permissions, and other ancillary structures matter, so these summaries are not a parcel-level eligibility decision. Check the current statutory text and ask the municipality how it applies the exemption to the proposed configuration.

Affordable-unit exemption

The Act also exempts the creation of a residential unit intended to remain affordable for at least 25 years from its first rental or sale. The municipality and the person who would otherwise owe the charge must enter an agreement requiring that period of affordability.

Ontario’s Affordable Residential Units for the Purposes of the Development Charges Act, 1997 Bulletin is effective July 1, 2026 until replaced. It sets market-based and income-based thresholds for different municipalities and unit types. For ownership housing, the purchase price is tested against the lower of an income-based price and 90% of the average purchase price for the same unit type in that municipality. For rental housing, the rent is tested against the lower of an income-based rent and the average market rent for that unit type. The bulletin also requires arm’s-length sale or rental. Check the current threshold data in Ontario’s Data Catalogue; a threshold from another municipality, unit type, or bulletin period may not apply.

What the exemption does not decide

The statute’s tests do not establish that a property is zoned for the proposed use, that the unit meets building requirements, or that the project is exempt from utility connection charges, permit fees, or every other municipal cost. Municipalities set development-charge by-laws and apply the relevant rules to the facts of a project. Confirm the current by-law, unit classification, charge calculation, required agreement, and any other fees with the authority before relying on an exemption.