An Additional Dwelling Unit (ADU) is a separate, self-contained dwelling unit that is subordinate or incidental to a principal dwelling unit on the same property. The dwelling unit usually contains cooking, eating, living, sleeping, and sanitary facilities, with private or shared laundry facilities. Access to the ADU can be from a private entrance or from a shared hallway or stairs. An ADU may be in the form of an Attached Accessory Dwelling Unit or a Detached Accessory Dwelling Unit.

Other common names for an ADU are accessory apartment, secondary suite, basement apartment, in-law suite, garden suite, granny suite, or coach house.

Applications for an Additional Dwelling Unit (ADU) building permit must have been submitted on or after July 2, 2025. Applications submitted before this date will not be accepted.

Applications that are eligible under the program will be accepted on an ongoing basis until funding has run out.

Homeowners in the Town may apply for a building permit to add up to three (3) ADUs to their detached dwelling, semi-detached dwelling, linked dwelling, street townhouse, or block townhouse, for a total of four (4) dwelling units per property.

Examples may include four (4) units in an existing dwelling; or three (3) units in an existing dwelling and one (1) Detached Accessory Dwelling Unit.

Approvals for ADUs are subject to the Zoning By-law, applicable law, and Ontario Building Code requirements.

ADUs cannot be built on hazardous lands, such as areas within the regulatory flood limits or erosion hazard limits. Please speak with your local Conservation Authority for more information. Limitations also apply to properties located in the Greenbelt Plan Area.

Central Lake Ontario Conservation Authority

Toronto and Region Conservation Authority

Don't know which conservation authority your property stands on? Please email buildingpermits@ajax.ca or call 905-619-2529 ext. 3652 for assistance.

If you cannot comply with the Zoning By-law, you can apply for a minor variance application, which is heard by the Town’s Committee of Adjustment. This five-member committee appointed by Ajax Council makes decisions on Minor Variance and Consent Applications. This process is approximately a two (2) month process from beginning to end. Building Permits can be reviewed during this period but cannot be issued until the Minor Variance Application is approved, and the statutory appeal period has ended.

Please contact Planning Services prior to applying for a Minor Variance application by phone at 905-619-2529, ext. 3631 or via email at planningservices@ajax.ca

To accommodate an ADU, the property must comply with the parking requirements:

• No additional parking space is required for the first ADU. One additional space per unit is required for the third and fourth ADU. This results in a ratio of one (1) parking space per unit as the primary existing dwelling (e.g., detached) requires a minimum of two (2) parking spaces.

• Tandem parking spaces are permitted. A tandem parking space is a parking space from which access to the adjacent public street or road, lane, or drive aisle is obstructed by the presence of an abutting parking space.

All ADU parking must be accommodated on the property, overnight street parking is prohibited. All general parking provisions established by the Town, which can be viewed here, apply to ADUs.

Yes! With the Build More, Get More Grant Program, ADU building permit applications have until March 1, 2027, to qualify and receive grant funding to support construction.  Click here to learn more.

ADUs on properties with municipal water and sewer services must be connected to these services through the existing house on the property. This will be reviewed through the building permit application. 

For ADUs on a private sewage system or well, homeowners should contact Durham Region’s Public Health Department at 1-800-841-2729 or by email, as a separate permit will be required.

Below grade entrances and uncovered steps are permitted in side yards if they meet the standards outlined in the Town’s Zoning By-law. 

• The following minimum setbacks are required: 

  • 0.0 metres from the front or exterior side yard lot line 

  • 1.8 metres from the rear yard lot line 

  • Interior setback: This varies based on property location - please contact Planning Services at 905-619-2529 ext. 3631 or buildingpermits@ajax.ca.

Residents in Ajax can build up to four units on one property, like basement apartments or small backyard houses.

Before they can start construction, however, homeowners must get approval for their new unit(s), including determining if their property has enough space for parking.

In 2020, the Town updated its rules to help with parking. Now, it’s okay to park on the paved part of your driveway, even the area between the road and the sidewalk.

You can learn more about parking rules in the Town’s brochure: AMPS-and-Traffic-Parking-Brochure---Updated-Jul-31-2024.pdf

Canada Post would ensure that either a mailbox is provided at the existing Community Mailbox, or a separate mailbox would be created for the ADU.

If the area is currently served via door-to-door mailboxes, a mailbox for the ADU would need to be supplied by the homeowner.