Residential Building & Renovation

Additional Dwelling Units (ADU)

ADU Team
For ADU questions related to buildings containing up to 2 dwelling units & including Detached ADUs
Additional Dwelling Unit Team
Call 905-546-2424 ext. 5117
Email [email protected]

ADU - Zoning
For any zoning questions related to Additional Dwelling Units
Call 905-546-2424 ext. 2719
Email: [email protected]

For Multi-Residential Building Permit Questions
For general building permit questions related to buildings containing 3 or 4 dwelling units.
Building Engineering
71 Main St W, 3rd Floor
Call 905-546-2424 ext. 4217
Email [email protected]

For Multi-Residential Zoning Questions
For general zoning questions related to buildings containing 3 or more dwelling units
Planning Division
City Hall, 5th Floor
Call 905-546-2424 ext. 2719
Email [email protected]

For Building Permit Questions
Building Division
City Hall, 3rd Floor
Call 905-546-2720
Email [email protected]

For General Building Inspection Questions
Building Inspections
Call 905-546-2424 ext. 7777
Email [email protected]

Sketch of Additional Dwelling Unit (ADU)

In May 2021, amendments were made to the City's Zoning By-laws to permit Additional Dwelling Units (ADUs) in Hamilton.

We have a dedicated Additional Dwelling Unit Team to review and issue ADU building permits for existing single family dwellings including up to two internal units & one detached unit.

Building Engineering will continue to review multi-residential permits.

What is an Additional Dwelling Unit?

An Additional Dwelling Unit (ADU) is type of residential unit. It is a separate self-contained unit located on the property of a principal (main) dwelling. The unit may be created within, added to, or detached from the principal dwelling. It is also referred to as a Secondary Dwelling Unit (SDU) within Zoning By-law documents. The Ontario Building code defines an additional dwelling unit as a secondary suite and is permitted on a single real estate entity (municipal lot).

According to the newly in effect Municipal Addressing By-Law, it will be a requirement to apply for a municipal address and post the address/unit number(s). To apply for a municipal address, visit Municipal Addressing. Additional fees apply.

Internal ADU

An internal Additional Dwelling Unit (ADU) is a conversion of interior space within an existing dwelling or through a new addition to an existing dwelling to provide one (1) additional dwelling unit to a maximum of four (4) dwelling units in some zones. A new detached dwelling can also be purpose-built to include an internal additional dwelling unit.

Diagram showing principal residential dwelling with additional dwelling unit in basement

Example 1: A basement in an existing dwelling to be converted into a separate residential unit (ADU).

Diagram showing principal residential dwelling with new addition with additional dwelling unit in basement

Example 2: A new addition constructed to an existing dwelling for the purpose of a separate residential unit (ADU).

Diagram showing principal residential dwelling with additional dwelling unit on top floor of dwelling

Example 3: A new house including a layout for a separate self-contained unit within the same building.

Diagram showing principal residential dwelling with dwelling units on each floor

Example 4: A single detached dwelling with two (2) new additional dwelling units for a total of three (3) dwelling units. This is multi-residential and will be reviewed by Building Engineering staff.

Diagram showing principal dwelling with dwelling unit and first and bottom floor and 2 dwelling units on main floor

Example 5: A two family dwelling with two (2) new additional dwelling units for a total of four (4) dwelling units. This is multi-residential and will be reviewed by Building Engineering staff.

Detached ADU (D-ADU)

A detached Additional Dwelling Unit (ADU) is a self-contained dwelling unit that is separate from the main dwelling on a lot. It may be newly constructed or created by converting an existing accessory building.

Residential dwelling with detached additional dwelling unit

Example 6: A detached garage in the rear yard of a dwelling to be converted into a self-contained residential unit. A new detached building containing a smaller self-contained residential unit on the same property as an existing dwelling.

Diagram showing principal residential dwelling with additional dwelling unit on top floor of dwelling and additional dwelling as separate unit.

Example 7: More than one ADU permitted on a property. A detached garage in the rear yard of a dwelling to be converted into a self-contained residential unit (Detached ADU) and an additional dwelling unit is constructed on the second floor of the principal dwelling (ADU).

To determine if a property is eligible for an Additional Dwelling Unit, look up the address using the Interactive Zoning Mapping. Refer to the appropriate section of the current Zoning By-Law for Secondary/Additional Dwelling unit regulations.

Note: There may be additional information such as site specific information, Conservation Authority, Heritage, Ministry of Transportation or other approvals required for a property. Contact the Zoning Section for further information.

A Detached ADU can be located in the rear yard or interior side yard of a property. These diagrams illustrate possible layouts of a Detached ADU on a lot, based on the requirements of the Zoning By-law. Refer to the Zoning By-law for the full set of regulations that apply to Detached ADUs.

D-ADU Interior Lot - Rear(File, 21.35 KB)

Detached ADU in the rear yard behind the primary residence on an interior lot

D-ADU Interior Lot - Side(File, 76.38 KB)

ADU in side yard, beside primary residence on an interior lot

D-ADU - Corner Lot(File, 75 KB)

ADU in the back yard of a primary residence with separate street entrance.

Note: All lots may not be able to accommodate a Detached ADU due to Ontario Building Code and Zoning By-Law requirements. Refer to the Secondary Dwelling Unit By-Law for the complete requirements of Detached - Additional Dwelling Units.

If the proposed ADU design does not conform to the Zoning By-law then an application can be made for a minor variance. If approved, a minor variance can grant permission for alternative provisions relating to the land, building or its use.

Note: Zoning inquiries related to multi-residential buildings containing three and four units can be directed to the Planning Division.

Contact: [email protected], Call 905-546-2424 ext. 2719

The process of building and renovating in established neighbourhoods is called ‘residential infill’. Residential infill developments may impact grading and drainage in the immediate and adjacent areas. To help mitigate impacts, the Building Division requires a professional grading design to be submitted for certain residential projects, including some additions and detached ADUs. Learn more about residential infill to determine if a grading plan is required for your ADU project.

Residential Infill Notice

Refer to the Good Neighbour Guide for the information notice required for detached additional dwelling units and large additions. This guide also provides requirements and best practices for residential infill construction, as well as communication tips to help everyone involved move smoothly through the project.

Apply Online for a Building Permit

Applications can now be submitted online by property owner, or agent acting on behalf of the owner.

If this is your first time applying online with the City of Hamilton, you’ll need to complete two simple steps.

Step 1: Create a City of Hamilton Account (my.hamilton.ca)

You will need to create an account at my.hamilton.ca/

This is the City’s centralized access point that allows you to easily view, access, and submit a wide range of City services using one account.
Once your City account is created, you can sign in anytime to manage your services online.

Step 2: Access the Customer Portal

After signing in to my.hamilton.ca, select the Building Permits category to create your Customer Portal account.
Once you are setup on the Customer Portal, navigate to Getting Started and select Permitting & Inspections to apply, for a Building Permit and follow the steps.

Need Help?

For assistance with my.hamilton.ca and login troubleshooting visit My.hamilton Portal FAQs
For assistance with applying, visit Planning, Permitting, Licensing & By-Law System

If you already have:

a my.hamilton.ca account, and
a Customer Portal account,

Visit my.hamilton.ca/ and select the Building Permits category. Navigate to Getting Started and select Permitting & Inspections. Select an action and follow the steps.

Need Help?

For assistance with my.hamilton.ca and login troubleshooting visit My.hamilton Portal FAQs
For assistance with applying, visit Planning, Permitting, Licensing & By-Law System

Drawings & Specifications

Fees

Applicable Law

Frequently Asked Questions (FAQs)

Can I do my own drawings?

As the owner, you may design your own project and produce your own drawings. Libraries and home improvement stores carry books with standard details that can be referenced when creating drawings. Discuss your project with material suppliers to establish costs, sizes and spans. Sample drawings can also be obtained from the Building Division to illustrate the quality of submission necessary for a permit application.

Delays in the issuance of your permit can arise if your drawing and specification submissions are not complete or do not conform to the Ontario Building Code and/or Zoning By-law.

If you are not familiar with various government regulations, by-laws and Ontario Building Code requirements, you may consider hiring a qualified designer. For more information, see Hiring a Designer For Building Permit Drawings.

You will need to provide architectural drawings, specifications, details and any other relevant information as per proposed ADU to be reviewed for permit application.

For details on what is to be included with a building permit submission for an ADU, see the ADU Checklist(PDF, 1.21 MB) and refer to specific type of ADU.

Ontario Building Code Requirements

The Ontario Building Code sets out minimum construction standards for how to build an additional dwelling unit. These minimum standards can include but are not limited to these considerations:

Age of the House - Different Building Code rules apply depending on the age of the house.
Water Service - Depending on the number of fixture units serving the buildings on the property, the water service line on the private and/or public side may need to be increased.
Location of the Additional Dwelling Unit -An additional dwelling unit can be built in any part of the house. It can be all on one floor, or on multiple levels. Most additional dwelling units are built in the basement or attic. Building Code rules can vary depending on where the additional dwelling unit is located in the house.
Room Sizes and Floor Area - The Building Code sets out minimum room sizes in additional dwelling units. Room sizes vary depending on whether rooms are separated by walls or the unit is open concept.
Ceiling Heights - Minimum ceiling heights in all rooms. Ceiling height requirements for additional dwelling units vary in different parts of the house, such as in the basement or attic.
Windows - Windows are required in an additional dwelling unit. Window sizes are also based on what type of room they are in.
Exits - The additional dwelling unit needs safe exits. The requirements for exits depend on where in the house the additional dwelling unit is located. Proposed means of egress to be clearly indicated.
Plumbing - At minimum the additional dwelling unit will need these plumbing requirements: hot and cold water supply, sink, bathtub or shower, toilet, kitchen sink and access to laundry facilities, which may be in a shared laundry room or a separate laundry area in the additional dwelling unit.
Smoke Alarms - The additional dwelling unit will need smoke alarms that meet the CAN/ULC S531 performance standard. A label on the alarm will indicate whether it meets this standard. Smoke alarms must be connected to an electrical circuit, interconnected with all other smoke alarms in the dwelling unit and have a flashing light when activated.
Carbon Monoxide Detectors - In addition to smoke alarms, carbon monoxide detectors are required in a home with a furnace that uses natural gas, propane, or other similar fuels. They are also required in homes with an attached garage. Carbon monoxide detectors can be either electrically powered or battery operated and be interconnected.
Heating and Ventilation - The Ontario Building Code allows a house with an additional dwelling unit to have a single furnace and common system of air ducts. For fire safety, a special type of smoke detector in the main supply or return air ducts must be installed. When activated, this device turns off the fuel supply and electrical power to the furnace, causing it to shut down and preventing the spread of smoke from one unit to the other. For newer homes recirculation of return-air is not permitted and two separate HVAC systems may be required to serve each dwelling unit.
Fire Separations - Fire separations are required between the internal additional dwelling unit and the rest of the house. Fire separations act as a physical barrier to slow the spread of fire from one part of the house to the other dwelling unit. Sound Transmission Class (STC) ratings may also be required in the wall and floor assemblies in a new house.
Septic Systems - Adding an additional dwelling unit to a house served by a septic system is permitted as long as the septic system has the capacity to handle the increase in sewage. Otherwise, a separate building permit may be required to upgrade the system or install a separate septic system to serve the ADU.

Water Service - Depending on the number of fixture units serving the buildings on the property, the water service line on the private and/or public side may need to be increased and necessary upgrades are to be carried out with the Hamilton Water / Wastewater Department. An extension of servicing from the primary dwelling unit is permitted. Separate servicing for a D-ADU is not permitted.
Fire Department Access - An unobstructed path of travel with a minimum 1.0 metre width and minimum 2.1 metre vertical clearance is required from the public street to the entry of the detached additional dwelling unit. City laneways are not permitted to provide fire department access.
Footings and Foundations - The Building Code has detailed requirements for footings and foundations.
Room Sizes and Floor Area - The Building Code sets out minimum room sizes in additional dwelling units. Room sizes vary depending on whether rooms are separated by walls or the unit is open concept.
Ceiling Heights - Minimum ceiling heights are required in an additional dwelling unit.
Windows - Windows are required in the additional dwelling unit. Window sizes are also based on what type of room they are in. The Building Code regulates the maximum amount of windows permitted in a wall in relation to the distance to the property lines and existing buildings.
Exits - The detached additional dwelling unit requires an exit door that is direct to the exterior and part of the required fire department access.
Plumbing - At minimum the additional dwelling unit will need these plumbing requirements: hot and cold water supply, sink, bathtub or shower, toilet, kitchen sink and access to laundry facilities.
Smoke Alarms -The additional dwelling unit will need smoke alarms that meet the CAN/ULC S531 performance standard. A label on the alarm will indicate whether it meets this standard. Smoke alarms must be connected to an electrical circuit, interconnected with all other smoke alarms in the dwelling unit, and have a flashing light when activated.
Carbon Monoxide Detectors - In addition to smoke alarms, carbon monoxide detectors are required if the additional dwelling unit has a furnace that uses natural gas, propane, or other similar fuels. ;They are also required if the detached additional dwelling incorporates a garage. Carbon monoxide detectors must be connected to an electrical circuit and shall be interconnected.
Heating and Ventilation - The additional dwelling unit is required to have heating and ventilation that conforms with the Building Code. An HVAC design package by a qualified professional is to be submitted for review for a new dwelling unit.

Building Permit Fees

Building permit fees are payable online through the City’s application portal. A building permit application is not considered accepted until full payment has been received by the City of Hamilton.

Development Charges

An Additional Dwelling Unit may be subject to Parkland and Development charges.

All applicable fees are to be determined by the plan reviewer and Financial Team during permit application review.

A Zoning Compliance Review under Applicable Law may be required in support of a building permit application for new construction of Single Detached Dwellings located in the ER zone of the former Ancaster Zoning By-law 87-57 or for new construction along the Hamilton Beach strip of the former Hamilton Zoning By-law 6593, including new Detached Secondary Dwelling Units. Where required, a final conforming Zoning Compliance report is to be submitted at the time of building permit application.

For further information regarding the Zoning Compliance Review process, please call 905-546-2424 ext. 2719 or by email at [email protected].

Common Applicable Laws

Is the Property Designated Heritage? A Heritage Permit is required for properties designated Heritage, or properties located within the boundaries of a Heritage Conservation District. Check the City’s Cultural Heritage Resource Mapping to determine if the subject property is designated.

Is the Property on Conservation Authority or Niagara Escarpment Commission Lands? Development approval is required for lands within the conservation authorities. Visit the applicable conservation authority webpage below to determine if conservation approval is required.

Hamilton Conservation Authority 905-525-2181
Conservation Halton 905-336-1158
Grand River Conservation Authority 519-621-2761
Niagara Peninsula Conservation Authority 905-788-3135

The Niagara Escarpment Commission (NEC) is an agency with a mandate to maintain and enhance the vitality of Ontario’s Niagara Escarpment. Development approval is required for lands within NEC jurisdiction. Visit escarpment.org/planning/ to determine if the subject property is within the NEC. Contact the Niagara Escarpment Commission: 905-877-5191.

View full list of Applicable Laws

Apply through the Property Records Search - request service available at City Hall.

As per amended Secondary Dwelling Unit By-Laws, additional parking spaces for up to 3 units are now exempt from providing additional parking spaces. Additional review is required to determine compliance for newer buildings and the relative date of the passing of the by-law.

This is determined by the Zoning By-Law and its permitted uses. To check which Zoning By-Law you can use the Interactive Zoning mapping, enter the address and click on the property to see the link to the Zoning By-Law.

The applicable zoning by-law will assist with the design in determining required setback dimensions to the property lines, building height restriction, ground floor area (footprint) and gross floor area (habitable area) based on the size of the existing principal (main) dwelling unit, etc. as well as considerations for the occupant(s) of the dwelling unit. The design must also include all requirements for a dwelling unit as per the Ontario Building Code which may also help determine the size of the overall building.

A detached ADU is permitted within some rural zones of the City of Hamilton Zoning By-laws. Please contact the Zoning Section at [email protected] for further information.

All contractors must have a valid Trade and Contractor License to operate in Hamilton. Visit our Open Data page to view a list of Licensed Contractors.

The City of Hamilton only permits servicing connected through the principal dwelling.

When proposing an Additional Dwelling Unit (ADU) additional plumbing fixtures will likely be added for a self-contained dwelling unit which includes a full kitchen, bathroom and laundry facility. Depending on the proposal the existing water service may not be adequate to service the total number of plumbing fixtures. A water service upgrade to a larger pipe size and larger water meter may be required. Also, depending on the material of the existing water pipe (i.e. lead), a replacement may be required. An ADU must have adequate servicing approved prior to issuance of the building permit.

Yes. The total hydraulic load is required to be determined due to additional plumbing that is required for an ADU. This information is to be completed and submitted for review.

Water pipe sizing form for more than one dwelling unit (combined servicing)(PDF, 176.29 KB)(PDF, 176.29 KB)

Yes. New home construction warranty also applies to new Detached Additional Dwelling Units (D-ADUs). Details are to be included in Section F of the application form. If owner built, the owner details must be completed in Section E - Builder section.

Apply for building permit in the normal manner with the Building Division. With your application form include the Fire Order Number for reference in the description of work. Submit a copy of the Fire Order and architectural drawings reviewed, approved and stamped by the Fire Department.

To learn more, visit Municipal Addressing.

Date modified

July 07, 2026