Additional Dwelling Units (ADU)

• 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.
• 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 also 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.
• 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.
• 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
• 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.

• 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.
• 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.
• 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.
• 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.

Apply through the Property Records Search - request service online.

As per amended Secondary Dwelling Unit By-Laws, additional parking spaces for up to 3 units are now exempt from providing additional parking spaces.

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.

There is not a specific size outlined in the By-Law. The overall design may be determined as per the Zoning By-Law, Secondary Dwelling By-Law and Ontario Building Code requirements. A designer may start by reviewing the Secondary Dwelling Unit By-Law which indicates setback dimensions, height restriction, area based on the size of the primary dwelling unit, etc. as well as considerations for the occupant(s) which may assist in the overall design for the ADU.

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.

There are two servicing options available for Detached Additional Dwelling units (D-ADUs).

1. You may extend servicing through the existing primary dwelling which will include combined total plumbing fixtures for both primary dwelling and D-ADU. We will request basic floor plans of the primary dwelling unit indicating all rooms/plumbing fixtures to confirm the total. Where an upgrade in water pipe size is required then a separate building permit application will be requested. This is determined at time of permit review.
2. You may apply for provide separate servicing to a D-ADU. This will require a Road Cut permit through Growth Management. You can contact their department at [email protected] or 905-546-2424 ext. 5539 for further assistance.

You will need to also apply for a separate water/sewer line permit for the new connection and only the total fixtures for the D-ADU will be required.

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 forms available:

• Water pipe sizing form for more than one dwelling unit (combined servicing)(PDF, 176.29 KB)
• Water pipe sizing form for one dwelling unit (separate servicing)(PDF, 154.92 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.