Ontario ADU regulations and rules

On November 28th, 2022, the Government of Ontario passed Bill 23, the More Homes Built Faster Act. This Bill allows for homeowners to build a secondary unit on their property within certain areas of Ontario. If you’re considering building an additional structure, make sure to review the following regulations beforehand.

What is a secondary unit?

A second unit is a type of dwelling unit with its own private kitchen, washroom and sleeping areas. These units can be found in your house, an extension of your property or above a garage. However, there can be some different rules that apply depending on which option you go with. Adding a secondary unit is another way to bring in extra income to help pay off your mortgage or provide space for family and guests.

prefab guest house

Things to do before building a second unit or ADU

Before moving forward with any construction, you must speak with your local municipality and building departments about any permits and regulations you need to follow. Based on the information you provide about your property, they can tell whether you can proceed with your plans. A few factors you should consider include:

Acquiring the right building permits
Designing and providing plans to the municipality
Staying up to code
Passing the zoning requirements
Getting the correct inspections during construction

Unless you have a background in design or architecture, we recommend hiring a qualified professional to help with the plans. Your contractors or architect can act as your representative when you meet with the Ontario government for approval. They can also help you with any additional questions, approvals, building permits and construction inspections.

prefab home

Municipal zoning and bylaws

Before beginning construction, ask your local municipality about the following:

Zoning requirements for your secondary unit. This includes parking, entrances and exits, proximity to fire hydrants and fire safety, and minimum or maximum unit sizes
Applying for rezoning or minor variance
Reviewing if your second unit needs to be licensed or registered to your local municipality or town

Building code requirements for secondary units

Ontario’s Building Code has minimum construction requirements for how to build a second unit in your current residence. Building above the minimum provides homeowners with more advantages including more occupants and extra comfort. However, we listed out the minimum requirements for the different aspects of a second unit below:

Room sizes and flooring

The Building Code has set standards for the room sizes in ADUs and secondary units. Room sizes can vary depending on whether they’re separated by walls or if the unit has an open concept design. The general minimum measurements for room sizes are as follows:

Living room area	13.5m2
Dining room	7m2
Kitchen	4.2m2
Combined living, dining & kitchen in one bedroom unit	11m2
Master bedroom (without closet)	9.8m2
Extra bedrooms (without closets)	7m2
Bathroom
Combined living, dining, sleeping and kitchen	13.5m2

Ceiling measurements

For second unit ceilings, you will also need to be aware of the minimum measurements. If you’re building another unit in your house, that can be more challenging. If you’re building above a garage or creating a separate ADU structure, you have more space to play with.

Window measurements

Windows are mandatory for any additional unit. The size of windows you need is determined by the actual size of the unit itself. The larger the unit, the larger windows you require. It’s important to note that some widows can also be used as another way to exit a secondary unit. Here are a few minimum window sizes to keep in mind:

Living and dining room	5% of the floor area
Bedroom	2.5% of the floor area
Bathroom, kitchen and extra space	Windows are not required

Plumbing measurements

Your ADU or second unit must have its own plumbing. The minimum water requirements you will need are:

Hot and cold water
Kitchen and bathroom sinks
Laundry facilities
Shower, toilet and bathroom sink

Heating and air conditioning

The Building Code allows a second unit to have a single furnace and air duct system. For fire safety purposes, you will need a specific type of smoke detector in the main supply. When this device is activated, it turns off the fuel supply and electrical power. This prevents the spread of smoke from the main residence to the second.

Doors and exits

Your secondary unit needs safe exits and doors. Depending on the dimensions of your ADU, there are different rules. Should your main residence and second unit connect, both structures will need a second means of escape. For example, in cases where one unit leads to another, you will need to install a window that a person can fit through.