Building more units on your property

If you own a detached, semi-detached or town house, you can build up to two additional residential units or a fourplex on your property, depending on the size of your lot. These units are self-contained living spaces that have cooking, sleeping and washroom facilities. Zoning approvals, permit fees and charges depend on which type of unit or units you intend to build.

Additional residential units

Additional residential units are second and third units on a residential property. They can be within the primary home, also known as attached units, or in a detached building. Please note: only one detached unit is permitted on a single lot.

Three examples of attached and detached additional residential units: a home with a basement apartment and separate units on the first and second floors; a home with an attached side unit and an attached rear unit; and a home with an attached garage conversion and a detached garden suite in the backyard.

The most cost-effective way to add units to your lot is by converting living space within your existing home. Ways to add attached units include:

  • Basement apartments, in-law suites and nanny suites
  • Attached garage conversions
  • Second floor conversions
  • Rear or side additions to accommodate new units
  • A new build with up to three units

For zoning regulations that apply to your property, use the property information tool.

If you have enough space on your lot, you may be able to build an additional unit in a separate building. Units that don’t share any walls with the primary home are referred to as detached additional residential units but are often called garden suites, coach houses, tiny homes or laneway suites. They can be one or two storeys, depending on the size and type of your lot.

Building a garden suite can cost more than adding a unit within the primary home, where connections to electrical and plumbing already exist. Some things to consider before getting started include:

  • Creating separate street addresses for each unit
  • Staying within maximum building heights and sizes
  • Limiting distance and area of window openings
  • Maintaining setback distance between the additional unit and property lines
  • Ensuring fire emergency access, with a maximum distance of 45 metres from the street to the front door, and a minimum width of 1.2 metres
  • Sharing or creating separate connections to municipal water and wastewater
  • Connecting new electrical and natural gas services

For detailed requirements, read the zoning regulations for detached ARUs.


A fourplex is a single low-rise residential building containing four separate units. You can’t build an additional residential unit on lot that has a fourplex. Different regulations apply based on whether the fourplex is converted from the existing home or a new build.

Fourplex conversions are low-rise residential buildings that have been remodelled to accommodate four separate units. In this case, all four units must fit within the building footprint of the home that existed as of December 6, 2023. Additions can’t be built to accommodate four units. For more information, review the fourplex by‑law.

A purpose-built fourplex is a new residential building that’s designed and built to accommodate four separate units. These fourplexes are subject to new zoning regulations, which provide more flexibility than conversions. That includes additional height, reduced setbacks and increased lot coverage. For more information, review the fourplex by‑law.

Submitting your permit application

You need a building permit to add units to your property. The City requires drawings of your proposal so we can determine if what you’re building is safe and complies with the Zoning By‑law, the Ontario Building Code, and any other applicable law. Work with a qualified designer to make sure your project meets regulations.

Required drawings and documents for your building permit application can include:

There may be additional submission requirements, depending on the type of unit you’re building.

Permit fees and charges

There’s a non-refundable $20 deposit to submit your permit request online. We’ll deduct this amount from the total cost of your permit. Total permit fees depend on the size and type of unit you’re building and will be calculated once we pre-screen your request. To find out how much a building permit costs, refer to the fee schedule.

Fourplexes are also subject to development charges, which must be paid before we can issue your permit.

Permit processing times

If your application is complete, the first review may take 15 business days. Applications that must be resubmitted may result in delays of two weeks or more.

For more information, refer to the times for processing and issuing a permit.

Contact us

If you have questions about building more units, call 311 (905-615-4311 outside City limits).