Starting April 1, 2025, all new and existing Additional Residential Units (ARUs) must be registered with the Town. An online registration application will be available at that time. Please ensure your ARU is registered to remain compliant.

What is an ARU?

An Additional Residential Unit (ARU), also called an Additional Dwelling Unit (ADU), is a small, fully equipped living space on the same property as the main house. It can be inside the main house, like a basement apartment, or in a separate building on the lot. ARUs can be part of detached houses, semi-detached houses, semi-link houses, or townhouses in Milton.

Why ARUs are Encouraged in Milton

The Government of Ontario has updated the Planning Act to allow up to three residential units on an urban residential lot. This includes the main house and two ARUs.

ARUs help increase housing options and make homes more affordable. They allow property owners to create extra living spaces for renters or family members. This supports a range of housing needs, including affordable rental housing and multi-generational living.

In Milton, zoning rules allow up to three ARUs, meaning there can be a total of four residential units on one urban residential lot with a detached, semi-detached, semi-link, or townhouse property.

Types of ARUs and Eligibility

ARUs come in many forms, like basement apartments, converted garages, or small standalone units. However, to add an ARU, your property must be in an urban area with municipal water and sewer services.

ARUs are not allowed in the following property types:

  • Back-to-back townhouses
  • Stacked townhouses
  • Duplexes
  • Triplexes

ARUs are also not currently allowed in rural areas, but changes to the rules are being worked on. For more details, contact the Planning Department or call 905-878-7252 x2398.

Not every lot can have an ARU, even if the zoning allows it. The property must follow Milton’s Zoning By-law and Ontario Building Code rules. If your property is part of a condominium, check with your condo corporation to see if there are any restrictions on ARUs.

Zoning and Building Requirements

Milton’s zoning laws set rules for ARUs, like size, location, and parking. You can check these rules in the Zoning By-law on the Town’s website. If your ARU plan doesn’t meet these rules, you can apply for a “minor variance” to ask for an exception.

The following sections of Zoning By-law 016-2014, as amended, apply to ADUs:

  • Section 4.10 applies to all ADUs
  • Section 4.2.2.2 applies to detached garages containing an ADU
  • Section 4.2.5 applies to accessory buildings, other than detached garages, containing an ADU
  • Sections 4.3, 4.4, 4.5, and 4.6 contain regulations for decks, porches, balconies, and HVAC units for accessory buildings containing an ADU
  • Section 4.19.5 contains general encroachment regulations applicable to the principal building as well as specific regulations for accessory buildings containing an ADU
  • Section 5.6.2 contains general residential driveway regulations and minimum parking space size requirements for lots with ADUs
  • Section 5.8.1 Table 5E contains minimum parking space requirements for residential uses, including ADUs

If you’re unsure what rules apply, contact the Zoning Division or 905-878-7252 x2329.

Building Permit Requirements

You’ll need a building permit to build an ARU. Hiring a professional designer can help with the process.

Here’s what you’ll need to apply for a permit:

  • Application for a Permit to Construct or Demolish
  • Designer form (Schedule 1) if someone other than an architect or engineer designs the project
  • A site plan
  • Layouts of the current and proposed floors
  • Construction details for walls, ceilings, and fire safety
  • Drawings showing entrances and windows for the ARU

For more information, check the Government of Ontario’s guide on building a second unit in your home.

Registration Requirements

As of April 1, 2025, all new and existing ARUs must be registered with the Town. This ensures all local and provincial regulations are followed. An online registration application will be available on April 1.

When you register, a Municipal Law Enforcement Officer and a Fire Prevention Officer will inspect your property. They will check that it meets zoning rules, safety standards, and the Fire Prevention and Protection Act.

Milton’s ARU Approval Process

Legalize and register an existing ARU
Existing on or prior to July 14, 1994
Review by:
  • Zoning Division to confirm ARU complies with the Zoning By-law or other applicable land use legislation.
Inspections by:
  • Milton Fire and Rescue Services for compliance with the Ontario Fire Code Retrofit, S. 9.8.
  • Municipal Law Enforcement for compliance with Property Standards By-law.
Registration of ARU:
  • The ARU will be registered after zoning approval and after all of the required inspections are passed.
  • Compliance with Zoning By-law or other applicable land use legislation required.
  • Municipal Law Enforcement for compliance with Property Standards By-law.
 Existing after July 14, 1994 (*1)
Building Permit
  • Provisions of Ontario Building Code Part 9.41 & Part 11 permitted to be applied.
  • Compliance with Zoning By-law or other applicable land use legislation required.
Inspections by:
  • Building Services to confirm compliance with Ontario Building Code after building permit is issued.
  • Municipal Law Enforcement for compliance with Property Standards By-law.
  • Milton Fire and Rescue Services for compliance with Ontario Fire Code.
Registration of ARU:
  • The ARU will be registered after all required inspections have been passed.

 

 Construct and register a new ARU within an existing building

Existing Building more than 5 years old 
 Building Permit

  • Provisions of Ontario Building Code Part 9.41 & Part 11 permitted to be applied.

  • Compliance with the Zoning By-law is required.

Inspections by:

  • Building Services to confirm compliance with Ontario Building Code after building permit is issued.

  • Municipal Law Enforcement for compliance with Property Standards By-law.

  • Milton Fire and Rescue Services for compliance with Ontario Fire Code.
Registration of ARU:

  • The ARU will be registered after all required inspections have been passed.

 Existing Building 5 years old or less
Building Permit

  • Provisions of Ontario Building Code Part 9 & S. 9.41 will be applicable.

  • Compliance with the Zoning By-law is required.

Inspections by:

  • Building Services to confirm compliance with Ontario Building Code after building permit is issued.

  • Municipal Law Enforcement for compliance with Property Standards By-law.

  • Milton Fire and Rescue Services for compliance with Ontario Fire Code.
Registration of ARU:
  • The ARU will be registered after all required inspections have been passed.

 
 Construct and register a new ARU in a new building or addition containing an ARU
 Building Permit:
  • Provisions of Part 9 and/or any other applicable part(s) of the Ontario Building Code will be applied to new buildings and additions to existing buildings.
  • Compliance with the Zoning By-law is required.
Inspections by:
  • Building Services to confirm compliance with Ontario Building Code after building permit is issued.
  • Municipal Law Enforcement for compliance with Property Standards By-law.
  • Milton Fire and Rescue Services for compliance with Ontario Fire Code.
Registration of ARU:
The ARU will be registered after all required inspections have been passed.
(*1) A building permit is not required where it can be demonstrated to the satisfaction of the Town of Milton that a building permit has already been issued for the exisiting ARU.