This page outlines what ARUs are, where they’re allowed, and how you can plan and apply for one. It includes zoning and building requirements, application steps, and helpful resources to guide you through the process.

↓ What is an ARU?

↓ Why ARUs are Encouraged in Milton

↓ Types of ARUs and Eligibility

↓ Zoning and Building Requirements

↓ Building Permit Requirements

↓ Registration Requirements

↓ ARU Approval Process

↓ Frequently Asked Questions

 

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

All existing and new ARUs must be registered with the Town to ensure compliance with the Ontario Building Code and Town Zoning By-laws, are legal and are identifiable for emergency services.

Residents must register their ARU in person at Town Hall or online. A one-time registration fee of $340 per ARU will be required. If registering in-person at Town Hall, please visit the Community Services Desk on the main level.  

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.

Register your ARU

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 existing ARU.

Frequently Asked Questions

What is the definition of an ARU?
An ARU is a self-contained dwelling unit, with its own kitchen, sleeping and bathroom facilities, located on a lot containing a detached house, semi-detached house, or townhouse. ARUs are also referred to as additional dwelling units, secondary suites, accessory units, basement apartments, coach houses, laneway houses, garden suites, tiny homes, granny flats, in-law apartments or nanny suites.

Why do ARUs need to be registered? 

The ARU registration system was established to ensure that all secondary and additional residential units in Milton are: 

  • Safe and legal 

  • Compliant with zoning by-laws 

  • Properly documented to support Fire and Rescue Services in an emergency response 

The registry plays a critical role in enhancing public safety, by-law compliance, and emergency response capabilities across Milton.  

Does it matter if the ARU is being used by a family member versus rented out?
All ARUs must be registered, regardless of whether they are being used by a family member or leased to another type of tenant. The registry helps to ensure the units are safe, legal, compliant with zoning by-laws, and properly documented to support Fire and Rescue services in the event of an emergency. 

What are the benefits of having an ARU Registry? 

The ARU registry offers several key benefits to the Town of Milton and its residents: 

  • Improved safety – Helps ensure ARUs are legal, safe, and suitable for living. Inspections reduce risks of fire, overcrowding, and unsafe conditions 

  • Faster emergency response – Registry data supports effective deployment of emergency services 

  • More affordable housing – Supports safe and legal expansion of housing supply 

  • Stronger enforcement – Helps the Town monitor and regulate ARUs, preventing unsafe living conditions  

What are the risks of not registering ARUs? 

Unregistered or unauthorized ARUs may pose significant safety risks, including fire hazards, inadequate exits, and overcrowding. Registry data allows the Town to: 

  • Identify the presence of ARUs during emergency response 

  • Verify ongoing safety and structural integrity

  • Ensure that ARUs do not contribute to illegal rooming houses or by-law violations

Do I need to register my existing ARU? 

Yes – As of April 1, 2025, all ARUs (existing and new) must be registered. You can register your ARU online or in person at Town Hall

How do I register my ARU? 

  • Property owners can apply online or in person at Town Hall 

  • Once an application is received, arrangements will be made for a property inspection 

  • Inspections will verify compliance with local zoning, property standards, and fire safety regulations 

  • A one-time registration fee of $340 per ARU is required to finalize registration  

I already paid for a building permit to construct my ARU, do I need to pay a separate ARU registration fee as well? 

Yes – Building permit fees support the work of the Building Division during construction. ARU registration fees support ongoing enforcement, public safety, and emergency response readiness.

Building permits and the ARU registry serve different functions at different stages, and both fees are required to support their respective services. This cost recovery model ensures the Town can sustainably manage the ARU program without impacting the general tax base.

There is a clear distinction between the two fees:

Building permits

  • Applied for during construction or renovation

  • Governed by the Ontario Building Code

  • Inspections are conducted by Building Inspectors to verify Ontario Building Code compliance during and immediately after construction

ARU registration

  • Focus on post-construction safety and ongoing compliance

  • Inspections conducted by Fire Prevention and Municipal Law Enforcement Officers

What is the Town looking for during an ARU registry inspection? 

The Town will verify the following:

  • No unauthorized modifications after construction

  • Safe and accessible entry/exit points

  • Proper house numbering for emergency response

  • Continued suitability of the unit for residential occupancy  

Why does the ARU registry cost $340? 

The ARU registry is a user-funded program. As part of the 2025 Budget, an ARU Compliance Program was established for a three-year pilot term. The registry fee is based on a cost recovery model to ensure the Town can sustainably manage the ARU program without impacting the general tax base. The fee is aligned with what other municipalities charge for similar services and was approved by Milton Town Council on March 17, 2025. The fee will be subject to annual increases based on the Town’s annual municipal price index.

The registration fee directly funds:

  • Additional staffing to support compliance inspections by Municipal Law Enforcement and Fire Prevention staff

  • Administration of the registry, including recordkeeping and coordination

  • Follow-up enforcement actions where needed

I know of an unregistered ARU (or an ‘illegal basement apartment’) – should I report it?  
Yes – please contact the Municipal By-law Enforcement team to report an unregistered ARU. You can reach the team by calling 905-878-7252 ext 2137 or by filling out this contact form on our website. ARU registration helps to ensure the units are safe, legal, compliant with zoning by-laws, and properly documented to support Fire and Rescue services in the event of an emergency. Town staff will help the homeowner understand the rules around ARUs and work with them to achieve compliance.

How do I report a concern?  Will it remain confidential will the homeowner be told who brought the complaint to the Town?

You can report a concern to the Town’s Municipal By-law Enforcement team to investigate. You can reach the team by calling 905-878-7252 ext 2137 or by filling out this contact form on our website. By-law Enforcement Officers do not disclose the identity of the complainant during the investigation of a complaint.