Additional Residential Units

An Additional Residential Unit (ARU) is a self-contained dwelling unit located within the same building, or on the same lot, as an existing residential unit. Self-contained means that it has its own kitchen and washroom facilities, and a separate entrance.

London is encouraging this form of residential development to improve housing diversity, affordability and sustainable land use. 

Financial incentives available! 

NEW! Limited-time incentives available.
Learn more about financial incentive programs and eligibility criteria. 

Types of ARUs

ARUs can be located within the interior of the existing house (for example in the basement), in an existing garage, as an addition to an existing building, or by constructing a detached tiny home on the property.  

There are four (4) main types of ARUs:  

visual showing 4 main types of ARUs including: Interior/Basement conversion, converted garage, detached ARU, and addition to existing building.

Two ARU designs available in the CMHC Design Catalogue

The City of London now supports use of all the Ontario region designs from the Canada Mortgage and Housing Corporation (CMHC) Housing Design Catalogue.  

The Additional Residential Units (ARU) types will work in many different zones in London, but please note that not all housing types are permitted on every lot.  Zoning regulations such as setbacks, minimum lot width, maximum lot coverage, parking, and driveway widths will apply. 

The catalogue helps homeowners and small builders construct housing more quickly and cost-effectively.

How It Works

  1. Choose a design from the CMHC Housing Design Catalogue
  2. Work with a qualified professional to prepare your lot-specific drawings. Catalogue designs are “near permit-ready” and must be adapted to your specific lot. You will need a qualified professional (e.g., licensed designer with BCIN, architect, or engineer where required) to:
    1. Prepare a site plan and confirm zoning compliance
    2. Design foundations and grading
    3. Complete servicing details and energy selections
    4. Finalize material and finish selections
  3. Submit a complete building permit application
  4. Receive review within 10 business days

Step-by-step planning guide:   

1. Determine ARU type

Each ARU type has different requirements, and the information needed for a building permit is different. 

There are four (4) main types of ARUs including: 

  1. interior/basement conversion
  2. converted garage
  3. detached
  4. addition to existing building
2. Zoning compliance

Zoning review is completed by the City as part of the building permit process, but zoning regulations may impact the type of ARU you can create on your property. 

ARUs are permitted when the zoning allows for single detached, semi-detached, duplex, triplex, converted or street townhouse dwellings, to a maximum of four (4) total dwelling units.

How to find your property's zoning

Additional requirements for detached ARUs 
If you are proposing a detached ARU, it must follow the Accessory Building regulations outlined in Section 4 of the Zoning By-law, including Section 4.1 – Accessory Uses and Section 4.37 – Additional Residential Units.

Please note: Certain zoning regulations related to ARUs are temporarily superseded by the Council-approved Interim Control By-law CP-1600-300, which introduces additional restrictions that apply while the by-law is in effect.

To confirm permitted uses and zoning regulations visit our zoning webpages, call 519-930-3510 or email zoning@london.ca 

What if my property does not meet zoning regulations? 
If your property or project does not meet the requirements of the zoning by-law you may apply for a minor variance or a zoning by-law amendment to change the regulations if you cannot change your project plans. 

Planning staff will review your project to determine if a minor variance is appropriate, or if the proposal requires a full by-law amendment. Learn more about planning and development applications. 

Important requirements when planning your ARU: 

Key regulations 

  • Under the Council-approved Interim Control By-law CP-1600-300, an Additional Residential Unit (ARU) cannot exceed 80% of the gross floor area of the primary dwelling.
  • ARUs are permitted on the same lot as a single detached, semi-detached, duplex, triplex, converted or street townhouse dwellings.
  • A maximum of three (3) ARUs are permitted per lot. Two (2) of the additional residential units can be in a detached building.
  • No additional parking is required for ARUs. Additional driveways to serve an ARU are not permitted.
  • Detached ARUs can only be in the rear or interior side yard. (It cannot be in the front yard or between the main dwelling and the street on a corner lot)
  • Detached ARUs must comply with the lot’s overall landscape open space and lot coverage requirements. The total combined footprint of all buildings on the property cannot exceed a percentage of lot area, and the lot must maintain a minimum percentage of landscaped open space that is not occupied by buildings or parking areas.
  • A building permit and a residential rental unit license are required for all ARUs.

3. Building permit process

An approved building permit is required prior to any construction. 

The property owner may submit their own plans or hire an architect or a qualified designer with a Building Code Identification Number (BCIN) to draft and sign the architectural floor plans for the proposed ARU. 

A qualified heating, ventilation, and air conditioning (HVAC) designer with a BCIN must design the proposed HVAC layout and where pre-engineered roof trusses are proposed, the roof design must be stamped by a Professional Engineer. 

There are different Ontario Building Code requirements depending on the project. Different properties and building types will have different submission requirements and fees.  

If you need assistance with your building permit application, please email building@london.ca or call 519-661-4555. 

4. Servicing 

Water and sewer servicing must be able to accommodate the increased residential development you want to build. 

To confirm servicing call 519-930-3500 or email PlanDev@london.ca 

Note: Internet, phone, gas, and electricity are not services delivered by the City of London. Please contact you local utility provider.    

5. Building and Fire Code

All construction must meet the requirements of the Ontario Building Code and Ontario Fire Code. 

6. Lot grading 

Detached ARUs must be designed to ensure existing drainage patterns on the property and surrounding area are maintained. 

Proper lot grading helps reduce the risk of flooding, drainage impacts and basement flooding to subject property and neighbouring properties.

Key requirements include:

  • Must take existing lot grading and drainage patterns into consideration during design.
  • Must not locate ARU within a swale or overland flow route.
  • Proper lot grading must be maintained to ensure drainage functions effectively on both the subject property and adjacent properties.
  • As part of the ARU approval process, you may be required to submit a lot grading plan for review.
  • Water from downspouts must not be forced onto neighbouring properties.

Email stormwater@london.ca for a copy of the lot grading plan for the area to ensure your ARU will not affect drainage on your property or neighbouring properties. 
 

Applying for a building permit 

Building permit requirements

When applying for a building permit, the following must be submitted:

1. Apply for a Permit to Construct or Demolish (15 business day review period).

2.Permit fee paid upon permit submission 

3.Schedule 1: Designer Information Form completed by:
- A qualified designer, minimum “House” BCIN qualification required (designer declaration required on all drawings),
- The registered homeowner, or
- Architect or engineer (form not required when all drawings are stamped).

4.Letter of Authorization from owner
- Required if the applicant is not the same as the property owner.

5.Plot Plan, Site Plan or Survey (drawn to scale) that clearly shows the following:
- Location of existing/proposed buildings.
- All setbacks of new building or additions.
- Lot coverage (if new buildings or additions are added).

6.Construction drawings (single line drawings not acceptable, drawn to scale):

  • Existing floor plans (all floors):
    • Window/door sizes & locations, room names, stair location, wall locations and construction, etc. (for all floors).
  • Proposed floor plans:
    • New wall construction, fire separations (new and existing), new windows and doors, room names, plumbing locations for kitchen, bathroom and laundry, ceiling heights (overall, under beams and ducts), egress/exits, etc.
    • Show accessory structure framing, plumbing, heating, etc. (if applicable).
  • Elevations (applicable if adding egress windows/doors)

Whether a house is more or less than 5 years old, different parts of the Ontario Building Code apply. The designer working on your drawings should be aware of these requirements and include the relevant information with the application submission.

The City of London has specified that if the house is less than 5 years old, the original building permit must be closed.

Site layout plan

Concurrent with the building permit application, the site layout plan of the property drawn to scale will be required, that clearly shows and notes the following: 

  • Location of existing/proposed buildings
  • All setbacks of new buildings or additions
  • Lot coverage (if new buildings or additions are added)
  • Landscape open space coverage (if new buildings or additions are added)
  • Parking area location
  • Parking area coverage (if parking area is expanded)
  • Sewer connection for new ARUs in accessory buildings
  • Number of bedrooms in each unit

Documents required to apply for a building permit:   

ARU within existing house 
  • Schedule 1 Designer Information Form filled out by a qualified designer or the homeowner.
  • Existing floor plans for all floors within the house.
  • Proposed architectural floor plans for the new ARU signed by the Schedule 1 designer. 

Please note: Additional documentation may be requested at time of application. 

ARU with addition to existing house 
  • Schedule 1 Designer Information Form filled out by a qualified designer or the homeowner.
  • Proposed plan showing the location of the proposed addition.
  • Existing floor plans for all floors within the house. 
  • Proposed architectural plans signed by the Schedule 1 designer including: 
  1. Proposed foundation plan
  2. Proposed floor plans
  3. Elevations
  4. Wall/building sections
  • Energy Efficiency Design Summary (EEDS) form completed by the Schedule 1 designer.
  • Schedule 1 HVAC Designer form filled out by a qualified BCIN HVAC designer.
  • HVAC packages complete with heat loss/gain calculations and HVAC layout completed by a qualified BCIN HVAC designer.
  • TJI floor joist package complete with member reports stamped by a Professional Engineer and floor joist layout signed by the Schedule 1 designer. (Only required if using pre-engineered TJI floor joists.
  • Roof truss package complete with truss member reports stamped by a Professional Engineer and truss layout signed by the Schedule 1 designer. (Only required if using pre-engineered roof trusses) 

Please note: Additional documentation may be requested at time of application. 

Converting an existing detached structure 
  • Schedule 1 Designer Information Form filled out by a qualified designer or the homeowner.
  • Proposed plan showing the location of the existing detached structure being converted to an ARU. 
  • Proposed architectural plans for the new ARU signed by the Schedule 1 designer including: 
  1. Proposed floor plan
  2. Elevations
  3. Wall/building sections
  • Energy Efficiency Design Summary (EEDS) form completed by the Schedule 1 designer.
  • Schedule 1 HVAC Designer form filled out by a qualified BCIN HVAC designer.
  • HVAC packages complete with heat loss/gain calculations and HVAC layout completed by a qualified BCIN HVAC designer. 

Please note: Additional documentation may be requested at time of application. 

Constructing a new detached ARU 
  • Proposed architectural plans for the new detached ARU signed by the Schedule 1 designer including: 
  1. Proposed foundation plan
  2. Proposed floor plans
  3. Elevations
  4. Wall/build
  • Energy Efficiency Design Summary (EEDS) form completed by the Schedule 1 designer.
  • Schedule 1 HVAC designer form filled out by a qualified BCIN HVAC designer.
  • HVAC packages complete with heat loss/gain calculations and HVAC layout completed by a qualified BCIN HVAC designer.
  • Roof truss package complete with truss member reports stamped by a Professional Engineer and truss layout signed by the Schedule 1 designer. (Only required if using pre-engineered roof trusses. 

Please note: Additional documentation may be requested at time of application. 

FAQs 

How many ARUs can I have?   

You can have up to four (4) total dwelling units on a residential property where the zoning permits single detached, semi-detached, duplex, triplex, converted or street townhouse dwellings. Only two (2) can be in a detached building.

The total is determined by adding together the number of ‘original’ and ‘additional’ units.

How many bedrooms are permitted in ARUs? 

These bedroom limits are temporary regulations established under Council-approved Interim Control By-law CP-1600-300.

Each ARU is limited to a maximum of two (2) bedrooms.

In addition to the per-unit limit, the regulations also include overall bedroom limits based on where the ARUs are located on the property:

 Bedroom Limits by Location

  • ARUs within or attached to the main building:
    A combined maximum of three (3) bedrooms is permitted across all ARUs located within or attached to the primary dwelling.
  • ARUs in accessory buildings (e.g., detached ARUs):
    A combined maximum of three (3) bedrooms is permitted across all ARUs located in an accessory building on the property.
How many total bedrooms are permitted in ARUs on a property?

These bedroom limits are temporary regulations established under Council-approved Interim Control By-law CP-1600-300.

You can have up to five (5) bedrooms total across all ARUs on a property.

This is because:

  • Each ARU can have a maximum of two (2) bedrooms, and
  • The Zoning By-law limits ARUs to three (3) bedrooms total within/attached to the main building and 3 bedrooms total in accessory buildings.

With up to three (3) ARUs allowed on a lot, the highest possible combination—while following both the per-unit and per-location limits - is five (5) bedrooms total.

Where can ARUs be built?   
  • convert space in your existing home (including your basement, attic or attached garage)
  • build an addition on your existing home
  • build a new detached dwelling on your property (including a ‘tiny home’)  
  • convert an existing shed or detached garage 
What about zoning regulations? 

The zoning by-law sets out the uses and regulations that apply to all properties in the city, including any ARU project. Zoning also includes detailed information about maximum floor area, building height, and required setbacks from property lines.  Learn more about zoning uses and regulations.  

Please note: Certain zoning regulations related to ARUs are temporarily superseded by the Council-approved Interim Control By-law CP-1600-300, which introduces additional restrictions that apply while the by-law is in effect. On March 3, 2026 City Council adopted a zoning by-law amendment to enact these changes on a permanent basis, and that amendment is currently under appeal. The Interim Control By-law will continue to apply until the appeals to this amendment are resolved.

What fees and costs are associated with ARUs? 

There are costs associated with the building permit, purchasing building materials, and any professionals needed to do the work. The following list is not comprehensive, and subject to change depending on your specific cost, but some of the typical costs include: 

Building Permit Fees 

A building permit will be required for any new ARU. The cost of a building permit is determined by the project's size, the amount of work done, and the type of building being constructed or renovated.  Learn more about building permits. 

Rental License Fee  

There is a licensing program for all rental units. The program's intent is to protect the health and safety of persons residing in residential rental premises. Licensing of ARUs will include inspections.  Learn more about More information can be found at residential rental unit licenses.  

Professional Fees 

Depending on your project's nature, you may be required to hire a professional designer, architect, or engineer for a variety of processes including preparing your building permit drawings.  

Development Charges 

Development charges are used by the City to pay for the capital costs infrastructure that supports new developments.  To encourage the supply of smaller housing units, the Province of Ontario has exempted certain ARUs from development charges, subject to specific conditions.  Learn more about development charges.    

To determine whether development charges apply to your ARU project, email building@london.ca  or call 519-661-4555. 

Are there any City programs to help offset the cost of constructing an ARU?  

Several ARU programs are available with forgivable loans of up to $45,000 for homeowners constructing a new ARU subject to eligibility requirements. 

Learn more about Community improvement and incentives. 

Will an ARU affect my property taxes?   

Yes, your property taxes will increase when you create an ARU. General information regarding assessment and property taxes is provided by the Municipal Property Assessment Corporation (MPAC). 

How do I connect to water, sewer, electricity, gas, etc.? 

You will need to contact the appropriate service providers and, in some cases, a qualified professional that can advise if your current service connections can accommodate the increase in service use, or if you will need to pay to have your services upgraded. In most cases, you should be able to connect through the existing dwelling and/or directly to the street.  

Listed below are some of the service providers: 

Can I use a shipping container for an ARU?  

Yes, a shipping container can be converted into an ARU. However, it must meet all the Building Code, Zoning By-law, and other regulatory requirements (including obtaining a building permit before starting construction), just like any other dwelling. A modified shipping container will need to be designed by a professional engineer (including the foundation).  

In some cases, there may be a Canadian Standards Association (CSA) approval on the design which may supersede local Ontario Building Code standards. 

Does my ARU need a separate address?   

No, a new municipal address will not be required for ARUs created on the same property as an existing dwelling. However, a new unit number must be created to ensure the safety of people residing in all dwelling units. 

To have new unit designations added to your existing address, please create a service ticket with Canada Post by calling 1-866-607-6301. 

Do I need insurance on my ARU?   

Yes, you will need to contact your individual property insurance provider for quotes and information on coverage for your ARU.   

Can an ARU be severed and sold separately?   

An ARU provides an additional unit on a property where a primary dwelling unit already exists. There may be opportunities for severance in settlement areas in specific situations, evaluated on a case-by-case basis. 

How much will my building permit cost? 

A building permit will be required for any new ARU. The cost of a building permit is determined by the size of the project, the amount of work done, and the type of building being constructed or renovated. Learn more about building permits.

Is there a minimum size for a dwelling unit? 

The Ontario Building Code specifies the minimum size for any dwelling unit, whether it is existing or additional. For a bachelor style ARU (where the sleeping, living, dining, and kitchen areas are combined as one space) a minimum floor area of 17.5 m2 is required. 

What can I do if my property does not meet the zoning regulations? 

If your property or project does not meet the requirements of the zoning by-law you may apply for a minor variance or a zoning by-law amendment to change the regulations if you cannot change your project plans. 

Planning staff will review your project to determine if a minor variance is appropriate, or if the proposal requires a full by-law amendment. Learn more about planning and development applications.    

Where can I find additional resources? 

Information and links provided on this page reflect the current process for planning and creating ARUs in London. This information is subject to change as staff work to make amendments to better facilitate the creation of ARUs. Each ARU project is unique, and applicants are urged to review all information and  contact us if you have questions. 

Last modified:Wednesday, July 22, 2026