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Second Units Info Sheet

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This document is to assist municipalities and the general public to better understand what second units are, why they are important, and the legislative authority behind second units. It provides some examples of specific second unit policy and zoning best practice approaches currently in use in official plans or zoning by-laws by Ontario municipalities.

What are second units?

Second units are self-contained residential units with a private kitchen, bathroom facilities and sleeping areas within dwellings or within structures ancillary to a dwelling (e.g., above laneway garages).

Second units are also referred to as secondary suites, basement apartments, accessory apartments, granny flats, in-law apartments, or nanny suites.

What are the benefits of second units?

Second units increase the supply and range of affordable rental accommodation. In addition, they benefit the wider community in many ways as they:

  • Allow homeowners to earn additional income to help meet the cost of homeownership
  • Support changing demographics by providing more housing options for extended families or elderly parents, or for a live-in caregiver
  • Help create mixed-income communities, which support local businesses and local labour markets
  • Make more efficient use of existing infrastructure, including public transit where it exists or is planned
  • Make more efficient use of the existing housing stock
  • Create jobs in the construction/renovation industry
  • Assist municipalities in meeting their goals regarding affordable housing, intensification and density targets, and climate change mitigation and greenhouse gas emissions reduction. 

Where are Second Units Located?

The majority of second units are created through internal alterations, although some are built as additions to the main house or in/above ancillary structures like garages. The size, type (e.g., internal, addition, ancillary structure) and location of the second unit will depend on the size and design of the house as well as its location on and the size of the lot.

Regardless of where they are located second units must comply with health, safety and municipal property standards, including but not limited to, the Ontario Building Code, the Fire Code and municipal property standards by-laws.

A neighbourhood diagram showing second units in primary buildings and accessory buildings (ex. basement, attic)


The Strong Communities through Affordable Housing Act, 2011, amended the Planning Act to require that municipalities authorize second units in their official plans and zoning by-laws. The changes took effect on January 1, 2012.

Ontario’s updated Long-Term Affordable Housing Strategy, 2016 continues this effort, with a focus on reducing the cost of constructing second units by:

  • proposing changes to the Building Code to reduce the cost of construction of a new dwelling with a second unit, while maintaining occupant health and safety
  • amending the Development Charges Act, 1997 that, when in effect, would exempt second units in new dwellings from development charges in the same manner as second units in existing dwellings are exempted, as specified in a regulation.

Legislative Framework

Planning Act

Section 16(3) of the Planning Act requires municipal official plans to authorize second units:

  • in detached, semi-detached and row houses if an ancillary building or structure does not contain a second unit; and
  • in a building or structure ancillary to these housing types provided that the primary dwelling does not contain a second unit.

Section 35.1 requires that each local municipality ensure that it’s zoning by-law gives effect to the policies described in Section 16.3.

No appeals to the Ontario Municipal Board

The Planning Act restricts appeals of second unit official plan policies and zoning by-law provisions to the Ontario Municipal Board except by the Minister.

Provincial Policy Statement, 2014 (PPS)

The Provincial Policy Statement, 2014 (PPS) directs and promotes the development of healthy and complete communities. The goal is to create strong, livable, healthy and resilient communities through efficient land use (s.1.1.1).

Section 1.4.3 of the PPS directs municipalities to permit all forms of housing to provide an appropriate range and mix of housing types and densities – including affordable housing. Further, municipalities should permit and facilitate all forms of residential intensification and redevelopment, including second units.

Provincial plans

Some provincial plans contain specific policy which directly or indirectly relates to second units in the geographic areas they apply to (eg. the Oak Ridges Moraine Conservation Plan and Niagara Escarpment Plan). Municipalities need to consider and reflect any such policies in developing their official plans and zoning by-laws.

A dwelling with both primary and second units (below ground-level unit)

Official Plans

Municipal official plans outline a community’s vision and priorities. They contain policies to guide development in order to achieve land use goals. Official plans must reflect any legislative requirements, be consistent with the PPS and conform to any applicable provincial plans.

Zoning By-laws

A zoning by-law sets standards for development and must conform to a municipality’s official plan. Zoning by-laws must be updated within three years of a new or amended official plan and must also reflect any requirements of the Planning Act, be consistent with the PPS and conform to any applicable provincial plan.

Best Practices

The Planning Act provides a broad legislative foundation for permitting second units by requiring that they be authorized in single detached, semi-detached and row dwellings, and in ancillary structures. In practice though, there are circumstances where second units are not appropriate based on good land use planning principles, including health and safety and environmental considerations. So while official plan policies should be permissive and zoning by-laws should generally allow second units to be established “as of right”, there may be situations where second units should not be allowed and/ or require some specific assessment prior to their establishment. The following are some examples of best practices in official plan policies and zoning by-laws, including specifics which relate to a number of these circumstances.

“As of right”

For the purposes of this document, “as of right”’ is a phrase used to refer to the ability to apply for a building permit without having to make a development application (e.g., an official plan or zoning bylaw amendment, a minor variance or a site plan). Similarly, homeowners generally should not need to produce any type of study to demonstrate that they conform to any policy or zoning provisions.

Housing types and ancillary building structures

The Planning Act provides that official plan policies and implementing zoning by-laws should permit second units in detached, semi-detached and row houses if an ancillary building or structure does not contain a second unit; and, in a building or structure ancillary to these housing types provided that the primary dwelling does not contain a second unit.

In municipalities with limited housing types (e.g. only single detached dwellings), second units would only need to be authorized for that housing type.

Township of Wainfleet Official Plan, August 14, 2014 Secondary suites

Secondary suites shall be permitted in all Residential Area designations, and shall be subject to the following criteria and the regulations of the Zoning By-law:

  1. Only one secondary suite per single detached, semi-detached, or townhouse dwelling is permitted;
  2. The secondary suite may be contained within the primary residential dwelling or in a building or structure accessory to the residential dwelling, but not in both;

Official plan designations

Municipalities should allow second units in designations or zones that permit detached, semi-detached, or row dwellings.

There may be circumstances where second units may not be appropriate given other planning considerations and policies, particularly relating to health and safety or the natural environment. For example:

  • areas that are prone to flooding
  • waterfront areas/developments on private roads that are not maintained and where emergency access may be limited
  • areas adjacent to lakes with limited lake capacity
  • areas of recreational dwellings where there may be a lack of year round roads and/or which lack other daily needs and services residents may require.

Tay Valley Township Official Plan, 2016


…an accessory apartment (secondary suite) is permitted in residential areas within a four-season single detached, semi-detached, or row-house dwelling unit, or attached to a detached garage, located on a road maintained year-round and accessible by Emergency Services, subject to considerations of carrying capacity of lakes and hydrological capacity….

A primary building and an accessory structure with a second unit

Second Units in existing dwellings and new dwellings

Second units should be allowed in both newly built and existing dwellings. Designing new houses to accommodate a second unit at the outset can be more efficient than retrofitting an existing home to have a second unit. Recent changes to the Development Charges Act, 1997 and a potential regulation to exempt second units in new homes from development charges (once in effect), and proposed changes to the Building Code, if approved, are expected to reduce the cost of constructing second units in new dwellings. A proposed regulation under the Planning Act, if made, would permit second units without regard to the date of construction of the primary building.

Town of Smiths Falls Official Plan, October 2014

LU-2.14 Second Residential Units

The Town will permit the addition of one self-contained residential dwelling unit (i.e. second unit), within single-detached and semi-detached and row house dwellings in both existing and newly developing residential neighborhoods.


The maximum parking required per second unit should be one space. In some jurisdictions where transit is available, some municipalities have eliminated parking requirements for second units. Tandem parking (a parking space that is only accessed by passing through another parking space) should also be permitted. A proposed regulation under the Planning Act would, if made, restrict the maximum parking requirement for a second unit to one space while also requiring that tandem parking be allowed.

City of Ottawa Zoning By-law 2012-147 (June 10, 2015)

Secondary Dwelling Units 

Sec. 133 (14)

Where a secondary dwelling unit is located on a lot subject to Section 139 - Low Rise Residential Development in Mature Neighbourhoods, no parking is required for the secondary dwelling unit.

Mississauga Zoning By-law 0158-2013 (July 2013)

Tandem parking spaces to accommodate a second unit shall be permitted.

City of Toronto Zoning By-law 569-2013

800.50 Defined Terms

(850) Tandem Parking Spacemeans a parking space that is only accessed by passing through another parking space from a street, lane, drive aisle or driveway.


In areas with municipal services, second units should be permitted without a requirement to demonstrate sewer or water capacity, unless there are previously documented servicing constraints.

For second units in dwellings serviced by septic systems and private wells, there should be a demonstration of capacity to the satisfaction of the municipality. This is because Building Code permits for septic systems are, in part, based on the number of bedrooms and plumbing fixtures, because septics may be old and/or in order to ensure there is sufficient potable water from the private well.

Howick Township OP, 2016

5. Settlement Areas

D. Policies and Actions

10.1 ... Second residential units are permitted in settlement areas and rural areas of the Township provided that:

f) It must be demonstrated that on-site servicing (e.g. water, sewage) have sufficient capacity for the additional dwelling unit.

A dwelling with both primary and second units (above ground-level unit)

Unit Size

The size of second units and the number of bedrooms should solely be regulated by the Building Code. The Building Code establishes health and safety standards for second units. As such, municipal by-laws should not seek to impose size or other standards that are regulated by the Building Code.

The Development Charges Act, 1997 (via Ontario Regulation 82/98) states that, in order for second units in existing homes to be exempt from development charges, they must be less than or equal to the size of the primary dwelling. This is the only potential size standard a municipality should contemplate including in a by-law.


Requirements for entrances or means of egress for second units are set by the Ontario Building Code and Ontario Fire Code (which need to be referred to for specific standards). In general, second units can share a joint entrance with the primary unit, subject to having a fire separation with appropriate fire resistance rating, and at least two means of egress (exit) that may include windows of an appropriate size. Therefore, there is a need to ensure that by-laws do not contain any standards/provisions that differ from those in the Codes.

Streetscape and Architectural Design

Given most second units are internal to a primary dwelling, second units should have limited impact on streetscape and architectural design. In the case of an addition to a primary dwelling, there may be valid design considerations, particularly in heritage areas. If municipalities establish design standards in relation to streetscape or architectural design, they should be clearly set out in the zoning by-law so a second unit can be planned in accordance with the by-law and a homeowner can proceed directly to obtain a building permit.

Owner occupancy

The Planning Act does not allow zoning to have the effect of distinguishing on the basis of relationship. Zoning by-laws should permit occupancy of the primary or second unit regardless of whether or not the owner of the home is a resident of either unit. A proposed regulation under the Planning Act, if made, would establish a provision which precludes establishing occupancy requirements for either the primary or second unit.

Tracking and monitoring

A municipality should have a means for tracking and monitoring second units. A registry, in some form, could help the municipality be aware of where second units existed. This could assist in establishing inspection processes to help ensure public safety. It could also provide emergency services with the knowledge that there are two units in the home.

A registry could be established through a mandatory enrollment by the applicant when constructing a second unit or by having the municipal building official inform the appropriate office that a building permit has been issued for a second unit on a property. Ideally, there would be no or only modest fees for registration in order to encourage the creation and registration of second units.

City of Brantford OP


The City shall permit the creation of a self-contained second unit dwelling on lands designated to permit single detached dwellings, semi-detached dwellings, street townhouse dwellings, or accessory structures in accordance with the applicable zoning bylaw regulations and the following provisions: OPA #125 Dec. 3/08 OPA #180 Dec. 17/12
6. Second unit dwellings shall be registered with the Building Department.

Additional Sources

For More Information, Contact:

Ministry of Municipal Affairs, Provincial Planning Policy Branch, (416) 585-6014

Municipal Services Offices:

  • Central (Toronto), 416-585-6226, Toll Free: 1-800-668-0230
  • West (London), (519) 873-4020, Toll Free: 1-800-265-4736
  • East (Kingston), (613) 545-2100, Toll Free: 1-800-267-9438
  • Northeast (Sudbury), (705) 564-0120, Toll Free: 1-800-461-1193
  • Northwest (Thunder Bay), (807) 475-1651, Toll Free: 1-800-465-5027

Note to User

This Info Sheet summarizes complex matters and reflects legislation, policies and practices that are subject to change. It should not be a substitute for specialized legal or professional advice in connection with any particular matter and should not be construed as legal advice. The user is solely responsible for any use or the application of this information. As such, the Ministry of Municipal Affairs does not accept any legal responsibility for the contents of this Info Sheet or for any consequences, including direct or indirect liability, arising from its use.