Legal Basement Apartment and Secondary Suite Rules in Peterborough

The short answer

Inside the City of Peterborough, a legal basement apartment is an additional residential unit, or ARU. The City permits one ARU in the house plus one in an accessory building, or two inside the house. Each can have at most two bedrooms and must be smaller than the main unit. Parking depends on your property's parking area (the City has five), and firefighters need a short, clear path to the door. The City asks for a building permit application with drawings. These are the City's rules only. Rules differ by property and change, so confirm with the City before you start.

The rules for a legal basement apartment depend on where the house is. Each municipality sets its own zoning, so the rules for a house inside the City of Peterborough are not the rules for a house in the next township. Below are the City's rules in the order a homeowner meets them.

Whose rules apply to your house

This page covers properties inside the City of Peterborough. If your house is outside the city limits, a township's rules apply instead. See what each township says about a basement suite and which office issues your renovation permit.

Ontario also sets a floor under local zoning. The province's Citizen's Guide to Land Use Planning, updated February 23, 2026, says the Planning Act overrides local zoning to permit up to three residential units in most existing urban residential areas. It adds that setbacks and height can still call for an amendment or a minor variance (a request to depart slightly from a zoning rule).

What the City counts as an additional residential unit

The City defines an ARU as a self-contained residential unit with a private kitchen, bathroom facilities and sleeping areas, either inside a dwelling or inside a structure that is accessory to a dwelling. Its ARU page lists the other names for the same thing: second units, basement apartments, accessory apartments, granny flats, in-law apartments and nanny suites.

The City's Building Services page lists them as "Additional Residential Units (Secondary Suites)," but the Building Code gives "secondary suite" a narrower meaning, a unit in a house that has only one other unit.

The two configurations the City allows

Subject to Zoning By-law 1997-123, the City's page on creating a new ARU permits ARUs in either of two configurations, inside a single detached, semi-detached or row dwelling that is itself a permitted use:

• Configuration 1: one ARU inside the house, plus up to one ARU in a building that is accessory to the house.
• Configuration 2: two ARUs inside the house.

Every ARU also has to meet these conditions:

• Its floor area must be less than the floor area of the principal dwelling unit.
• It can have a maximum of two bedrooms.
• It must be served by public water and wastewater services, unless the main dwelling is not required to have them. In that case private services can serve the ARU.
• It must not be in a floodway as the Provincial Policy Statement defines one. The City sends you to the conservation authority's property inquiry page, where you submit an electronic ticket to learn where your property sits.

A suite in a separate building has its own City limits on height, setbacks, lot coverage and services; the garden suite rules cover them.

Parking: how many spaces, and where

The City divides its territory into five Parking Areas and sets the requirement by area. You find yours by typing your address into the City's interactive map and clicking inside the highlighted property. Spaces in the road right of way do not count. Tandem parking, one space behind another, is allowed for an ARU in every area.

The table shows the City's requirement for a single detached or semi-detached house, and what it adds up to with one suite. Where the requirement comes out as a fraction, the City rounds up. Row dwellings and townhouses have a different line in the City's table.

Here is a hypothetical. Say a detached house is in Parking Area 2 and the owner plans one basement suite. The house needs 1 space and the suite 0.5, which is 1.5, and the City rounds that up to 2 spaces. A second suite would add another 0.5, for 2.0 in total, or 3 spaces if the City rounds each suite up separately. The City's page doesn't say which way it counts, and the difference only shows up in Area 2. The by-law (version dated May 6, 2025) calls the two requirements "cumulative" (section 6.33.3(h)). That may point to adding first, but ask Building Services.

A space in Areas 1 and 2 must be at least 2.5 metres by 5.5 metres (8.2 by 18 feet). In Areas 3, 4 and 5 it must be at least 2.7 metres by 5.7 metres (8.9 by 18.7 feet).

Firefighter access and the path to the door

The City sets two distance limits for how firefighters would reach a suite:

• An unobstructed path from a pumper vehicle (a fire engine) to the suite's primary entrance cannot exceed 45 metres (147.6 feet).
• The route from a fire hydrant to the pumper, plus that path, cannot exceed 90 metres (295 feet).

Where those distances cannot be met, the City requires an alternative firefighting or access solution that satisfies Peterborough Fire Services and the Building Services Division. The exterior route to the suite also has rules. It must be clear and unobstructed, including utilities that stick out from the building, with a hard, stable surface at least 0.9 metres wide, about 35 inches. Its cross-fall (the side-to-side slope) must run between 2% and 5%, and its slope along the path between 2% and 8%. The City says to avoid stairs wherever feasible, and shared access across property lines needs registered easements on title.

The City wants this path drawn. The site plan and the lot grading and drainage plan must show it, and Engineering Development must approve it before a permit can be granted.

What the Building Code adds for a suite

The Building Code treats a house with one suite differently from a house with two. The 2024 Building Code, as the City quotes it, defines a "secondary suite" as a self-contained dwelling unit in a building of only residential occupancy that contains only one other dwelling unit and common spaces, where both units form a single real estate entity. Secondary suites get special exceptions in the Code. The City states that if you propose two ARUs in one house, those provisions do not apply to them.

For a house with one suite, the Code sets a ceiling height of not less than 1.95 metres (about 6 feet 5 inches) in the suite and a clear height of not less than 1.85 metres (about 6 feet 1 inch) under beams and ducting. That is Article 9.5.3.1., Sentences (2) and (3), of the 2024 Building Code, O. Reg. 163/24, as shown in the Ministry's 2024 Building Code Compendium (page updated October 20, 2026), as of October 27, 2026. The ceiling alternatives the City describes for older homes in its basement guide do not apply to secondary suites. The basement permit guide covers the finish-level rules that apply to any basement, such as windows, alarms, doors and hallways.

The Compendium home page says its web version reflects amendments up to and including O. Reg. 242/26 (July 22, 2026). The province's e-Laws site also shows O. Reg. 325/26, filed October 2, 2026, which changes the date of the Ontario Amendments document that section 1 of the Building Code adopts, from July 17, 2026 to October 1, 2026. The Compendium home page doesn't list it among the amendments it says it reflects.

The City's ARU page adds a few design points of its own:

• Carbon monoxide alarms are required next to each sleeping area.
• The minimum dwelling unit size is 30 square metres, about 323 square feet, and rooms must meet the Code's minimum room sizes.

Some City pages still cite the 2012 Code, O. Reg. 332/12, so check which edition you are reading. Rules differ by property and change; confirm with the City before you start.

Drawings and the permit application

Permit applications for ARUs go through the City's online application portal. The City's ARU page lists what to submit:

• The building permit application form, generated in the portal and signed.
• Drawings to scale and fully dimensioned, in metric or imperial but not both: a site plan, existing floor layouts, proposed floor layouts, cross sections with wall, ceiling and fire separation construction details, elevations showing the suite's entrance and egress window (a window you could escape through), and HVAC (heating and ventilation) and mechanical drawings.
• A site plan and lot grading and drainage plan that show the firefighter path described above.
• For a suite in an accessory building, proof that the existing sanitary and domestic cold water services can carry the added load.

The City says drawings are to be prepared by a professional such as an engineer, an architect or a designer with a Building Code Identification Number (BCIN). With one suite in the dwelling, the homeowner may be permitted to prepare them, though the City recommends a BCIN designer qualified at least in House. With three dwelling units within the dwelling (the house and two ARUs), the City says a designer qualified at least in Small Buildings is required. For a configuration with one ARU in a separate building, ask Building Services which qualification applies. The City also keeps a catalogue of pre-approved plans for new ARUs that it says can fast-track a permit.

Ask whoever you hire to build the suite who will apply for the permit and who will book the inspections. The basement permit guide explains the City's agent form and the duties the City puts on the owner. Rules differ by property and change; confirm with the City before you start.

If the property is designated heritage

A suite's drawings must show its entrance and egress window. The City's heritage permit page lists alterations to windows and doors, or their openings, and health, safety or accessibility modifications among the work that needs a heritage permit on an individually designated property or in a Heritage Conservation District. The City says the process may take several months. It says that by law it has 90 days to decide once it issues a notice of receipt, and that a building permit can only be issued after the heritage application is approved. Before you commission drawings, ask Building Services and the City's heritage staff whether your property is designated.

Tax and rental questions to put to the City

A finished suite can change what your property is worth on paper. The City warns that additions, new construction or changes to occupancy may change your property valuation, and points owners to the Municipal Property Assessment Corporation or to Service Peterborough at 705-742-7777, extension 1865.

Renting is a separate question from building. The City has a Rental Premises Licences page under By-law 17-067. The licence descriptions on that page cover rental dwelling units with four or more bedrooms and lodging houses. They do not mention basement suites, and this page doesn't say whether the by-law reaches yours. Treat licensing as a question for the Clerk's Office, at 705-742-7777, option 3, not something to assume either way. Rental income has tax rules too, and an accountant is the person to ask; see CRA's page on rental income.

For the money side, see how a suite is paid for and whether an in-law suite qualifies for the multigenerational tax credit.

Legalizing a unit that already exists

The City's page on legalizing an existing unit splits the question by date.

Units that existed on November 16, 1995 may be exempt from the City's zoning rules for ARUs under Ontario Regulation 384/94. The unit must have been in a single detached, semi-detached or row house, with conditions on how a semi-detached or row house was created. The City lists further conditions the dwelling had to meet on that date. The owner gives the Building Division:

• a declaration, sworn before a Commissioner of Oaths or a lawyer by someone with personal knowledge, that the house was two residential units on that date;
• printed proof the unit existed then, such as rent receipts or tax records;
• documentation of a successful Fire Code compliance inspection and an Electrical Safety Authority inspection; and
• the ARU processing fee.

Units built after that date must comply with the zoning by-law, get a building permit to recognize the existing construction, and pass all the inspections tied to it.

When a unit falls short. The City says a unit that fails the Building Code or the Electrical Safety Code cannot be legalized until it is renovated to comply. If it fails zoning, the City lists alterations such as removing a bedroom or expanding a driveway, a rezoning, or folding the unit back into the main home. A unit built legally under an earlier by-law may count as a legal non-conforming use (legal when it started, but not under today's by-law) if the owner can show it was once permitted and has been used that way continuously since.

Questions to answer before you pay for drawings

1. Confirm the municipality

   Your address must be inside the City of Peterborough. If not, start with your township.

2. Check the floodway

   Use the conservation authority's property inquiry page that the City links.

3. Find your Parking Area

   Look up the address on the City's map, then count the spaces your lot can hold at the size that area requires.

4. Measure the firefighter path

   Pace out the route from where a pumper could stop to the suite's door.

5. Count bedrooms, then call Building Services

   Two bedrooms at most, and a suite smaller than the main unit. Ask the City what it will want on your lot before you pay a designer, and confirm with the City before you start.

If you want someone to look at the space, Gilbert Brothers renovates basements, including secondary suites: see basement renovations, or request a free estimate. The estimate is free at your home, the quote covers the whole job before work starts, and you get a reply within one business day.

Frequently asked questions

Can a basement suite in Peterborough have three bedrooms?+

Not under the City's ARU rules, which cap an ARU at two bedrooms and require its floor area to be less than the main dwelling unit's.

Can I have a suite in the house and another in a separate building?+

Configuration 1 allows one ARU inside the house plus up to one in an accessory building. The detached building has its own limits on height, setbacks, lot coverage and services.

Does a basement suite need a building permit?+

The City asks for a building permit application with drawings, through its online portal, for a new ARU. A basement finish with no suite needs one too, as the basement permit guide explains.

Do these rules apply in Selwyn or the other townships?+

No. They are the City of Peterborough's. See what each township says and the permit office guide.