Building a Garden Suite in Peterborough: What the City Allows and How to Plan for Spring
Updated · 8 min read · By Gilbert Brothers
In this guide
The short answer
What people search for as a garden suite, the City of Peterborough calls a detached additional residential unit, or ARU: a self-contained home in a building that is accessory to the house. The City lists it as one half of a pair: one ARU in the house and up to one in an accessory building. A detached unit is limited in distance from the house and lot lines, height (4.3 metres at most, as the by-law measures it), lot coverage (10% across all accessory buildings) and bedrooms (two at most). Rules differ by property and change, so confirm with the City before you start.
Search for "garden suite Ontario" and the answer depends on whose rules you mean: the province's, the City's or a township's. This page follows the City's own pages and zoning by-law, and ends with what to settle over the winter so paperwork doesn't hold up a spring start.
What the City calls a garden suite
The City's pages on additional residential units do not use the words "garden suite". Its ARU page defines an ARU as a self-contained residential unit with a private kitchen, bathroom facilities and sleeping areas, within a dwelling or within a structure ancillary to a dwelling. A permanent backyard home is a detached ARU.
The province uses "garden suite" for something else. Ontario's Citizen's Guide to Land Use Planning (updated February 23, 2026) describes a garden suite as a one-unit detached residential structure with bathroom and kitchen facilities, additional to an existing structure and designed to be portable. A municipality can authorize one by temporary use bylaw for up to 20 years. If your lot is in a township, start with the office that issues your permit.
Where a detached suite fits among the options
The City permits ARUs in one of two configurations, inside a single detached, semi-detached or row dwelling. Configuration 1 is one ARU within the dwelling and up to one in a building that is accessory to it. Configuration 2 is two ARUs within the dwelling. A detached suite is the accessory half of Configuration 1.
The City's page doesn't say outright whether a lot can have a detached ARU with no ARU in the house. The City's Zoning By-law 97-123, section 6.33.3(a), words it the same way, as one ARU in the dwelling with one in an accessory building. Ask the City that first, because the rest of this page depends on it.
| Option | What the City's pages say | What starts the process |
|---|---|---|
| A suite inside the house, such as a basement suite | Configuration 1 or 2. The rules are in the basement suite guide. | A building permit application with drawings, through the City's online portal. |
| A new detached suite | The accessory-building half of Configuration 1, with the limits below. | The City's ARU pages say to apply through its online portal. Its general permits page says detached garages, sheds and accessory structure permits are applied for by email. Ask the building division which route a detached unit takes. The permit list includes constructing a new building of more than 15 square metres (161 square feet). |
| An existing garage turned into a suite | The ARU pages do not mention garage conversions. The by-law lets a required parking space sit inside a private garage (section 4.2.A(i)(a)). | Ask the City how it would treat your garage, and whether the conversion removes a parking space the house needs. |
The limits for a detached unit
These are the figures on the City's page on creating a new ARU, which gives the distance, height and coverage figures for detached accessory buildings on a lot with one or two principal dwelling units. The 30 square metre minimum is on the City's main ARU page.
| Limit | The City's figure |
|---|---|
| Distance from the rear of the house | At least 1.2 metres (about 4 feet) from the rear of the principal dwelling |
| Distance from a side or rear lot line | At least 0.6 metres (about 2 feet) |
| Height | No more than 4.3 metres (about 14 feet) |
| Lot coverage | 10% for all accessory buildings together, with the overall coverage rule for the zoning district still applying |
| Bedrooms | Two at most |
| Size | Floor area less than the principal dwelling unit, and a dwelling unit of at least 30 square metres (323 square feet) |
| Water and sewer | Public services, unless the house is not required to have them |
| Floodway | Not in a floodway |
The by-law's definitions decide how two of these are measured. Height on a flat roof is to the highest point. On a gable, hip, gambrel or shed roof it is to the average level between the eaves and the ridge, and a shed roof under 20 degrees counts as flat. Coverage is the building area divided by the lot area, and building area includes horizontal projections of more than 0.6 metres from the foundation, but not platforms, decks or verandahs. Both definitions are in Section 1 of the by-law. The posted PDF's pages are dated May 6, 2025, and the City says its current consolidation includes all amendments up to July 15, 2026.
Here is a hypothetical. Say a lot is 600 square metres, about 6,450 square feet. Ten per cent is 60 square metres for every accessory building together. If a detached garage already covers 28 square metres and a shed 9, that leaves 23 square metres. A one-storey suite at the City's 30 square metre minimum would not fit under the published limit. The garage and shed sizes are invented; the 10% and the 30 square metres are the City's.
The province's guide complicates that arithmetic. It says its ARU framework removes or updates local zoning requirements on maximum lot coverage, minimum lot size and similar limits, and that setbacks and height may still need a zoning amendment or a minor variance (a request to depart slightly from a zoning rule). The City still publishes the 10% and does not say how the two fit. Ask which limit it applies to your lot.
Services, the fire path and the floodway
Services. The City allows one sanitary (sewer) and one domestic cold water service from City services per property. For a unit in an accessory building it asks for proof that the existing services will carry the added load, and an engineer with a PEO (Professional Engineers Ontario) designation has to verify or design the plumbing.
Fire path. A firefighter's unobstructed path from a pumper vehicle (a fire engine) to the unit's main entrance cannot exceed 45 metres (147.6 feet). The route from a hydrant to the pumper plus that path cannot exceed 90 metres (295 feet). The route must be clear, hard and stable, at least 0.9 metres (about 3 feet) wide. The site plan and the lot grading and drainage plan have to show it, and the City's Engineering Development staff must approve it before a permit is granted. Where those distances cannot be met, the City requires an alternative firefighting or access solution that satisfies Peterborough Fire Services and its Building Services Division. The basement suite guide has the rest of the fire-access rules.
Floodway. The City sends you to the conservation authority's property inquiry page, where you submit an electronic ticket.
The City's pre-approved plans for detached units
The City runs a Pre-Approved Plans Program for detached ARUs. It says local professionals with a BCIN (Building Code Identification Number) or P.Eng. (professional engineer) designation designed the plans, which are already checked for Building Code compliance, to speed up the permit process. Its steps for an owner:
Browse the catalogue
On October 27, 2026 the City's catalogue listed one plan and said more options are coming. Read its drawings for size and bedroom count before you settle on it.
Contact the designer
The designer can help with modifications, but the City says changes may take extra review time.
Check your site
Confirm the zoning allows the building, using the City's mapping or the Plan-Build Peterborough Counter at City Hall.
Apply
The program page says to apply through the City's online portal. Include the construction drawings, a site servicing report, a site plan and any heritage or conservation authority approval, and put the catalogue number in the permit description.
Wait for the City's check
The City checks that your plan matches the approved design. If nothing has changed, it says it will prioritize your application. A modified plan goes through the usual review.
The pre-approval is for the building's design. Your lot is still reviewed: the City checks zoning and whether other agencies need to approve. It states no review time, so ask Building Services what to expect.
Planning the paperwork over the winter
Ground work depends on the weather. Paperwork does not. The Building Code sets the minimum depth of a foundation by soil type, by whether it contains a heated basement or crawl space, and by drainage. Several combinations call for a depth "below the depth of frost penetration" (Table 9.12.2.2, 2024 Building Code Compendium, updated October 20, 2026). What you can control is having an approved permit in hand by the time the ground is workable.
Take these questions to the City before you pay for drawings:
- Can the lot have a detached ARU without an ARU in the house?
- Does a detached unit apply through the portal or by email?
- Does the 10% coverage limit apply, given what the province's guide says?
- How many parking spaces does the house plus the unit need, and where do they go?
- Is the lot in a floodway, or does heritage or the conservation authority need to approve?
- Who may prepare the drawings for a detached unit?
- Do any other fees or charges apply?
Confirm the municipality and ask the questions above
Your address must be inside the City. Use the Plan-Build Peterborough Counter at City Hall, or call Building Services.
Choose the drawings route and draw the site plan
Pick a catalogue plan, or hire a designer, engineer or architect. The site plan has to show setbacks, the fire path, services and grading.
Settle who applies
Write into the contract who applies for the permit and who books the inspections. See hiring a renovation contractor.
The City warns that new construction or a change in occupancy may change your property valuation. What MPAC does after a permit explains the process.
If your plan also covers work inside the house, 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
Is a garden suite the same as a detached ARU in Peterborough?
The City's pages call a permanent backyard unit a detached additional residential unit. The province's guide uses "garden suite" for a portable structure authorized by a temporary use bylaw. Check which meaning a page uses before you rely on its numbers.
Does a pre-approved plan guarantee a permit?
No. The City says it checks that your plan matches the approved design, reviews zoning and other approvals, and prioritizes an application that has no changes. Modified plans go through the usual review.
Do these rules apply in the townships around Peterborough?
No. They are the City of Peterborough's. Each township has its own building office and by-laws, and the permit office guide shows how to find yours.