Basement Suites in the Townships Around Peterborough: What Each One Requires

The short answer

Whether you are planning a Selwyn secondary unit or a Cavan Monaghan accessory apartment, each township around Peterborough writes its own basement suite rules into its own zoning by-law, and the rules don't match. Selwyn, Douro-Dummer and Asphodel-Norwood allow one second unit per house, in the house or in a separate building. Cavan Monaghan allows one, inside the house only. Otonabee-South Monaghan's guide and its by-law text give different counts, so ask its building office. Ontario's framework can allow more on lots it covers, so ask your township. All five by-laws ask for one extra parking space. This is what each township's own documents said on October 27, 2026. Rules differ by property and change, so confirm with your township's building office before you start.

What this page covers

This page covers five townships: Selwyn, Cavan Monaghan, Otonabee-South Monaghan, Douro-Dummer and Asphodel-Norwood. It draws on each township's own zoning by-law text and its own suite guide or permit page. The City of Peterborough has different rules, set out in the City's basement suite rules. Which office issues your permit, and what each one says needs a permit, is in which office issues your renovation permit.

This page answers a different question: can your house take a suite, and what does your township ask for? The by-laws use four names for the same idea: second unit (Selwyn), accessory apartment (Cavan Monaghan), secondary dwelling unit (Otonabee-South Monaghan) and second dwelling unit (Douro-Dummer and Asphodel-Norwood). Each describes a separate dwelling unit that is subordinate to the main house.

Ontario's own framework applies too. 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 3 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 small exception to the by-law). Whether your lot counts is a question for the township, so a by-law count below may not be the last word for your lot.

The five townships side by side

In the table, "Not in the pages read" means the by-law and township pages checked for this article did not mention it. It does not mean the township has no such requirement, so ask.

The townships do agree on one number. Each by-law asks for one parking space for the suite, on top of the spaces the house needs, and each asks for two spaces for a house. That is three spaces for a house with one suite.

Selwyn

Selwyn's Comprehensive Zoning By-law, No. 2009-021, is consolidated to February 2026. Section 3.41 covers second units. The township's Second Units guide, revised July 2025, explains the same rules in plainer words.

• Number. One second unit per single detached, semi-detached or townhome dwelling. It may be in the house or in a building accessory to it, in the rear or an interior side yard, but not both.
• Size. Clearly subordinate to the main dwelling and no larger in area.
• Zones. The guide lists Agricultural, Rural, Residential Type One, Residential Type Two, Rural Residential and Lakeshore Residential.
• Not allowed. A dwelling in an Environmental Protection zone or a floodplain, and a lot with a garden suite or sleeping cabin. A second unit cannot share a lot with a garden suite, with rooming units such as a bed and breakfast, or with a group home. The by-law also bars a property without frontage on a municipally maintained road. The guide words it differently: a property that fronts onto a private road.
• Inside the house. The by-law says the outside of the dwelling is unaltered to fit the unit.
• Parking and outdoor space. One extra space. The spaces for the house and the unit may be stacked, up to two. The unit also needs private outdoor space of at least 7.5 square metres, with no side under 1.5 metres.
• Separate building. No more than 30 metres from the house, not in the front or exterior side yard, no basement, and not in the Lakeshore zone. Its footprint is capped at 40 percent of the main dwelling's footprint in Residential One, Residential Two and Rural Residential, and 60 percent in Agricultural and Rural.

Selwyn requires registration before you apply for the building permit. The guide lists a form, the deed, a property sketch showing parking spaces of 3 metres by 6 metres, floor sketches, elevation drawings and a fee. The township then inspects the whole house, both units, with its building and fire departments.

Selwyn's own pages disagree on how to apply. Its Building Services page says to call before visiting the office and to book inspections by phone. Its July 20, 2026 permit package says applications and inspections go through Cloudpermit, an online permit system. Ask the building office which route applies.

Cavan Monaghan

Cavan Monaghan's zoning by-law, No. 2018-58, calls it an accessory apartment: a separate dwelling unit inside and subordinate to a detached, semi-detached or townhouse dwelling. The township's Secondary Suites page splits the idea into two options: an accessory apartment, or a garden suite, which has different requirements.

• Number. One per dwelling.
• Where. The by-law's online consolidation says the accessory apartment must be in the main building. The township's guide adds that it may not be in a garage, workshop or barn.
• Size. At most 45 percent of the gross floor area of the building it is in.
• Parking. One extra space, on top of the two the house needs.
• Permit. The township's Accessory Apartments page says these always require a permit. It also says to contact the Planning department first with the Land Use Inquiry form, and to hire a qualified designer, architect or engineer.

A detached unit is different. In an April 14, 2026 public notice, the township said a zoning amendment was needed to establish a detached accessory apartment as a permitted use on one Rural Residential lot. That notice also repeats the 45 percent limit.

Check the dates. The township's accessory apartment guide is dated November 20, 2019. The online by-law consolidation runs to a by-law of May 16, 2022. The 2019 guide sends septic proof to the Peterborough County Health Department, but the township's current Sewage Systems page says the township reviews existing systems through Cloudpermit. Ask Planning what has changed since the guide was written.

Otonabee-South Monaghan

Here the township's own documents disagree on the count.

• The 2025 Building Permit Guide says secondary units are permitted in most zones and that a maximum of three are permitted on any single property. It shows three layouts: inside the house, attached through an addition, and detached in an accessory building. It lists "Secondary Suites (Converted Dwelling)" among the work that needs a building permit.
• The zoning text the township posts as its office consolidation, section 4.3 of the General Provisions, allows up to two on a property, with no more than one in the main building and no more than one in an accessory structure. It lists the Rural, Agricultural, Rural Residential, Hamlet Residential, Shoreline Residential and Estate Residential zones.

Don't plan around three. Ask the building office which document governs your lot.

The zoning text adds conditions. The township must be satisfied that adequate water and sewage services are available. The lot needs frontage on an improved public street or road, and the unit is reached through an existing residential driveway entrance. It is not allowed in a regulated floodplain. One parking space is reserved for the unit's occupants. A unit in an accessory structure is limited to 70 percent of the ground floor area of the main dwelling, may be no more than 50 metres from the main building, and may be up to 9 metres tall. New units are registered with the Building and Planning Department.

Douro-Dummer

Douro-Dummer's Comprehensive Zoning By-law is consolidated to By-law 2025-05, dated February 2025. Section 3.39 covers second dwelling units.

• Zones. A second dwelling unit is a listed permitted use in the Residential, Hamlet Residential, Shoreline Residential and Rural zones. The Limited Service Residential list does not include it.
• Number. One per primary dwelling unit. It may be attached or detached, but not both. It must be clearly subordinate and no larger in area than the primary unit.
• Parking. One extra off-street space, with stacking allowed up to two spaces.
• Not allowed. In a floodplain, in a dwelling in an Environmental Conservation zone, on a property reached by a private road, on a lot with a sleeping cabin, or within the 30 metre water yard setback, with an exception for an existing house that is not extended closer to the water.
• Stand-alone building. A stand-alone unit is no taller than 4.5 metres, never taller than the house, no more than 70 percent of the house's ground floor area, and within 30 metres of the house. A minor variance is not needed if health or safety makes 30 metres impossible.
• Inside an accessory building, such as a garage. Section 3.39.3 says the building height shall not exceed 7.5 metres, measured from the finished grade at the front of the building to the highest point. It also says a maximum of 10 percent of the first storey floor area can be associated with the unit.

The township's Building and Sewage System Permits page lists an additional dwelling unit under its Dwelling application and treats a sewage system permit as a separate application. The pages checked for this article say nothing about registering the unit.

The township's Official Plan page says the County is revising the new Official Plan, and its zoning page says the zoning by-law must conform to the Official Plan. Ask whether a change to the count is coming.

Asphodel-Norwood

Asphodel-Norwood's Comprehensive Zoning By-law, No. 2009-08, is consolidated only to By-law 2020-22. Section 3.41 covers second dwelling units.

• Zones. A second dwelling unit is a listed permitted use in Residential One, Residential Two, Rural Residential, Rural and Agricultural. Residential Three and Limited Service Residential do not list it.
• Number. One per single detached, semi-detached or row house. It sits in the house or in an accessory building, but not both, and must be clearly subordinate.
• Parking. One extra off-street space, and the spaces may be stacked.
• Not allowed. In a dwelling in an Environmental Protection zone or a floodplain, or in a dwelling that is accessory to a non-residential use.
• Separate building. It follows the zone's residential rules, cannot be a mobile home, and in a serviced area connects to municipal water and sewer.

The township's Building Permit page says an interior renovation needs a permit where it creates a new dwelling unit or apartment. The by-law text checked for this article says nothing about registering the unit. Because the consolidation stops at a 2020 by-law, ask the township whether anything newer applies to your lot, including the provincial framework above.

If your house is on a well and septic

A suite adds a kitchen and a bathroom, and several townships tie septic review to changes of that kind.

• Selwyn. The guide says a second unit may trigger an upgrade to your septic system, or a separate system. You may also have to show enough potable water.
• Cavan Monaghan and Asphodel-Norwood. Both publish the same triggers for an existing septic system review: more occupants, more bedrooms, construction over 15 percent of the finished area or a finished area over 200 square metres, or new plumbing fixtures.
• Otonabee-South Monaghan. The guide lists added bedrooms, bathrooms or kitchen facilities, and an addition over 15 percent of the floor area. It says the township took over septic permits in November 2024.
• Douro-Dummer. Its page lists a separate sewage system permit for new and replacement systems.

These are the townships' lists, not a ruling on your system. Ask the building office whether a suite on your lot triggers a review, and who does the reviewing.

What to ask the building office, in order

1. Confirm your township and your zone

   Look up the zone on your property. The office guide lists each township's phone number.

2. Ask how many units your zone allows, and where

   Ask whether the unit may be inside the house, in a separate building, or either. Ask whether Ontario's framework changes the answer for your lot.

3. Ask about registration, and the order

   Selwyn registers a unit before the building permit. Ask whether your township registers units, and what comes first.

4. Ask the septic and water question

   If you have a well and septic, ask whether a suite triggers a review and who does it.

5. Ask which document governs when two disagree

   Ask the office to name the by-law section it applies to your lot, then decide on drawings. Finishing the basement itself has its own requirements in finishing a basement in Peterborough.

Gilbert Brothers renovates basements, including secondary suites: see basement renovations. This page reports what each township's rules say, not where Gilbert Brothers works. Check the service area on the FAQ first. If your address is inside it, you can 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 I put a suite in a detached garage in Cavan Monaghan?+

The township's by-law says an accessory apartment must be in the main building, and its guide says not in a garage, workshop or barn. A 2026 public notice describes a rezoning sought to allow a detached one on a single lot.

How many suites can I have in Otonabee-South Monaghan?+

Its 2025 permit guide says up to three. Its zoning text says up to two, with no more than one in the main building. The two disagree, so ask the building office.

Does a suite need extra parking in these townships?+

Each by-law asks for one extra parking space for the unit, on top of the two for the house. Selwyn, Douro-Dummer and Asphodel-Norwood allow the spaces to be stacked; Selwyn and Douro-Dummer cap it at two.

Do I have to register a suite in Selwyn?+

Selwyn's by-law says second units shall be registered, and its guide says registration comes before the building permit application.

Do these rules apply inside the City of Peterborough?+

No. They are the townships' own. The City's are in the City's basement suite rules.