A duplex is a single property with two self-contained homes in it, each with its own kitchen, bathroom and entrance. One owner holds the title to the whole building and its land, which is what separates a duplex from a semi-detached house. This page covers the kinds of duplex, what makes one legal, what converting a house involves and how a duplex is financed. It is part of our guide to property types in Canada, and the types of houses in Canada page compares duplexes with every other kind of home.
Types of duplexes
| Type | Description | Common in |
|---|---|---|
| Side-by-side | Two units share a centre wall; each has its own entrance | Ontario, the Prairies |
| Stacked (up/down) | One unit above the other, with separate entrances | Montreal, older urban areas |
| Converted house | A single-family house divided into two units | Everywhere, with permits |
| Purpose-built duplex | Designed and built as two units from the start | New construction |
Duplex vs semi-detached house
A semi-detached house is sometimes loosely called a duplex, but it is two separate properties that share a wall, each with its own owner, lot and title. A true duplex is one property with two units, so selling, insuring or mortgaging it covers both units at once. With three or four units the building becomes a triplex or fourplex, still financed as a residential property; buying a duplex, triplex or fourplex covers those purchases.
Living in one unit or renting both
A duplex owner can live in one unit and rent the other, which is known as house hacking, or rent out both units as an investment. The down payment, how lenders count the rent and worked cash-flow examples for both approaches are in buying a multiplex.
Financing a duplex
A duplex has one to four units, so it is financed with a residential mortgage. If you will live in one unit, the usual down payment rules apply. The minimum down payment is 5% of the first $500,000 and 10% of the rest for homes under $1.5 million, and 20% at $1.5 million or more. A home of up to four units can be insured with a smaller down payment if you live in one of the units: CMHC lends up to 95% of the value for one or two units and 90% for three or four. A duplex you won’t live in is treated as a rental. CMHC insures two- to four-unit rentals the owner won't live in only up to 80% of a value below $1 million, so the minimum down payment stays at 20%.
The rent from the other unit can help you qualify. For an insured mortgage, CMHC sets a specific limit for a two-unit home. In an owner-occupied two-unit home, up to 100% of the secondary suite's gross rent can count. Lenders apply their own methods for uninsured mortgages; qualifying with rental income explains them, and CMHC mortgage rules covers the insurance itself. A lender may count rent only from a unit that is legal, which is one reason the checks below matter.
What makes a duplex legal
A legal duplex is one where the municipality allows two units on the lot and the second unit was built or converted with permits that meet the building and fire codes.
| Factor | What to check |
|---|---|
| Zoning | Whether the lot is zoned for two units, or the municipality allows a second unit as of right |
| Building permits | Whether the second unit was built or converted with permits that were closed |
| Fire separation | Fire-rated separation between the units, as the building code requires |
| Exits and entrances | Each unit has its own way in and out |
| Services | Ideally separate electrical panels, water heaters and heating, or a clear split of shared ones |
| Parking | Some municipalities require parking for each unit |
| Legal non-conforming | A duplex that existed before the current zoning can remain legal, with limits on changing or expanding it |
| Unpermitted unit | A second unit created without permits may not count as a legal unit, which can raise insurance and liability problems |
Legal duplex vs unpermitted conversion
| Factor | Legal duplex | Unpermitted conversion |
|---|---|---|
| Building permit | Issued and closed | None on file |
| Fire separation | Meets the building code | May not meet it |
| Exits | An independent exit for each unit | May share an entrance |
| Insurance | Can be insured as a two-unit home | The insurer needs to know about the unit, and coverage can be affected if it doesn’t |
| Mortgage | Rent from both units can be considered | A lender may not count rent from a unit that isn’t legal |
| Municipal enforcement | None | The municipality can order the unit brought up to code or closed |
| Resale | Sold as a legal two-unit property | Buyers and their lenders face the same questions |
Provincial rules on second units
| Province | Status |
|---|---|
| Ontario | Provincial legislation allows additional units on most residential lots, subject to local rules |
| British Columbia | Secondary suites and laneway houses are permitted in many municipalities |
| Alberta | Set by each municipality; Edmonton and Calgary have expanded where second units are allowed |
| Quebec | Duplexes are long established, and urban zoning often allows them |
| Manitoba | Set by each municipality; Winnipeg has expanded where secondary suites are allowed |
| Atlantic provinces | Set by each municipality, with many widening where second units are allowed |
Grants and loans for adding a unit are covered in secondary suite incentives.
Converting a house into a duplex
The steps below show what a conversion usually involves. The cost ranges are rough illustrations; real quotes vary widely with the house, the city and the trades available.
| Step | Details | Rough cost range |
|---|---|---|
| 1. Confirm zoning | Ask the municipality whether a second unit is permitted on the lot | Usually free |
| 2. Plans | An architect or designer draws plans that meet the building code | $2,000 to $8,000 |
| 3. Permits | Building, plumbing and electrical permits | $500 to $3,000 |
| 4. Fire separation | Fire-rated drywall and doors between the units | $3,000 to $10,000 |
| 5. Second kitchen | A full kitchen in the new unit | $10,000 to $30,000 |
| 6. Second bathroom | If the house doesn’t already have one in the right place | $8,000 to $20,000 |
| 7. Separate entrance | An outside door, if there isn’t one | $3,000 to $10,000 |
| 8. Electrical | A separate panel for each unit, or sub-metering | $3,000 to $8,000 |
| 9. Egress and safety | Egress windows, smoke alarms, carbon monoxide detectors | $1,000 to $5,000 |
| 10. Inspections | Municipal inspections at each stage | Usually covered by the permits |
Financing for the work is covered in renovation loans.
Pros and cons of owning a duplex
| Pros | Cons |
|---|---|
| Rent from the other unit offsets the mortgage | You become a landlord, with a landlord’s duties |
| An owner who lives in one unit can buy with an insured mortgage | Less privacy than a detached house |
| Two units can be rented separately | Two units to maintain |
| Flexibility to move out later and rent both units, or house family | Living beside your tenant if you live there |
| A step toward a larger multi-unit property | Zoning limits in some areas |
| Insurance is more involved than for a single-family home |
Duplex due diligence checklist
- Zoning allows two legal units
- Building permits for both units (if converted) are on file and closed
- Current leases and rental history reviewed
- Fire separation meets the building code
- Separate entrances, kitchens and bathrooms checked
- Utility setup reviewed (separate meters or shared)
- Structural condition assessed (roof, foundation, systems) through a home inspection
- Parking confirmed
- Property tax classification checked
- Insurance quote obtained for a duplex (owner-occupied or landlord)
- Cash flow worked out with vacancy and maintenance allowances
- The province’s rent increase rules reviewed
Sources
The figures and rules on this page come from these sources, last checked against them on September 29, 2026. How we check facts.
- Canada Guaranty: Rental Advantage - Canada Guaranty Mortgage Insurance Company
- CMHC: CMHC Improvement
- CMHC: CMHC Purchase
- CMHC: Rental Income
- CMHC: Mortgage Loan Insurance for Standard Rental Housing
- CMHC: Calculating GDS / TDS
- Financial Consumer Agency of Canada: How much you need for a down payment