Durham Region Second-Suite Specialists

Legal Basement Apartment
in Oshawa

Turning your basement into a legal, income-generating apartment in Oshawa means meeting two sets of rules: the City's Zoning By-law and the Ontario Building Code. Here's exactly what Oshawa requires — and how Cornerstone gets your suite approved, built, and registered the right way.

Start Your Basement Diagnostic Call 1-888-404-7383

The Two Rule Books

What Makes a Basement Apartment "Legal" in Oshawa

An accessory apartment — officially an Additional Residential Unit (ARU) — only becomes legal when it satisfies both the City of Oshawa's Zoning By-law 60-94 (which governs parking, lot layout and where a unit is allowed) and the Ontario Building Code (which governs the inside of the unit — room sizes, ceiling height and safe exits).

Oshawa Zoning

Sets the outside rules: how many units your lot allows, parking, landscaping, setbacks and where the suite entrance can go.

Ontario Building Code

Sets the inside rules: minimum room dimensions, ceiling height, fire separation, smoke/CO alarms and a safe means of escape.

Rule Book 1

Oshawa Zoning Requirements

Under Oshawa Zoning By-law 60-94, these are the property-level rules your home must satisfy to add a legal second unit.

Parking

  • One additional space is required for the accessory suite, on top of the two required for the main home — three spaces total for a two-unit property.
  • Each space must measure at least 2.75 m × 5.75 m (about 9 ft × 19 ft).
  • Two of the spaces must have unobstructed street access — they can't all be lined up single-file. The third may be tandem.
  • At least one space must sit in a side yard, rear yard, or garage.
  • Creating street-accessible spaces often requires a curb cut, which must be approved by the City (city street) or the Region of Durham (regional road).

Landscaping & Lot

  • At least 50% of the front yard (and exterior side yard on a corner lot) must stay as landscaped open space — you can't pave the whole yard for parking.
  • A hard-surface, unobstructed walkway at least 0.81 m (32 in) wide must run from the suite's exterior entrance to the street line.
  • Maximum 3 residential units per lot, of which a maximum of one accessory unit may be inside an accessory building (garden suite).
  • Minimum lot frontage varies by zone (R1-A, R1-B, R1-C and so on) under By-law 60-94. Cornerstone confirms your property's exact zoning and frontage requirement during the planning stage.

Location Limits

  • The suite can't be on hazard lands or areas without safe access identified by CLOCA (Central Lake Ontario Conservation Authority).
  • Properties near an MTO highway corridor (Hwy 401/407) or a Metrolinx transit corridor may need separate agency approvals.
  • If your lot doesn't quite meet a zoning rule, a minor variance through the Committee of Adjustment may still make it possible.

Rule Book 2

Ontario Building Code: Inside the Suite

Oshawa doesn't set a single minimum apartment size in its zoning. Instead the interior is governed by the Ontario Building Code, which sets minimum areas room by room.

Separate (Walled-Off) Rooms

RoomMinimum Floor Area
Living Room13.5 m² (145 ft²)May reduce to 11 m² if combined with other space in a one-bedroom unit.
Kitchen4.2 m² (45 ft²)May reduce to 3.7 m² in a one-bedroom unit.
Dining Room7.0 m² (75 ft²)May reduce to 3.25 m² if combined with another room.
Primary Bedroom9.8 m² without a closet, or 8.8 m² with a built-in closet.
Additional Bedrooms7.0 m² without a closet, or 6.0 m² with a closet.
BathroomNo set area — must fit a toilet, sink and tub/shower with proper clearance.

Open-Concept / Bachelor

For a studio or bachelor unit, the combined sleeping, living, dining and kitchen space must be at least 13.5 m² (145 ft²) total, designed for no more than two occupants.

Ceiling height rule: across living areas the ceiling must be at least 1.95 m (6 ft 5 in). It may drop to 1.85 m directly under beams or HVAC ducting. Low basement headroom is the most common reason a suite needs design work before it can be approved.

Carbon monoxide alarms (effective Jan 1, 2026): in addition to CO alarms outside all sleeping areas, Oshawa now requires a CO alarm on every storey of the dwelling.

Permit & Registration

How a Legal Suite Gets Approved

A legal second unit isn't just built — it's permitted, inspected and registered. Here's the path.

Confirm Your Zoning

We check your property's zone, frontage, parking feasibility and any CLOCA, MTO or Metrolinx considerations before committing to a layout.

Design & Drawings

Scaled drawings showing existing and proposed floor plans, room areas, egress, fire separations, and smoke/CO alarm locations — prepared to Oshawa's submission standards.

Building Permit

The application is submitted through Oshawa's portal as an added dwelling unit. A building permit is required for any second unit created after July 1994.

Build & Inspections

We build to code and pass the required inspections — fire separation, egress, plumbing and electrical — through to final sign-off.

Automatic Registration

When a suite is created through the building-permit process, it's registered as a two-unit house. Your certificate is issued within 60 days of the inspector's final inspection.

Already have an unregistered unit? A suite created before July 1994 may be legalized through Municipal Licensing & Standards (a registration application, a $500 fee and a declaration) instead of a building permit. We can tell you which path your home falls under.

Why Build It Legal

A Registered Suite Is Worth More

Real Rental Income

A legal, registered unit can be advertised and rented with confidence — tenants can even verify its registration with the City.

Resale Value

Officially recognized as a two-unit house, the property is worth more and simpler to sell — buyers aren't inheriting an unpermitted risk.

Safety & Insurance

Code-built fire separation, egress and alarms protect your tenants and your home — and keep your insurance valid.

Built Once, Built Right

An unpermitted suite can be ordered closed and torn out. Doing it legally the first time protects the investment for good.

Common Questions

Oshawa Basement Apartment FAQ

How many units can I have on my Oshawa lot?
Up to three residential dwelling units per lot under By-law 60-94, of which a maximum of one accessory unit may be located inside an accessory building (such as a garden suite or converted garage).
Do I really need extra parking?
Yes. One additional space is required for the suite, bringing a two-unit property to three spaces total — each at least 2.75 m × 5.75 m, with two spaces having unobstructed street access. Creating those spaces sometimes needs an approved curb cut.
My basement ceiling feels low — is that a dealbreaker?
Not necessarily. The Code requires about 1.95 m (6 ft 5 in) across living areas, dropping to 1.85 m under beams and ducts. Many Oshawa basements qualify; where they're tight, design choices (relocating ducts, adjusting the layout) often solve it. We assess this early so there are no surprises.
What lot frontage do I need?
Minimum frontage isn't a single number — it varies by your property's zone (R1-A, R1-B, R1-C and so on) under By-law 60-94. We confirm your exact zoning and the frontage requirement during the planning stage, before any work begins.
Does the suite get registered automatically?
When you create the unit through the building-permit process, it's registered as a two-unit house and you receive your certificate within 60 days of the final inspection. A suite built before July 1994 follows a separate legalization path through Municipal Licensing & Standards.
What affects the cost of a legal basement apartment?
Ceiling height and whether the floor needs lowering, a separate entrance, egress windows, parking and curb-cut work, the kitchen and bathroom layout, fire separation, and electrical/HVAC separation all drive cost. After a site visit we give you a clear, locked scope and price — not a guess.
Bylaw information last reviewed June 2026. Municipal requirements can change — Cornerstone confirms current City of Oshawa requirements with the building department on every project. Sources: City of Oshawa Accessory Apartments & Two-Unit Houses pages and Zoning By-law 60-94; Ontario Building Code.
Part of Our Durham Legal Suites Guide
See requirements for every Durham town, plus the full second-suite overview
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Legal Basement Apartments Across Durham
We also build legal second suites in nearby Whitby, Clarington, and across Durham Region.

Thinking About a Legal Basement Apartment in Oshawa?

Start with a basement diagnostic. We'll confirm whether your property qualifies, map out the path to a legal, registered suite, and give you a clear scope and price — built once, built right.

Start Your Basement Diagnostic Call 1-888-404-7383

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