Three Parking Spaces Come Before a Second Unit in Oshawa

Second units and basement work in Oshawa

Oshawa's zoning wants three parking spaces on a two-unit property and four on a three-unit property, each one 2.75m by 5.75m. At least one of them has to sit in a side yard, rear yard or garage — not on the front pad — and the remaining spaces have to reach the street on their own, not stacked in tandem behind each other. On a 1960s single-wide driveway in Donevan or Eastdale, that is the whole conversation. We measure the driveway and the side yard on the first visit, before anyone talks about framing, because it decides whether you're building a registered two-unit house or an expensive rec room.

The second Oshawa-specific thing worth knowing: the city allows up to three dwelling units on a lot, and a maximum of one of those can be in an accessory building — a garden suite or a converted detached garage. That's a genuinely good deal for an investor. But Oshawa's own building services guide is blunt about the catch: once you go to three units, the Building Code treats the house as an apartment building, and the drawings have to be prepared and signed by an architect, engineer or BCIN designer certified in Small Buildings. A one- or two-unit conversion has a lighter path. We tell people which side of that line their plan lands on before they commit.

Oshawa's housing stock splits cleanly, and it maps almost exactly onto which houses are worth converting. O'Neill and Central are early-1900s — Edwardian, Tudor, Arts and Crafts — with low, cramped, often stone-walled basements that rarely hold a suite without underpinning. Vanier is 1940s–60s bungalows and 1.5-storeys, decent footprint, mixed headroom. The big band of 1960s–80s brick two-storeys, backsplits and sidesplits across McLaughlin, Eastdale, Donevan, Northglen and Centennial is where most of the real work is: generous lots, side yards you can actually run an entrance through, and lower levels that are already part-way above grade. Samac and Pinecrest are 1980s–90s and usually fine. Taunton and Windfields are 2000s and newer with tall basements — the easiest suites in the city, and the ones where a walkout does the most for resale.

Those Oshawa split-levels deserve their own note. Because the lower level is only partly below grade, a walkout or a separate entrance is often a shorter, cheaper dig than on a full-depth basement. What catches people is headroom: the Code allows 1.95m of clear ceiling in a basement secondary suite and 1.85m under beams and ductwork, and on a mid-century split with a low main beam and a duct trunk running the length of the house, the tape decides the layout. We shoot heights and mark the duct runs before we draw anything.

Our flagship is the separate entrance and walkout — typically built in three days. Excavation, engineered stairwell or grade-level walkout, waterproofing, drainage tied in properly, door, railings, backfill and restoration. Done as a standalone job it makes the basement rentable, or simply makes it liveable and lit. Done as step one of a suite, it becomes the dedicated exit the Code wants, and everything after it gets simpler.

From there we do the full legal second unit: fire separation between suites, egress and escape windows, interconnected smoke and CO alarms, return-air and ventilation, sound separation, separate kitchen and bath, and the drawings and permit work handled in-house. We also build garden suites and garage conversions, home additions when going out beats going down, and full home renovations — kitchens, bathrooms, basements, flooring, tile, countertops.

HMH Construction Inc. has been building in the GTA for over 25 years. WSIB covered, fully insured, permits handled in-house so you're not chasing a designer and an expediter yourself. Call 905-749-4608 and we'll tell you straight whether your Oshawa lot works.

Units per Lot

Oshawa permits a maximum of 3 residential dwelling units on a lot, of which a maximum of 1 accessory unit may be in an accessory building. Accessory apartments are permitted in single detached, semi-detached, duplex and street townhouse dwellings, and in residential accessory buildings, in R1, R2, R3, R5, OSR-A, OS-ORM, AG-A, AG-B and AG-ORM zones. Governed by Section 5.12 of Zoning By-law 60-94.

PARKING (the binding constraint in Oshawa) — Two units: 3 parking spaces, each 2.75m x 5.75m; at least one must be in a side yard, rear yard or garage; two must have unobstructed street access (not tandem). Three units: 4 spaces, same dimensions; one in side yard, rear yard or garage; three must have direct street access (not tandem).

Garden Suite / Accessory Building

Max height 4.5m (5m in R1-G and R1-H). Minimum 0.6m side/rear setback, minimum 3m from the main dwelling. Lot coverage capped at 8% of lot area / 50% of the house's coverage (100% for R1-G and R1-H) / 60m² ground floor (90m² for R1-G, R1-H). Exterior entrance needs an unobstructed 0.81m walkway to the street. Generally not permitted in the front yard.

Registration

Oshawa has a Two-Unit House Registration By-law; registration is mandatory and failure to register is an offence. Where the unit is built through the building permit process, the registration certificate is issued within 60 days of the building inspector's final inspection. Units created before July 1994 are legalized through a separate application to Municipal Licensing and Standards with a $500 fee and a two-unit declaration form. Municipal Licensing and Standards 905-436-3311 ext. 2299; Building Services ext. 2290.

RENTAL LICENSING (Oshawa-specific, distinct from registration) — Rental properties inside the Residential Rental Housing Licensing area around Durham College / Ontario Tech and the Simcoe Street North corridor also need a licence under the Licensing By-law (Schedule P). Class A = individually-owned dwelling units; Class B = 3+ units under single ownership. $50 application fee; Class A $275 base + $75/bedroom, valid 2 years. Council has directed consultation on a possible city-wide expansion. Relevant to any investor buying near the universities.

Conservation / Hazard

The city explicitly requires that an accessory apartment not be located within hazard lands or areas without safe access as identified by Central Lake Ontario Conservation Authority (CLOCA). Zoning By-law Subsection 5.12 was amended to ensure ADUs aren't built where there's no safe access during a natural hazard emergency. Properties in CLOCA regulated lands need a CLOCA permit; MTO and Metrolinx approvals may also apply. CLOCA has a two-zone flood policy and updated mapping for an area of Oshawa Creek upstream of the CP rail line, and reports roughly 2,510 flood-prone buildings across the watershed — Oshawa Creek, Harmony Creek and Farewell Creek all run through built-up older neighbourhoods.

CEILING HEIGHTS / OBC (from Oshawa's own OBC 2024 Basement Secondary Suites guide, last revised 2026-02-11) — Minimum 1.95m clear in a basement secondary suite; minimum 1.85m under beams and ducting. Part 11 of the OBC may allow more lenient requirements depending on building age. Oshawa's guide notes that a 3-unit building is an apartment building under the OBC (drawings must be prepared and signed by an architect, engineer or BCIN designer certified in Small Buildings) even though zoning treats it as a single detached dwelling with two accessory apartments. Drawings for a unit in an accessory building may be prepared by the owner or a design professional.

Walkout Detail Worth Using

Oshawa's guide states that where a basement walk-out is the dedicated exit, any existing sliding door serving as that exit needs a keyed mechanism so it can be locked from both inside and outside. Also: where an unenclosed exterior exit stair with more than 3 risers is the only egress, openings from the upper dwelling unit within 3m horizontally and less than 5m vertically above the stair must be protected with wired glass in fixed steel frames or glass block — or an alternative escape window solution is used.

Housing Stock

O'Neill and Central: early 1900s Edwardian/Tudor/Arts and Crafts plus some mid-century bungalows and splits. Vanier: mainly 1940s–60s bungalows and 1.5-storeys. McLaughlin, Eastdale, Donevan, Northglen, Centennial: 1960s–80s two-storey detached, backsplits and sidesplits, brick or brick-and-siding, generous lots. Samac and Pinecrest: later north-end subdivisions. Taunton and Windfields: 2000s and newer. Kedron is largely rural/unbuilt. Lakeview and Farewell are the south-end neighbourhoods near the lake.