Modular Homes & Garden Suites in Oshawa, Ontario

Getting your building permit in Oshawa

An eligible lot still needs a building permit before anything is delivered. Here's how Oshawa's process actually works — verified against the Oshawa building department's own pages.

How do you apply for an ADU building permit in Oshawa?

Through Oshawa Application Portal (application portal ↗). Building-permit applications are submitted online through the Oshawa Application Portal (servicecv.oshawa.ca) — you create an account, select 'add dwelling unit', upload the required PDF documents to the City's digital submission standards, then check status, request inspections and pay fees through the same account. A permit is only issued after fees are paid. Oshawa's building-permit page ↗

1. Confirm your lot qualifies under Zoning By-law 60-94, s. 5.12 — a detached ADU (an 'accessory apartment within an accessory building') is capped at 60 m² ground floor (90 m² in R1-G/R1-H zones), 4.5 m height, max 1 per lot within a 3-unit maximum, and needs a 0.81 m hard-surfaced walkway from its entrance to the street
2. Clear 'applicable law' items before you apply — a CLOCA permit if the lot touches regulated hazard lands, Region of Durham approval for sewer and water connections, and MTO/Metrolinx clearances near Highway 401/407 or transit corridors
3. Prepare the drawing package: a plan of survey sealed by an Ontario Professional Engineer or Land Surveyor (required for a new accessory-building dwelling), site plan, architectural/structural drawings, HVAC design (SB-12) and plumbing information, formatted to the City's digital submission standards
4. Apply on the Oshawa Application Portal — select 'add dwelling unit', complete the provincial Application for a Permit to Construct or Demolish with Schedule 1 (designer information) and the Applicable Law Checklist, enter the new unit's area, and upload the documents as PDFs
5. Respond promptly to Building Permit Services review comments, then pay the permit fee through your portal account before the permit is issued
6. Build with mandatory inspections at each stage; a final Roadway Restoration (R.R.A.F.) inspection is required after construction to close the file
7. Registration is automatic: when the unit is created through the building-permit process, the City issues your two-unit house registration certificate within 60 days of the building inspector's final inspection

What does a Oshawa ADU permit application need?

• Provincial Application for a Permit to Construct or Demolish (2026 form)
• Schedule 1: Designer Information
• Owner's authorization form (if the applicant is not the property owner)
• Applicable Law Checklist
• Plan of survey sealed by an Ontario Professional Engineer or Land Surveyor (required for a new accessory-building dwelling)
• Site plan showing lot dimensions, all buildings, setbacks, both unit entrances, parking spaces (2.75 m × 5.75 m) and the 0.81 m unobstructed walkway to the street
• Architectural drawings — floor plans, cross-sections and elevations with limiting-distance calculations, window/door sizes, fire separations, smoke/CO alarm locations
• Structural drawings
• HVAC design summary with heat loss/gain calculations (SB-12 EEDS form)
• Plumbing information form for water-distribution sizing (plumbing drawings waived if a provincially licensed plumber does the work)
• Region of Durham approval for sewer and water connections, if applicable
• Roadway Restoration Deposit Form
• All files as PDFs meeting Oshawa's digital submission standards

How much does an ADU building permit cost in Oshawa?

Expect roughly $870 in City of Oshawa building-permit fees for a typical ~600 sq ft (56 m²) detached ADU at the 2026 house-class rate of $15.56 per square metre ($160 minimum), with plumbing included when installed with the build, plus a roadway-restoration deposit — an estimate; the exact fee is calculated when you apply through the Application Portal.

Oshawa's development-charge page lists full DC rates by unit type ($40,720 for a single-detached under By-law 91-2024) without an ADU-specific note, but provincially the Development Charges Act exempts up to two additional residential units on an existing single-detached lot — including one in an ancillary structure like a garden suite — subject to the regulation's rules; Development Charges Information Forms (City, Region of Durham, school boards) are part of the application package, so confirm the exemption applies to your project with Building Services.

How long does an ADU building permit take in Oshawa?

Ontario's Building Code requires a decision on a complete house-class application within 10 business days. Oshawa cautions that processing times vary with the type of construction, plan quality and application volume — the City notes record-breaking application volumes mean review timeframes may not always be met, and incomplete or premature applications (e.g., those needing rezoning or site-plan approval first) fall outside the standard timelines.

Registration: Oshawa's Two Unit House Registration By-law 41-2001 requires registration of two-unit houses city-wide (failure to register is an offence). When you create the unit through the building-permit process, registration is automatic — the certificate arrives within 60 days of the final inspection at no separate fee; the $500 application fee applies only when legalizing a unit created before July 1994. Separately, rental properties in the licensing area around Durham College and Ontario Tech University need a Residential Rental Housing licence ($275 base + $75 per bedroom + $50 application, 2-year term) — that regime is area-specific, not city-wide.

Worth knowing before you apply

• A new detached ADU triggers a sealed plan of survey requirement (Ontario Professional Engineer or Land Surveyor) — budget for the survey before applying
• The detached unit is size-capped by three tests at once: max 8% of lot area OR 50% of the house's lot coverage OR 60 m² ground floor (90 m² in R1-G/R1-H) — the smallest governs, plus a 4.5 m height limit and 3 m separation from the main dwelling
• ADUs are prohibited on hazard lands regulated by the Central Lake Ontario Conservation Authority (CLOCA) — a CLOCA inquiry/permit is a pre-step for lots near creeks, valleys or the shoreline
• Zoning requires a hard-surfaced, unobstructed walkway at least 0.81 m wide from the ADU entrance to the street, and a three-unit lot needs 4 parking spaces (2.75 m × 5.75 m, at least 1 in a side/rear yard or garage) with 50% of the front yard kept landscaped
• Applications must meet the City's digital submission standards (PDF format rules) — non-conforming uploads stall the review clock
• Applications deemed premature — needing rezoning, Official Plan amendment, site-plan agreement or subdivision registration first — will not be processed
• Permit fees rose 3% on January 1, 2026 (the $15.56/sq. m rate reflects this), and fees over $10,000 must be paid by cheque; a final R.R.A.F. roadway-restoration inspection is needed to close the permit file

Fees and timelines are estimates from Oshawa's published schedules, verified July 9, 2026. Rates and processes change — always confirm current requirements with the building department before you apply.