BuildRules/Oshawa/Basement secondary suite

Oshawa project guide

What do you need for a basement secondary suite in Oshawa?

Check Oshawa basement secondary-suite building permit requirements using the City’s updated 2024 Ontario Building Code guide.

1 min readReviewed Oct 1, 2026

The short answerConditional

Adding a dwelling unit or apartment requires a building permit, and Oshawa publishes a dedicated 2024 Building Code guide for basement secondary suites.

The guide is for basement secondary suites in existing buildings and distinguishes those projects from detached accessory-building units or third units.

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Know what matters

What changes the answer.

Start with these conditions. The official reference is attached to each one.

Dwelling unit / apartmentPermit requiredConditional

Oshawa lists adding a dwelling unit or apartment among projects requiring a building permit.

Official sourceCity of OshawaBuilding Permits · Residential permit triggers and project resources

Verified2026-10-01Open proof

Basement secondary suiteDedicated 2024 OBC guidanceInfo

Oshawa publishes a current guide for basement secondary suites in existing buildings.

Official sourceCity of OshawaOntario Building Code Guide to Basement Secondary Suite · Basement secondary-suite Building Code guidance

Verified2026-10-01Open proof

Project scopeDetached accessory units / third units use different requirementsConditional

The City guide states that its basement-secondary-suite content does not apply to an accessory-building dwelling unit or addition of a third unit.

Official sourceCity of OshawaOntario Building Code Guide to Basement Secondary Suite · Basement secondary-suite Building Code guidance

Verified2026-10-01Open proof

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Building permit application
Existing and proposed floor plans
Life-safety and separation details
Plumbing/mechanical information
Project-specific designer information

Open the focused permit checklist

Fees and timing

TimelineConfirm the current municipal review timeline after the application is accepted as complete.

FeesConfirm the current Oshawa permit fee for the exact project class before filing.

Next steps

Confirm this is a basement second unit in an existing building
Review the City’s 2024 OBC guide
Prepare the complete permit drawings
Submit before construction

Same project, different city

See how this rule changes across Ontario.

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BuildRules principle

Do not confuse “no permit” with “no rules.”

Zoning, overlays, safety rules and other constraints can still apply.

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The addition permit must also meet applicable zoning, Building Code and other municipal requirements.

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