BuildRules/Mississauga/Additional residential unit / second unit

Mississauga project guide

What do you need to create a basement apartment or second unit in Mississauga?

Check Mississauga second-unit and additional-residential-unit requirements, including permits, registration, drawings, zoning and inspections.

1 min readReviewed Oct 1, 2026

The short answerConditional

A new or converted second unit needs the applicable building permit work and must meet Building Code, Fire Code and zoning requirements; second units are also registered with the City.

Mississauga treats an additional residential unit as more than a basement finish. Conversion drawings, applicable-law information and registration are part of the route.

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What changes the answer.

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

PermitBuilding permit route appliesConditional

Mississauga lists basement apartments among permit-required projects and publishes an ARU conversion submission checklist.

Official sourceCity of MississaugaWhen a building permit is required · Permit-required and permit-exempt project examples

Verified2026-10-01Open proof

Conversion documentsDedicated checklistInfo

The City requires project-specific forms and drawings when converting existing space into a second, third or fourth unit.

Official sourceCity of MississaugaAdditional residential unit conversions · Second, third and fourth unit conversion documents

Verified2026-10-01Open proof

RegistrationRequired for second unitsConditional

Mississauga states that second units must meet code and zoning requirements and be registered with the City.

Official sourceCity of MississaugaRegistering a second unit · Registration, permit and inspection requirements

Verified2026-10-01Open proof

Your preparation checklist

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Applicable Law Form
Application to Register a Second Unit where applicable
Schedule 1 Designer Information
Existing and proposed floor plans
Site plan and service information required for the conversion

Open the focused permit checklist

Fees and timing

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

FeesConfirm the current Mississauga fee schedule for the exact permit class.

Next steps

Confirm the property and unit configuration
Prepare conversion drawings
Apply for the building permit
Complete inspections and registration requirements

Same project, different city

See how this rule changes across Ontario.

Compare the source-reviewed answer for this project across every municipality BuildRules currently covers.

Compare additional residential unit / second unit rules by city

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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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Do you need a permit to finish a basement in Mississauga?

Mississauga explicitly lists finishing a basement to create rooms or living space as permit-required. A basement apartment is a different scope and uses the additional-residential-unit conversion route.

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The City also has zoning provisions controlling where basement entrances can be located. The permit package includes site, basement/foundation, floor-plan and section information.

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