Legal Basement Apartments
Fully permitted secondary suites, built to current code.
Design-build basement apartments across Mississauga and the GTA — engineered, permitted, inspected, and finished to a standard that lasts.
What We Build
A legal basement apartment — also called a secondary suite or additional residential unit — is a self-contained dwelling within an existing home, built to the 2024 Ontario Building Code and your municipality's zoning bylaws. Once permitted and inspected, it can be legally rented or occupied by extended family.
ScaleBig handles the project end-to-end: design, engineering coordination, permits, construction, and final municipal sign-off. Each suite includes a separate entrance, full kitchen and bath, fire and sound separation from the main dwelling, egress windows, dedicated mechanical systems, and finishes selected during the design phase.
A fully legal suite is meaningfully different from a finished basement. The construction is more complex, the inspections are real, and the result is an income-generating asset with insurance coverage and resale value — not an off-the-books arrangement that puts homeowners and tenants at risk.
Our Approach
Most basement apartments fail in one of three places: ceiling height, separate entrance, or zoning. We address those before design begins. A site visit and feasibility review establishes what's possible on your specific property before any drawings or budget commitments are made.
Design is led by Dina, in-house. Layouts, finish selections, and photorealistic 3D renderings are developed before construction starts. The same trades — vetted, accountable, and consistent across our projects — handle every phase of the build, and Ahmad manages the project on site from start to handover.
We coordinate engineering for any structural work, pull every required permit, and schedule each inspection at the right stage. The result is a suite that passes municipal sign-off the first time — not one that requires renegotiation with the city after the fact.
What's Included
A complete legal basement apartment build typically includes the following scope. Specific inclusions vary by site conditions and the homeowner's selections.
Site Assessment & Feasibility
Ceiling height verification, separate entrance review, zoning confirmation, and structural assessment before design begins.
Design & 3D Renderings
Full layout, finish selection, fixture specification, and photorealistic renderings produced by Dina before construction starts.
Architectural & Engineering Drawings
Stamped drawings as required for permit submission and any structural modifications.
Permit Application & Coordination
Building permit application, electrical (ESA) permit, and coordination with the municipality through every inspection stage.
Structural Work
Beam installations, load-bearing modifications, and below-grade entrance construction where required, executed from engineered drawings.
Rough-Ins
Framing, plumbing, electrical, HVAC, and ventilation rough-ins to current code, including dedicated panel and separate water lines where applicable.
Fire & Sound Separation
Code-compliant fire-rated assemblies between units, plus acoustic upgrades that meaningfully reduce sound transmission beyond minimum requirements.
Egress Windows
Window sizing, cutting, and installation to meet egress requirements for any bedroom location.
Insulation & Waterproofing
Wall and ceiling insulation to current OBC requirements, plus waterproofing at affected foundation areas.
Drywall & Finishing
Drywall installation, taping, mudding, sanding, and primer.
Flooring, Tile, and Trim
Luxury vinyl plank, tile, baseboards, trim, and door installation to the finish standard selected during design.
Kitchen & Bathroom Build-Out
Cabinetry, countertops, plumbing fixtures, custom tile work in wet areas, lighting, and appliance integration.
Electrical & Lighting
Fire-rated pot lights, dedicated circuits, separate panel for the suite, and any required upgrades to the main panel.
Life Safety Systems
Interconnected smoke and carbon monoxide alarms across the full home, sized and wired to current code.
Final Inspections & Sign-Off
Coordination of every municipal inspection through to occupancy and final approval.
Project Management
Daily on-site management by Ahmad from start to handover, with direct contact throughout the project.
What Determines the Cost
Legal basement apartments in the GTA typically range from $75,000 to $150,000 or more. The number depends less on basement size than on the specific conditions of the property and the finish level selected. The factors below are what move the budget within and beyond that range.
Existing Conditions
Whether the basement is unfinished, partially finished, or has prior unpermitted work that needs to be opened up and verified. Older homes with low ceilings, small windows, or limited foundation drainage typically require more work to bring to code.
Below-Grade Entrance
If a separate entrance does not already exist, adding one involves excavation, retaining walls, drainage, waterproofing, and engineered stairs. This is one of the most cost-significant items in a basement project.
Structural Modifications
Removing a load-bearing wall to open the floor plan, or underpinning to gain ceiling height, requires engineered drawings and substantially different construction. Both are routine for us; both meaningfully change the budget.
Egress Window Requirements
If bedroom windows are undersized, they need to be cut to egress specifications — work that involves the foundation wall and typically requires engineering review.
Mechanical & Electrical Scope
Separate electrical panel, dedicated HVAC strategy, separate water lines, and code-compliant ventilation all add real cost. Older homes sometimes require main-panel upgrades to support the additional load.
Finish Level
The same suite can be built to a tenant-suitable standard or to a near-main-floor standard. Cabinetry, tile, fixtures, flooring, and trim choices have significant cumulative impact.
Permit & Inspection Coordination
This is included on every project, but the time and detail involved varies by municipality and scope. Larger structural projects involve more inspection stages.
A specific budget for your project is developed during the site assessment, after we've reviewed the conditions and discussed the scope you're looking for.
The Process
Every legal basement project at ScaleBig follows the same sequence. The timeline below reflects an average project — specific milestones vary by scope and municipal review times.
- 01
Site Assessment
We visit the property, measure finished heights, review existing conditions, and confirm zoning. We give you an honest read on whether the project is feasible and what scope it will likely require.
- 02
Design & Renderings
Dina develops layout options, finish selections, and photorealistic 3D renderings. You see the finished space in detail before construction begins, and material decisions are made with full visibility.
- 03
Drawings & Permits
Architectural drawings and any required engineered drawings are produced. We submit the permit application to the municipality and manage the review process.
- 04
Proposal & Agreement
A complete, itemized proposal is presented with a fixed price, clear scope, milestones, payment schedule, and exclusions. Once signed, the project is scheduled.
- 05
Construction
Ahmad manages the project on site daily, with the same trades on every phase. Inspections are coordinated at each stage. You're informed of progress and consulted on decisions in real time.
- 06
Final Inspection & Handover
Municipal sign-off, ESA certification, a complete walkthrough, and handover of all documentation — permits, warranties, manuals, and inspection records.
Typical timelines: 4–8 weeks for design and permits, then 10–16 weeks of active construction depending on scope.
Where We Don't Compromise
Some elements of a legal basement build are easy to cut corners on. We don't.
Engineering
Any structural modification — load-bearing wall removal, beam installation, or below-grade entrance — is built from stamped drawings produced by a licensed Professional Engineer. No exceptions.
Sound Separation
We use resilient channel, Roxul Safe and Sound acoustic insulation, and 5/8" drywall as our standard sound assembly. This goes beyond minimum code and is the difference between a suite people can comfortably live in long-term and one that generates complaints.
Fire Separation
Every fire-rated assembly is built to the specified rating using the right materials, in the right sequence, with no substitutions. Self-closing fire-rated doors are sized and installed correctly, not retrofitted from standard hardware.
Permits & Inspections
We pull every required permit and schedule every required inspection. If your project requires a permit, it gets one. If it doesn't, we'll be straight with you about that as well.
Trades Accountability
The same plumbers, electricians, tilers, and finishers across projects. If work doesn't meet our standard, it gets corrected before the next phase begins.
Tools for Your Project
Two tools to help you evaluate whether a legal basement apartment is right for your home.
Basement Apartment Qualifier
A short assessment that estimates whether your basement may qualify under the current Ontario Building Code — ceiling height, entrance, egress, zoning, and a few other factors. Takes about two minutes.
Take the QualifierBasement Income Calculator
Estimate the rental income, payback period, and 10-year return on a legal basement apartment in the GTA. A simple tool for framing the project as an income asset.
Open the CalculatorFrequently Asked Questions
Selected Work
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Meadowvale Legal Basement — Hero Photo
Legal Basement Apartment
A Legal Basement in Meadowvale
Mississauga, ON
2-Bedroom · 1,200 sq ft · Structural
More case studies are published as projects complete. View all selected work →
Start with a site assessment.
Every legal basement project begins with a visit to the property — to verify the conditions, confirm what's possible, and produce a realistic scope and budget. If you're considering a basement suite for income or family, this is the right next step.
Book a Site AssessmentOr call Ahmad at 647-289-2823