Legal Basement Apartment Requirements Ontario 2026: What the Code Actually Says (And What Inspectors Actually Check)

If you’ve been thinking about turning your basement into a legal rental unit, welcome to the club — half of Ontario seems to have the same idea. With GTA rents pushing past $2,400/month for basement apartments and the government actively encouraging secondary suites, the math makes sense. But the keyword here is legal. An illegal suite doesn’t just risk fines — it voids your insurance, tanks your resale value, and puts real people at real risk if something goes wrong.

This guide covers the actual 2024 OBC requirements that are now mandatory across Ontario. No guesswork, no outdated references to the 2012 code. Just the stuff your plans examiner and inspector will be checking — written by someone who’s watched both sides of the process more times than he can count.

📏 Ceiling Height: The First Thing to Measure

This is where most basement apartment projects die — not dramatically, but with a quiet tape measure and a long sigh. The 2024 Ontario Building Code requires a minimum ceiling height of 1.95 metres (6 feet 5 inches) throughout all habitable rooms in a secondary suite. Under beams, ducts, and other obstructions, you get a reduced clearance of 1.85 metres (6 feet 1 inch).

Before you call a contractor, before you draw plans, before you even daydream about rental income — go downstairs with a tape measure. Measure from the top of the concrete floor to the underside of the joists. Then subtract the thickness of your planned finished floor (typically 1–2 inches) and finished ceiling (½-inch drywall minimum). If you’re under 1.95m after those deductions, you have two options: underpin (excavate and lower the floor) or reconsider. Underpinning typically costs $40,000–$80,000+ in Ontario depending on soil conditions and access. It’s a real cost — but it’s also the only way to legally add height that doesn’t exist.

The 2024 code also lowered the basement design temperature from 22°C to 18°C. This doesn’t mean your tenant will be cold — it means the insulation and HVAC calculations are slightly different. Your mechanical designer should account for this. For a full breakdown of what changed, see the 2024 OBC changes overview.

Article 9.5.3 Part 9 – Housing and Small Buildings

🔥 Fire Separation: The Non-Negotiable

If inspectors had a greatest hits album, fire separation would be track one. The wall and ceiling assembly between your main dwelling and the basement apartment must provide a fire-resistance rating — and the specifics depend on whether your home is new construction or a retrofit of an existing building.

For new construction, you need a minimum 45-minute fire-rated separation between units. This typically means 5/8″ Type X drywall on both sides of the assembly, with all penetrations (electrical boxes, pipes, ducts) sealed with fire-stop materials. Every. Single. One. Inspectors carry flashlights and check behind things. They’re remarkably thorough when it comes to fire.

For existing homes (more than 5 years old), the requirements offer more flexibility. If you have fully interconnected smoke alarms throughout both units, the fire separation requirement may be reduced to 15 or 30 minutes depending on conditions. This is a significant cost saving for retrofit projects — but your plans examiner determines what applies to your specific situation.

One area where ICF construction has a distinct advantage is fire resistance — concrete walls inherently provide fire separation that wood framing can’t match without additional layers. If you’re building new, it’s worth considering for the foundation and basement walls.

🚨 Smoke and CO Alarms

Every secondary suite needs smoke alarms on every storey and in every bedroom. They must be interconnected between units — so if one triggers in the basement, the alarm in the upstairs hallway sounds too. Carbon monoxide alarms are required near sleeping areas if there’s a fuel-burning appliance (furnace, water heater) or an attached garage anywhere in the building. The 2024 OBC now permits wireless interconnection, which eliminates the need to run new wiring between floors — a real cost saver in existing homes.

Section 9.10 Article 9.10.9

🪟 Egress Windows: Your Exit Plan

Every bedroom in a basement suite needs an egress window large enough for a person to escape through in an emergency. The OBC specifies a minimum unobstructed clear opening of 0.35 m² (about 3.8 square feet), with no dimension less than 380 mm (15 inches). The maximum sill height from the finished floor is 1,500 mm (59 inches).

The word “clear opening” is where projects go sideways. This is not the size of the glass. It’s not the size of the frame. It’s the actual open space after you crank or slide the window open. Many homeowners buy a nice big window only to discover the clear opening is too small because of the sash mechanism. Casement windows (hinged on one side, swings fully open) generally provide the best clear opening for their size — and they’re the go-to choice for basement egress.

If your egress window sits below grade, you need a window well — and the well has its own requirements. It must be large enough for a person to stand in, and if the depth exceeds 600 mm (24 inches), it needs a permanently attached ladder or steps. Plan this during the foundation stage, not during finishing. If you’re retrofitting, budget for excavation along the foundation wall, cutting concrete, installing the window, and building the well with proper drainage.

Article 9.9.10 Part 9 – Housing and Small Buildings

🌡️ Heating, Ventilation & Insulation

Your basement suite must be independently heated to maintain livable temperatures. This doesn’t require a separate furnace — it can be a zone from the main system, electric baseboards, a mini-split, or another HVAC approach that suits your building. What matters is that the tenant can control the temperature in their unit independently.

The 2024 OBC requires full-height insulation on all basement walls — from floor to ceiling, not just partway up. Combined with a proper vapour barrier, this keeps the suite warm, reduces energy costs, and prevents the moisture and mould problems that plague uninsulated basements. If you’re building with insulated concrete forms (ICF), the insulation is already built into the wall system — which simplifies this entire requirement.

Ventilation is equally critical. Bathroom and kitchen exhausts must vent to the outdoors — not into a soffit, not into the joist space, not “close enough.” Fresh air supply must be adequate for the suite’s occupancy. If you’re in Simcoe County or anywhere in central Ontario, remember that our winters are long — an HRV (heat recovery ventilator) is an excellent investment for maintaining air quality without losing all your heat out the exhaust duct.

🔌 Plumbing & Electrical

A legal secondary suite needs its own kitchen and bathroom, which means plumbing work. You’ll need proper drain connections, venting (improper vent routing is a very common inspection failure), and in many cases a backwater valve to protect the suite from sewer backup. Your building permit application will need to show all plumbing layouts.

Electrical work must be inspected and approved by the Electrical Safety Authority (ESA) — this is a separate permit from your building permit. You’ll need dedicated circuits for the kitchen (fridge, range, dishwasher), GFCI-protected receptacles in the bathroom and kitchen, and adequate general lighting and outlets. If you’re unsure whether your existing service can handle the additional load, use the Electrical Load & Wire Size Calculator to get a starting estimate before calling your electrician.

📋 The Permit Process

You cannot legally build a secondary suite without a building permit. Full stop. The process: submit professional drawings showing the floor plan, elevations, fire separation details, HVAC layout, and plumbing/electrical plans. Your plans examiner reviews everything for OBC compliance. Once the permit is issued, you build — and you’ll face several rounds of inspections at key milestones: framing, rough-in (plumbing, electrical, HVAC), insulation, and final.

Don’t start work before the permit is issued. Don’t deviate from the approved plans without getting a revision approved. And don’t — under any circumstances — cover up framing or rough-in work before the inspector signs off. If they can’t see it, they’ll make you open it up. At your expense. For a full walkthrough, see our complete guide to getting a building permit in Ontario.

🎯 Are You Ready? The Self-Qualification Checklist

Before you spend money on drawings or contractors, run through this honest self-assessment. If you can’t check most of these boxes, you may want to do more research before committing.

💰 What It Actually Costs

Let’s talk numbers — because that’s really why you’re here. A legal basement apartment in Ontario typically costs $80–$150 per square foot in the GTA, depending on scope and finishes. For a 700-square-foot suite, that’s roughly $56,000–$105,000. Add underpinning if needed and the total can push past $150,000. Factor in permit fees ($500–$2,000+), ESA inspection fees, professional drawings ($2,000–$5,000), and a 10–15% contingency — because something always surprises you.

The payoff: rental income of $1,500–$2,500/month in most Ontario markets — that’s $18,000–$30,000 per year. Most homeowners recover their investment in 3–5 years while adding permanent value to the property.

If you’re building a new home and want to include a secondary suite from day one, the cost is dramatically lower because the foundation, plumbing rough-ins, and separate entrance can be designed in from the start. This is especially true with ICF custom home construction where the basement walls are already insulated, fire-rated, and moisture-resistant — three expensive problems solved before framing even starts.

🔧 Ontario-Specific Realities

A few things that national guides won’t mention but Ontario builders deal with constantly:

Frost depth: If your egress window well needs new footings, they must extend below the frost line — which varies from about 1.2m in southern Ontario to 1.8m+ in Simcoe County and northern areas. This affects excavation cost and timeline.

Radon rough-in: The 2024 OBC now requires all new Ontario homes to have a sub-floor depressurization rough-in for radon mitigation. If you’re building new with a suite, this is part of the package. For existing homes, it’s not retroactively required — but it’s smart practice, especially in areas with known radon levels like parts of the Ottawa Valley and eastern Ontario.

Scheduling trades: In the GTA, booking a plumber, electrician, and HVAC contractor for a coordinated basement project can take 4–8 weeks of lead time. In Simcoe County and Georgian Bay, it can stretch longer during building season (May–October). Start booking trades early — ideally before your permit is issued.

Insurance: Tell your insurance company about the suite before you start renting. A legal, permitted suite is typically covered. An undisclosed or illegal suite can void your entire policy — not just for the basement, but for the whole house. This is not an area where “what they don’t know won’t hurt them” applies.

Winter construction: If you’re planning excavation for window wells or underpinning, schedule it for spring through fall. Frozen ground in Ontario adds significant cost and complexity. The best time to start the planning and permit process is January–March, so you’re ready to break ground when the frost comes out.