Ontario Building Code
Basics Every Homeowner Should Know

A homeowner called us last spring after a friend-of-a-friend "framer" finished her basement. The bedroom had a 14-inch by 24-inch window. She thought it looked small but was told it would pass. The City inspector took one look and red-tagged the room. The window was nowhere near OBC egress dimensions. She had to rip the wall back open and cut a new opening to bring it into compliance, a cost that never needed to happen.

The Ontario Building Code (OBC) is the rulebook every Ontario inspector uses. It is roughly 1,200 pages, organized into Divisions and Parts. Most of it does not apply to your house. The pieces that do apply are clear, specific, and worth knowing before you sign a contract.

OBC Structure: Part 9 vs Part 3

The Code splits buildings by size. Almost every Ottawa home falls under Part 9: Housing and Small Buildings.

Part 9 covers buildings that are:

• Three storeys or less in building height
• 600 m² or less in building area
• Of residential, business, mercantile, or low-hazard industrial occupancy

If your house is bigger than that, it is governed by Part 3: Fire Protection, Occupant Safety and Accessibility, which is the "large buildings" framework. Part 3 means more fire-rating requirements, accessibility provisions, and engineered everything. For a typical Ottawa single-detached, semi, or row house, Part 9 is the document.

Part 9 is itself broken into 36 sections (9.1 through 9.36). The ones that come up in renovations are 9.5, 9.7, 9.9, 9.10, 9.11, 9.13, 9.25, 9.32, and 9.36. Here is what each one actually says, in plain language.

Section 9.10: Fire Protection

This is the section that drives basement legalization, secondary suite design, and any project where two dwelling units share a building.

Key rules:

• Fire separation between dwelling units: 45-minute fire resistance rating. Achieved with one layer of 5/8" Type X drywall on each side of the assembly with resilient channels and proper insulation.
• Smoke alarms: hardwired with battery backup, interconnected, on every floor including the basement, in every bedroom, and in the hallway outside bedrooms (Section 9.10.19).
• Carbon monoxide alarms: outside every sleeping area in any home with a fuel-burning appliance or attached garage (9.33.4).
• Service room separation: furnace room must be separated from the dwelling unit with a 45-minute fire-rated assembly.

If you are creating a second unit, budget for fire separation as a line of its own. The drywall, resilient channels, fire-rated doors, and labour to assemble each rated wall add up, and the scope scales with how much shared structure has to be separated. We itemize it in the written proposal so it is never a surprise.

Section 9.36: Energy Efficiency

The Code's energy section was overhauled in 2017 and updated in 2024. For Ottawa (Climate Zone 6), Section 9.36 sets minimum thermal performance for the building envelope.

Two compliance paths:

1. Prescriptive path (SB-12): pre-set R-values for each component. Walls R-22 effective, attics R-60, basement walls R-12 to R-20, slab R-7.5, windows U-1.6.
2. Performance path (HOT2000): model the whole house with energy software, achieve at least the equivalent reference performance. Lets you trade off (lower-R wall + higher-R attic).

For an addition or new dwelling unit, your BCIN designer will pick a path and submit the form. For a basement legalization, you typically use the prescriptive path with batt or rigid insulation on framed walls plus a 6-mil poly vapour barrier on the warm side.

Section 9.9.10: Egress from Bedrooms

This is the rule that saves lives in fires and that fails the most basement reno inspections.

Every bedroom must have a window that opens to the outside, with:

• Minimum 0.35 m² (about 3.8 sq ft) unobstructed openable area
• No dimension less than 380 mm (15 inches) when open
• Sill no higher than 1.5 m (about 4'-11") above the bedroom floor
• If the window is in a basement window well, the well must be at least 760 mm (30 inches) clear of the open sash

That last point is what trips contractors who measure the window opening but forget the well depth. We have a separate article on egress windows with the install details.

Skipping a window because "the homeowner doesn't want one" is not optional. A room without compliant egress is a "den" or "office," not a bedroom, and cannot be advertised or rented as a bedroom.

Section 9.5: Stairs, Ramps, Handrails

The most over-looked section in renovations. Every interior stair in a dwelling unit must have:

• Run (tread depth) between 235 mm and 355 mm (about 9¼" to 14")
• Rise (riser height) between 125 mm and 200 mm (about 5" to 7⅞")
• Width minimum 860 mm (34") clear between handrails and walls
• Headroom minimum 1.95 m (6'-5") measured vertically from the leading edge of the tread
• Handrail on at least one side, 865 mm to 965 mm above the nosing
• Guard at least 900 mm where stairs are open to a drop greater than 600 mm

If you are basement-finishing in an older Ottawa home built before 1990, the existing stair to the basement may not meet these. The OBC has retention rules for existing stairs (you can keep what's there if it serves the original layout), but the moment you change the access, the new stair has to comply.

Section 9.25: Heat, Air, and Moisture Control

This is the building science section. It covers:

• Insulation minimum thicknesses by component
• Air barrier continuity (the layer that stops air leakage; can be drywall, OSB, or membrane)
• Vapour barrier on the warm side
• Drainage layer behind cladding (rainscreen)
• Foundation dampproofing or waterproofing below grade

The headline issue in Ottawa is that older basements were never dampproofed properly. Before you finish a 1960s basement, run a dehumidifier for two months and watch the foundation walls. If you see efflorescence (white powder) or active staining, you need to fix the exterior or add an interior drainage system before any framing goes up.

Section 9.32: Ventilation

Every dwelling unit needs mechanical ventilation. The Code requires a Heat Recovery Ventilator (HRV) or principal exhaust fan sized to the dwelling.

For a typical 1,500 to 2,000 sq ft Ottawa home: HRV at 60 to 70 L/s (about 130 to 150 CFM) continuous capacity. Bathroom fans, kitchen range hoods, and dryer exhausts are separate.

For a new secondary suite, the basement unit needs its own HRV or its own balanced exhaust system. You cannot share the upstairs HRV across two dwelling units. This is a commonly overlooked cost driver on most basement legalizations, so we flag the separate ventilation system in the scope up front.

"The OBC is not picking on you. Every section exists because someone died or a building burned. Egress rules came from a fatal Toronto basement fire in 1995. Vapour barrier rules came from a wave of mouldy walls in the 1980s."

How the Code Gets Enforced in Ottawa

The City of Ottawa Building Code Services group enforces the OBC under the Building Code Act. The path is:

1. You submit the application via MyServiceOttawa
2. A plans examiner reviews the drawings against the OBC and By-law 2008-250
3. If the drawings comply, the permit issues
4. An inspector visits the site at the milestones (footing, framing, insulation, drywall, occupancy, final)
5. Each inspection either passes or generates a deficiency notice listing the OBC clauses you missed
6. You fix and re-inspect
7. Final inspection signs off the file

The whole framework runs on the OBC. Your contractor's opinion does not override the inspector's reading of the Code. Your designer's stamp does not override it either. The inspector is the final word on site.

What Homeowners Actually Need to Do

You do not have to memorize the OBC. You have to:

• Hire a designer who is BCIN-certified in the right field of practice
• Hire a contractor who has built to OBC for at least a decade
• Get a permit before work starts
• Be home for inspections when the inspector wants to come
• Read the deficiency list when one comes back, and not let your contractor brush it off

If you want a sanity check on whether your project plan is OBC-compliant before you spend on drawings, our permits team runs a free 48-hour lot feasibility review and will flag the Code issues we see most often on similar projects.