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Ontario Building Code Window Requirements: Glass Area, Ventilation and Safety

Window rules in the 2024 Ontario Building Code: 5% glass for bedrooms, 10% for living rooms, bathroom vents, egress windows, guards and safety glass.
glass area for a bedroom, of the floor area
5%
glass area for a bedroom, of the floor area
glass area for living and dining rooms
10%
glass area for living and dining rooms
openable area per finished room or room group
0.28 m²
openable area per finished room or room group
openable area for a naturally vented bathroom
0.09 m²
openable area for a naturally vented bathroom

Last updated

Under the 2024 Ontario Building Code, a bedroom needs unobstructed window glass of at least 5% of its floor area and a living or dining room at least 10%, while bathrooms, laundries and basements need no window at all where electric lighting is provided (OBC Div. B 9.7.2.3.OBC Div. B 9.7.2.3. Minimum Window Areas(1) Except as required in Article 9.9.10.1. and Sentence (3), the minimum window glass areas for rooms in buildings of residential occupancy or rooms that are used for sleeping shall conform to Table 9.7.2.3. (2) The unobstructed glass area of a door or skylight is considered equivalent to that of a window. (3) Work…, Table 9.7.2.3.OBC Div. B Table 9.7.2.3. Glass Areas for Rooms of Residential Occupancy — Forming Part of Sentence 9.7.2.3.(1)Table 9.7.2.3 — Glass Areas for Rooms of Residential Occupancy — Forming Part of Sentence 9.7.2.3.(1) Location | Minimum Unobstructed Glass Area — With No Electric Lighting | Minimum Unobstructed Glass Area — With Electric Lighting Laundry, basement recreation room, unfinished basement | 4% of area served | Windows…). Windows also count toward natural ventilation, bedroom egress and fall protection, each with its own article.

This page covers windows in houses and other residential Part 9 buildings. Your building department has the final say. Energy performance of windows is set by Part 12 and SB-12, and window area near property lines is limited by the spatial separation rules, both covered elsewhere.

Window rules at a glance

Room or topic Rule in short Where to look
Living and dining rooms glass of 10% of the area served, with or without electric light Table 9.7.2.3.
Bedrooms and other finished rooms glass of 5% of the area served Table 9.7.2.3.
Kitchens 10% only if there is no electric lighting Table 9.7.2.3.
Bathroom (water-closet room) 0.37 m² only if there is no electric lighting Table 9.7.2.3.
Laundry, basement rec room, unfinished basement 4% only if there is no electric lighting Table 9.7.2.3.
Combined rooms the stricter requirement governs 9.7.2.3.(4)
Doors and skylights their glass counts as window area 9.7.2.3.(2)
Natural ventilation, finished rooms 0.28 m² openable per room or combination of rooms Table 9.32.2.2.
Natural ventilation, bathroom 0.09 m² openable Table 9.32.2.2.
Bedroom egress window 0.35 m² opening, no dimension under 380 mm 9.9.10.1.
Low windows on upper floors guard or opening limiter 9.8.8.1.
Safety glazing sliding doors, sidelights, shower enclosures and more 9.6.1.4.

This is our own summary. The code tables have more rows and notes, so read them before you rely on a value.

Natural light: minimum glass area

9.7.2.3.OBC Div. B 9.7.2.3. Minimum Window Areas(1) Except as required in Article 9.9.10.1. and Sentence (3), the minimum window glass areas for rooms in buildings of residential occupancy or rooms that are used for sleeping shall conform to Table 9.7.2.3. (2) The unobstructed glass area of a door or skylight is considered equivalent to that of a window. (3) Work… sends you to Table 9.7.2.3.OBC Div. B Table 9.7.2.3. Glass Areas for Rooms of Residential Occupancy — Forming Part of Sentence 9.7.2.3.(1)Table 9.7.2.3 — Glass Areas for Rooms of Residential Occupancy — Forming Part of Sentence 9.7.2.3.(1) Location | Minimum Unobstructed Glass Area — With No Electric Lighting | Minimum Unobstructed Glass Area — With Electric Lighting Laundry, basement recreation room, unfinished basement | 4% of area served | Windows… for the minimum unobstructed glass area in rooms of residential occupancy and rooms used for sleeping. The table has two columns: one for rooms with no electric lighting and one for rooms with it. The pattern is simple:

  • Living rooms, dining rooms and bedrooms always need windows, because the requirement is the same with or without electric light.
  • Kitchens, bathrooms, laundries and basement spaces need windows only where there is no electric lighting, which is rare in a new house.

The percentage is of the floor area the window serves. Only the clear glass counts, not the frame or sash.

Our worked example

A 12 m² bedroom needs at least 12 × 0.05 = 0.6 m² of unobstructed glass. An open living and dining area of 30 m² needs 30 × 0.10 = 3.0 m². If a den is open to that living room, the combined space takes the stricter value (9.7.2.3.(4)OBC Div. B 9.7.2.3. Minimum Window Areas(1) Except as required in Article 9.9.10.1. and Sentence (3), the minimum window glass areas for rooms in buildings of residential occupancy or rooms that are used for sleeping shall conform to Table 9.7.2.3. (2) The unobstructed glass area of a door or skylight is considered equivalent to that of a window. (3) Work…). A glazed patio door or a skylight in the room counts toward the total (9.7.2.3.(2)OBC Div. B 9.7.2.3. Minimum Window Areas(1) Except as required in Article 9.9.10.1. and Sentence (3), the minimum window glass areas for rooms in buildings of residential occupancy or rooms that are used for sleeping shall conform to Table 9.7.2.3. (2) The unobstructed glass area of a door or skylight is considered equivalent to that of a window. (3) Work…).

Ventilation: openable area

Light and air are separate tests. Every residential occupancy needs non-heating-season ventilation (9.32.1.2.OBC Div. B 9.32.1.2. Required Ventilation(1) Every residential occupancy shall incorporate (a) provisions for non-heating-season ventilation in accordance with Subsection 9.32.2., and (b) except as required by Sentences (2) and (3), if supplied with electrical power and a heating system, provisions for heating-season ventilation in accordance with Part 6…), which can be natural (openable windows) or mechanical. For natural ventilation inside a dwelling unit, Table 9.32.2.2.OBC Div. B Table 9.32.2.2. Natural Ventilation - Forming Part of Sentence 9.32.2.2.(1)Table 9.32.2.2. Natural Ventilation - Forming Part of Sentence 9.32.2.2.(1) Forming Part of Sentence 9.32.2.2.(1) Application | Location | Minimum Unobstructed Area Within a dwelling unit | Bathrooms or water-closet rooms | 0.09 m² Within a dwelling unit | Unfinished basement space | 0.2% of the floor area Within a… asks for:

  • 0.28 m² of openable area per finished room or combination of rooms, such as living rooms, bedrooms and kitchens;
  • 0.09 m² for a bathroom or water-closet room;
  • 0.2% of the floor area for unfinished basement space.

A room without that natural ventilation needs a mechanical system instead, sized under 9.32.2.3.OBC Div. B 9.32.2.3. Non-Heating-Season Mechanical Ventilation(1) Where a habitable room or space is not provided with natural ventilation as described in Article 9.32.2.2. and is mechanically cooled, its non-heating-season mechanical ventilation system shall (a) have the capacity to exhaust air from inside the room or space, or to introduce outdoor air into that room or space…. That is how a windowless bathroom complies: with an exhaust fan. Heating-season ventilation for houses is a separate topic in Subsection 9.32.3.

Bedroom egress windows

Every floor level with a bedroom needs at least one outside window, openable from inside without tools, with an unobstructed opening of at least 0.35 m² and no dimension less than 380 mm, unless a door on that level opens directly outside (9.9.10.1.OBC Div. B 9.9.10.1. Egress Windows or Doors for Bedrooms(1) Except where a door on the same floor level as the bedroom provides direct access to the exterior, every floor level containing a bedroom in a suite shall be provided with at least one outside window that (a) is openable from the inside without the use of tools, (b) provides an individual, unobstructed open…). Above the basement, the sill can be no higher than 1,000 mm. The full rules, including window wells, are on our bedroom egress window page.

Low windows and falls

In residential buildings, an openable window on an upper floor with a low sill needs a guard or an opening limiter that keeps the opening to 100 mm, unless the sill is high enough above the floor or close enough to the ground outside (9.8.8.1.OBC Div. B 9.8.8.1. Required Guards(1) Except as provided in Sentence (2) and except at the leading edge at the top of a flight, every surface to which access is provided, including but not limited to flights of steps and ramps, exterior landings, porches, balconies, mezzanines, galleries and raised walkways, shall be protected by a guard on each side…). The exact heights are explained on our guard height page. Note the tension with egress: an egress window cannot be blocked by a limiter that needs tools to release.

Safety glass

9.6.1.4.OBC Div. B 9.6.1.4. Types of Glass and Protection of Glass(1) Glass sidelights greater than 500 mm wide that could be mistaken for doors, glass in storm doors and glass in sliding doors within or at every entrance to a dwelling unit and in public areas shall be (a) safety glazing of the tempered or laminated type conforming to CAN/CGSB-12.1, "Safety Glazing," or (b) wired… requires tempered or laminated safety glazing, or wired glass, in places where people are likely to walk into glass:

  • sidelights more than 500 mm wide that could be mistaken for doors, storm doors and sliding glass doors at dwelling entrances and in public areas;
  • glass over 0.5 m² in other entrance doors where it extends to less than 900 mm from the bottom of the door;
  • shower and bathtub enclosures, which need Class A safety glazing.

Pane size limits for wind loads are in 9.6.1.3.OBC Div. B 9.6.1.3. Structural Sufficiency of Glass(1) Except as provided in Sentence (2), glass shall be designed in conformance with Article 4.3.6.1. (2) Where the building has an essentially uniform distribution of paths for air leakage, including operable openings, but no large openings that would permit wind gusts to rapidly enter the building and the building is….

Other window rules worth knowing

The general list in 9.7.2.2.OBC Div. B 9.7.2.2. Other Requirements for Windows, Doors and Skylights(1) Minimum sizes of doorways and doors within a barrier-free path of travel shall conform to Section 9.5. (2) The protection of window and door openings to protect persons from falling through them shall conform to Article 9.8.8.1. (3) Properties of windows and doors within exits shall conform to Section 9.9. (4)… points to every other article that touches windows: fall protection, exits, bedroom egress, fire spread (spatial separation), garage doors, firefighter access and ventilation. Main entrance doors to a dwelling unit need a viewer, glazing in the door, or a sidelight (9.7.2.1.OBC Div. B 9.7.2.1. Entrance Doors(1) A door shall be provided at each entrance to a dwelling unit. (2) Main entrance doors to dwelling units shall be provided with (a) a door viewer or transparent glazing in the door, or (b) a sidelight.).

Common mistakes

  1. Counting the whole window instead of the unobstructed glass.
  2. Forgetting the combined room rule for open-plan spaces.
  3. Confusing glass area with openable area. A big fixed window gives light but no ventilation.
  4. A bedroom egress window that is too small or has a high sill.
  5. Ordinary glass in a shower screen or patio door.

How to look it up yourself

In Division B, Part 9 of the 2024 Compendium, search for these phrases from the code text:

  • "Minimum Window Areas" (9.7.2.3.)
  • "Glass Areas for Rooms of Residential Occupancy" (the table)
  • "Natural Ventilation" (Table 9.32.2.2.)
  • "Egress Windows or Doors for Bedrooms" (9.9.10.1.)
  • "Types of Glass and Protection of Glass" (9.6.1.4.)

You can also open Table 9.7.2.3. in the code viewer.

BCIN exam angle

Glass area percentages and ventilation areas are easy marks on the House and Small Buildings exams, as long as you read the right column of the table. Study the free House chapter on rooms, spaces, glass, windows and doors or the Small Buildings chapter on Part 9 structure, rooms, glass and windows, and practise the area math in the areas and heights method. Then try the free quiz on the House exam or Small Buildings exam page.

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

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Frequently asked questions

What is the minimum window size for a bedroom in Ontario?
For natural light, a bedroom needs unobstructed glass of at least 5% of the floor area it serves (Division B, Table 9.7.2.3.). Separately, every floor level with a bedroom needs an egress window with an openable area of at least 0.35 m² and no dimension under 380 mm, unless a door on that level leads directly outside (Division B, Article 9.9.10.1.).
How much window does a living room need?
Living rooms and dining rooms need unobstructed glass of at least 10% of the floor area served, whether or not there is electric lighting (Division B, Table 9.7.2.3.).
Does a bathroom need a window in Ontario?
No. A water-closet room with electric lighting does not need a window for light. If it is not naturally ventilated through an openable area of at least 0.09 m², it needs mechanical ventilation instead (Division B, Table 9.7.2.3., Article 9.32.2.2. and Article 9.32.2.3.).
Does a basement need windows?
Laundry rooms, basement recreation rooms and unfinished basements need glass of 4% of the area served only where there is no electric lighting. With electric lighting, no window is required for light, but a basement bedroom still needs its egress window.
Do skylights or glass doors count toward window area?
Yes. The unobstructed glass area of a door or skylight counts the same as a window (Division B, Sentence 9.7.2.3.(2)).
When is safety glass required?
Among other places, in sliding glass doors, storm doors and sidelights over 500 mm wide that could be mistaken for doors at dwelling entrances, in larger glass panels low in entrance doors, and in shower and bathtub enclosures (Division B, Article 9.6.1.4.).