Skip to content
BCIN ExamBCIN Exam

Code guide

Ontario Building Code Basement Requirements

Basement rules in the 2024 Ontario Building Code: 2,100 mm ceilings, 1,950 mm under beams, bedroom egress windows, insulation, framing on concrete, alarms.
basement ceiling over 75% of the area
2,100 mm
basement ceiling over 75% of the area
under beams and ducts
1,950 mm
under beams and ducts
bedroom egress window opening
0.35 m²
bedroom egress window opening
wood above ground without dampproofing
150 mm
wood above ground without dampproofing

Last updated

A finished basement in Ontario needs a ceiling height of 2,100 mm over at least 75% of the basement area, dropping to 1,950 mm under beams and ducts (OBC Div. B Table 9.5.3.1.OBC Div. B Table 9.5.3.1. Room Ceiling Heights — Forming Part of Sentences 9.5.3.1.(1) and (4)Table 9.5.3.1 — Room Ceiling Heights — Forming Part of Sentences 9.5.3.1.(1) and (4) Room or Space | Minimum Heights[1] Living room or space, dining room or space, kitchen or kitchen space | 2,300 mm over at least 75% of the required floor area with a clear height of 2,100 mm at any point over the required area…). A basement bedroom needs an egress window with an opening of at least 0.35 m² and no dimension less than 380 mm (OBC Div. B 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…), and the basement needs a smoke alarm interconnected with the rest of the house (9.10.19.3.OBC Div. B 9.10.19.3. Location of Smoke Alarms(1) Except as permitted in Article 9.10.19.8., within dwelling units, sufficient smoke alarms shall be installed so that (a) there is at least one smoke alarm installed on each storey, including basements, and (b) on any storey of a dwelling unit containing sleeping rooms, a smoke alarm is installed (i) in each…).

This page gathers the main 2024 Building Code rules for finishing a basement in a house, with links to our detailed guides on each topic. Most basement finishing needs a building permit, and your building department decides how the code applies, so talk to them before you frame.

Basement rules at a glance

Item Rule in short Where to look
Ceiling height 2,100 mm over 75% of the area; 1,950 mm under beams and ducts Table 9.5.3.1.
Secondary suite ceiling 1.95 m; 1.85 m under beams and ducts 9.5.3.1.(2) and (3)
Bedroom egress window 0.35 m², no dimension under 380 mm, no basement sill limit 9.9.10.1.
Window well 550 mm clear in front of the window 9.9.10.1.(3)
Stair width and headroom 860 mm wide, 1,950 mm headroom 9.8.2.1., 9.8.2.2.
Smoke alarms every storey, every bedroom, interconnected 9.10.19.3., 9.10.19.5.
Wall insulation full height of foundation walls; SB-12 values 9.25.2.3.(4); SB-12
Wood on concrete poly or roll roofing unless treated or 150 mm up 9.23.2.3.
Joist ends in concrete treated, or a 12 mm air space 9.23.2.2.
Slab 100 mm granular fill under floors-on-ground 9.16.2.1.
Soil gas radon rough-in in new construction 9.13.4.

This is our summary of the articles, not a copy of the code. Read the full text before you build.

Permits first

Finishing a basement with new walls, a bedroom, a bathroom or any plumbing is usually a material alteration, and the Building Code Act treats plumbing as a building, so a permit is normally required. Cosmetic work such as painting or new flooring normally is not. Our building permit guide explains the rules and what to expect from inspections.

Ceiling height

Table 9.5.3.1.OBC Div. B Table 9.5.3.1. Room Ceiling Heights — Forming Part of Sentences 9.5.3.1.(1) and (4)Table 9.5.3.1 — Room Ceiling Heights — Forming Part of Sentences 9.5.3.1.(1) and (4) Room or Space | Minimum Heights[1] Living room or space, dining room or space, kitchen or kitchen space | 2,300 mm over at least 75% of the required floor area with a clear height of 2,100 mm at any point over the required area… sets 2,100 mm over at least 75% of the basement area, with 1,950 mm allowed under beams and ducts. A finished room in the basement, such as a bedroom or a family room, still has to meet the height rule for that room type, and the area with the full height must connect to the room's entry (9.5.3.1.(4)OBC Div. B 9.5.3.1. Ceiling Heights of Rooms or Spaces(1) Except as provided in Sentences (2) and (3), the ceiling heights and clear heights in rooms or spaces in residential occupancies and live/work units shall conform to Table 9.5.3.1. (2) Ceiling heights in secondary suites shall be not less than 1.95 m. (3) Clear heights under beams and ducting in secondary suites…).

A secondary suite has its own lower numbers: 1.95 m, and 1.85 m under beams and ducting (9.5.3.1.(2) and (3)OBC Div. B 9.5.3.1. Ceiling Heights of Rooms or Spaces(1) Except as provided in Sentences (2) and (3), the ceiling heights and clear heights in rooms or spaces in residential occupancies and live/work units shall conform to Table 9.5.3.1. (2) Ceiling heights in secondary suites shall be not less than 1.95 m. (3) Clear heights under beams and ducting in secondary suites…). Older houses may qualify for Part 11 alternatives. See ceiling heights and room sizes for the full table.

Basement bedrooms and egress windows

Every floor level with a bedroom needs at least one outside window, unless a door on that level leads directly outside. The window must open from the inside without tools, give an unobstructed opening of at least 0.35 m² with no dimension less than 380 mm, and stay open without extra support (9.9.10.1.(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…).

Two basement-specific points:

  • The 1,000 mm maximum sill height does not apply in basement areas (9.9.10.1.(2)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…), though a high sill is harder to climb out of in an emergency.
  • A window opening into a window well needs 550 mm of clear space in front of it, and any cover over the well must open from the inside without keys or tools (9.9.10.1.(3) and (5)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…).

Bedroom size rules also apply. See the bedroom egress window guide.

Basement stairs

Basement stairs inside a house are private stairs: at least 860 mm wide with 1,950 mm of headroom (9.8.2.1.OBC Div. B 9.8.2.1. Stair Width(1) Except as provided in Sentence (2) and Article 9.8.4.7., required exit stairs and public stairs serving buildings of residential occupancy shall have a width of not less than 900 mm. (2) Exit stairs serving a single dwelling unit or a house with a secondary suite including their common spaces shall have a width of…, 9.8.2.2.OBC Div. B 9.8.2.2. Height Over Stairs(1) The clear height over stairs shall be measured vertically, over the clear width of the stair, from a straight line tangent to the tread and landing nosings to the lowest point above. (See Note A-3.4.3.4.) (2) Except as provided in Sentences (3) and (4) and Article 9.8.4.7., the clear height over stairs shall not…), and a rise between 125 mm and 200 mm with a run between 255 mm and 355 mm (Table 9.8.4.1.OBC Div. B Table 9.8.4.1. Rise for Rectangular Treads, Tapered Treads and Winders and Run for Rectangular Treads — Forming Part of Sentences 9.8.4.1.(1) and 9.8.4.2.(1)Table 9.8.4.1 — Rise for Rectangular Treads, Tapered Treads and Winders and Run for Rectangular Treads — Forming Part of Sentences 9.8.4.1.(1) and 9.8.4.2.(1) Stair Type | Max. Rise, mm, for All Steps | Min. Rise, mm, for All Steps | Max. Run, mm, for Rectangular Treads | Min. Run, mm, for Rectangular Treads Private…). A new bulkhead or duct over the stair is the usual way basement renovations break the headroom rule. Our stairs guide covers handrails and guards.

Insulation and moisture

Insulation must cover the full height of foundation walls enclosing a basement (9.25.2.3.(4)OBC Div. B 9.25.2.3. Installation of Thermal Insulation(1) Insulation shall be installed so that there is a reasonably uniform insulating value over the entire face of the insulated area. (2) Insulation shall be applied to the full width and length of the space between furring or framing. (3) Except where the insulation provides the principal resistance to air leakage…), and in a finished area it must be protected by a covering such as gypsum board (9.25.2.3.(7)OBC Div. B 9.25.2.3. Installation of Thermal Insulation(1) Insulation shall be installed so that there is a reasonably uniform insulating value over the entire face of the insulated area. (2) Insulation shall be applied to the full width and length of the space between furring or framing. (3) Except where the insulation provides the principal resistance to air leakage…). The R-values for new houses come from Supplementary Standard SB-12, explained in our basement insulation guide.

Moisture rules that matter when framing:

  • Wood on concrete. Untreated wood framing supported on concrete in contact with the ground needs at least 0.05 mm polyethylene or Type S roll roofing between the wood and the concrete, unless the wood is at least 150 mm above the ground (9.23.2.3.OBC Div. B 9.23.2.3. Protection from Dampness(1) Except as permitted in Sentence (2), wood framing members that are not pressure-treated with a wood preservative and that are supported on concrete in contact with the ground or fill shall be separated from the concrete by not less than 0.05 mm polyethylene film or Type S roll roofing. (2) Dampproofing material…).
  • Joist and beam ends. Members framing into concrete at or below ground level must be treated against decay, or have a 12 mm air space at the end and sides that insulation must not block (9.23.2.2.OBC Div. B 9.23.2.2. Protection from Decay(1) Ends of wood joists, beams and other members framing into masonry or concrete shall be treated to prevent decay where the bottom of the member is at or below ground level, or a 12 mm air space shall be provided at the end and sides of the member. (2) Air spaces required in Sentence (1) shall not be blocked by…).
  • Floors. New floors-on-ground sit on at least 100 mm of coarse clean granular fill (9.16.2.1.OBC Div. B 9.16.2.1. Required Installation of Granular Fill(1) Except as provided in Sentence (2), not less than 100 mm of coarse clean granular material containing not more than 10% of material that will pass a 4 mm sieve shall be placed beneath floors-on-ground. (See also Subsection 9.13.4. and Note A-9.13.4.) (2) Granular material need not be installed under (a) slabs in…), and dampproofing rules for walls and floors are in 9.13.2.1.OBC Div. B 9.13.2.1. Required Dampproofing(1) Except as provided in Sentence (4) and Article 9.13.3.1., where the exterior finished ground level is at a higher elevation than the ground level inside the foundation walls, exterior surfaces of foundation walls below ground level shall be dampproofed. (2) Except as provided in Sentence (3) and Article 9.13.3.1.…

Smoke alarms, CO alarms and ventilation

A house needs a smoke alarm on every storey including the basement and in every bedroom, all interconnected (9.10.19.3.OBC Div. B 9.10.19.3. Location of Smoke Alarms(1) Except as permitted in Article 9.10.19.8., within dwelling units, sufficient smoke alarms shall be installed so that (a) there is at least one smoke alarm installed on each storey, including basements, and (b) on any storey of a dwelling unit containing sleeping rooms, a smoke alarm is installed (i) in each…, 9.10.19.5.OBC Div. B 9.10.19.5. Interconnection of Smoke Alarms(1) Where more than one smoke alarm is required in a dwelling unit, the smoke alarms shall be wired so that the activation of one alarm will cause all alarms within the dwelling unit to sound. (2) Smoke alarms in a house with a secondary suite shall be wirelessly interconnected or interconnected by hard-wiring so that…). Where there is a fuel-burning appliance or an attached garage, carbon monoxide alarms are needed next to each sleeping area, which includes basement bedrooms. See smoke and CO alarms.

A basement bathroom needs exhaust ventilation; the bathroom requirements guide explains the 25 L/s fan rule.

Radon

New construction must resist soil gas and include a rough-in for a subfloor depressurization system (9.13.4.OBC Div. B 9.13.4.1. Application and Scope(1) This Subsection applies to (a) wall, roof and floor assemblies separating conditioned space from the ground, and (b) the rough-in to allow the future protection of conditioned space that is separated from the ground by a wall, roof or floor assembly. (2) This Subsection addresses the leakage of soil gas from the…). When finishing an older basement, testing for radon before closing in the walls is a good idea. Our radon guide explains the rough-in.

Turning the basement into a suite

A basement apartment is a secondary suite under the 2024 code, with its own rules on fire separation, smoke alarms and ceiling height. Zoning decides whether a suite is allowed at all. Start with our secondary suite guide.

Common mistakes

  1. Finishing without a permit. New walls, bedrooms and plumbing usually need one.
  2. Low bulkheads. Beams and ducts can drop to 1,950 mm, and a stair needs the same 1,950 mm of headroom along its length.
  3. A "bedroom" with no egress window. Without the window or a door outside, the room cannot be called a bedroom.
  4. Bare wood plates on the slab. Use treated wood or a poly or roll roofing break.
  5. Insulation stopping short. It must cover the full height of the foundation wall.

How to look it up yourself

Open Division B, Part 9 of the 2024 Compendium. Search terms that appear in the code text:

  • "Basement space" (Table 9.5.3.1.)
  • "Egress Windows or Doors for Bedrooms" (9.9.10.1.)
  • "Protection from Dampness" (9.23.2.3.)
  • "Installation of Thermal Insulation" (9.25.2.3.)
  • "Required Installation of Granular Fill" (9.16.2.1.)

Read the article in the code viewer alongside the ceiling height table.

BCIN exam angle

Basement ceiling heights, egress windows and wood-to-concrete protection are typical House exam questions. Study the House chapter on rooms, spaces, glass, windows and doors and the chapter on means of egress, then try the free quiz on the House exam page.

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

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

Sources

Free accountNo card needed

Start practising for your BCIN exam, free

  • A free practice quiz for each exam
  • Every answer cites its 2024 OBC article
  • Full 70 question timed simulations with a paid plan
  • Works on phone, tablet and computer
Create a free account

Frequently asked questions

Do I need a permit to finish a basement in Ontario?
Usually yes. Building new walls, adding a bedroom, a bathroom or other plumbing is a material alteration, and plumbing counts as a building under the Building Code Act. Painting, flooring and other cosmetic work normally does not need a permit. Ask your building department before you start.
What is the minimum basement ceiling height in Ontario?
2,100 mm over at least 75% of the basement area, with 1,950 mm allowed under beams and ducts. In a secondary suite, the ceiling must be at least 1.95 m and at least 1.85 m under beams and ducting (Division B, Article 9.5.3.1. and Table 9.5.3.1.).
Does a basement bedroom need a window in Ontario?
Yes, unless the floor level has a door directly to the outside. The window must open from the inside without tools and give an opening of at least 0.35 m² with no dimension less than 380 mm. The 1,000 mm sill height limit does not apply in basements, and a window well needs 550 mm of clearance in front of the window (Division B, Article 9.9.10.1.).
Can I put wood studs directly on a basement floor?
Wood that is not pressure-treated and sits on concrete in contact with the ground must be separated from the concrete by at least 0.05 mm polyethylene or Type S roll roofing, unless the wood is at least 150 mm above the ground (Division B, Article 9.23.2.3.).
Does a finished basement need a smoke alarm?
Yes. A house needs a smoke alarm on every storey including the basement, and in every bedroom, interconnected with the other alarms (Division B, Articles 9.10.19.3. and 9.10.19.5.).