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Code guide

Do I Need a Building Permit in Ontario?

When Ontario requires a building permit: the 10 m2 rule, the 15 m2 shed exemption, decks, basements, suites, permit timelines, inspections and fines.
structures larger than this are a building
10 m²
structures larger than this are a building
max size of a permit-exempt shed
15 m²
max size of a permit-exempt shed
permit decision for a house
10 days
permit decision for a house
for the inspection after you give notice
2 days
for the inspection after you give notice

Last updated

In Ontario you need a building permit to construct or demolish a building (Building Code Act s. 8BCA s. 8 Building permits(1) No person shall construct or demolish a building or cause a building to be constructed or demolished unless a permit has been issued therefor by the chief building official. (1.1) An application for a permit to construct or demolish a building may be made by a person specified by regulation and the prescribed form…), and the Act treats any structure larger than 10 m², any smaller structure with plumbing, and plumbing itself as a building (BCA s. 1, buildingBCA s. 1 building“building” means, (a) a structure occupying an area greater than ten square metres consisting of a wall, roof and floor or any of them or a structural system serving the function thereof including all plumbing, works, fixtures and service systems appurtenant thereto, (b) a structure occupying an area of ten square…). The main exception for homeowners is a storage shed of 15 m² or less that meets every condition in OBC Div. C 1.3.1.1.OBC Div. C 1.3.1.1. Requirement for Permits(1) A person is exempt from the requirement to obtain a permit under section 8 of the Act, (a) for the demolition of a farm building located on a farm, (b) subject to Sentence (2), for the construction or demolition of a building in territory without municipal organization, or (c) for the construction of a Class 1…

"Construct" is broad: it covers erecting, installing, extending, and any material alteration or repair (BCA s. 1, constructBCA s. 1 construct“construct” means to do anything in the erection, installation, extension or material alteration or repair of a building and includes the installation of a building unit fabricated or moved from elsewhere and “construction” has a corresponding meaning; (“construire”, “construction”, “travaux de construction”)). This page explains the rules, gives our summary of common projects, and covers timelines, inspections and penalties. Municipalities issue permits and can set their own application requirements, so your building department has the final say on your project.

Common projects: our summary

Project Permit? Why
New house or addition Yes Construction of a building (Act s. 8)
Shed 15 m² or less, one storey, detached, storage only, no plumbing No Exempt, Div. C 1.3.1.1.(6)
Shed over 15 m², or with plumbing, or attached Yes Not within the exemption
Deck over 10 m² Yes A structure over 10 m² is a building
Small deck, 10 m² or less Check Depends on attachment and local rules
Finishing a basement with new walls or plumbing Usually yes Material alteration; plumbing is a building
Adding a secondary suite Yes Construction, and splitting a residential suite is a change of use, Div. C 1.3.1.4.(1)(b)
New plumbing, even outdoors Yes Plumbing is a building under the Act
Retaining wall over 1,000 mm next to public property or a building access Yes Designated structure, Div. A 1.3.3.5.
Re-roofing with the same material Check Depends on whether it is a material repair
Replacing a window with the same size Check Enlarging an opening or changing structure needs one
Fence Not a Building Code permit Municipal fence by-laws apply
Demolishing a building over 10 m² Yes Demolition needs a permit (Act s. 8)

This is our own reading of the Act and Division C, not a list from the code. "Check" means the answer depends on the details and your municipality.

What the law says

The permit requirement. No person may construct or demolish a building, or cause one to be built or demolished, unless the chief building official has issued a permit (BCA s. 8(1)BCA s. 8 Building permits(1) No person shall construct or demolish a building or cause a building to be constructed or demolished unless a permit has been issued therefor by the chief building official. (1.1) An application for a permit to construct or demolish a building may be made by a person specified by regulation and the prescribed form…). Work must then follow the approved plans, and material changes need the chief building official's authorization first (s. 8(12) and (13)BCA s. 8 Building permits(1) No person shall construct or demolish a building or cause a building to be constructed or demolished unless a permit has been issued therefor by the chief building official. (1.1) An application for a permit to construct or demolish a building may be made by a person specified by regulation and the prescribed form…).

What a building is. The Act's definition has five parts (BCA s. 1BCA s. 1 building“building” means, (a) a structure occupying an area greater than ten square metres consisting of a wall, roof and floor or any of them or a structural system serving the function thereof including all plumbing, works, fixtures and service systems appurtenant thereto, (b) a structure occupying an area of ten square…): a structure occupying more than 10 m² with a wall, roof or floor (or a structural system doing their job), including its plumbing and services; a structure of 10 m² or less that contains plumbing; plumbing not located in a structure; a sewage system; and structures the code designates. The designated list includes retaining walls over 1,000 mm in exposed height next to public property, a building access or private property open to the public, pedestrian bridges, building-mounted solar collectors and dish antennas of 5 m² or more, and outdoor pools (Div. A 1.3.3.5.OBC Div. A 1.3.3.5. Designated Structures(1) The following structures are designated for the purposes of clause (d) of the definition of building in subsection 1 (1) of the Act: (a) a retaining wall exceeding 1,000 mm in exposed height adjacent to (i) public property, (ii) access to a building, or (iii) private property to which the public is admitted, (b) a…).

Exemptions. Division C exempts a few things from the permit requirement (Div. C 1.3.1.1.OBC Div. C 1.3.1.1. Requirement for Permits(1) A person is exempt from the requirement to obtain a permit under section 8 of the Act, (a) for the demolition of a farm building located on a farm, (b) subject to Sentence (2), for the construction or demolition of a building in territory without municipal organization, or (c) for the construction of a Class 1…): demolishing a farm building on a farm, most construction in territory without municipal organization (but not sewage systems), a Class 1 sewage system, tents of not more than 60 m² in aggregate that are not attached to a building and are more than 3 m from other structures, demountable stages, and sheds meeting all five conditions:

  • not more than 15 m² in gross area,
  • not more than one storey in building height,
  • not attached to a building or any other structure,
  • used only for storage ancillary to a principal building on the lot, and
  • no plumbing.

Change of use. Even with no construction, changing the use of a building in a way that increases hazard needs a permit (BCA s. 10BCA s. 10 Change of use(1) Even though no construction is proposed, no person shall change the use of a building or part of a building or permit the use to be changed if the change would result in an increase in hazard, as determined in accordance with the building code, unless a permit has been issued by the chief building official. (2)…). Division C lists those changes, including converting one residential suite into more than one (Div. C 1.3.1.4.OBC Div. C 1.3.1.4. Permits Under Section 10 of the Act(1) Except as provided in Sentence (2), the following changes in use of a building or part of a building constitute an increase in hazard for the purposes of section 10 of the Act and require a permit under section 10 of the Act: (a) a change of the major occupancy of all or part of a building that is designated with…).

How long a permit decision takes

Once an application is complete, the chief building official must issue the permit, or refuse it with written reasons, within a set period (Div. C 1.3.1.3.OBC Div. C 1.3.1.3. Period Within Which a Permit is Issued or Refused(1) Subject to Sentences (2) and (3) and unless the circumstances set out in Sentence (6) exist, if an application for a permit under subsection 8(1) of the Act that meets the requirements of Sentence (5) is submitted to a chief building official, the chief building official shall, within the time period set out in…). Our summary of the periods in Table 1.3.1.3.:

  • 10 days for a house where no dwelling unit is above another, and its detached accessory structures up to 55 m².
  • 15 days for other Part 9 buildings and farm buildings up to 600 m².
  • 20 to 30 days for larger and more complex buildings.

Days exclude Saturdays, holidays and other days the office is closed, and the clock starts the day after a complete application is submitted. If the application lacks required documents or would break another law, the official can stop the clock by telling you so in writing within two days (Div. C 1.3.1.3.(6)OBC Div. C 1.3.1.3. Period Within Which a Permit is Issued or Refused(1) Subject to Sentences (2) and (3) and unless the circumstances set out in Sentence (6) exist, if an application for a permit under subsection 8(1) of the Act that meets the requirements of Sentence (5) is submitted to a chief building official, the chief building official shall, within the time period set out in…).

During construction: posting, notices, inspections

  • Post the permit, or a copy, in a conspicuous place on the property for the whole job (Div. C 1.3.2.1.OBC Div. C 1.3.2.1. Permit Posting(1) Where a permit has been issued pursuant to the Act, the person to whom it is issued shall have the permit or a copy of it posted at all times during construction or demolition in a conspicuous place on the property in respect of which the permit was issued.).
  • Notify the building department at each stage the code lists, such as readiness to construct footings, completion of footings and foundations before backfilling, framing, insulation and vapour barriers, air barrier systems, and plumbing ready for testing (Div. C 1.3.5.1.OBC Div. C 1.3.5.1. Prescribed Notices(1) This Article sets out the notices that are required under section 10.2 of the Act. (2) The person to whom a permit under section 8 of the Act is issued shall notify the chief building official or, where a registered code agency is appointed under the Act in respect of the construction to which the notice relates…).
  • The inspector must inspect within 2 days of a notice, or 5 days for a sewage system, and may inspect remotely (Div. C 1.3.5.3.OBC Div. C 1.3.5.3. Prescribed Inspections(1) Except as provided in Sentence (2), an inspector or registered code agency, as the case may be, shall, not later than two days after receipt of a notice given under Sentence 1.3.5.1.(2), undertake a site inspection of the building to which the notice relates. (2) Where a notice given under Sentence 1.3.5.1.(2)…).

If you build without a permit

Building without a permit, or not following the permit, is an offence. Maximum fines are $50,000 for an individual's first offence and $100,000 for a later one, and $500,000 and $1,500,000 for a corporation, plus up to $10,000 a day for ignoring certain orders (BCA s. 36BCA s. 36 Offences(1) A person is guilty of an offence if the person, (a) knowingly furnishes false information in any application under this Act, in any certificate required to be issued or in any statement or return required to be furnished under this Act or the regulations; (b) fails to comply with an order, direction or other…). A permit can also be revoked if work is not seriously started within six months, or is suspended for more than a year (BCA s. 8(10)BCA s. 8 Building permits(1) No person shall construct or demolish a building or cause a building to be constructed or demolished unless a permit has been issued therefor by the chief building official. (1.1) An application for a permit to construct or demolish a building may be made by a person specified by regulation and the prescribed form…).

Common mistakes

  1. Measuring a shed wrongly. The 15 m² is gross area, and the shed must also be detached, storage-only and plumbing-free.
  2. Assuming small means exempt. A 6 m² structure with a sink is a building.
  3. Forgetting change of use. Turning part of a house into a second unit triggers a permit even before you build anything.
  4. Skipping inspection notices. You must call for each listed stage, not only at the end.

How to look it up yourself

Start in the Building Code Act on e-Laws: section 1 for the definitions of "building" and "construct", section 8 for permits. Then open Division C, Part 1, of the 2024 Compendium (Div. C Section 1.3 in our viewer). Search terms that appear in the code text: "Requirement for Permits", "shed", "Period Within Which a Permit is Issued or Refused", "Prescribed Notices" and "Designated Structures".

The BCIN exam angle

Permits, timelines, notices and exemptions are core questions on the General Legal/Process exam and the Designer Legal/Process exam. Read the free chapters on permits, construction and demolition and Division C administration. Exam questions often hinge on the exact shed conditions or the number of days for a building class. The areas and heights method helps when a question turns on a building's area.

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

Do I need a building permit for a shed in Ontario?
Not if the shed is 15 m2 or less in gross area, one storey, not attached to any building or structure, used only for storage ancillary to the main building, and has no plumbing. Such a shed is exempt from the permit and from the Building Code (Division C, Sentence 1.3.1.1.(6)). Zoning rules can still apply.
Do I need a permit for a deck in Ontario?
A deck larger than 10 m2 is a building under the Building Code Act, so it needs a permit. Smaller decks, especially ones attached to a house, depend on your municipality, so ask the building department before you start.
How long does it take to get a building permit in Ontario?
For a complete application, the chief building official must issue or refuse the permit within 10 days for a house where no dwelling unit is above another, and within 15 days for other Part 9 buildings, not counting Saturdays, holidays or days the office is closed. Larger buildings get 20 or 30 days (Division C, Article 1.3.1.3.).
What happens if I build without a permit in Ontario?
It is an offence under the Building Code Act. An individual can be fined up to $50,000 for a first offence and $100,000 for a later one; a corporation up to $500,000 and $1,500,000 (Act, s. 36).
Does a building permit expire in Ontario?
The chief building official may revoke a permit if the work has not been seriously started within six months of issue, or if it is substantially suspended for more than a year (Act, s. 8(10)).
Do I need a permit to finish my basement?
Usually yes when you build new walls, add plumbing, change structure or create a bedroom or a second unit, because construction includes material alteration and plumbing counts as a building. Confirm with your municipality.