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Code guide

Retaining Walls and the Ontario Building Code

When a retaining wall needs a building permit in Ontario: over 1,000 mm exposed height next to public property, building access or public areas. Part 4 design, guards.
exposed height that can trigger a permit
1,000 mm
exposed height that can trigger a permit
structural design for designated walls
Part 4
structural design for designated walls
public property, building access, public areas
3 places
public property, building access, public areas
where the public can reach the top
Guards
where the public can reach the top

Last updated

Under the 2024 Ontario Building Code, a retaining wall becomes a designated structure, and so a "building" that needs a permit, when it exceeds 1,000 mm in exposed height and is adjacent to public property, access to a building, or private property to which the public is admitted (OBC 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…). Those walls must be designed under Part 4 (Div. A 1.3.3.2.(2)OBC Div. A 1.3.3.2. Application of Parts 3, 4, 5 and 6(1) Subject to Articles 1.3.3.1A., 1.3.3.3B., Parts 3, 4, 5, and 6 of Division B apply to all buildings described in Article 1.1.1.1. and (a) classified as post-disaster buildings, (b) used for major occupancies classified as (i) Group A, assembly occupancies, (ii) Group B, care, care and treatment or detention…) and need guards where the public can reach the top (OBC Div. B 4.4.4.1.OBC Div. B 4.4.4.1. Guards Over Retaining Walls(1) Every retaining wall that is designated in Sentence 1.3.1.1.(1) of Division A shall be protected by guards on all open sides where the public has access to open space at the top of the retaining wall.).

This page explains when the Building Code reaches a retaining wall and what it requires. Municipal by-laws, site plan and grading rules, and conservation authority permits can apply to walls the Building Code does not cover, so check with your municipality before you build.

Retaining wall rules at a glance

Item Rule in short Where to look
When a wall is a "building" designated structures in Div. A 1.3.3.5. BCA s. 1, building (d)
Height trigger more than 1,000 mm exposed height Div. A 1.3.3.5.(1)(a)
Location trigger next to public property, building access, or private property open to the public Div. A 1.3.3.5.(1)(a)
Permit required for a designated wall BCA s. 8
Design Part 4 structural design Div. A 1.3.3.2.(2)(a)
Guards on open sides where the public reaches the top Div. B 4.4.4.1.

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

When a retaining wall is a building

The Building Code Act defines "building" to include structures designated in the building code (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…), and the Act requires a permit to construct a building (BCA 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…). Division A designates, among other structures, a retaining wall exceeding 1,000 mm in exposed height adjacent to (Div. A 1.3.3.5.(1)(a)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…):

  • public property, such as a sidewalk, road or park,
  • access to a building, such as a walkway or driveway leading to an entrance, or
  • private property to which the public is admitted, such as a store parking lot.

Both tests must be met. A 1.5 m garden wall at the back of a private yard, well away from any building access, is not designated. A 1.2 m wall along the sidewalk is.

Exposed height is the part of the wall that shows above the finished ground at its base. The buried footing and the part below grade do not count.

Design under Part 4

Designated retaining walls fall under Part 4 of Division B, the structural design part of the code (Div. A 1.3.3.2.(2)(a)OBC Div. A 1.3.3.2. Application of Parts 3, 4, 5 and 6(1) Subject to Articles 1.3.3.1A., 1.3.3.3B., Parts 3, 4, 5, and 6 of Division B apply to all buildings described in Article 1.1.1.1. and (a) classified as post-disaster buildings, (b) used for major occupancies classified as (i) Group A, assembly occupancies, (ii) Group B, care, care and treatment or detention…), not the prescriptive Part 9 rules used for houses. Part 4 design means calculations for soil pressure, surcharge from cars or slopes above, drainage and the footing, so in practice a professional engineer designs and often reviews these walls. Ask your building department what drawings it needs with the permit application.

Guards on top

Every designated retaining wall needs guards on all open sides where the public has access to open space at the top (4.4.4.1.OBC Div. B 4.4.4.1. Guards Over Retaining Walls(1) Every retaining wall that is designated in Sentence 1.3.1.1.(1) of Division A shall be protected by guards on all open sides where the public has access to open space at the top of the retaining wall.). Guard heights and opening sizes follow the guard rules in the code. See our guard height guide for the numbers used in Part 9.

Walls the Building Code does not cover

A wall of 1,000 mm or less, or a taller wall that is not next to one of the listed areas, is not a designated structure, so the Building Code does not require a permit for it. That does not mean anything goes:

  • Municipal by-laws can regulate walls, fences, grading and drainage onto neighbouring lots.
  • Conservation authorities regulate work near rivers, shorelines, wetlands and steep slopes.
  • A wall that supports a building or its footings is part of that building's structure.

A wall that fails can still cause damage and liability, so good drainage behind it and a sound footing matter at any height.

Common mistakes

  1. Measuring total height instead of exposed height. Only the face above the finished grade at the base counts.
  2. Ignoring the location test. The 1,000 mm trigger applies only next to public property, building access or public areas.
  3. Using Part 9 rules. Designated walls are designed under Part 4.
  4. No guard where the public can reach the top.
  5. Assuming no permit means no rules. Municipal and conservation rules may still apply.

How to look it up yourself

Open Division A, Part 1 of the 2024 Compendium. Search terms that appear in the code text:

  • "Designated Structures" (Div. A 1.3.3.5.)
  • "retaining wall exceeding 1,000 mm in exposed height"
  • "Guards Over Retaining Walls" (Div. B 4.4.4.1.)

Read the article in the code viewer alongside the Part 4 guard article.

BCIN exam angle

Designated structures, including the 1,000 mm retaining wall, are a standard General Legal/Process question, because they decide what counts as a building. Study the General Legal/Process chapter on code structure and scope, then try the free quiz on the General Legal/Process 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

Do I need a permit for a retaining wall in Ontario?
Under the Building Code, a retaining wall is a building, and needs a permit, when it exceeds 1,000 mm in exposed height and is adjacent to public property, access to a building, or private property to which the public is admitted (Division A, Article 1.3.3.5.). Lower walls and walls away from those areas are not designated structures, but municipal by-laws, grading rules and conservation authorities can still apply.
How high can a retaining wall be without a permit in Ontario?
The Building Code trigger is an exposed height over 1,000 mm, in the locations listed in Division A, Article 1.3.3.5. A wall of 1,000 mm or less is not a designated structure under the code. Check your municipality's by-laws before building, because some regulate walls, fences and grading separately.
Does a retaining wall need an engineer in Ontario?
A designated retaining wall must be designed under Part 4 of Division B, the structural design part of the code (Division A, Sentence 1.3.3.2.(2)). Part 4 design is engineering design, so in practice a professional engineer designs these walls.
Does a retaining wall need a guard or railing?
Every designated retaining wall must have guards on all open sides where the public has access to open space at the top of the wall (Division B, Article 4.4.4.1.).
What is the exposed height of a retaining wall?
It is the height of the wall face that shows above the finished ground at its base, not the buried part. A wall can be taller overall and still have an exposed height of 1,000 mm or less.