Ontario OHSA: owner vs constructor duties

Ontario's Occupational Health and Safety Act (OHSA) does not let an owner hand off all safety risk by signing a construction contract. The Act gives the widest project duties to one party, the constructor, but it also places duties on the owner that no contract can transfer. This lesson covers who the constructor is, what the owner still owes, and a 2023 Supreme Court of Canada decision that changed how owners should act on site.

Learning outcomes

• Explain the OHSA meanings of owner, constructor and project, and test who the constructor is on a given set of facts.
• List the constructor's general duties under section 23 and the owner's duties under sections 29 and 30.
• Describe the owner's designated substances duty, when the list is due, and the liability for leaving a substance off it.
• Explain what R. v. Greater Sudbury (City) means for owners who use a general contractor as constructor.

The lesson

Three definitions that decide everything

Section 1(1) of the OHSA sets the vocabulary. An owner is read widely: it includes trustees, receivers, mortgagees in possession, tenants, lessees and occupiers of the lands, and anyone acting as the owner's agent or delegate. A project is, broadly, a construction project. A constructor is a person who undertakes a project for an owner, and the definition also catches an owner who undertakes all or part of a project alone or with more than one employer. "Undertakes" means taking on responsibility for the project.

The practical rule follows: every project has a constructor, and if no one else has taken the role, the owner likely has it.

How an owner becomes the constructor

The province's constructor guideline covers the common cases. If the owner contracts with one contractor for all the work, that contractor is the constructor, even if it subcontracts most of the work. If the owner hires several contractors and does not designate one of them, the owner will likely be treated as the constructor. If one contractor, or a third party, accepts the role and the owner gives up control, that party is the constructor even though the owner pays the others directly.

Two details matter for owner-side PMs. First, an owner whose own employees work on a general contractor's site can become the constructor if the contractor did not agree to those workers and does not direct them. Second, section 1(3) says that an owner who engages an architect, engineer or other person solely to oversee quality control does not, by that alone, become the constructor. That protects the normal owner's representative and consultant model, as long as the oversight stays on quality and compliance with the contract.

Ministry inspectors decide who the constructor is from the facts on site. A contract clause is strong evidence, but an owner who behaves like the constructor can be found to be one.

What the constructor must do: section 23

Section 23(1) gives the constructor three general duties on the project: make sure the measures and procedures the Act and regulations prescribe are carried out; make sure every employer and every worker on the project complies with the Act and regulations; and make sure the health and safety of workers on the project is protected. Section 23(2) adds that, where a regulation requires it, the constructor must notify the Ministry before work begins. For construction that means the Notice of Project under O. Reg. 213/91, covered in lesson 7.

The construction regulation adds specific constructor duties on top, such as appointing a supervisor for any project where five or more workers will work at the same time, and setting written emergency procedures. The constructor also reports deaths, critical injuries and certain other occurrences to the Ministry. These are the duties an owner pays a general contractor to carry.

What the owner still owes: sections 29 and 30

Section 29 is the general owner duty. Under s. 29(1), the owner must provide and maintain prescribed facilities, make sure the workplace complies with the regulations, and make sure no workplace is built, altered or added to except in compliance with the Act and regulations. Where a regulation requires it, the owner must also give the Ministry drawings, plans or specifications.

Section 30 is the one owners most often miss. Before a project begins, the owner must find out whether any designated substances are present at the project site and prepare a list of them. If the owner tenders the work, the list must be part of the tender information. Under s. 30(3) the owner must give the constructor the list before a binding contract, and under s. 30(4) the constructor must pass it to each prospective contractor and subcontractor before they sign. Section 30(5) makes an owner who fails these duties liable to the constructor, contractors and subcontractors for losses caused by a designated substance the owner ought reasonably to have known about but did not list.

The designated substances are a short prescribed set that includes asbestos, lead, mercury and silica. On an existing building the list comes from a hazardous materials survey; on a vacant site it may say none were found, but it must still be issued.

The owner can still be an employer: R. v. Greater Sudbury

In 2015 a pedestrian was killed by a road grader on a City of Sudbury water main repair. The City had contracted a paving firm as constructor, but the Ministry also charged the City as an employer.

In November 2023 the Supreme Court of Canada, in a split decision, held that the City was an employer under the OHSA, through its own inspectors on the project and its contract for the constructor's services, and that the Crown did not have to prove the City controlled the workers or the workplace to show a breach of s. 25. Control still matters, but at the second stage, where the owner can argue due diligence: that it took every reasonable precaution in the circumstances.

In 2024 the Ontario Superior Court of Justice upheld the trial finding that the City had been duly diligent and had not taken over the constructor role. The helpful factors are worth copying: a contractor with the safety expertise the City lacked, inspections limited to contract quality, hazards raised with the contractor, and attendance at progress meetings. The City had not used its contract rights to remove workers or stop the work.

The lesson is not to stay away from site. It is to keep evidence that you chose a competent constructor, raised hazards you saw, and left direction of the work to the constructor.

Where the contract fits

CCDC 2-2020 rewrote its health and safety clause (GC 9.4) and does not name the constructor for you, as lesson 3 explained. Owners should name the constructor in the Supplementary Conditions, state that it covers the whole project for its full duration, and say how separate contractors and the owner's own forces will be brought under its control. The stakes are real: Ontario's guide lists maximum fines of $2,000,000 for a corporation and $1,500,000 for a director or officer.

Northgate worked example

Northgate Logistics Inc. (fictional) is building the 12,000 m² Northgate Distribution Centre in Vaughan under a CCDC 2-2020 stipulated price contract with Halvorsen Builders Ltd. (fictional), signed on Monday, January 11, 2027. As set out at kickoff in lesson 3, the owner's Supplementary Conditions name Halvorsen as constructor for the whole project, including the owner's racking installer who starts after Ready-for-Takeover. (See the Northgate fact sheet.)

Section 30. Before tender, Northgate commissioned a designated substances assessment of the vacant 2.6 ha site. It found no designated substances on the site. The report and list went into the tender package, so bidders had them before tender close on Tuesday, December 8, 2026, and the executed contract lists them among Halvorsen's documents. That closes the s. 30(3) duty.

Section 23. Halvorsen runs the safety program, appoints the supervisor, files the Notice of Project and controls every trade from mobilization on Monday, March 1, 2027.

The hard case: racking. Ready-for-Takeover is Friday, January 14, 2028, but Halvorsen's deficiency crews stay on site until final completion on March 31, 2028. Northgate's separate racking contractor starts on Monday, January 17, 2028. Without the SC clause, Northgate would be an owner with two employers on its site at once, which is the fact pattern that makes an owner the constructor. Because Halvorsen has agreed to coordinate and control the racking crew, it stays the constructor. The racking contract makes this practical: the installer must follow Halvorsen's site rules, attend its orientation and complete its own registration before starting.

Owner as employer. The owner's representative and Northgate's facilities staff will walk the site. Following the Sudbury factors, they record what they check (quality and contract compliance), raise any hazard they see to Halvorsen's superintendent in writing the same day, and never instruct a trade directly.

Owner's move

Demand a Supplementary Conditions clause that names the constructor for the whole project and its full duration, including any separate contractors and owner forces, and that requires the constructor to control their access.

Check that the s. 30 list exists, was in the tender, and is listed in the contract documents the constructor received. Review the constructor's safety record before award and keep the review on file.

Reject any plan that puts owner staff or a second contractor on site outside the constructor's control, and any habit of owner staff instructing trades directly. Raise hazards through the constructor, in writing.

Common mistakes

1. Assuming the contract settles it. An inspector looks at who actually controls the site. A named constructor with an owner who runs its own trades is a weak position.
2. Forgetting the overlap periods. Early works, owner-supplied equipment installers and post-takeover fit-out all put a second employer on site. Each needs a constructor answer.
3. No designated substances list on a "clean" site. Section 30 still applies. Issue a list that says what was assessed and found.
4. Owner inspectors who direct work. After Sudbury, owner staff on site make the owner an employer; directing trades weakens due diligence and can shift the constructor role.

Quick quiz

1. An owner hires three trade contractors directly and names none of them as constructor. Who is likely the constructor?

   1. The largest trade contractor
   2. The owner
   3. The architect
   4. No one, since there is no general contractor

2. Which OHSA section requires the owner to list designated substances present at a project before it begins?

   1. Section 23
   2. Section 25
   3. Section 29
   4. Section 30

3. Under s. 23(1), the constructor must ensure all of the following except:

   1. Prescribed measures and procedures are carried out on the project
   2. Every employer and worker complies with the Act and regulations
   3. The owner's finished building meets the Building Code
   4. The health and safety of workers on the project is protected

4. The owner hires an engineer only to inspect concrete quality for contract compliance. Under s. 1(3), this:

   1. Makes the owner the constructor
   2. Does not, on its own, make the owner the constructor
   3. Makes the engineer the constructor
   4. Requires a second Notice of Project

5. What did the Supreme Court decide in R. v. Greater Sudbury (City), 2023 SCC 28?

   1. Owners can never be employers on a project with a constructor
   2. The City was an employer, and control is relevant to due diligence rather than to proving the breach
   3. The contractor was not the constructor
   4. Owners must file the Notice of Project

Key terms

Owner (OHSA)

A broad term in s. 1(1) that includes trustees, receivers, mortgagees in possession, tenants, lessees, occupiers and anyone acting as the owner's agent or delegate.

Constructor

The person who undertakes a project for an owner, including an owner who undertakes all or part of a project alone or with more than one employer. Each project has one.

Designated substance

One of a short list of hazardous substances prescribed under the OHSA, such as asbestos, lead and silica, that the owner must identify and list before a project begins.

Employer (OHSA)

A person who employs or contracts for the services of workers. After the Sudbury decision, an owner with its own staff on a project can be an employer there.

Due diligence

The defence that a party took every reasonable precaution in the circumstances.

References

1. Government of Ontario, Occupational Health and Safety Act, R.S.O. 1990, c. O.1, ss. 1, 23, 25, 29, 30 (e-Laws).
2. Government of Ontario, Guide to the OHSA, Part III: Duties of employers and other persons (updated March 24, 2025).
3. Government of Ontario, Constructor guideline (updated August 13, 2026).
4. Government of Ontario, Guide to the OHSA, Part IX: Offences and penalties.
5. Supreme Court of Canada, Case in Brief: R. v. Greater Sudbury (City), 2023 SCC 28 (November 10, 2023).
6. Cassels, Due diligence deliverance: court upholds due diligence defence in R. v. Greater Sudbury (2024 ONSC 3959).
7. Canadian Construction Documents Committee, CCDC 2-2020 Stipulated Price Contract, GC 9.4. See lesson 3 for sources.

Verified on November 4, 2026.