If two or more employers are working at a construction site in Alberta, that site must have a prime contractor. There is no size threshold, no dollar threshold and no exemption for a job that only takes a morning. The requirement comes from section 10 of the Occupational Health and Safety Act, and it catches far more concrete projects than most builders expect, because a single pour routinely brings four or five different employers onto the same patch of ground within two hours.
After 38 years of scheduling foundations and flatwork in Calgary, we have watched this one quietly decide who answers the questions when an officer shows up. It is worth understanding before the trucks are booked, not after.
The short answer
Every construction work site with 2 or more employers involved in the work must have a prime contractor. The person in control of the site designates that prime contractor in writing, and the name has to be posted somewhere visible on site. If nobody makes the designation, the law does not leave a gap: the person in control of the work site is deemed to be the prime contractor, whether they intended it or not.
That last sentence is the one worth reading twice. The designation is not what creates the responsibility. It only decides who carries it.
What the Act actually says
Section 10 of the Alberta OHS Act sets out the requirement in a few short subsections:
- Section 10(1) — every construction work site and oil and gas work site, plus any site or class of sites a Director designates, must have a prime contractor if there are 2 or more employers involved in work at the site.
- Section 10(2) — the person in control of the work site shall designate, in writing, a person as the prime contractor.
- Section 10(3) — if no designation is made, the person in control of the work site is deemed to be the prime contractor.
- Section 10(7) — the prime contractor must establish a system or process that will ensure compliance with the Act at the site, must designate a person in writing responsible for ensuring cooperation between employers and workers, and must conduct its own activities so that no person is exposed to hazards.
The other work site parties sit in their own sections, and they do not disappear when a prime contractor is named. Employers are section 3, supervisors section 4, workers section 5, suppliers section 6, and owners section 9. A prime contractor designation layers coordination duties on top of all of that; it does not transfer anybody’s own obligations to someone else.
Counting the employers on a pour day
This is where the arithmetic surprises people. “Two or more employers” does not mean two or more trades in the contract. It means two or more employers whose workers are involved in work at the site. On a routine Calgary foundation or a commercial slab, the count on pour morning often looks like this:
| Who shows up | Whose employee are they? |
|---|---|
| Forming and placing crew | The concrete contractor |
| Ready-mix or volumetric driver | The concrete supplier |
| Pump or conveyor operator | The pumping company |
| Rebar placers | The reinforcing subcontractor |
| Field technician taking cylinders and air content | The testing agency |
| Excavator backfilling later the same day | The earthworks contractor |
That is up to six employers on a job a builder would describe as “just the basement.” The threshold is crossed before the first truck discharges. A site that had one employer on it all week becomes a multi-employer site at 7:15 a.m. and stops being one by noon, and the Act does not care that the window was short.
Two practical consequences follow. First, a prime contractor has to be in place for that window, not designated after the fact. Second, on small residential work where a homeowner is the person in control of the site, the deeming rule in section 10(3) can land the designation on a homeowner who has never heard the phrase. Builders and contractors are usually better placed to hold it, and saying so early is a kindness rather than a negotiation.
How the designation is made
Three things have to happen, and all three are simple enough to complete before mobilization:
- Put it in writing. The designation has to be written, not understood. A clause in the subcontract or a one-page site-specific designation letter both work. Verbal agreement on the tailgate does not satisfy section 10(2).
- Post the name on site. The name of the prime contractor must be posted in a visible place at the work site. On a fenced Calgary commercial site that is usually the site trailer or the gate board. On a residential lot it is whatever board the site notices already live on.
- Name the coordination person in writing. Section 10(7) requires the prime contractor to designate, in writing, a person responsible for ensuring cooperation between employers and workers. In practice this is the superintendent, but the paperwork has to say so.
None of this takes long. What takes long is reconstructing it under audit six months later, after a near-miss, when the only evidence that anyone coordinated anything is a group text.
What the prime contractor has to do once designated
The duty is coordination, not supervision of everybody else’s trade. A prime contractor is not expected to know how to run a screed or set an anchor bolt. It is expected to run a system that makes the overlaps safe. On concrete work the overlaps that matter most are predictable:
- Access and traffic. A loaded mixer, a pump, and a backfill machine all want the same approach. Sequencing that is coordination work, and it belongs to whoever holds the designation.
- Open excavations. The hole is the hazard other trades walk into. Protection of an excavation, who inspects it, and who is allowed near the edge are coordination questions before they are technical ones.
- Overhead and suspended loads. A boom over another trade’s work area is a scheduling decision, not an accident.
- Hazard communication between employers. The testing technician needs to know what is buried. The driver needs to know where the overhead lines are. Nobody’s own safety program covers information they were never handed.
- Emergency response. One plan for the site, not one per subcontract.
We ask for the designation in writing on every commercial project we take on, and we are content to hold it on packages where our crew controls the sequence. Our commercial concrete contractors in Calgary page sets out where our scope usually starts and stops, which is the same conversation in different words.
Where this page stops
This is not a page about checking whether a subcontractor is safe to hire. Reviewing a Certificate of Recognition, asking for an experience rating, confirming coverage is in good standing — that is procurement due diligence, and it happens weeks earlier, on a different document, with different questions. Our guide to common mistakes when hiring a concrete contractor covers that ground, and the questions worth asking a concrete contractor list gives you the short version.
Prime contractor status is a different animal. It is a statutory role attached to a specific site for a specific period, it exists whether or not anybody filled in a form, and a spotless safety record does not satisfy it.
What getting it wrong costs
Section 48 of the Act sets the ceiling. A first offence carries a fine of not more than $500,000, plus up to $30,000 for each day the offence continues, or imprisonment for a term not exceeding 6 months, or both. A second or subsequent offence doubles the exposure: not more than $1,000,000, plus up to $60,000 per day, or up to 12 months, or both. Failing to comply with a stop work order carries the $1,000,000 ceiling on its own.
Those are maximums, not typical outcomes. The more common cost is smaller and more certain: a stop work order at 8 a.m. with six cubic metres already in the truck, a return trip nobody budgeted, and a cold joint where the drawings did not show one.
How we approach it
Across 52,000+ projects the pattern has not changed much. The jobs that go smoothly are the ones where somebody answered three questions before the concrete was ordered: who is the person in control of this site, who has been designated in writing, and who is the named coordination person for pour day. When those three answers exist on paper, the pour is a technical problem — footing depth, the right cement type for Calgary’s sulphate soils, weather, finishing window. When they do not, the pour becomes an argument.
If you are planning a commercial pour in Calgary and you are not certain where the designation currently sits, ask us before you book the trucks. It is a five-minute conversation, and it is cheaper than every alternative. Talk to our commercial team about your schedule and we will tell you plainly what we can hold and what needs to stay with the general contractor.
FAQ
Is a prime contractor the same thing as the general contractor? No. General contractor is a commercial role defined by the contract. Prime contractor is a statutory role defined by section 10 of the OHS Act. They are often the same company, but not always, and the contract alone does not create the designation.
Do I need a prime contractor if my concrete crew is the only trade on site? If only one employer is involved in work at the site, section 10(1) is not triggered. The difficulty is that a concrete pour rarely stays at one employer once the supplier, the pump and the testing agency arrive.
Who is the prime contractor if nobody signs anything? The person in control of the work site is deemed to be the prime contractor under section 10(3). On an owner-managed project, that is frequently the owner.
Does the prime contractor become responsible for my workers? No. Employers keep their own obligations under section 3, supervisors under section 4 and workers under section 5. The prime contractor adds a coordination layer; it does not absorb anyone else’s duties.
Can the designation move partway through a project? Yes, and on phased work it often should. What matters is that the written designation and the posted name reflect who actually controls the site during each phase, rather than who controlled it at groundbreaking.
Does the requirement apply to residential work? Yes. Section 10(1) applies to construction work sites generally. A single-family basement with a supplier, a pump and a testing technician on site is a construction work site with multiple employers.
Sources
- Alberta.ca — Obligations of work site parties
- Alberta OHS Act — Part 1, General Obligations (section 10, prime contractors)
- Alberta OHS Act — Part 9, Offences and Penalties (section 48)