Commercial Roofing Contractor: How to Choose One
The checks, the questions to ask and the quote details that separate a solid commercial roofer from a risky one.
Call 1-833-775-7663 Oakville head office · Flat roof repairs, replacements and inspections for commercial, industrial and institutional buildings across Ontario
Karol Rajkowski
Vice President, OYH Roofing
Published October 8, 2026 · 8 min read
Short answer
To choose a commercial roofing contractor in Ontario, check a current WSIB clearance and liability insurance, ask for similar projects and the manufacturer warranty they can register, and get a written scope that covers deck repairs, permits and safety. Compare quotes line by line, and pay with the 10 per cent holdback the Construction Act requires.
What should you check before hiring a commercial roofing contractor?
Nine things: a WSIB clearance, liability insurance, training, manufacturer approval for the warranty you want, similar projects, a safety plan, a written scope, who handles approvals, and payment terms that follow the Construction Act. Ontario does not license roofers, so these checks fall to the owner.
| Check | What to ask for | Why it matters |
|---|---|---|
| 1. WSIB clearance | The clearance number, checked online, and renewed on long jobs | A valid clearance gives the principal assurance that the WSIB will not hold it liable for the contractor's unpaid premiums; it lasts up to 90 days |
| 2. Liability insurance | A certificate of insurance for the project | Covers damage to your building and to others during the work |
| 3. Training | Red Seal or apprenticeship certificates for the crew leads | Roofer is a non-compulsory trade in Ontario, so certification is voluntary and worth asking about |
| 4. Manufacturer approval | Proof they can register the system warranty you want | Many manufacturer warranties require an approved installer |
| 5. Similar projects | Addresses or case studies of roofs of similar size and system | A 50,000 sq ft industrial roof is a different job from a small plaza |
| 6. Safety plan | How they handle fall protection and hot work on your roof | O. Reg. 213/91 requires fall protection, and a barrier 2 m from the edge on built-up roofs |
| 7. Written scope | System, tear-off or recover, insulation, flashings, drains and unit prices for deck repairs | Most disputes start with what the quote did not say |
| 8. Approvals | Who handles any permit, the Notice of Project and the asbestos report | The Notice of Project applies over $50,000; the owner must arrange the asbestos examination before tendering |
| 9. Payment terms | A payment schedule that keeps the holdback | The Construction Act requires a 10 per cent holdback and sets 28-day payment of proper invoices |
WSIB clearances take a minute to check online, and the WSIB says they must be in place before construction work begins and for the duration of the work. Our roof replacement permit guide covers permits, the Notice of Project and the other approvals in more detail, and our commercial roof warranty guide explains system warranties.
What questions should you ask a commercial roofing contractor?
Ask what system they recommend and why, whether they will tear off or recover, how they will check for wet insulation, who runs the crew, how they protect the building and its occupants, and what the warranty covers. A good commercial roofing contractor answers in writing, with specifics.
| Question | A solid answer includes |
|---|---|
| Which system do you recommend, and why? | A reason tied to your building: traffic, grease or chemicals, reflectivity, budget |
| Tear-off or recover? | What the moisture survey and core cuts showed, and how many roofs are already on the building |
| How will you find wet insulation? | An infrared or similar survey confirmed with core cuts, and a plan to replace wet boards |
| What happens if the deck is damaged? | Unit prices for deck repair written into the quote |
| Who is on site every day? | A named supervisor, and the crew size and schedule |
| How will you keep the building running? | Phasing, daily tie-ins, protection of entrances and rooftop units |
| What warranty will I get? | The manufacturer's system warranty and the contractor's workmanship warranty, each in writing |
| Who handles permits and the Notice of Project? | A clear yes or no for each, written into the contract |
System choice is where owners hear the most conflicting advice. Our comparisons of modified bitumen vs TPO, TPO vs EPDM and PVC vs TPO show where each one wins.
Comparing commercial roofing quotes?
We will assess the roof and give you a written quote with the scope, the system and the warranty spelled out.
Call 1-833-775-7663Request an assessmentHow do you compare commercial roofing quotes?
Line by line, not by the total. Two quotes for the same roof can differ because one includes tear-off, new insulation, flashings and drains while the other assumes a recover and leaves deck repairs out.
| Line item | What to look for |
|---|---|
| Scope | Tear-off to the deck or recover; area in square feet |
| System | Membrane type, thickness and manufacturer |
| Insulation | Type, thickness and tapered insulation for drainage |
| Flashings and details | Parapets, curbs, drains, edges and penetrations |
| Deck repairs | Unit prices per square foot or sheet |
| Warranty | Manufacturer system warranty term and contractor workmanship term |
| Schedule and access | Start date, duration, crane or hoist, site protection |
| Exclusions | What is not included, such as asbestos abatement, mechanical disconnects or electrical work |
What are the red flags when hiring a roofing contractor?
Watch for a contractor who cannot produce a WSIB clearance or insurance certificate, wants a large deposit up front, gives a one-line quote, will not name the system or warranty, or tells you no permit or survey is ever needed without seeing the roof.
- No paperwork. No clearance, no certificate of insurance, no written scope.
- Pressure to skip the holdback. The Construction Act requires it; your lawyer can advise on the details.
- A price far below the others. Usually a smaller scope, a thinner system or a recover over wet insulation.
- No safety plan. Ontario requires fall protection on roofs, and the owner's site is where any incident happens.
What are the most common commercial roof problems?
On Ontario flat roofs, the usual five are failed flashings, ponding water, membrane damage such as blisters and open seams, blocked drains, and wet insulation hidden under the membrane. A good commercial roofing contractor checks all five at every inspection.
Our guides cover each one: roof flashing repair, ponding water, membrane roof repair and tar and gravel roofs. For inspections, see how to prepare a flat roof for winter, and for leaks, our guides to commercial roof leak repair in Toronto and Mississauga. You can see our own work on the completed projects page, including Millomat Stampings in Mississauga, a 50,000 sq ft addition and re-roof in 60 mil TPO.
Frequently asked questions
What questions should I ask when hiring a roofing contractor?
Ask which system they recommend and why, whether they will tear off or recover, how they will find wet insulation, how deck repairs are priced, who supervises the crew, what warranty you will get, and who handles permits. Also ask for a WSIB clearance, a certificate of insurance and examples of similar commercial roofs.
What are the most important questions to ask a contractor?
The ones about risk: is your WSIB clearance current, what insurance do you carry, what exactly is in the price, what is excluded, and what warranty is in writing. On an Ontario job, also ask how payments will work with the 10 per cent holdback the Construction Act requires.
What are the five most common roofing problems?
On commercial flat roofs, the five most common are failed flashings at walls and curbs, ponding water, membrane damage such as blisters and open seams, blocked drains, and wet insulation under the membrane. Most of them can be caught early with inspections in spring and fall by a roofing crew.
What is the best commercial roofing system?
There is no single best system. Two-ply modified bitumen is tough under foot traffic, TPO is white and reflective, PVC resists grease and chemicals, and EPDM stays flexible in the cold. The right choice depends on the building, its rooftop traffic and exposure, and the warranty you want.
How much holdback should I keep on a roofing contract in Ontario?
Ten per cent. Ontario's Construction Act requires each payer to retain a holdback of 10 per cent of the price of services and materials as they are supplied, until the lien period has passed. The Act also requires owners to pay a proper invoice within 28 days unless they give notice of non-payment.
Karol Rajkowski
Vice President · OYH Roofing
Karol Rajkowski is Vice President of OYH Roofing, an Oakville-based ICI flat-roofing contractor whose projects include the City of Mississauga building at 3185 Mavis Rd and the Marriott Hotel in Vaughan. Learn more about the OYH team.
Sources
- Questions and answers: Clearances, WSIB, updated July 20, 2026, and Clearances, WSIB, updated May 5, 2026.
- Roofer, trade information, Skilled Trades Ontario.
- Construction Act, sections 6.4 and 22, Ontario e-Laws.
- O. Reg. 213/91: Construction Projects, sections 6, 26, 26.1 and 207, Ontario e-Laws.
- O. Reg. 278/05: Designated Substance, Asbestos on Construction Projects and in Buildings and Repair Operations, section 10, Ontario e-Laws.
- Building Code Act, 1992, Ontario e-Laws.
- OYH Roofing project records: Millomat Stampings, Mississauga; Devi Mandir, Pickering (October 2026).
OYH Roofing, 2120 Speers Rd, Oakville, ON L6L 2X8 · 1-833-775-7663 · info@oyhroofing.ca