Industrial Roof Repair: Factory and Manufacturing Roofs

Karol Rajkowski

Vice President, OYH Roofing

Published October 17, 2026 · 12 min read

What makes industrial roof repair different?

The membrane and the repair methods are the same as on any flat roof. What changes is everything around them: what comes out of the stacks, how big the roof is, what happens below it, and who else is responsible for safety. Industrial and factory roof repair goes better when these seven points are settled before the work starts.

Which roof membranes stand up to chemicals and oils?

None stands up to everything. The Canadian Roofing Contractors Association (CRCA) puts it bluntly: all membranes are vulnerable to something. On an industrial roof the risk arrives through up-blast and down-blast exhaust fans and direct pipe exhaust, so the membrane around each discharge point is where damage starts.

So the right membrane depends on what actually comes out of the stacks, and the makers do not always agree: Johns Manville (U.S.) steers chemical plants toward PVC, while Sika's own PVC data sheet warns against oils and solvents. Elevate asks owners to contact its technical staff about chemical compatibility, and that is the step to take before a repair or replacement: give the maker a list of what the plant exhausts.

CRCA's own options for heavy effluent are a resistant special membrane around the source and filter units on the fans, and it warns that damage from effluent is not covered by roof warranties. For kitchen grease, see our restaurant roofing guide; for the PVC and TPO comparison, see PVC vs TPO.

How are hot stacks and exhaust fans flashed?

With a metal sleeve and rain hood that keep the membrane away from the heat. Industrial roofs carry process stacks and exhaust fans that run hot, and a membrane flashed tight to a hot pipe softens and fails.

The trigger temperature varies by maker. IKO's detail says TPO must not touch any service line above 160°F (71°C) and calls for an insulated metal sleeve fixed to the deck, Tremco uses 160°F, and Sika's U.S. detail and IIBEC's thermoplastic guidance use 150°F (66°C). IIBEC also asks for penetrations to be at least 12 inches apart, so each can be flashed properly. Ask the plant's maintenance staff for the surface temperature of every stack before the roofer details them.

Fans and smaller vents follow the rules for any rooftop equipment: curbs fixed to the structure, flashings high enough to survive the roof around them, and walkways on the service routes. Our rooftop equipment guide and roof flashing repair guide cover both.

Why do leaks on large steel-deck roofs spread before they show?

Because water travels sideways through the insulation and along the deck flutes before it finds a way down. On a 50,000 sq ft roof, a large area can be wet before anyone sees a drip, and by then the insulation, fasteners and deck may all need attention.

• Deck corrosion. CRCA reports that zinc-coated steel decks in Canada generally perform well, but corrosion has been found under all types of insulation after long-term leaks, and salts and acid gases such as sulphur dioxide speed it up.
• Weakened attachment. IIBEC's guidance on moisture-damaged roofs says corrosion of fasteners and plates can compromise wind uplift resistance, and that moisture-damaged components should be replaced, not covered over.
• Moisture from inside. Research by the National Research Council Canada found that indoor air leaking up into mechanically attached roofs carries water vapour with it, and that an air and vapour barrier cut that air intrusion by 50 to 80 per cent.

That is why industrial repairs start with finding the wet area, not just the hole. Our flat roof leak detection guide explains the methods.

Is it a roof leak or condensation?

In a humid plant it can be either, and the two look alike. The National Research Council Canada warned decades ago that winter condensation in roofs can cause problems as obvious as rain leakage, and that air leaking out of the building is the prime cause of most condensation in roof spaces. A 2023 Construction Canada article makes the same point: condensation like this is often mistaken for membrane leaks.

Drips that appear on cold, dry days, or over the most humid processes such as washing, cooking or drying, usually point to condensation; drips that follow rain point to the roof. CRCA notes that high-humidity buildings, such as pools, arenas and paper mills, may need a higher-quality vapour retarder than a typical roof, which is a design question for the next re-roof rather than a patch.

How do you repair a large industrial roof without shutting the plant?

By finding the wet areas first, repairing or replacing in sections, and closing the roof watertight at the end of every working day. Plants rarely stop for a roof, so the work is planned around production instead.

• Survey before you scope. NRCA recommends a moisture survey confirmed by test cuts, and does not recommend re-covering over wet insulation or a deteriorated deck.
• Re-cover only over a dry, sound roof. CRCA credits a re-cover with less disturbance to building operations, but its bulletin cites NRCA data showing re-covered roofs with about twice the problem rate of new ones.
• Seal every night. Most commercial roofs take more than a day, so the crew installs a temporary seal along the edge of each day's work. Carlisle's instructions place those seals so they do not block drainage, and IIBEC notes that on a steel deck the membrane should be adhered to the top of the ribs with the flutes filled, because mastic alone is risky.
• Coordinate with the plant. Agree work zones, crane lifts, material storage and noisy or smelly tasks with the plant's maintenance lead before the crew mobilizes.

For what a roof survey covers, see our commercial roof inspection guide; for re-cover and coating options, see the commercial roof coating guide.

Is torch-on roofing safe over a working plant?

It can be, if the Fire Code is followed and the torch stays away from the details where fires start. Ontario's Fire Code has its own section for torch roofing, and its firewatch rule is longer than many people expect: someone must watch from the start of torching until at least 3 hours after it stops, or 2 hours if a hand-held thermal imaging camera is used to find hidden hot spots.

Roofing practice adds more. CRCA says most torch-related rooftop fires start at flashings, perimeters and penetrations, and recommends picture-framing those areas with flameless materials at least 915 mm into the field. Its manual also says to shut down air conditioning, exhaust and intake fans in the work area, because a flame can be sucked into the building, while NRCA (U.S.) warns that closing intakes can leave a building under negative pressure that pulls flames inside. Either way, the plant's maintenance staff belong in that decision.

Insurers watch this closely. FM Global, which insures many industrial plants, treats torch roofing as high-risk hot work, and its 2020 data sheet calls for 2 hours of fire watch and 2 hours of monitoring afterwards. The reason is hidden fire: in Listowel, Ontario, in 2011, a fire started by a propane torch during roof repairs burned undetected above a suspended ceiling, and two firefighters died when the roof collapsed.

Where a flame is not wanted at all, there are torch-free choices: self-adhered modified bitumen (SOPREMA's Sopraply Stick Duo, for example, installs down to 0°C), cold-applied adhesives, and heat-welded single-ply membranes such as TPO and PVC. Our modified bitumen vs TPO guide compares the two main systems.

What safety duties apply when roofers work in a plant?

Ontario treats roof repair as construction, even inside a factory. The Occupational Health and Safety Act counts repair as construction, Ontario guidance says the construction regulation applies to construction projects inside a workplace, and the Ministry of Labour's constructor guideline says that when an owner hires one contractor to do all the work, that contractor is the constructor.

• Designated substances. Whoever tenders the work must include the owner's list of designated substances, such as asbestos, in the tender documents (OHSA s. 30). Our roof replacement permit guide covers asbestos checks on older roofs.
• Debris. Under the construction regulation, debris may not fall freely; it goes down by chute, container, crane or hoist and is removed at least daily.
• Edges and openings. Built-up roofing work needs a barrier at least 2 m from the perimeter, and openings need a guardrail or a secured, marked cover.
• Skylights. The Ministry says every skylight must be treated as a fall hazard when workers are on a roof; one fatality it lists happened during repairs to skylight curbing on an industrial roof.
• The building in use. CRCA's re-roofing guidance says to tear off only what can be made watertight the same day, warns that debris piles can overload a deck, and asks the crew to learn the fire safety plan and sprinklers and to tell the fire department when hot work is planned.
• Fumes. For adhesive and asphalt fumes, the New York State Department of Health (U.S.) treats closing air intakes as a last resort and suggests working near them when the building is unoccupied.

How do plants check a roofing contractor?

Not by a roofing licence, because Ontario does not require one. Roofer is a voluntary trade: it is not on the list of compulsory trades in O. Reg. 876/21, and Skilled Trades Ontario says the roofer certificate (trade 449A) does not have to be renewed. Toronto and Mississauga license building renovators rather than roofers, and Mississauga's licence requires $2 million in liability insurance.

Industrial clients usually look further: WSIB clearance, Working at Heights training, insurance certificates and a safety program. IHSA's Certificate of Recognition (COR) is voluntary but often required on Ontario construction contracts, and it is valid for three years with audits in years two and three. Many plants also screen contractors through platforms such as ISNetworld, Avetta or ComplyWorks, which collect safety, insurance and training records. Our guide to choosing a commercial roofing contractor covers the rest of the checklist.

How does OYH Roofing handle industrial roof repair?

OYH Roofing repairs, re-roofs and replaces flat roofs on industrial and manufacturing buildings across Ontario, including the 50,000 sq ft TPO roof at the Millomat Stampings plant in Mississauga and a 53,000 sq ft 2-ply modified bitumen roof on an industrial building in Mississauga, both with 20-year warranties on labour and materials. Before work starts, we can survey the roof, map the stacks, fans and wet areas, and plan the work zones and firewatch with your maintenance team.

See the Millomat Stampings project, the 53,000 sq ft industrial roof and our other completed projects. For a full replacement, see the warehouse roof replacement guide; for leaks, see commercial roof leak repair in Toronto and in Mississauga.

Frequently asked questions

Do roofers use blowtorch?

Yes, for torch-applied modified bitumen. A propane torch melts the back of each sheet so it bonds to the layer below. Because that is an open flame, Ontario's Fire Code requires a firewatch until at least 3 hours after torching stops, and CRCA recommends flameless materials at walls, curbs and penetrations. Single-ply membranes such as TPO and PVC are welded with hot air instead.

What is the most common roof repair?

On commercial flat roofs, repairs at flashings and penetrations. The Canadian Roofing Contractors Association reports that penetrations, openings and terminations account for most reported roofing problems, and its torch guideline notes that most torch fires start at the same details. Other common repairs are open seams, punctures from foot traffic and blocked drains.

Do roofers need to be licensed in Ontario?

No. Roofer is a voluntary trade in Ontario, not one of the compulsory trades listed in O. Reg. 876/21, so a certificate of qualification is not required to do roofing work. Some cities license building renovators, and commercial clients often ask for WSIB clearance, Working at Heights training, liability insurance and safety certification such as COR.

What are the downsides of torch down roofing?

The main one is fire risk. Torch-applied modified bitumen uses an open flame, so Ontario's Fire Code requires a firewatch until at least 3 hours after torching stops, and the torch must never directly heat wood decks, insulation, flashing or openings. Near walls, curbs and penetrations, CRCA recommends flameless materials instead.

What is the best material to seal roof leaks?

The one the membrane's maker approves for that membrane. A lasting repair uses matching membrane: a heat-welded patch on PVC or TPO, or new modified bitumen on a modified bitumen roof. Sealants and mastics are temporary or maintenance items; Sika treats sealant as a maintenance item outside its warranty, and IKO allows temporary repairs only in an emergency.

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

• Ontario: Fire Code, O. Reg. 213/07, Division B, Subsection 5.11 (consolidated January 1, 2026); Occupational Health and Safety Act, ss. 1 and 30; O. Reg. 213/91, ss. 26.3, 35 and 207; O. Reg. 876/21 (compulsory trades).
• Ministry of Labour, Immigration, Training and Skills Development: Constructor guideline (August 2026); Workers falling through skylights (April 2022); Application of the industrial and construction regulations.
• Skilled Trades Ontario: Roofer (449A). City of Toronto: Building Renovators. City of Mississauga: Business Licensing By-law 0001-2006. IHSA: COR FAQs. ISNetworld, Avetta, ComplyWorks.
• CRCA Technical Bulletins: Vol. 41, Steel deck and fastener corrosion (1994); Vol. 44A, Roof top effluence management (1996); Vol. 45, Chemical resistance of single-ply membranes (1996); Vol. 48, Roof re-covering (1999); Torch application guideline to mitigate rooftop fires (November 2020).
• CRCA Canadian Roofing Reference Manual (2020): 1.5.3 Torching, 3.1.6 Vapour retarders, 3.2 Re-roofing operations, 13.1.1 Locate the problem area.
• National Research Council Canada: Two decades of SIGDERS research (Baskaran); Canadian Building Digests CBD-73 (1966) and CBD-175 (1976), archived copies. Construction Canada: Using roofing parapets for airtight roofs, October 2023.
• Makers: ARMA contaminants on modified bitumen (April 2024, U.S.); Tremco thermoplastic chemical resistance chart (2026, U.S.) and high-temperature stack detail (U.S.); Sika Sarnafil PVC data sheet (2022), Canadian warranty sample (2022) and hot stack detail (U.S.); IKO detail T-P-4, hot pipe (2025) and Building Owner's Guide (February 2026).
• Warranties and data (U.S. unless noted): Elevate Red Shield warranty (2026) and UltraPly TPO XR data (2026); Johns Manville Peak Advantage guarantee sample and roofing for automotive and battery plants; SOPREMA Sopraply Stick Duo data sheet (Canada).
• IIBEC: Thermoplastic roofing best practices, part 3 (2023); TA-013-2017, moisture-damaged roof materials; Tie-ins (October 2012) (U.S.). NRCA, Professional Roofing: moisture surveys and re-cover (July 2005); torch safety and air intakes (May 2004) (U.S.). Carlisle: A daily seal for roofing projects (2020, U.S.).
• FM Global Property Loss Prevention Data Sheet 10-3, Hot Work Management (2016, interim revision April 2020). New York State Department of Health: Roofing and indoor air (2023, U.S.). Wellington Advertiser: Cause of fire announced (Listowel), November 10, 2011.
• OYH Roofing project records: Millomat Stampings, Mississauga; 53,000 sq ft industrial roof, Mississauga (October 2026).

OYH Roofing, 2120 Speers Rd, Oakville, ON L6L 2X8 · 1-833-775-7663 · info@oyhroofing.ca