Repair or Replace a Commercial Roof? How to Decide

Karol Rajkowski

Vice President, OYH Roofing

Published October 18, 2026 · 13 min read

What are the options besides repair or replace?

There are four, not two. Between a repair and a full tear-off sit a restoration, which renews the surface of a sound roof, and a recover, which puts a new roof over the old one. Each fits a different condition, and each comes with a different warranty from the membrane maker.

Our guides go deeper on each one: membrane roof repair and flashing repair, commercial roof coatings, and full replacements on a warehouse or a tar and gravel roof. This page is about choosing between them.

What decides whether to repair or replace a commercial roof?

Six checks, and the moisture survey carries the most weight. NRC Canada's guidance on reroofing lists the classic triggers for replacement: repair spending becomes excessive, leaks become intolerable, the risk of a leak is unacceptable, or the roof fails outright. The checks below tell you which side of that line your roof is on.

Age is a guide, not a verdict. Most commercial flat roofs in Ontario last 20 to 30 years, as our commercial flat roof lifespan guide explains, but a 15-year-old roof with wet insulation everywhere can be past saving while a well-kept 25-year-old roof is still worth repairing.

Why does a moisture survey come first?

Because wet insulation is what separates a repair from a replacement, and you cannot see it from the roof surface. NRC's reroofing guidance says re-covering over an existing wet roof system is not recommended, and both IKO and SOPREMA require wet areas to be removed before they will warrant a recover.

• Infrared (ASTM C1153) scans the whole roof at night and finds the location of wet insulation, but not where the water got in.
• Impedance (ASTM D7954) uses a meter on a grid. It does not work on metal roofs, black EPDM or roofs covered with ballast.
• Nuclear surveys follow ANSI/SPRI/RCI NT-1.
• Core samples confirm what any scan suggests. ASTM's own standards call for them, and CRCA warns that a few test cuts alone should never be relied on.

Wet insulation matters for the energy bill too. CRCA Technical Bulletin 47 cites research proposing that insulation is wet, and unacceptable, once it keeps less than 80 per cent of its dry thermal resistance, and adds that less moisture than that can still cause corrosion or rot. NRC also notes that one large wet area is cheaper to remove than the same amount scattered across the roof. Our commercial roof inspection guide explains how a survey fits into an inspection.

No Canadian standard sets a percentage of wet area at which a recover is ruled out. The figure of 25 per cent often quoted online comes from GAF (U.S.) guidance for its liquid-applied coatings, which says a complete tear-off may be considered when moisture is found in 25 per cent or more of the roof area. It is not from a code or from CRCA.

How do roof consultants score a roof's condition?

Some use a condition index from 0 to 100. The best known is the Roof Condition Index from the U.S. Army's ROOFER system, which NRC Canada adopted for its building asset management research. It combines separate scores for the membrane, the flashings and the insulation, and the insulation score comes from a moisture survey.

The report itself warns that the index alone cannot set the repair plan, and that a score for one roof section does not signal replacement of the whole roof. In its own worked example, a roof scoring 31 with wet insulation over 17 per cent of its area was still cheaper to repair than to replace.

When is a recover allowed on a commercial roof?

When the old roof is dry, well attached and sitting on a sound deck, and the membrane maker agrees in writing. A recover saves the tear-off, but it covers the old roof instead of fixing it, so the makers set conditions before they will warrant one.

• A moisture report first. IKO's Re-Cover warranty needs a third-party thermographic scan, done within 90 days of the start, stating that the existing roof is suitable for another layer. SOPREMA asks for a thermography or moisture report from no more than three months before work begins, plus an exploratory cut.
• Wet areas come out. Both makers require wet or moist areas to be removed and replaced with new material before the new roof goes on.
• A sound, bonded base. IKO requires the new system to be fully adhered or properly fastened to the existing roof or the deck. For its TPO over an existing roof, IKO does not allow adhesive bonding to the old roof at all; it needs new insulation or a cover board.
• Not every system qualifies. SOPREMA does not offer recover or resurfacing warranties over built-up (BUR) or hot rubber roofs, and IKO does not accept its TPO in its Re-Cover program.

The trade-off is real. CRCA's bulletin on re-covering cites NRCA project data showing that re-covered roofs have problems at about twice the rate of new roofs, and warns that a few test cuts should never be relied on to find moisture. A recover also hides the deck: CRCA's reference manual says any deck problems must be corrected before roofing starts during a re-roof, and NRCA (U.S.) does not recommend a recover over a damaged or deteriorated deck. Every recover also adds weight, which is a question for an engineer on older buildings.

What does each option do to your roof warranty?

A repair keeps an existing warranty only if the maker approves it, and a recover never warrants the layers left underneath. Read the warranty before you choose, because both makers we checked put the rules in writing.

• Repairs on a warranted roof. SOPREMA says any additions, alterations or repairs must be pre-approved in writing, and that changes made without its recommendations could void the warranty. IKO's warranty excludes damage after the roof is altered unless IKO is asked first, an approved contractor does the work and IKO gives written permission, and it does not pay for repairs it has not authorized in writing.
• Recovers. IKO's and SOPREMA's recover warranties exclude the existing roofing left in place, and IKO also excludes failures of the bond between old and new. The terms are shorter than for a new roof.
• Replacement. SOPREMA treats a roof as new when all the insulation is removed and only the vapour barrier is kept, so it qualifies for a new-roof warranty. Both makers want the warranty application about two weeks before work starts.
• Maintenance. IKO's warranty requires a maintenance program recommended by CRCA or NRCA, and SOPREMA's maintenance guide asks for inspections at least twice a year and leaks reported within 30 days. Our commercial roof warranty guide explains the warranty types.

Which Ontario rules change the answer?

Fewer than most owners expect. Ontario's Building Code sets no limit on the number of roof layers and no clause that says a re-roof must add insulation, but it does govern fire ratings, wind uplift and loads, and a full tear-off can be treated as a new roofing system.

A commercial re-roof can also need a building permit, and older roofs may contain asbestos that has to be identified before work is tendered. Our roof replacement permit guide covers both.

How do you compare repair and replacement quotes?

By what each option costs per year of roof life it buys, not by the price on the quote. The U.S. Army's ROOFER method divides the repair cost by the years of life the repair adds, and compares it with the replacement cost divided by the new roof's expected life. If that ratio is under 0.8, it says repair; over 1.2, replace; in between is a judgement call.

ASTM E917 sets out the fuller version, life-cycle cost analysis, which brings in maintenance, energy and what is left at the end in present-value terms. A 1996 NRC seminar paper by CRCA's Kalinger used a life-cycle comparison to show that a maintained roof lasting 20 years beats an unmaintained one lasting 15, which is why our commercial roof maintenance guide matters even when you plan to replace.

If the new roof adds insulation in a gas-heated building, ask about Enbridge Gas's Commercial Custom Retrofit program, which offers incentives for insulation upgrades, capped at $100,000 per project for most commercial customers. Projects must be pre-approved, so check the current terms with Enbridge before you sign. Reflective roofs in Toronto may qualify for the city's Eco-Roof incentive, covered in our cool roof guide.

Can a roof replacement wait until spring?

Often, if a repair keeps the water out until then. CRCA treats 4.4°C as the threshold for cold-weather roofing, and IKO says applications below 5°C need special measures and should stop if the cold prevents proper work. Many sheets and adhesives have their own minimums; SOPREMA's self-adhered base sheet, for example, is rated to 10°C in its summer grade and -10°C in its winter grade.

• Keep the building dry first. CRCA says no roofing should be removed unless the space below can be kept watertight, and every open edge is sealed at the end of the day. IKO only allows as much roof to be opened as can be covered by the finished assembly the same day, and the night seal is cut away before work resumes.
• Plan around the people inside. IKO's notice to proceed covers working hours, noise and complaints. NIOSH guidance written with NRCA (U.S.) says to keep asphalt kettles away from air intakes, doors and windows, and to agree with the owner whether intakes should be shut off.
• Leave time for the paperwork. SOPREMA and IKO want warranty applications about two weeks before work starts, and a commercial re-roof may need a permit; see our roof replacement permit guide.

So in Ontario it often makes sense to repair what leaks in winter, survey the roof, and schedule a replacement for the warmer months. Our winter preparation guide covers what to do before the snow.

How does OYH Roofing help you decide?

OYH Roofing repairs and replaces flat roofs on commercial, industrial and institutional buildings across Ontario from its head office in Oakville. We look at the roof and at the building from inside, check the insulation for water, and put the options in writing with the one we recommend and why. When a repair will do the job, we say so.

Recent replacements include the 50,000 sq ft Millomat Stampings roof in Mississauga, where one 60 mil TPO system now covers a re-roofed building and a new addition with 20 years on labour and materials, and the Devi Mandir in Pickering. See also the 53,000 sq ft industrial roof in Mississauga, our other completed projects, and our pages on commercial roof leak repair in Toronto and in Mississauga.

Frequently asked questions

Is it better to repair or replace a roof?

It depends on the condition, not the age. A repair is better when the damage is local, the insulation around it is dry and the membrane is sound. Replacement is better when a moisture survey finds wet insulation across large areas, leaks keep moving, the deck is damaged or two roofs are already in place. Compare the cost per year of life each option buys.

How many layers are allowed on a roof?

Ontario's Building Code sets no limit on the number of roof layers. U.S. building codes do, banning a recover where two roof coverings are already in place. In practice the membrane maker decides, because IKO and SOPREMA only warrant a recover over a dry, sound existing roof, and their recover warranties exclude the old layers left underneath.

Is it okay to put a new roof over an old roof?

Sometimes. A recover can work over one dry, well-attached roof on a sound deck, after wet areas are cut out and the maker approves it in writing. NRC advises against re-covering a wet roof, CRCA cites data showing that re-covered roofs have problems at about twice the rate of new ones, and a recover warranty is shorter than a new roof's.

Is roof restoration worth the money?

It can be, on the right roof. A coating or a new cap sheet renews the surface of a roof that is dry, well attached and draining, and SOPREMA warrants its resurfacing systems for 10 or 15 years. It is not worth it over wet insulation or a failing membrane, because the problem stays underneath. A moisture survey tells you which case you have.

Does a 30 year roof really last 30 years?

Not necessarily. A figure like 30 years is a warranty term or a product rating, not a promise about your roof. Commercial membrane warranties from IKO and SOPREMA run up to 20 or 25 years, and how long a roof actually lasts depends on the installation, the drainage and the maintenance. Most commercial flat roofs in Ontario last 20 to 30 years.

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

• National Research Council Canada: Smith, Reroofing Considerations, Building Science Insight (2005); Kalinger, Benefits of preventative roof maintenance (1996); Hassanain, Froese and Vanier, BELCAM roofing asset management (1999).
• U.S. Army Construction Engineering Research Laboratory: Bailey et al., ROOFER, technical report M-90/04 (1989, U.S.).
• CRCA: Technical Bulletins Vol. 48, Roof Re-Covering: An Alternative? (1999) and Vol. 47, Methods for Determining Moisture in Roofing Materials (1998); Canadian Roofing Reference Manual, 3.1 deck preparation, 3.2 re-roofing operations and 3.3 cold weather conditions (2020).
• IKO: Commercial Technical Specification Manual, Part 2, pre-job general requirements and Part 15; instructions for commercial limited warranty applications (December 2022); BUR limited labour and material warranty; limited warranty programs brochure.
• SOPREMA Canada: General Conditions for roofing warranties (March 30, 2026); Warranty Program (March 2026); Preventive Maintenance Guide; Sopraply Flam Stick data sheet.
• NRCA, Professional Roofing (U.S.): Bollnow and Crowe, Low-slope reroofing guidelines (July 2005). NIOSH: Reducing Roofers' Exposure to Asphalt Fumes (2003, U.S.). GAF: roof coating vs commercial replacement (U.S.).
• ASTM International: C1153-23 (infrared), D7954/D7954M-22a (impedance) and E917-17(2023) (life-cycle cost). ANSI/SPRI/RCI NT-1 (nuclear moisture surveys). International Building Code, Section 1512 (U.S.).
• 2024 Building Code Compendium, January 16, 2025 edition: Volume 1 (Div. A 1.3.3; Div. B 3.1.15, 4.1.4.1, 5.2.2.2, Part 11, 12.2.1.2) and Volume 2 (SB-10). Enbridge Gas: insulation incentives.
• OYH Roofing project records: Millomat Stampings, Mississauga; Devi Mandir, Pickering; 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