Commercial Roof Coating: Restore or Replace?
When a coating adds years to a flat roof, when it only hides a failing one, and what Ontario's weather and rules mean for the job.
Call 1-833-775-7663 Oakville head office · Flat roof coatings, repairs, replacements and inspections for commercial, industrial and institutional buildings across Ontario
Karol Rajkowski
Vice President, OYH Roofing
Published October 12, 2026 · 12 min read
Short answer
A commercial roof coating can replace a tear-off only when the roof under it is dry, sound and draining. It will not fix wet insulation, open seams or a membrane at the end of its life. In Ontario, most coatings also need mild, dry weather, so the work fits best between late spring and early fall.
Can you coat a commercial roof instead of replacing it?
Yes, when the existing roof is dry, well attached and still has working seams, flashings and drainage. A commercial roof coating is a maintenance layer over a sound roof, not a new roof over a failed one.
The Roof Coatings Manufacturers Association (RCMA) says a properly applied coating can typically extend roof life by up to 10 years or more, and that almost every roof type can be coated. GAF, which sells coatings, is just as direct about the limit: coatings protect a structurally sound low-slope roof and are not meant for a failing one. The condition of the roof decides, not its age.
| What the assessment finds | Direction | Why |
|---|---|---|
| Dry insulation, sound seams, surface wear only | A coating can work | The membrane still has life, and the coating renews its surface |
| A few wet areas found by a moisture survey | Cut out and replace the wet areas, then coat | Makers require wet insulation to be removed before coating |
| Moisture in 25 per cent or more of the roof area | A tear-off may be the better choice | GAF's guidance on when a complete tear-off may be considered |
| Leaks in several places that repairs do not stop | Replace | A coating is not a leak repair |
| Water still standing 48 hours after rain | Fix the drainage first | Ponding harms acrylic coatings, and GAF's coating warranty excludes ponding areas |
| Gravel-surfaced built-up roof (tar and gravel) | Not a coating candidate | Coating makers exclude gravel surfaces |
| A second roof or an old coating over a failing membrane | Tear-off | Another layer only covers the problem |
| Roof still under the membrane maker's warranty | Get written approval first | Unapproved alterations can void the warranty |
The honest comparison is three-way. A coating renews the surface, a recover adds a new membrane over a dry old roof, and a replacement starts again from the deck. Our commercial flat roof lifespan guide explains how each choice changes the years you get.
What should be checked before a commercial roof coating goes on?
Seven things: moisture in the insulation, wet areas to cut out, seams and flashings, active leaks, drainage, adhesion, and the roof type and warranty. All seven are settled before the coating is priced, because any one of them can change the answer from coat to replace.
| Check | What it involves | Who says so |
|---|---|---|
| 1. Moisture survey | An infrared scan at night or an electrical impedance scan, confirmed with core cuts | ASTM C1153, ASTM D7954, IIBEC |
| 2. Wet insulation | Cut out and replaced with like materials before any coating | Henry, Tremco, SOPREMA Canada |
| 3. Seams, flashings and penetrations | Every seam walked and repaired; failed flashings rebuilt | IIBEC Interface |
| 4. Active leaks | Found, repaired and left to dry; a coating does not find leaks | RCMA, GAF |
| 5. Drainage | No water standing 48 hours after rain; drains cleared and low spots corrected | GAF, RCMA |
| 6. Adhesion test | Test patches pulled after curing; Henry asks for at least 2.0 lb per linear inch, with one test per 10,000 sq ft | Henry, NRCA |
| 7. Roof type and warranty | No gravel surfaces; written approval from the membrane maker if a warranty is in force | RCMA, SOPREMA, IKO, Sika, Elevate |
How wet is too wet? GAF's guidance says a complete tear-off may be considered when a survey finds moisture in 25 per cent or more of the roof area. We could not trace that percentage to any standard, and Tremco's Canadian guidance is stricter: no restoration product "should be applied over wet insulation, even when the roof membrane is functioning." An IIBEC Interface article adds that the area of wet insulation to cut out usually decides whether a coating or a tear-off makes more sense.
A scan alone is not proof. ASTM C1153 covers infrared surveys done at night and states that it does not find the cause of the moisture or where it got in, and IIBEC's technical advisory says every non-destructive survey has to be confirmed with core samples. Our commercial roof inspection guide explains the survey methods, and our guides to roof flashing repair, membrane roof repair and ponding water on a flat roof cover the repairs that come first.
Not sure if your roof can be coated?
We will assess the roof, check for wet insulation and tell you whether a coating, a recover or a replacement makes sense, with a written quote.
Call 1-833-775-7663Request an assessmentWhat are the main types of commercial roof coatings?
Four chemistries cover most commercial work: acrylic, silicone, polyurethane and aluminum-pigmented asphalt. Reinforced liquid-applied membranes such as PMMA sit above them as full resurfacing systems. They differ most in how they handle standing water and cold weather.
| Coating | ASTM specification | Standing water | Lowest application temperature | Good to know |
|---|---|---|---|---|
| Acrylic (water-based) | D6083 | Ponding can harm long-term performance (GAF) | 10°C and rising (GAF, Henry) | Needs 8 to 12 dry hours after application; white and reflective |
| Silicone | D6694 | Sold as ponding-resistant, but makers still require positive drainage | 0 to 5°C, depending on the product (Gaco, Henry, GAF) | Slippery when wet; an old silicone coating is recoated with silicone |
| Polyurethane | D6947 | Not for continuous immersion (Sika, Tremco) | 2 to 10°C, depending on the product (Sika, Tremco) | Often reinforced with fabric at seams and details |
| Aluminum-pigmented asphalt | D2824 | Not where water ponds (Henry 588) | 10°C and rising (Henry 588, water-based) | For smooth asphalt roofs; less reflective than white |
| Reinforced PMMA liquid membrane | No ASTM product specification found | Set by the maker | Winter grade down to -5°C (SOPREMA) | A resurfacing system, thicker than a coating |
Three details matter on Ontario's asphalt-based roofs. White coatings over modified bitumen or built-up roofing need a bleed-blocking base coat, or oils from the asphalt stain them. Gravel-surfaced roofs are not coating candidates at all. And single-ply roofs such as TPO need adhesion tests, and often a primer, before a coating will bond.
Silicone has its own trade-offs. Henry's data sheet warns that silicone-coated surfaces are extremely slippery, and an RCMA technical note says an existing silicone coating should only be recoated with silicone-based products. Choosing silicone today largely decides what the next coat will be.
When can a roof be coated in Ontario?
Water-based coatings need about 10°C and rising with dry weather, which in most of Ontario means roughly June to early September. Silicone and winter-grade liquid membranes extend the season into spring and fall, but every coating needs a dry surface and a rain-free cure.
| Month | Toronto Pearson | Ottawa (Airport) | Sault Ste. Marie |
|---|---|---|---|
| May | 8.2°C, 12.7 days | 7.5°C, 13.4 days | 3.5°C, 11.8 days |
| June | 13.9°C, 10.8 days | 12.9°C, 13.9 days | 8.5°C, 11.6 days |
| July | 16.6°C, 10.3 days | 15.4°C, 12.1 days | 11.6°C, 12.7 days |
| August | 15.8°C, 9.8 days | 14.3°C, 11.2 days | 11.5°C, 10.7 days |
| September | 11.6°C, 10.2 days | 9.6°C, 12.3 days | 8.0°C, 14.9 days |
| October | 5.3°C, 12.8 days | 3.4°C, 13.6 days | 2.7°C, 16.5 days |
Read the table against the data sheets. GAF and Henry set 10°C as the minimum for acrylic, and Henry adds that temperatures must stay above it for 12 hours after application. At Toronto Pearson the average overnight low is above 10°C only from June to September; in Ottawa, June to August; in Sault Ste. Marie, July and August. Rain falls on about 10 or 11 days a month in Toronto through that season, so crews work around the forecast.
Silicone goes on in cooler weather: Gaco's sheet stops at 0°C, Henry's at 2°C and GAF's at 5°C, with rain-safe times from 15 minutes to 2 hours. Makers also ask for a surface about 3°C above the dew point, which rules out many cool, damp mornings. By mid October, with Toronto's average low at 5.3°C, the practical step is to book the assessment and repairs now and coat when the weather allows. Our guide to the best flat roofing material for Ontario winters covers cold-weather limits for full roof systems.
How thick is a commercial roof coating, and what does the warranty cover?
Warranty length follows thickness. Published tables call for about 22 to 44 dry mils of silicone for 10 to 20 years, and many base warranties cover only the coating material, not the labour or the roof under it.
| Maker and coating | 10 years | 15 years | 20 years |
|---|---|---|---|
| GAF Unisil silicone | 23 mils | 31 mils | 40 mils |
| Henry Pro-Grade 988 silicone, smooth surface | 22 mils | 30 mils | 37 mils |
| Henry Pro-Grade 988 silicone, granulated cap sheet | 30 mils | 37 mils | 44 mils |
| GAF Acrylic Top Coat | 24 mils | 32 mils | Not offered |
| Henry acrylic system, smooth surface | 26 mils | 30 mils | 43 mils |
Read the coverage, not just the years. GAF's limited warranty on its coatings covers leaks from a manufacturing defect, with replacement product as the remedy, and it excludes workmanship and areas that pond water. Henry offers a paid upgrade that adds labour and workmanship after an inspection by its representative, and Gaco's material warranty is prorated. Ask who stands behind the labour, whether ponding areas are covered and whether a final inspection is part of the warranty.
If the roof is still under its original warranty, ask the membrane maker first. SOPREMA Canada requires written pre-approval for any addition or alteration during the warranty period, IKO and Sika Canada have similar terms, and Elevate treats a coating as overburden that needs a waiver. Our commercial roof warranty guide explains what to keep on file.
What Ontario rules and incentives apply to a roof coating job?
A coating job is still construction work on a roof, so Ontario's fall protection, training and Notice of Project rules apply, along with municipal rules on wash water. Toronto also pays an incentive for reflective coatings. Permit rules are set city by city.
| Topic | What applies | Source |
|---|---|---|
| Fall protection | Required where a worker could fall more than 3 metres; when a built-up roof is resurfaced, a barrier at least 2 metres from the edge | O. Reg. 213/91, ss. 26 and 207 |
| Notice of Project | Filed before work starts when labour and materials are expected to exceed $50,000 | O. Reg. 213/91, s. 6 |
| Training | Working at Heights training, valid for three years | O. Reg. 297/13 |
| Wash water (Toronto) | Water from outdoor power washing must not reach catch basins; whoever hires the work shares the responsibility | City of Toronto |
| VOC content | 250 g/L for non-bituminous roof coatings and 300 g/L for other bituminous roof coatings; the limits apply to makers, importers and sellers | SOR/2009-264 |
| Building permit (Toronto) | Not needed to replace existing roofing material where no structural work is required; coatings are not named | City of Toronto |
| Toronto Eco-Roof Incentive | $2 per m² for a cool roof coating over an existing roof, up to $50,000 per project | City of Toronto |
| Income tax | Restoring a property to its original condition is usually a current expense; a lasting improvement is usually capital | Canada Revenue Agency |
Two of these catch owners out. Toronto's Eco-Roof Incentive Program must approve the application before any work starts on the roof, and it asks for a Solar Reflectance Index of 78 or more on a flat roof; our cool roof guide covers the program in detail. Cleaning also comes before coating: Toronto's guidance says water from outdoor power washing must not reach catch basins, so ask how the wash water will be handled.
On permits, Toronto says none is needed to replace existing roofing material when no structural work is involved. None of the city pages we checked names coatings, so confirm with your building department; our roof replacement permit guide lists what does need one. For taxes, the Canada Revenue Agency's test turns on whether the work restores the property or improves it beyond its original condition. Ask your accountant how it applies to your building.
Does a white coating pay off this far north? A National Research Council Canada simulation of white and black modified bitumen roofs in Toronto found that the white roof lost somewhat more heat, the black roof gained about five times more, and the white roof came out ahead over the year with a low risk of moisture damage. The model left out snow cover, so treat it as a direction, not a savings estimate.
When is replacement better than a coating?
Replacement is the better choice when wet insulation is widespread, leaks keep coming back in new places, the membrane is at the end of its service life or the roof already carries extra layers. A coating over a failing membrane hides the problem for a while, and the tear-off still comes.
We have seen where that ends. At Devi Mandir in Pickering, the old roof was two layers of modified bitumen with a coating on top. All of it came off before we installed a 60 mil TPO roof across 6,500 sq ft, with a 20-year warranty on labour and materials.
There is a middle option. On a 53,000 sq ft industrial building in Mississauga, we recovered the existing roof with 2-ply modified bitumen, backed by 20 years on labour and materials. The Canadian Roofing Contractors Association calls a re-cover an acceptable alternative when the owner has realistic expectations, and it asks for the same homework as a coating: find the cause, find the moisture and correct the defects first.
Some roofs skip the coating question entirely. Coating makers exclude gravel-surfaced built-up roofs, so our tar and gravel roof guide covers repair and replacement instead, and our warehouse roof replacement guide shows how a replacement runs while the building stays open.
How does OYH Roofing approach roof coatings?
We start with the roof, not the product. OYH Roofing applies roof coatings to restore sound membranes on commercial, industrial and institutional buildings across Ontario, and we recommend a recover or a replacement when the assessment shows a coating would not last.
An assessment covers the membrane, seams, flashings and drains, with a moisture survey and core cuts where the roof's history calls for them. A commercial roof coating costs less than a replacement, but the price depends on the repairs and preparation the roof needs, so we quote after the assessment. Building staff should stay off the roof; a roofing crew with fall protection does the checking.
You can see our work on the completed projects page, and our guide on how to choose a commercial roofing contractor lists the questions to ask any bidder.
Frequently asked questions
Is roof coating a good idea?
Yes, on the right roof. A coating suits a low-slope roof that is dry, well attached and draining, where the surface is worn but the membrane still works. It is a poor idea over wet insulation, open seams or a roof past its service life, because the coating hides the problem and the leaks return. A moisture survey and an adhesion test settle the question.
What are the different types of commercial roof coatings?
The main types are acrylic, silicone, polyurethane and aluminum-pigmented asphalt, plus reinforced liquid-applied membranes such as PMMA. Acrylic is water-based and needs about 10°C and dry weather. Silicone handles standing water better and cures in cooler weather. Polyurethane is often reinforced at seams and details. Aluminum coatings protect smooth asphalt roofs. The right commercial roof coating depends on the existing roof, its drainage and the season.
What are the downsides of using silicone roof coating?
Silicone is very slippery when wet, so foot traffic needs planning. Most white silicones lose some reflectance as they age and collect dirt. Once a roof has a silicone coating, the next coat generally has to be silicone too, because other products bond poorly to it. And like any coating, silicone fails over wet insulation or a poorly prepared surface.
How long does a flat roof coating last?
Coating warranties usually run 10, 15 or 20 years, depending on the product and how thick it is applied. The Roof Coatings Manufacturers Association says a properly applied coating can typically extend roof life by up to 10 years or more, and most coatings can be renewed with another coat as they wear. The roof under the coating still sets the limit.
Do roof coatings actually work?
They work when the roof under them is sound. Makers and roofing associations set the same conditions: dry insulation, repaired seams and flashings, positive drainage, a clean surface and a passing adhesion test. They do not work as a leak fix. Leaks have to be found, repaired and dried before coating, and where that is skipped, coatings blister, peel and leak again.
Can you repair a roof instead of replacing it?
Often, yes. A commercial flat roof with a few failed details can be repaired, and one with a worn surface but dry insulation can be coated or recovered. Replacement is the answer when wet insulation is widespread, leaks keep returning in new places or the roof already has extra layers. An inspection with a moisture survey shows which applies.
Thinking about coating your roof?
Call for an assessment and a written recommendation: coat, recover or replace.
Call 1-833-775-7663Request an assessment
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
- Roof coatings FAQs and Coatings Tech Note: Use of Primers Prior to Roof Coating, Roof Coatings Manufacturers Association.
- Roof Coating vs. Commercial Replacement, GAF, January 13, 2026; Technical bulletin TAB-C-47, May 2024; Limited Warranty on GAF Liquid-Applied Roof Coatings, 2026; and the Unisil silicone and High Tensile Acrylic Top Coat data sheets.
- Henry (U.S. editions): Pro-Grade 988 silicone data sheet, September 2023; silicone system application guide and acrylic system application guide, April 2024; silicone warranty program; and Pro-Grade 588 aluminum data sheet, September 2022.
- GacoFlex S42 silicone data sheet, June 2025, and sample material warranty, Gaco.
- Sikalastic-641 Lo-VOC data sheet, Sika Canada, 2017; AlphaGuard MTS Top Coat data sheet, Tremco; ALSAN RS 230 Field data sheet, SOPREMA, 2016.
- Is your roof a good candidate for restoration?, Tremco Roofing, 2023.
- ASTM International: D6083 (acrylic), D6694 (silicone), D6947 (polyurethane), D2824 (aluminum-pigmented asphalt), C1153-23 (infrared moisture surveys) and D7954-22a (impedance moisture surveys).
- Your First Step to Coating Success: Substrate Preparation, IIBEC Interface, October 2017, and Technical Advisory 016-2018: Reuse of Roof Insulation, IIBEC.
- Roof coatings: for better or worse, Professional Roofing (NRCA), May 2006.
- Roof Re-Covering: An Alternative?, Technical Bulletin No. 48, Canadian Roofing Contractors Association, June 1999.
- Warranty terms: General Conditions for Roofing Warranties, SOPREMA Canada; BUR limited labour and material warranty sample, IKO; Sarnafil system warranty sample, Sika Canada, 2022; Painting of Single-Ply Membranes, Elevate technical bulletin, February 2025.
- Canadian Climate Normals 1991 to 2020, Environment and Climate Change Canada: Toronto Pearson, Ottawa (Airport) and Sault Ste. Marie.
- O. Reg. 213/91: Construction Projects, sections 6, 26 and 207, and O. Reg. 297/13: Occupational Health and Safety Awareness and Training, Ontario e-Laws.
- City of Toronto: Eco-Roof Incentive Program, When Do I Need a Building Permit? and Washing Cars and Outdoor Surfaces.
- Volatile Organic Compound (VOC) Concentration Limits for Architectural Coatings Regulations, SOR/2009-264, Justice Laws.
- Current expenses or capital expenses, Canada Revenue Agency.
- Hygrothermal simulations of cool reflective and conventional roofs, Saber, Swinton, Kalinger and Paroli, National Research Council Canada, 2011.
- OYH Roofing project records: Devi Mandir, Pickering; Mississauga industrial recover; City of Mississauga, 3185 Mavis Rd (October 2026).
OYH Roofing, 2120 Speers Rd, Oakville, ON L6L 2X8 · 1-833-775-7663 · info@oyhroofing.ca