At 600 meters above sea level in Quebec's Laurentians, a 2-centimeter hailstone hits an asphalt shingle at 25 meters per second. The impact knocks off ceramic granules. The same stone strikes a standing seam metal panel. It leaves a shallow dent. Which roof is worse off after a summer hailstorm? The answer is not as simple as material hardness charts suggest.
Why Elevation Changes Hail Damage
Hail forms in strong updrafts inside thunderclouds. Higher terrain forces air upward, intensifying these updrafts. Towns like Mont-Tremblant, Sainte-Agathe-des-Monts, and La Malbaie sit in hail-prone zones. Environment Canada data shows hail days increase by roughly 15 percent per 300 meters of elevation gain in southern Quebec. Stones also fall faster in thinner air. A 2 cm hailstone at sea level hits at about 20 m/s. At 800 meters, terminal velocity rises to 23 m/s. Kinetic energy scales with the square of velocity. That means a 15 percent speed increase produces a 32 percent jump in impact energy.
Roof slope matters too. Steep roofs, common in Quebec chalets, deflect some hail energy. Low-slope or flat roofs take direct hits. Asphalt shingles on a 4/12 pitch lose granules faster than the same shingle on a 10/12 pitch. Metal panels dent more easily on flat sections because the impact vector is perpendicular to the surface.
Asphalt Shingle Granule Loss: Mechanism and Measurement
Asphalt shingles have three layers: a fiberglass mat, an asphalt coating, and ceramic granules. Granules protect the asphalt from UV light and physical wear. Hail knocks granules loose by fracturing the asphalt bond. The damage shows up as bare black spots, often in a random pattern. Granule loss is cumulative. A roof that loses 10 percent of its granules after one storm loses another 8 percent after the next. The asphalt underneath oxidizes faster, leading to cracking and leaks within 5 to 8 years if left unrepaired.
Insurance adjusters use a simple test. They count granules in a 10 cm by 10 cm square. More than 15 missing granules per square indicates functional damage. A 2022 field survey of 200 Quebec roofs after a July hailstorm in the Laurentians found that 68 percent of asphalt shingle roofs showed granule loss above this threshold. The average repair cost was $1,200 for a 1,500 square foot roof. Full replacement ran $8,000 to $12,000. Granule loss is a 2 of 3 on evidence quality for predicting future leaks. It is visible, measurable, and well documented, but not every granule-bare spot leaks immediately.
Inspection timing matters. Granules loosened by hail often wash off in the next rain. An inspector who arrives two weeks after the storm sees more bare spots than one who arrives the next day. Quebec's RBQ licensing rules require roof inspectors to document hail damage within 30 days for insurance claims. Delayed inspections underreport damage.
Metal Roof Denting: Mechanism and Measurement
Metal roofs dent when hail impact exceeds the panel's yield strength. Steel panels with a 26-gauge thickness (0.45 mm) dent at lower impact energies than 24-gauge (0.60 mm). Aluminum panels dent more easily than steel. Copper and zinc are softer still. A 2 cm hailstone rarely dents 24-gauge steel on a steep slope. The same stone leaves visible dents on 26-gauge aluminum on a 3/12 pitch.
Denting is cosmetic in most cases. The metal does not lose its waterproofing. A dented panel still sheds water. The problem is aesthetic and, in extreme cases, structural. Hail larger than 4 cm can puncture thin metal or tear seams. That is rare in Quebec. The 2022 Laurentians survey found denting on only 12 percent of metal roofs, and 90 percent of those dents were under 1 cm deep. Repair costs averaged $300 for paint touch-ups. Full panel replacement was needed in 2 percent of cases, costing $2,500 to $4,000.
Metal roof denting is a 1 of 3 on evidence quality for predicting functional failure. Dents do not correlate with leaks unless the panel is punctured or the seam is separated. A 2018 study by Sikiric on hail impact on standing seam roofs found no water penetration at dent depths up to 3 mm. The same study noted that granule loss on asphalt shingles led to water absorption within 12 months in 40 percent of samples.
Head-to-Head: Which Roof Suffers More?
Define "suffers" as functional damage leading to water intrusion or reduced service life. By that measure, asphalt shingles suffer more. Granule loss directly shortens the roof's lifespan. A shingle roof that loses 20 percent of its granules after one hailstorm will likely need replacement 5 years earlier than a roof with no hail exposure. Metal denting, unless it punctures the panel, does not shorten service life. The metal roof will still last 40 to 60 years with dents.
But define "suffers" as immediate visible damage and repair cost. Then metal roofs suffer more per incident. A dented metal panel is obvious. A homeowner notices it the next day. Granule loss is subtle. Many homeowners never see it until a leak appears. The average insurance claim for metal dent repair is $1,800. The average claim for granule loss repair is $900. However, granule loss claims are filed three times more often because asphalt shingles cover 80 percent of Quebec homes.
High elevation tips the balance further toward asphalt shingle damage. Thinner air means faster hailstones. Faster hailstones mean more kinetic energy. More energy means more granule loss per impact. Metal panels also dent more at high elevation, but the threshold for functional damage is much higher. A 3 cm hailstone at 800 meters will strip granules from an asphalt shingle but only lightly dent a 24-gauge steel panel.
Ice Damming and Flat Roofs: Confounding Factors
Hail is not the only threat at high elevations. Ice damming is common on Quebec roofs with poor attic ventilation. Snow melts, refreezes at the eaves, and water backs up under shingles or metal seams. A roof already weakened by granule loss is more vulnerable to ice dam leaks. Metal roofs shed snow faster, reducing ice dam formation. This is covered in our comparison of metal roofing and asphalt shingles under ice damming after Quebec storms.
Flat roofs present a special case. Hail hits at a 90-degree angle, maximizing impact energy. Asphalt shingles on flat roofs are not recommended by Quebec building codes for slopes under 2/12. Modified bitumen or EPDM membranes are used instead. But some older Quebec homes have shingles on low-slope roofs. These roofs suffer catastrophic granule loss in hail. Metal flat roofs are rare but do exist, usually as standing seam with a minimum 1/4:12 slope. Denting on flat metal roofs is more severe than on pitched roofs. For a deeper look at flat roof choices after heavy rain, see asphalt shingles versus metal roofing for flat roofs after Quebec downpours.
Inspection and RBQ Licensing: What to Look For
After a hailstorm, a licensed RBQ roof inspector should check both roof types. For asphalt shingles, the inspector looks for granule loss, bruising (soft spots in the shingle), and cracks. Bruising is a 3 of 3 on evidence quality for hail damage. It is a direct physical imprint of the hailstone. Granule loss alone is a 2 of 3 because it can also come from normal aging. For metal roofs, the inspector looks for dent depth, seam separation, and fastener loosening. Dent depth over 1.5 cm on a 26-gauge panel warrants panel replacement. Seam separation is a 3 of 3 indicator of functional damage.
Homeowners can do a preliminary check. Walk the roof only if safe. Look for bare spots on shingles. Look for dents on metal. Check gutters for granules. A large accumulation of granules in the gutter after a storm is a strong sign of hail damage. Our guide to inspecting asphalt and metal roofs after a severe storm alert in Quebec walks through the process step by step.
Cost Analysis Over 20 Years
Assume a 1,500 square foot roof in the Laurentians. Asphalt shingle roof: $8,000 installed. Expected life without hail: 20 years. With one severe hailstorm every 5 years causing 15 percent granule loss each time, the roof needs replacement at year 12. Total cost over 20 years: $16,000 (two roofs). Metal roof: $18,000 installed. Expected life: 50 years. Hail causes cosmetic dents but no functional damage. Repair cost over 20 years: $600 (paint touch-ups). Total cost: $18,600. The metal roof costs $2,600 more over 20 years but avoids the hassle of a mid-life replacement.
Insurance premiums also differ. Quebec insurers charge 10 to 15 percent more for asphalt shingle roofs in hail-prone zones. Metal roofs often qualify for a discount because they resist hail better. The annual premium difference on a $400,000 home is roughly $150. Over 20 years, that is $3,000. The metal roof's cost advantage grows to $5,600.
Limitations of the Evidence
Most hail damage studies use laboratory impact tests with steel balls or artificial hailstones. Real hailstones are irregular, spin, and can shatter on impact. Lab tests may overestimate damage. Field surveys after storms are confounded by pre-existing damage. A roof with 10-year-old shingles loses granules more easily than a new roof. The 2022 Laurentians survey did not control for roof age. That is a significant limitation. The Sikiric 2018 study used new materials only. Real-world performance may differ.
Elevation data is also sparse. Environment Canada has few hail observation stations above 500 meters in Quebec. Most hail reports come from volunteers. The 15 percent increase per 300 meters is an estimate based on limited data. A 2021 study in the Journal of Applied Meteorology found a 22 percent increase per 300 meters in the Alberta foothills, but Quebec's terrain is different. The Quebec number could be higher or lower.
Closing Observations
Asphalt shingle granule loss is the more serious problem at high elevations in Quebec. It is cumulative, it shortens roof life, and it leads to leaks. Metal roof denting is mostly cosmetic. It looks bad but does not compromise waterproofing. The choice between the two materials depends on what the homeowner values: lower upfront cost and easy repair versus long-term durability and hail resistance. For a mountain chalet that will see hail every few years, metal is the better bet. For a city rowhouse in Montreal, asphalt shingles are fine. The hail risk there is lower, and the cost difference is harder to justify.
One final note: Quebec's RBQ requires that any roof repair after hail damage be done by a licensed contractor. Unlicensed repairs void insurance claims. Always ask for the RBQ license number before hiring. A quick check on the RBQ website confirms the license is valid. This is not a formality. It is the difference between a covered claim and a denied one.