A roof is something most homeowners rarely think about—until winter reminds them it is working harder than they realize. After a heavy snowfall in London, Ontario, the quiet buildup of melting snow and freezing temperatures can create hidden problems above your ceiling. What starts as a small ridge of ice along the roof edge can eventually lead to blocked drainage, trapped moisture, and costly repairs.
Ice dams are not just a roofing problem; they are a sign that your entire roofing system is dealing with changing temperatures, heat loss, and moisture management challenges. While both metal and asphalt roofing systems can face ice-dam issues, the way they respond to winter conditions can be very different.
Understanding how each roofing material performs through Ontario’s freeze-thaw cycles can help you make a more informed decision when planning your next roof upgrade. In this guide, we’ll compare metal roofing and asphalt shingles, explain what actually helps reduce ice dams, and discuss why proper installation matters for long-term winter performance.
What Causes Ice Dams on Residential Roofs?
Ice dams form when different sections of a roof remain at different temperatures during winter.
Warmth from the living space can heat the roof’s underside. Snow sitting over the warmer area begins to melt, and the water travels toward the colder eaves. Once it reaches that colder section, it can freeze again.
Over several freeze-thaw cycles, the ice builds into a dam.
The problem is not simply the ice itself. Once the dam blocks normal drainage, additional meltwater may collect behind it. That water can potentially work beneath roofing materials and reach vulnerable areas around underlayment, flashing, or roof penetrations.
Several conditions can contribute to ice dams:
- Inadequate attic insulation
- Poor attic ventilation
- Uneven roof temperatures
- Heavy snow accumulation
- Repeated winter freeze-thaw cycles
- Heat escaping around attic openings
This means changing roofing material alone does not necessarily eliminate ice dams. The entire roof assembly needs to work together.
How Does Ice Damming Affect Metal Roofing?
Metal roofing has a smooth surface that allows snow and water to behave differently than they do on asphalt shingles.
Depending on the panel profile, slope, coating, snow conditions, and installation, snow may slide more readily from a metal roof. However, that does not mean metal roofing is immune to ice dams.
If an ice dam forms along the eaves, the metal panels themselves can remain intact while water becomes trapped above the blockage.
The critical concern is therefore water management, not simply whether the metal can withstand contact with ice.
Properly designed metal roofing can provide a durable exterior layer, but it still requires appropriate flashing, underlayment, drainage details, and ventilation. Snow guards may also be appropriate on certain roofs where uncontrolled snow release could create a safety concern.
How Does Asphalt Roofing Respond to Ice Dams?
Asphalt shingles have a textured surface that generally resists sliding snow. During heavy snowfall, snow can remain on the roof until it gradually melts.
If an ice dam forms at the eaves, meltwater can collect behind it and potentially reach areas beneath the shingles.
Repeated exposure to moisture and freezing conditions can also contribute to deterioration over time, particularly where existing roofing is already aged or damaged.
That does not mean asphalt shingles are unsuitable for Canadian homes. They remain a common roofing choice, but their performance against winter moisture depends heavily on roof design, installation, ventilation, underlayment, and metal roofing maintenance.
Metal vs. Asphalt: Which Handles Ice Dams Better?
No single material is a universal winner just because one roof is metal and the other is asphalt.
Metal roofing can offer advantages during snowy conditions because of its smooth surface and durability. However, the system’s design and installation strongly influence how it handles winter moisture.
Asphalt roofing can also perform reliably through Canadian winters when installed and maintained correctly. Problems become more likely when an older roof has deteriorated components or when the attic allows excessive heat to reach the roof deck.
A useful comparison looks like this:
| Factor | Metal Roofing | Asphalt Roofing |
| Snow shedding | Often easier on suitable slopes | Generally slower |
| Ice-dam resistance | Good system-dependent performance | Good when properly designed |
| Maintenance | Generally low | Periodic inspection recommended |
| Winter durability | Strong when properly installed | Reliable with proper maintenance |
| Ice-dam prevention | Requires roof and attic measures | Requires roof and attic measures |
The takeaway is straightforward: treat neither roofing material as an ice-dam solution on its own.
What Factors Reduce Ice-Dam Problems?
If your goal is to reduce winter roofing problems, look beyond the surface material.
- Improve attic insulation
Adequate insulation helps reduce heat transfer from the living space into the attic. Keeping the roof deck closer to outdoor temperatures can reduce uneven snow melting.
- Maintain proper ventilation
A well-designed attic ventilation system moves air through the attic and helps manage temperature and moisture.
- Seal attic air leaks.
Warm air can escape through openings around fixtures, ducts, attic hatches, and other penetrations. Air sealing can help limit this unwanted heat movement.
- Pay attention to flashing and drainage
Valleys, roof-to-wall transitions, chimneys, skylights, and eaves require careful detailing. These areas can become especially vulnerable when ice restricts normal water flow.
- Remove snow safely when necessary
Large snow accumulation can increase the potential for ice formation and roof loading. Homeowners should avoid climbing onto an icy roof and instead use qualified professionals when snow removal is necessary.
What Are the Best Ice Blockers for Metal Roofs?
Homeowners sometimes search for ice blockers as though one product can prevent ice dams completely. In practice, the best approach is usually a combination of proper roof design, insulation, ventilation, underlayment, and appropriate snow-management components.
For certain metal roofs, snow guards can help control where accumulated snow releases from the roof. They are particularly useful above entrances, walkways, driveways, or other areas where sliding snow could pose a hazard.
Ice-and-water protection may also be incorporated into vulnerable roof areas, depending on the roof design and local building requirements.
A roofing professional should assess the roof’s slope, panel system, snow exposure, drainage pattern, and surrounding conditions before recommending a specific solution.
Why Proper Installation Matters in London’s Climate Conditions
A roofing system must handle more than summer heat and occasional rain. Ontario winters bring snow, ice, wind, and repeated temperature changes that can expose weaknesses in an improperly installed roof.
When comparing roofing contractors in London, Ontario, you should ask how the proposed system will address drainage, flashing, attic ventilation, snow management, and vulnerable roof transitions.
Treat the installation as a complete system, not just new material on top of the roof deck.
When choosing the best roofing company in London, make sure they can explain what the chosen material can realistically achieve. If a contractor claims that metal roofing alone will completely prevent ice dams, that deserves closer scrutiny.
Why Consider AM Group Exteriors for Metal Roofing?
For homeowners exploring a new roof, AM Group Exteriors offers a locally established option, having served customers since 1956. Our approach combines roofing expertise with warranty-backed products and professional installation.
A few points worth considering include:
- Lifetime Platinum Warranty: Available for qualifying sloped roofing systems.
- Long-term protection: Our stated coverage includes blow-off protection for the first 15 years and a TRU Protection Period covering the first 50 years.
- Algae resistance: Protection is provided for the first 25 years on applicable products.
- Post-50-year coverage: After the first 50 years, materials-only coverage applies under the stated warranty structure.
For homeowners comparing local roofing companies, the useful part is not simply the length of a warranty. It is understanding exactly what the warranty covers and how the roofing system is expected to perform.
Our knowledgeable team can also help determine whether metal is appropriate for your roof rather than recommending it simply because it is durable. That assessment is especially useful when the existing property has recurring ice-dam issues that may also involve attic conditions or roof design.
The Bottom Line
Ice dams are ultimately a winter moisture and temperature-management problem, not simply a roofing-material problem. Metal roofing can offer strong winter performance and efficient snow shedding, but it still needs proper ventilation, insulation, flashing, underlayment, and drainage details.
Asphalt shingles can also perform well through Ontario winters when the complete roofing system is correctly designed and maintained.
If your roof regularly develops heavy ice buildup, start with a professional assessment of the entire system. Rather than simply replacing shingles or choosing metal because it is marketed as winter-ready, identify why the ice is forming and address the underlying conditions.
If you are considering a durable roofing upgrade, Contact AM Group Exteriors to evaluate your options and plan a roofing system suited to your home and local winter conditions. Contact us today!
FAQs
Metal roofs can shed snow more readily, but neither material completely prevents ice dams. Proper insulation, ventilation, flashing, and drainage remain essential.
Snow guards can control snow release, while proper underlayment protects vulnerable areas. The right combination depends on roof slope, design, and snow exposure.
Ice dams can restrict drainage and allow water to collect around vulnerable areas. Proper installation and winter roof maintenance help reduce these risks.
No, metal roofing does not guarantee ice-dam prevention. Attic insulation, ventilation, air sealing, and effective drainage are also important.
