Metal Roofs and Ice Dams: What Metal Can and Can't Do

Do metal roofs prevent ice dams?

Metal roofs do not prevent ice dams. An ice dam forms when heat from the house warms the upper roof deck, melts snow from below, and the water refreezes at the cold overhang. That process depends on the attic, not on what the roof is made of. If heat is leaking into the attic, water can melt and refreeze at the eaves of a metal roof just as it can on asphalt, wood or slate. You may see claims that switching to metal ends ice dams. It doesn't, and expecting it to leads to disappointment. Ice damming is a stated exclusion of the Guardian Lifetime Limited Material Warranty on the Interlock® roofing system. That warranty covers material and finish for the original purchaser while they own the home, is transferable once, and does not cover workmanship or damage from ice dams.

What does a metal roof change in winter?

A metal roof changes how snow behaves once it lands. Its coated surface is smoother and harder than most other roofing, so snow tends to release and slide sooner, especially when sun warms the panels or temperatures climb toward freezing. On a roof that clears faster, less snow stays on the warm upper deck to melt and feed a dam. How much that helps varies from house to house. Pitch, orientation, roof shape, profile and the weather all play a part. A steep, south-facing slope on the Rhode Island shore may clear within a day or two after a storm, while a shallow north slope in the Green Mountains can hold snow for weeks. Faster shedding is a real benefit, but it works best as a partner to a cold, well-ventilated attic rather than a replacement for one.

Can ice dams still form on a metal roof?

Yes, ice dams can still form on a metal roof whenever the attic below is warm enough to melt snow on the upper roof. Meltwater runs down the panels and freezes at the eave overhang or in the gutter, the same way it would on any other roof. Ice can also build where sliding snow piles up at a lower edge, a valley or against a wall. The practical difference lies in the layers below the panels. Interlock® panels interlock with one another and are installed over underlayment, and a properly installed roof in New England includes an ice barrier membrane at the eaves, as codes in cold-climate areas generally require. Those layers are there to deal with water that backs up. They are a backup to good attic conditions, which is why we look at insulation and ventilation with homeowners rather than relying on the roof alone.

Why does sliding snow need planning?

Sliding snow needs planning because a metal roof that sheds well can drop a large amount of snow at once. After a nor'easter, heavy wet snow coming off a roof can land on a walkway, a deck, a car, a lower roof or shrubs, and it can carry chunks of ice with it. On homes with entries under the eaves, that is a safety issue, not just an inconvenience. Snow retention devices, such as snow guards or bar-style systems, hold snow in place so it melts gradually or releases in smaller amounts. They are typically placed above doorways, walkways, driveways, decks, lower roofs and gas meters or vents. Where they belong depends on the layout of the house, the pitch and where people walk. Holding snow on the roof also keeps it near the eave, so retention works best on a home where attic heat loss has already been addressed.

Will a new metal roof fix existing ice dam problems?

A new metal roof by itself will not fix a house that already gets ice dams, but a reroof is a good moment to fix the underlying causes. With the old roofing off, it is easier to find and replace rotted sheathing at the eaves, add or correct soffit and ridge ventilation, and install a fresh ice barrier membrane along the eaves and in valleys. Air sealing and insulation in the attic can be scheduled before or alongside the roof work. If you've had leaks from ice dams, tell your contractor where and when they happened. A stain on one particular ceiling, a dormer that leaks every February, or ice that builds over a bathroom are clues that help pinpoint heat leaks. Fixing those along with the roof details gives a much better result than replacing the roofing and hoping the problem goes away.

Why do New England homeowners still choose metal?

New England homeowners choose metal for reasons that go well beyond ice dams: durability through long freeze–thaw winters, wind resistance when installed to manufacturer specification, and, along the coast, aluminum that does not rust in salt air. That last point matters on Cape Cod, the Islands, the North Shore and the Maine coast, where salt spray is hard on steel fasteners and flashings. The Interlock® roofing system is heavy-gauge aluminum with a 30 Year Alunar® coating warranty, and its panels weigh roughly 0.4 to 0.7 lb per square foot, light compared with many roofing materials. It comes in Slate, Cedar Shingle, Shake, Mediterranean Tile and Standing Seam profiles. If ice dams are part of why you're looking at metal, an in-home consultation lets us look at your attic, eaves and roof lines and explain what a new roof will and won't change.

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