Ice Dams on Metal Roofs: Why They Form and What Works

Yes, ice dams form on metal roofs. A metal roof does not stop attic heat from melting the snow above it, and that meltwater still runs to the cold eave and refreezes. Metal does change where and how long the ice stays, because snow slides off slick panels more easily, but valleys, gutters, low roofs and snow-guard lines can all build ice.

Do ice dams form on metal roofs? The cause is the same

An ice dam needs three things: snow on a sloping roof, air below freezing, and heat that melts the snow from underneath. National Research Council Canada also lists an open edge of snow where ice can form. The roofing material is not on that list. If the attic is warm, the roof deck above it is warm, and the snow in contact with it melts. The water runs down under the snow until it reaches the cold overhang, where it freezes.

A metal roof does not change that chain. What it changes is what happens to the snow and ice afterward, which is where the confusion comes from. It is easy to watch snow slide off in a big sheet and assume the problem is solved. It may reduce the problem. It does not remove the cause.

How a metal roof changes where ice builds up

National Research Council Canada, in an archived building digest, notes that where a strip of exposed metal is used at the eaves, ice damming is generally less of a problem because snow tends to slide off, and ice tends to slide off more quickly during thaws. It adds that the hazard from falling snow and icicles is still present. So metal can shorten the life of a dam. It does not guarantee one will not form.

Ice is still likely to build where snow is held or water collects:

• Behind snow guards. The same digest says snow guards at the eaves will usually prevent snow slides but may cause an increase in ice formation. If you have snow guards above an entry, the snow stays on the roof longer, and the melt-and-refreeze cycle at the eave can last longer too.
• In and around the eavestrough. Gutters may increase ice formation. Sliding snow can also damage a gutter.
• In valleys. Where two slopes meet, meltwater collects, and the digest says large dams can form at the lower end of a valley.
• On low or shaded roof sections, such as an addition, porch roof or north slope, where snow stays put and the roof stays cold.

Can ice dams make a metal roof leak?

They can. A metal roof sheds flowing water well. Water that is held back and standing behind a dam is a different test. The same building digest says that on buildings with overlapping water-shedding units, including corrugated sheet roofing, backed-up water may leak into the building. Standing seam panels have raised, tight seams, but they still have eave trim, valley and wall flashings, panel ends and penetrations.

The places worth asking a roofer about are:

• panel laps and end laps;
• exposed fasteners and their washers or sealant on roofs that use them;
• eave, valley and wall flashings and trim;
• the underlayment at the eave.

If water has been getting in at the eave, a metal roof is not exempt from the usual interior damage. Our post on ice dam water damage in Ontario covers what to look for inside.

What works on a metal roof compared with shingles

How to prevent ice dams on a metal roof

The long-term fix is inside the house, and it is the same as for any roof. Natural Resources Canada says to seal all attic air leaks and insulate thoroughly. The National Research Council digest adds ventilation of the space above the insulation, with inlets low at the eaves and outlets high near the ridge, so the roof deck stays cold. Our posts on attic insulation and ice dams and attic ventilation and ice dams explain both.

Then work on the edge:

• Keep eavestroughs and downspouts clear before freeze-up, so meltwater has a path.
• Plan snow guards with the eave in mind. They protect people and gutters from sliding snow, but ice can build behind them, so pick the layout with a roofer who knows your roof.
• Use heating cable only along the edge, gutter and downspout where drainage keeps freezing. It melts channels. It does not remove the dam.

Our post on metal roof snow retention in Ontario goes into how guards work.

If you already have an ice dam on a metal roof

Stay off the roof. A metal roof with snow or ice on it is slippery. Do not chip, hammer or scrape the ice, since it can dent panels and scratch the paint finish. If water is coming in, contact your insurer right away, as the Insurance Bureau of Canada advises, and move belongings away from wet walls.

D&D Snow Services handles ice dam removal with low-pressure steam, which cuts channels and releases the ice without hammering or chipping. Raking along the lower roof edge reduces the snow load that feeds a dam. It starts with a free written estimate. Afterward, fix the attic so the dam does not rebuild.

Ice dams and metal roofs: common questions

Can ice dams form on metal roofs?

Yes. The cause is the same on any sloping roof: attic heat melts snow from below, the water runs to the cold eave and refreezes. Metal can reduce the problem because snow and ice slide off more easily, but it does not remove it, especially behind snow guards, in valleys and at gutters.

Can you get ice dams with a metal roof that has snow guards?

Yes, and snow guards may add to ice buildup at the eave. National Research Council Canada notes that guards at the eaves usually prevent snow slides but may cause an increase in ice formation. Guards still protect people, entries and gutters, so plan the layout with the eave in mind.

Do metal roofs prevent ice dams?

No. They can lessen them, because snow and ice shed more readily from slick panels, but ice dams depend on heat loss from the house. Sealing attic air leaks, adding insulation and ventilating the attic are what prevent them, whatever the roofing material.

Is it safe to remove ice from a metal roof myself?

It is not advisable. Metal with ice on it is slippery, and chipping can dent panels and scratch the finish. Stay on the ground, protect the inside of the house, and have a professional clear an established dam with low-pressure steam.

Devon Moore, Operations Lead Co-Founder & Operations Lead — D&D Snow Services

Devon Moore is the co-founder and Operations Lead at D&D Snow Services, providing reliable residential and commercial snow removal across Waterloo Region.