An ice dam is a buildup of ice that forms at the edge of your roof and blocks melting snow from draining off. The water that can't drain pools behind the ice — and standing water on a roof is the whole problem. Shingles and metal panels are built to shed water flowing downhill; they were never waterproof against water sitting still.
There's a second thing working against you, and most explanations skip it. The snowpack itself is insulation. A deep blanket of snow holds your roof's escaping heat against the roof surface instead of letting it vent to the sky, so the melting underneath runs faster and longer than the outside temperature would suggest. That meltwater stays liquid under the snow, and when it reaches the cold eave and stops, it has nowhere to go — and it isn't just sitting there. It's under pressure, weighed down by the ice and snow stacked on top of it. Pressurized water finds the seams: it gets pushed up under the shingle laps and in behind them, against the direction water is supposed to travel. The flatter your roof, the worse this gets — a low-pitched roof gives the water less help draining and more time to work its way in.
From there it moves into the roof cavity, through the insulation, and shows up as stained ceilings, wet exterior walls, peeling paint — and, left alone, mold.
Gutter ice weighs around 60 pounds per cubic foot — enough to tear gutters off the house.
In the Municipality of Anchorage's own words: if it happened last winter, it will likely happen again. It's a property of the roof, not the weather.
Three things have to be true at the same time: snow on the roof, air below freezing, and a roof surface that's above freezing higher up while the eave edge stays below freezing. Take away any one of the three and no dam forms. Here's the sequence:
Warm air from your living space leaks up through openings in the ceiling — recessed lights, attic hatches, plumbing and wiring penetrations, the tops of interior walls — and heat conducts through thin spots in the insulation. Air leaks matter even more than insulation depth: moving air carries heat past insulation instead of through it.
The escaped heat warms the roof deck above freezing, and the bottom layer of the snowpack starts to melt — even while the air outside is well below freezing. The snow itself makes this worse: snow is an insulating blanket (roughly R-0.5 to R-1 per inch), so a deep snowpack holds the roof's heat in. Deeper snow, warmer roof.
The water travels along the roof surface, beneath the snowpack, where you can't see it. It flows down until it crosses the line where your heated house ends and the unheated roof overhang begins.
The overhang is the coldest part of the roof — there's no heated room beneath it, just winter air on both sides. The water freezes there, and every melt cycle adds a layer. The ice ridge grows until water pools behind it, deeper and wider, until it finds its way under the roofing.
That's why the dam always forms right around the eave line, why icicles are the visible symptom of an invisible process, and why the fix is never "more cold" — it's managing where the heat and the water go.
Already seeing water inside? Here's what an emergency visit looks like →
It seems backwards, but the coldest places get the fewest ice dams — with no melt, there's no water to refreeze. Ice dams thrive where there's lots of snow and marginal cold: exactly Southcentral. Anchorage averages around 79 inches of snow a year, roofs carry snowpack for four to five months, and midwinter warm spells drive melt-refreeze cycles all season long.
Some roofs have it worse:
Anchorage's older housing stock was built with less insulation and far more air leakage than today's code — more heat reaching the roof deck.
Valleys, dormers, and multi-level roofs concentrate meltwater and are genuinely hard to insulate and ventilate well. Valleys collect snow from two roof planes and funnel all their meltwater through one path.
Cathedral ceilings, flat and low-slope roofs, and rooms finished up into the roofline — A-frames, bonus rooms over garages, knee-wall upper floors — put the ceiling right against the roof deck. With little or no attic space to insulate and ventilate, house heat goes straight into the snow.
Sun melts snow from the top down — on south- and west-facing slopes, and wherever the roof clears first around skylights, vents, and chimneys. That meltwater runs down under the snow and refreezes at the cold eave, which is why even a perfectly insulated roof can grow ice on its south side.
The building-science fix for ice dams is your attic: seal the air leaks in the ceiling, insulate deeply, and ventilate the roof deck so escaping heat gets flushed out before it can melt snow. Alaska building guidance calls this a "cold roof," and done right it dramatically reduces ice damming. If your attic has never been air-sealed and an energy retrofit is in the cards, do it — it cuts your heating bill too, and we'll tell you the same thing standing in your driveway.
So why does a company that installs heat cable exist? Because in Alaska, the attic fix often isn't the whole answer:
Snow insulates the roof from the cold air above it. Under enough snowpack, even an airtight, heavily insulated roof deck creeps above freezing — building scientists have documented thick eave ice on roofs insulated far beyond code. Physics doesn't care how good your attic is; it cares about the temperature at the roof surface.
Hot roofs (cathedral ceilings, flat roofs, rooms built into the roofline), scissor trusses, complex rooflines, and historic buildings often can't reach the insulation and ventilation levels the cold-roof approach needs — not without reconstruction.
Solar gain melts snow on properly built roofs, and that water still refreezes at the cold eave.
A full attic retrofit is a construction project measured in months and tens of thousands of dollars. Managing this winter's water is not.
The playbook, straight from the authorities: fix the heat loss you reasonably can, manage the roof's snow load, and keep the drainage path open where Alaska's physics wins anyway. That last job is what heat cable does.
And it's worth being plain about the economics, because most homeowners end up choosing between three very different price tags. Hardware-store constant-wattage cable is the cheap fix — and it's the product we're most often called to tear out a few winters later. The full cold-roof rebuild is the thorough fix: tear-off, new insulation and ventilation, new roofing — a project that starts near the cost of a roof replacement, roughly $15,000–$25,000 for a typical Anchorage shingle roof and well beyond that for larger homes and metal, before the attic work is counted. A professionally designed self-regulating system is the middle path: engineered to your actual roof, built to run for the long haul, and priced far closer to the first number than the second. That's the slot we exist to fill.
Heat cable has one job, and it's worth stating precisely: it keeps a melted drainage path open so water gets off your roof instead of ponding behind ice.
A properly designed system traces the zones where refreeze happens — along the eaves (extending up-roof past the exterior wall line into the warm zone), up valleys, along the gutter, and down inside every downspout to discharge. That last part matters: a system that melts water at the eave but lets it refreeze in the downspout has just moved the dam. The drainage path has to be continuous, roof to ground.
What it doesn't do — and you should be suspicious of anyone who claims otherwise:
The self-regulating cable we install adjusts its heat output along its length — putting out more heat where it's cold and iced, throttling down where it's warm — which is what makes it safe to run and efficient to operate. The design of the layout is the product: where the runs go, how the valleys are handled, and whether the path reaches all the way to discharge is what separates a system from a decoration.
If you see any of these, water is already going where it shouldn't:
Ice damming is predictable; last year's dam is this year's forecast.
The visible symptom of the melt-refreeze cycle.
Meltwater is backing up into the overhang.
The dam is established and growing.
Water has found a path into the wall cavity.
Backed-up water travels inside wall and ceiling cavities and can surface far from the roof edge.
That last point is the sneaky one: by the time water shows at a window frame, it may have been traveling through your walls for a while. If you're seeing signs 3 through 6, don't wait for spring.
Ice dams need melt as much as they need freeze. The snowiest, moderately cold climates get the worst ice dams, which is why Anchorage sees more damming than far colder Interior towns.
Ice dams form with or without gutters — the dam is made on the roof, by heat loss. But gutters full of ice add real risk of their own: at around 60 pounds per cubic foot, gutter ice can tear the gutter off the house.
Air sealing comes first — warm air leaking through ceiling openings carries more heat to your roof than conduction through insulation. And under deep snowpack, even excellent roofs can dam.
Rock salt and calcium chloride corrode roofing, gutters, and flashing, kill the plants below, and at best carve a short-lived channel. Steam removal takes the ice off without touching the roof.
Ice dams form at skylights, in valleys, above dormers, and under the snowpack — often invisible from the driveway. Water damage is frequently the first visible sign.
On low-pitch roofs especially, an inch of ice ridge is enough to pond water behind it. Dam height matters less than what's pooling upslope of it.
It keeps the drainage path open so meltwater gets off the roof instead of ponding behind ice and backing up under your roofing — that's the real job description, and on most roofs it's exactly the protection needed. What it won't do: remove snow, heat your whole roof, or fix the attic heat loss driving the melt. We'll tell you at the assessment which of those your roof actually needs — sometimes the answer includes things we don't sell.
Attic heat loss is one of the root causes, and if yours has never been air-sealed, that work is worth doing — it can lower your heating bill too. Go in with eyes open, though: done properly, air sealing can be an expensive and time-consuming job — pulling back insulation, finding and sealing every leak, then re-insulating — and on a hot roof it can mean opening up finished ceilings. And it isn't a guaranteed fix for ice dams: even a fully air-sealed attic can leave the ice unchanged. Many Alaska roofs need both: deep snow, hot roofs, complex rooflines, and sun-driven melt can produce dams even over a well-built attic. We're straight with you about which case your house is.
Snow removal genuinely works — the Municipality of Anchorage calls removing roof snow before it melts and refreezes the most effective cure, and notes that clearing only the eaves usually isn't enough, because the melt is happening over your whole heated roof. The catches: it has to be done repeatedly all winter, raking can damage roofing, and winter roof work is dangerous — Anchorage's guidance points homeowners to professionals for a reason.
Different attic, different roofline, different exposure. More ceiling air leaks, a valley or dormer concentrating meltwater, a hot roof, or a sunny southern exposure can put a dam on your house while the same storm leaves your neighbor's alone. It's the roof, not the winter.
Not necessarily. Ice dams are a heat-and-water problem, not a shingle problem — even correctly installed roofing sheds flowing water but can't hold back standing water. That said, an eave membrane under the shingles (standard practice here) limits how much a dam can damage; it just doesn't prevent the dam.
Before the snow flies. Summer and fall installs mean your system is tested and running before the first melt-refreeze cycle — and you're not booking emergency work in January. If you already have a dam and water inside now, steam removal comes first, then prevention.
Free on-site assessment — we'll show you where your roof melts, where it refreezes, and what actually needs doing. If the right answer is 'rake your roof and seal your attic hatch,' that's what we'll say.
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