Worth doing
- Rake snow off the lower 3–4 feet of roof, from the ground
- Lay a calcium chloride sock across the dam as a stopgap
- Call for steam removal if water is pooling or already inside
- Photograph any interior damage for your insurance company
Winter Roof Guide
What Causes Ice Dams (And How To Stop Them For Good)
The ridge of ice on your gutter isn't the problem — it's the symptom. Here's what's actually happening under the snow, what's safe to do about it this week, and the two fixes that keep it from coming back.
Interactive Cutaway
Watch An Ice Dam Form
This is a cutaway of a New England gable roof — the warm living room, the attic above it, and the snow on the shingles. Step through the six stages of a bad winter week, then switch to the fix and run the same storm again.
Everything the cutaway shows is written out below, step by step.
What Causes Ice Dams?
An ice dam needs three things: snow on the roof, escaping heat that melts the underside of it, and a cold roof edge for the meltwater to refreeze on. Snow is the one ingredient you can't control. The other two live in your attic, and that's why some houses on a street grow ice dams every winter while their neighbors stay clean under the identical storm.
Here's the sequence. Warm air from your living space leaks into the attic — through recessed lights, the attic hatch, gaps around plumbing and wiring, and thin insulation. That warmth heats the roof deck from below, and the snow sitting on the warm part of the roof starts melting from the bottom. The meltwater runs downhill under the snowpack until it crosses the eave — the overhang past your exterior wall. There's no heated room under an overhang, so that stretch of roof stays at the same temperature as the air. The water refreezes on contact, and every melt-and-refreeze cycle stacks another layer of ice along the roof edge.
That ridge of ice is the dam. Once it's tall enough, new meltwater pools behind it with nowhere to drain. Shingles are built to shed water running downhill, not to hold back standing water — so the pond works uphill, under the shingle line, through nail holes and seams in the deck, and into the house. That's why the stain usually shows up on a ceiling or wall near an exterior wall, sometimes a long way from the ice you can see.
Two details most homeowners find surprising. First, icicles and ice dams aren't the same thing — icicles hanging off a gutter are common on cold roofs too, but a thick shelf of ice sitting on the roof itself means damming. Second, bitter cold isn't what causes it. The dangerous weather is a deep snowpack with daytime temperatures near freezing — which is a normal week in a Tewksbury or Billerica January.
How To Get Rid Of Ice Dams (Without Wrecking Your Roof)
If the dam is already built, the goal is to give the trapped water a way off the roof without damaging the shingles underneath. Most of the ice dam damage we repair wasn't caused by the ice — it was caused by the removal. Ice bonds hard to shingles; anything that chips at the ice takes granules and shingle edges with it, and every hit turns into a leak point come spring.
What actually works: a roof rake to pull fresh snow off the lower few feet (that starves the dam of new meltwater), and low-pressure steam to cut drainage channels through the ice — which is how we do it. Steam melts the ice off the shingle surface instead of breaking it off, and it's the only removal method we consider safe on an asphalt roof. Calcium chloride in a sock laid across the dam can buy you time by melting a small channel, but it's slow, it can corrode aluminum gutters, and the runoff is hard on plants below — treat it as a stopgap, not a fix.
Never do
- Chip at the ice with a hatchet, hammer, or ice pick
- Throw rock salt on the roof — it stains and corrodes
- Use a pressure washer or open-flame torch on ice
- Climb onto a snow-covered roof, for any reason
Should You Rake Snow Off Your Roof?
Yes — with a long-handled roof rake, standing on the ground, after any storm that drops six inches or more. You're not trying to clear the whole roof. Pulling snow off the first three to four feet above the eave removes the raw material the dam is built from: if there's no snowpack over the cold edge, meltwater from higher up has open shingle to run across and drain off. It's the single most effective thing a homeowner can do in-season, and it costs about forty dollars at the hardware store.
Use a rake with a plastic edge or rollers, and don't scrape down to bare shingle — leave an inch of snow rather than grinding the granules off. Work from the ground only; the fall risk on a ladder next to an icy roof is not worth any amount of ice. And if your roof is more than one storey up, or the snow is wet and heavy, that's the point where it stops being a homeowner job — our crews handle roof snow removal in Tewksbury all winter with the right equipment.
How To Prevent Ice Dams For Good
Everything above manages the symptom. Prevention happens in the attic, and it comes down to one sentence: keep the roof deck cold, end to end. If the deck over your living space is the same temperature as the deck over your eaves, snow melts evenly in the sun and wind instead of melting from below and refreezing at the edge — and the dam never gets a start.
Seal the ceiling, then insulate it
Air leaks move more heat than thin insulation does, so sealing comes first: the attic hatch, recessed light housings, and the gaps where plumbing, wiring, and chimneys pass through the ceiling. Then insulation depth. Many attics around here still carry a fraction of what today's Massachusetts energy code calls for, and it shows up every winter as a bare-roofed house in a snowy neighborhood — that melted stripe is your heating bill leaving through the roof.
Let the attic breathe
Ventilation carries away whatever heat still gets through: cold outside air enters at the soffit vents, washes up along the underside of the roof deck, and exits at the ridge vent. Baffles hold that channel open where the insulation meets the eaves. A sealed, insulated, vented attic is the combination that ends repeat ice dams — and it pays for itself in summer too, when the same airflow keeps the attic from cooking your shingles.
Back it up at the roof edge
When a roof is replaced, Massachusetts code requires an ice and water barrier — a waterproof membrane under the shingles at the eaves — so that even if a dam forms, backed-up water hits rubber instead of bare deck. If your roof predates that requirement, it's one more reason an aging roof and a history of ice dams often get solved together; see our roof replacement page. And keep the gutters clean going into winter — a gutter full of leaves holds meltwater exactly where the dam wants to start. Our seamless gutter crews see the aftermath every spring.
If ice dams hit the same spot on your roof every winter, that pattern is diagnostic — it's telling you where the heat is escaping. We look at the attic, the ventilation, and the roof itself during a free assessment, and we'll tell you which fix your house actually needs before anyone talks about price. Already have water coming in? Start with ice dam removal and we'll trace the leak damage once the roof is safe.
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Ice dam questions we hear every winter
Do heat cables stop ice dams?
They manage the symptom, and only where they run. Heat cables melt drainage channels along the roof edge, which can protect a stubborn trouble spot — a north-facing eave, a tricky valley — but they don't touch the heat loss that causes the melting, and they cost electricity all winter. We treat them as a last-resort patch for spots that insulation and ventilation can't fully solve, not as the fix.
Are icicles a sign of an ice dam?
Sometimes. Small icicles on a cold, sunny day are normal — a little surface melt refreezing as it drips. What you're watching for is a thick shelf of ice sitting on the roof itself, big icicles that grow week after week, or ice showing on the siding below the gutter, which means water is already overflowing where it shouldn't. If the ice keeps building, the dam is building too.
Do clogged gutters cause ice dams?
They don't cause the melt, but they make everything worse. A gutter packed with leaves holds meltwater right at the cold roof edge — the exact place a dam wants to form — and a gutter full of solid ice gives the dam a foundation. Clean gutters won't stop a badly leaking attic from making ice, but they remove the head start. It's the cheapest item on the prevention list.
How much snow on the roof is too much?
As a rule of thumb, start paying attention after six inches of accumulation, and take it seriously after a foot of wet snow or repeated storms with no thaw between them. Wet snow is the heavy kind — a foot of it weighs three to four times what the same depth of powder does. If you hear creaking, see a sagging ceiling, or interior doors suddenly stick, that's a load problem, not just an ice problem — call right away.
Will removing the ice dam fix my leak?
It stops the water at the source, which is the urgent part. But water that already got in has soaked insulation, sheathing, or drywall, and shingles above the dam may have lifted. Once the roof is clear we trace where the water traveled and repair what it touched — otherwise you find the rest of the story as mold in June. Removal first, then the repair; we handle both.