How to Deal With an Ice Dam Safely and Stop It Coming Back
Rake from the ground, melt a channel, never chip the ice, and fix the warm attic that caused it.
- Intermediate
- 1 to 3 hours
- Updated
The short answer
An ice dam forms when heat escaping into the attic melts snow on the upper roof, and the water refreezes at the cold eave. To deal with it safely, rake snow from the eaves with a roof rake from the ground, melt channels with calcium chloride in a fabric tube laid across the dam, and never chip or hack the ice. Then fix the cause: air sealing, insulation and ventilation.
Ice dams are ridges of ice that form at the eave of a roof. They happen when heat from the house leaks into the attic and warms the roof, melting the snow on the upper slope. The meltwater runs down to the cold eave, which overhangs the warm walls and stays below freezing, and refreezes. The ridge grows until meltwater backs up behind it, and then the water runs up under the shingles and into the house.
In the Fraser Valley, ice dams are less frequent than in colder regions, but they happen in cold snaps after heavy, wet snow, and they are common at higher elevations and up the Fraser Canyon toward Hope, where the snow sits longer. Because freeze-thaw cycles can be rapid, a roof can go from fine to leaking in a day or two. See the ice dam guide for background.
The quick response is to remove the snow and open a path for water. The real fix is in the attic: less heat escaping, more insulation, and an even cold roof deck. Hacking the ice off does more harm than the dam, and the shortcut that sounds easiest, going up with a shovel or axe, is the most dangerous one.
Tools
- Roof rake with a long pole and wheels or a slide
- Garden hose (optional, for carefully run warm water from the ground)
- Sharp scissors
- Ladder base only to reach the eave, never to climb onto snow
- Headlamp or flashlight for attic check
Materials
- Calcium chloride ice melter (not rock salt)
- Nylons, stockings or fabric tubes to hold the melter
- Buckets, towels and plastic sheeting for interior water
- Attic air sealing and insulation materials (for the permanent fix)
Safety first
- Never go onto a snow-covered or icy roof. There is no traction, and snow hides edges, vents and weak spots. Work from the ground.
- Do not chip, chop or pry ice with a hammer, axe, pick or shovel. You will damage the shingles, flashing and gutters, and ice can fall on you.
- Watch for falling ice and snow from the roof. Stand out of the drop zone, and keep children and pets away.
- Stay clear of power lines when using a long pole, and do not rake near the service mast or overhead wires.
Step by Step
Step 1: Stay off the roof and deal with water inside first
Move belongings and put buckets under drips. A ceiling that bulges with water can be punctured at its lowest point to drain it in a controlled way. Turn off power to any circuit where water is dripping through a fixture.
Then decide on the exterior approach. Nothing you do on the roof is worth a fall on an icy surface.
Watch out: Never climb onto a roof covered with snow or ice. Even a low roof is dangerous.
Step 2: Rake snow from the eave zone with a roof rake
Removing the snow above the dam stops more meltwater feeding it. Use a roof rake with wheels or a slide that rides on the shingles, and pull the snow down in layers, leaving a thin layer so you do not scrape granules. Do not hit the shingle edge or the gutter.
Work from the ground, standing well out of the fall path. Check overhead for power lines before raising a long pole. Wet snow is heavy, and a large slab can come down all at once.
Step 3: Fill fabric tubes with calcium chloride
Calcium chloride melts ice at lower temperatures than rock salt and is less damaging to most roofing, but it can still corrode some metals and harm plants, so use it sparingly and follow the label. Rock salt (sodium chloride) is harsher and is not recommended.
Tie each tube closed. A tube about 4 to 5 feet long works well. They let the melter work without scattering loose granules on the roof.
Step 4: Lay the tubes across the dam from the ground
Place them perpendicular to the eave, about 2 to 3 feet apart, so they melt channels that let water drain. You are creating channels, not trying to melt the whole dam. Do not go up a ladder onto the roof to do this. If you cannot reach from the ground, stop.
Channels take a few hours to form. Keep containing any water inside while you wait.
Step 5: Keep gutters and downspouts in mind
Ice can fill a gutter and downspout and push water back up. If you can see an opening, melt it from the bottom up with warm, not boiling, water. Never use boiling water on a roof, which can crack gutters and shingles and refreeze in a thicker layer.
Step 6: Do not chip, chop or scrape the ice
Hammers, axes, picks and shovels break shingles, tear flashing and bend gutters, often leaving damage that is worse than the dam. They also cause dangerous ice falls. If the ice will not clear and water keeps coming in, call a roofer with steaming equipment, who can remove it without damage.
Step 7: Find and fix the cause in the attic once it is safe
The usual culprits are gaps around attic hatches, light fixtures and chimneys, bath fans dumping into the attic, and too little insulation. Air sealing and insulation keep heat in the house, and intake and exhaust vents keep the roof deck cold. See attic ventilation basics and how to calculate attic ventilation.
Also check that soffit vents are not blocked by insulation, see how to install attic baffles. An ice and water membrane along the eaves helps protect a roof, see how to install ice and water shield, but it does not stop the dam forming.
Why Ice Dams Form
Three things have to be present together: snow on the roof, heat leaking from the house into the attic, and cold outside air. Take away any of them and the dam does not form. Since you cannot control snow and weather, the fix is the heat, through air sealing, insulation and ventilation so that the whole roof deck stays close to outdoor temperature.
What Not to Use
- Rock salt: corrodes metal, stains and kills plants, and is less effective in the cold.
- Boiling water: can crack gutters and shingles, and refreezes into thicker ice.
- Heat guns, torches or pressure washers: damage shingles and can start fires.
- Axes, picks and shovels: damage the roof and cause dangerous ice falls.
Common Mistakes
- Climbing onto the roof to chip ice. It is the most dangerous option and damages the roof.
- Using rock salt. It corrodes metal and harms plants and is not as effective as calcium chloride.
- Using boiling water. It can crack gutters and shingles, and refreezes.
- Only removing the dam and not the cause. The dam will form again at the next cold snap.
- Raking down to bare shingles. It scuffs off granules. Leave a thin layer of snow.
- Blocking soffit vents with insulation. It kills the airflow that keeps the roof cold.
When to Call a Professional
Call a roofer if water is coming inside and you cannot control it, if the dam is large or on a steep or high roof, or if a dam has caused damage to shingles, gutters or ceilings. Professionals can remove ice without damaging the roof and can also assess and repair the cause.
Also call an insulation or energy specialist if the attic is leaky, poorly insulated or badly ventilated. Fixing that is what ends the problem.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Emergency Roof Repair service or the towns we cover.
How to Deal With an Ice Dam Safely: Questions
What is the safest way to remove an ice dam?
Rake the snow off the lowest few feet of the roof with a roof rake from the ground, then lay tubes of calcium chloride across the dam to melt channels for the water to drain. Never climb onto the roof, and never chip the ice with a hammer or axe. If water is still coming in, call a roofer with steam equipment.
What causes ice dams on a roof?
Heat escaping from the house into the attic warms the roof deck and melts snow on the upper roof. The meltwater runs to the cold eave and refreezes, building a ridge of ice. Water then backs up behind it and gets under the shingles. The root cause is heat loss, not the weather itself.
Is calcium chloride safe for roofs?
Used sparingly in fabric tubes, calcium chloride is generally gentler on roofing than rock salt, but it can corrode some metals and harm plants and concrete if it runs off in quantity. Follow the product label, use only what you need, and consider the gutters and landscaping below. Do not spread loose granules over the roof.
Will ice and water shield stop ice dams?
It does not stop them forming, but it stops the water that backs up behind a dam from getting through the roof deck, because the membrane seals around nails and is sticky and waterproof. It is a protection, not a cure. Stopping heat loss with air sealing, insulation and ventilation is what prevents ice dams.
Do I need to remove an ice dam?
Not always. A small dam with no leaking inside may melt away on its own. But if water is getting in, or the dam is large, it should be dealt with, because trapped water can soak insulation, stain ceilings and rot the deck. Clear the snow and create channels safely, and plan to fix the cause.
Related Guides
All Roof Repair guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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