How to Prevent and Remove Ice Dams

How to Prevent and Remove Ice Dams

Diagram showing how ice dams form through the heat loss, snowmelt, and refreeze cycle on a roof

Ice dams are one of the most damaging and persistent winter roofing problems in cold climates. They form ridges of ice along the eaves that trap water on the roof, forcing it backward under shingles and into the home. Understanding the underlying cause -- attic heat loss -- is essential, because ice dams are fundamentally a building performance problem, not just a roofing problem.

How Ice Dams Form

Heat cable installed in zigzag pattern along roof eave and through gutter to prevent ice dams

Ice dams develop through a specific and predictable process:

1. Heat escapes from the living space through the ceiling and into the attic. Common escape routes include unsealed light fixtures, plumbing penetrations, attic hatches, and inadequate insulation.
2. The attic warms up above freezing, even while outdoor temperatures remain below 32 degrees Fahrenheit.
3. Snow on the upper roof melts because the roof surface above the heated attic is warm.
4. Meltwater flows downhill toward the eaves.
5. The eave overhang is cold because it extends beyond the heated building envelope and has no attic warmth beneath it.
6. Water refreezes at the eave, forming a ridge of ice -- the dam.
7. More meltwater pools behind the dam with nowhere to go. Pooled water finds its way under shingles, through the Roof Deck, and into the attic, ceilings, walls, and insulation below.

The key insight is that ice dams are caused by heat loss from the attic, not by the amount of snow or the type of roofing material. Solving the heat loss problem eliminates ice dams permanently.

Prevention: Root Cause Fixes

These solutions address the underlying reason ice dams form. They are the only permanent fixes. Everything else is a temporary measure.

Improve Attic Insulation

The goal is to keep attic temperatures as close to outdoor temperatures as possible. The Department of Energy recommends R-49 to R-60 of insulation for attic floors in cold climates (Zones 4 through 8). Many older homes have far less.

• Check your current insulation depth and type. See Roof Insulation and Attic Ventilation and Insulation Guide.
• Blown-in cellulose or fiberglass is the most common and cost-effective upgrade.
• Pay special attention to areas where insulation is thin or compressed -- around attic hatches, over knee walls, and above additions.
• Cost: $1,500 to $3,500 for professional insulation upgrade; $500 to $1,500 DIY.

Seal Attic Air Leaks

Air leaks carry far more heat into the attic than conduction through insulation. Even R-60 insulation is ineffective if warm air bypasses it through holes. Common air leak locations include:

• Around plumbing vent pipes -- where pipes pass through the attic floor
• Around electrical wires and boxes -- recessed lights are particularly bad
• At the attic hatch or pull-down stair -- seal with weatherstripping and an insulated cover
• Around HVAC ducts -- ducts in unconditioned attics should be sealed and insulated
• At partition wall top plates -- where interior walls meet the attic floor, gaps in the framing allow warm air to rise into the attic
• Around chimney and flue chases -- fire-rated caulk and metal flashing required here

Use expanding foam, caulk, and rigid foam board to seal these penetrations. Air sealing is often more effective than adding insulation and costs less.

Ensure Proper Ventilation

A well-ventilated attic flushes out any residual heat and keeps the underside of the roof deck cold and uniform. Proper ventilation requires balanced intake and exhaust:

• Intake air enters through soffit vents along the eaves
• Exhaust air exits through ridge vents, gable vents, or roof-mounted vents at or near the peak
• The standard minimum ratio is 1 square foot of net free vent area per 150 square feet of attic floor (or 1:300 with a vapor barrier and balanced intake/exhaust)

Verify that soffit vents are not blocked by insulation -- this is extremely common and defeats the entire ventilation system. Install baffles between rafters above the soffit to maintain a clear air channel from the soffit into the attic. See Roof Ventilation and Attic Ventilation and Insulation Guide.

Prevention: Band-Aid Solutions

These measures reduce ice dam severity but do not address the root cause. Use them while planning permanent fixes or in situations where root cause fixes are impractical.

Heat Cables

Electric heat cables (also called heat tape) are installed along the eave in a zigzag pattern, extending 2 to 3 feet up the roof from the edge. They melt channels in the ice, allowing trapped water to drain off the roof.

• Installation: zigzag pattern with loops extending into gutters and downspouts
• Cost: $100 to $300 in materials; $500 to $1,000 professionally installed
• Energy cost: $50 to $200+ per winter depending on usage
• Drawback: treats the symptom, adds ongoing energy cost, creates a tripping hazard for maintenance, and cables themselves have a limited lifespan

Ice and Water Shield Underlayment

During a re-roofing project, install self-adhering ice and water shield membrane along the eaves, extending at least 24 inches past the interior wall line (many codes require this in cold-climate zones). This membrane does not prevent ice dams, but it prevents water from penetrating the deck when water does pool behind a dam.

This is a code requirement in most northern states and Canadian provinces. See Roof Underlayment Guide for details on underlayment selection.

Snow Removal

Using a roof rake to keep the first 3 to 4 feet of the eave area clear of snow prevents the melt-refreeze cycle from starting. This is effective but requires regular effort after every significant snowfall.

Ice Dam Removal

When an ice dam has already formed, safe removal options are limited. The priority is preventing ongoing water intrusion while avoiding damage to the roof.

Calcium Chloride Method

This is the safest and most commonly recommended DIY removal method:

1. Fill a leg of old pantyhose or a thin fabric tube with calcium chloride ice melt pellets
2. Lay the filled tube across the ice dam, perpendicular to the eave, so it extends from the gutter up over the dam
3. The calcium chloride slowly melts a channel through the ice, allowing pooled water behind the dam to drain
4. Reposition or add tubes as needed to create multiple drainage channels

Important: Use calcium chloride only, never sodium chloride (rock salt). Rock salt damages Asphalt Shingles, corrodes metal flashing, stains siding, and kills vegetation below. Calcium chloride is less corrosive and effective at lower temperatures.

Roof Rake Clearing

If the dam is still mostly snow with a thin ice edge, a roof rake operated from the ground may be able to pull enough snow off the eave area to reduce the dam. This works best early in the dam formation process. Once solid ice has built up, the rake alone will not break through.

Professional Steam Removal

For severe ice dams, professional roofing companies use low-pressure steam equipment to melt ice without damaging the roof surface. This is the safest method for removing established dams. Expect to pay $300 to $700 per visit depending on dam size and access difficulty.

What You Must NEVER Do

Calcium chloride filled stocking laid across an ice dam to melt a drainage channel

These actions cause far more damage than they prevent:

• Never chip at ice dams with a hammer, axe, chisel, or pick. You will crack shingles, puncture the Roof Deck, and damage flashing. Every gouge becomes a future leak point.
• Never use a pressure washer on ice. Water pressure damages shingles and forces water into the roof assembly.
• Never use a torch, heat gun, or open flame. Fire risk is extreme, and concentrated heat damages shingles, underlayment, and flashing.
• Never apply rock salt or sodium chloride directly on the roof. It corrodes metal, stains, and damages roofing materials.
• Never walk on an icy or snow-covered roof. Falls from icy roofs are a leading cause of winter fatalities. All removal work should be done from the ground or by professionals with proper equipment.

Long-Term Strategy

The most cost-effective approach to ice dams combines immediate mitigation with permanent fixes:

1. This winter: use a roof rake after storms, apply calcium chloride to active dams, and monitor for interior water intrusion
2. Spring: schedule an energy audit to identify attic air leaks and insulation deficiencies (Spring Roof Inspection Checklist)
3. Summer: complete air sealing and insulation upgrades when attic access is comfortable and materials install easily
4. Next fall: verify ventilation pathways are clear, add baffles if needed (Fall Roof Winterization Guide)
5. Following winter: monitor for improvement; if ice dams persist, additional air leak sealing may be needed

For most homes, the combination of air sealing, insulation to R-49 or above, and proper ventilation eliminates ice dams entirely. The energy savings from reduced heat loss typically pay for the upgrades within 3 to 7 years, making this one of the best return-on-investment home improvements in cold climates.

Climate Zones and Ice Dam Risk

Ice dams are most common in USDA Climate Zones 5 through 7 -- the northern United States and southern Canada. Homes in these regions should incorporate ice dam prevention into every roofing and insulation decision. See Best Roofing Materials by Climate Zone for material recommendations specific to cold climates.

See Also

• How to Use a Roof Rake for Snow Removal
• Attic Ventilation and Insulation Guide
• Roof Insulation
• Roof Ventilation
• Roof Underlayment Guide
• Fall Roof Winterization Guide
• Spring Roof Inspection Checklist
• Roof Safety Guide for Homeowners
• Common Roof Problems
• Seasonal Roof Care
• Best Roofing Materials by Climate Zone
• DIY Roofing Guide