How Ice Dams Form, and How to Prevent Them

Roofs can handle wet weather.

But they’re not built to handle standing water. 

If snow lingers on your roof and thick icicles show up along the edge, you may already have an ice dam. Ice dams are ridges of ice that can damage even the toughest roof and are especially common in Wisconsin. They mean meltwater from your roof hits a frozen ridge at the eaves and backs up under shingles, infiltrating your home. Here’s how ice dams form, how to spot them, why they matter, and how to prevent costly damage.

What Is an Ice Dam?

An ice dam is a ridge of ice that forms along the edge of your roof and prevents melting snow from draining off properly. Instead of water flowing into your gutters and safely away from your home, it backs up behind the wall of ice and often finds its way under shingles and into your attic, ceilings, or walls.

Ice dams can cause:

• Roof leaks

• Rot and mold

• Damaged insulation

• Interior water damage

  
  

Even if your roof looks perfectly fine from the outside, trapped water can find hidden pathways inside your home. That’s why understanding this process is so important.

How Ice Dams Form

Step-by-step formation:

1. Snow falls and accumulates on the roof.

2. Heat escapes from your attic and melts the snow near the top.

3. Melted water flows down the roof toward the colder eaves.

4. Water refreezes near the roof edge, forming a growing ridge of ice.

5. Water from new snowmelt backs up behind the ice dam, pushing under shingles.

Ice dam formation on a home in Madison’s Nakoma neighborhood. Notice how the main roof plane is clear while ice and snow persist along the colder overhang. This temperature difference is a classic setup for ice dams and often points to heat loss from the attic above.

Why Do Ice Dams Form?

• Warm attic air caused by poor insulation or air leaks

• Rapid freeze-thaw temperature swings, even with proper ventilation

• Direct sunlight melting snow unevenly across different parts of the roof

  
  

Conventional, rack-mounted solar panels can also be a culprit. They shade and cool roof areas, disrupt melt patterns, and their hardware that can catch snow and slush, obstructing draining.

Learn more about the causes of roof leaks in winter.

Common Signs You Have an Ice Dam

​​How do you know if you’re dealing with an ice dam? Here are the most frequent indicators:

• Large, thick icicles hanging from your gutters

• Water stains on ceilings or walls inside your home

• Visible ice ridges along the roof edge

• Frost buildup, moisture, or a musty smell in your attic

• Peeling paint or warped trim near your roofline

  
  

Not all icicles are bad, but significant buildup can be a red flag. Ice dams tend to form when snow lingers on the roof and temperatures repeatedly fluctuate around freezing.

Ice dams don’t always look dramatic. This Shorewood Hills home showed only light ice along the roof edge and minor icicles, but meltwater still backed up under the shingles and caused significant leaks through the roof and siding.

Why Ice Dams Are A Bigger Problem in Wisconsin

Wisconsin homeowners deal with multiple risk factors:

• Frequent freeze-thaw cycles throughout the winter

• Heavy, wet snow that accumulates on rooftops

• Older homes that may lack modern insulation or ventilation

• Some of our coldest days are also our sunniest days!

  
  

Even newer roofs can be affected, especially if conventional rack-mounted solar panels are installed. These panels alter melt patterns and increase penetrations in the roof, creating more opportunities for water infiltration. If you're considering solar, learn why solar shingles may be a better option than panels in our climate.

Wisconsin winters add a twist! Sunny winter days can still trigger ice dams. Even on a well-insulated and ventilated roof.

It takes just a clear, cold morning followed by bright sunshine to melt snow on the sun-facing slopes. That meltwater runs down toward the eaves where the temps are still much colder, and refreezes, forming ice ridges. Homeowners in Wisconsin often see this pattern: a bright southern exposure after a cold snap, leading to unexpected ice dam formation.

To prevent this “sun-melt” effect, consider carefully removing snow from south-facing slopes with a roof rake after sunny winter days (or calling a professional to do it for you!), and keep gutters and downspouts clear so meltwater drains properly instead of refreezing at the roof edge.

Short-Term Ice Dam Prevention Tips

If you already see signs of an ice dam forming, here’s what can help right away:

• Use a roof rake to remove snow safely from the edge of your roof. Never use sharp tools or climb onto an icy roof.

• Apply non-corrosive ice melt in problem areas (leave this to professionals).

• Install temporary heat cables to melt pathways through ice dams and help prevent buildup. These cables can prevent water backup and reduce ice accumulation, but they are often unsightly, have limited effectiveness in extreme cold, and may increase your energy bills.

  
  

These measures may reduce short-term damage, but they don’t solve the root causes.

Need help with rooftop snow removal? We can help!

Safe snow removal is one of the few winter actions that can reduce ice dam risk immediately. It should always be done from the ground or ladder using the right tools, not from the roof itself.

Long-Term Ice Dam Prevention Solutions

To eliminate ice dams for good, focus on addressing heat loss and roof design:

• Improve attic insulation to reduce heat transfer to the roof

• Seal attic air leaks around vents, lighting, and chimneys

• Upgrade attic ventilation for better airflow and roof temperature control

• Install ice and water shield underlayment when replacing your roof

• Choose high-performance shingles designed for Midwest winters

  
  

If your roof is already due for replacement, addressing insulation and ventilation issues during that project can significantly reduce future ice dam risks - learn more about replacing a roof in winter. 

Do You Need Snow Guards?

Ice dams start with snow buildup. Most asphalt roofs in Wisconsin are designed to shed snow naturally and don’t require permanent snow management systems.

But in certain situations (like steep roofs, high-wind areas, or metal roofing) additional snow management may help.

Options include:

• Snow guards or retention bars: Help hold snow in place and prevent sudden roof avalanches. However, if placed incorrectly, they can trap snow in the wrong areas and make ice dams worse. They’re also expensive (up to $40/linear foot).

  • Snow guards are especially common on metal roofs due to their slippery surface. Without them, snow can slide off in dangerous sheets, damaging property/landscape or injuring people.

• Built-in roof edge heating systems: Designed to melt snow at critical points. These may add visual clutter and may only treat symptoms, not causes. Installation also requires an accessible, nearby exterior outlet or a licensed electrician if they are to be hardwired.

  
  

Related Reading: Metal vs. Asphalt Roofs

In most cases, you should skip these options. Asphalt shingles paired with a well-insulated attic is your best bet.

What NOT to Do About Ice Dams

Avoid these common mistakes:

• Climbing on an icy roof (fall risk!)

• Chipping ice with metal tools (damages shingles)

• Ignoring small leaks or repeated ice dam formation

  
  

Small signs often become expensive problems if left unchecked.

When to Call a Roofing Professional (and Why It Matters)

If you're dealing with repeated ice dams, visible roof leaks, or water damage inside your home, it's time to bring in a professional. These are signs that your roofing system may need more than just a temporary fix.

A certified local contractor (like Sun Vault Roofing) can:

• Perform a full roof and attic inspection

• Recommend tailored insulation and ventilation upgrades

• Safely remove snow and ice without damaging your shingles

• Identify long-term fixes to prevent recurring winter issues

  
  

Don’t wait for minor leaks to become major problems. Preventing ice dams protects your roof, your attic, and your peace of mind. With proper insulation, quality materials, and expert installation, you can winter-proof your home and avoid costly water damage.

📞 Call 608-608-1082 or Schedule a Free Roof Inspection with Sun Vault Roofing.