Ice Dams in New England: What Causes Them and How to Prevent Them

Ice dams are one of the most common—and destructive—winter roofing issues for New England homeowners. They form when melting snow refreezes at the roof’s edge, causing water to back up under shingles and leak into your home. Left untreated, ice dams can lead to serious structural damage, mold growth, and expensive repairs.

If you live in Massachusetts or anywhere else in New England, understanding how ice dams form—and how to prevent them—is critical to protecting your home during the cold season.

What Is an Ice Dam?

An ice dam is a ridge of ice that forms at the edge of your roof, usually near the gutters. It prevents melting snow from draining off the roof, trapping water behind it. This water can seep beneath shingles and into your attic or walls, leading to:

• Roof leaks

   

• Damaged insulation

   

• Stained ceilings and walls

   

• Mold and mildew growth

   

• Wood rot and structural issues

   

How Ice Dams Form

Ice dams are caused by a combination of four main factors:

1. Snow on the roof

    

2. Heat escaping from your attic

    

3. Uneven roof temperatures

    

4. Cold exterior air at the eaves

    

Here’s the process:

• Heat rises from the inside of your home and escapes through the roof deck due to poor insulation or ventilation.

   

• This heat melts the snow near the roof’s ridge.

   

• The melted snow runs down the roof slope.

   

• When it reaches the colder, unheated eaves, it refreezes and forms a wall of ice.

   

• Water behind the dam gets trapped, backs up, and eventually finds its way under shingles and into your home.

   

Signs of Ice Dam Damage

If you suspect you’ve had an ice dam, look for the following signs:

• Water stains or peeling paint on your ceilings or walls

   

• Icicles hanging from your gutters or roof edge

   

• Ice buildup along eaves or in gutters

   

• Cold spots in upstairs rooms

   

• Moldy smells coming from the attic

   

Catching these signs early can save you from massive repair bills.

How to Prevent Ice Dams

Preventing ice dams requires a combination of good roof design, proper insulation, and timely maintenance.

Improve Attic Insulation

The most effective long-term solution is preventing warm air from escaping your attic in the first place. Make sure your attic has:

• At least 12–14 inches of high-quality insulation

   

• Sealed air leaks around recessed lights, chimneys, and attic hatches

   

• A consistent temperature that matches the outdoor air

   

Upgrade Roof Ventilation

Attic ventilation allows cold air to circulate and helps keep your roof surface evenly cold. A balanced ventilation system includes:

• Soffit vents at the eaves

   

• Ridge or gable vents at the top of the roof

   

• Clear pathways for airflow between insulation and roof sheathing

   

Install Ice and Water Shield

During roof replacement or major repairs, install an ice and water membrane under the shingles along the eaves. This waterproof layer:

• Protects vulnerable areas from water penetration

   

• Acts as a final barrier if ice dams form

   

• Is required by code in most of Massachusetts

   

Keep Gutters Clean

Clogged gutters can trap water, leading to freeze-ups. Before winter hits:

• Remove leaves and debris

   

• Check for sagging or improperly pitched sections

   

• Install gutter guards if trees are nearby

   

Rake Snow Off the Roof

If snow has accumulated after a storm, use a roof rake (with an extension handle) to remove it from the lower 3–4 feet of your roof. This:

• Prevents melting snow from reaching the eaves

   

• Reduces the likelihood of refreezing and damming

   

• Keeps roof loads lighter and safer

   

Install Heat Cables (Optional)

In persistent problem areas, heat cables can be installed along roof edges and in gutters to keep ice from forming. These should be used as a supplemental solution—not a primary fix.

What to Do If You Already Have an Ice Dam

If you’re currently experiencing an ice dam:

• Do not attempt to chip away the ice. You could damage shingles and create leaks.

   

• Use a roof rake to remove snow safely from the edge.

   

• Place calcium chloride ice melt in pantyhose and lay it vertically across the ice dam to create channels for melting.

   

• Call a professional to safely remove large dams and assess for damage.

   

At Zen Roofing, we offer winter roof care, ice dam removal, and emergency inspections throughout the Merrimack Valley, Greater Boston, and Southern New Hampshire.

Protect Your Roof Before It’s Too Late

The best defense against ice dams is prevention. With a fall inspection and proper insulation and ventilation, you can eliminate the conditions that lead to ice buildup and water damage.

Don’t wait until icicles are forming—get ahead of the cold now.