How to Prevent Ice Dams

In snowy climates, ice dams are a common winter problem that can cause significant damage to your home’s roof and interior. Heavy, unchecked ice dams can compromise a roof’s structural integrity, so preventing them also means preventing costly repairs. This Old House general contractor Tom Silva demonstrates a super-insulation method using closed-cell spray foam in the video above. In this article, we’ll explore effective methods to prevent ice dams, including proper insulation and ventilation techniques. 

*Unless otherwise noted, costs in this article reflect an average of prices that our team found from hardware stores like Lowes and Home Depot, and on Amazon.com.

Understanding Ice Dams

Ice dams form when warm air from your home’s interior escapes into the attic, heating the underside of the roof. This causes snow on the roof to melt and run down to the colder eaves, where it refreezes. As this process continues, a dam of ice forms, trapping water behind it. This trapped water can then seep under shingles and into your home, causing damage to walls, ceilings, and insulation.

Several factors contribute to the formation of ice dams:

• Poor attic insulation
• Inadequate attic ventilation
• Air leaks from the living space into the attic
• Complex roof designs with many valleys and dormers
• Fluctuating temperatures during winter months

Some of these factors, like fluctuating temperatures, aren’t under your control, but there’s plenty you can do about air leaks, insulation, and ventilation.

Preventing Ice Dams Through Proper Insulation

One of the most effective ways to prevent ice dams is by ensuring your attic is properly insulated. This helps maintain a consistent temperature on your roof’s surface, preventing the freeze-thaw cycle that leads to ice dam formation.

Insulation Options

There are several insulation options available for attics:

• Fiberglass batts
• Blown-in cellulose
• Spray foam insulation
• Rigid foam boards

Each type has its advantages, but polyurethane spray foam insulation, particularly closed-cell spray foam, offers superior insulation and air-sealing properties. If you want to keep your attic warm enough to use for living space or storage, as the homeowner in the video does, we recommend closed-cell spray foam.

Benefits of Closed-Cell Spray Foam Insulation

Closed-cell spray foam insulation keeps insulating gasses trapped inside as it expands and hardens, allowing it to effectively block heat transfer. Here are some of the advantages this material offers when it comes to preventing ice dams:

• High R-value of about R-7 per inch (open-cell is about R-3.6 per inch)
• Acts as an air barrier and vapor retarder
• Expands to fill gaps and cracks
• Adheres well to various surfaces
• Resistant to water absorption

In the video, Silva demonstrates the application of closed-cell spray foam insulation in an attic space to achieve an R-value of 38, which is ideal for preventing heat loss and ice dam formation. Technicians apply it in a series of 2-inch layers until it reaches the edges of the joists, then the excess is removed and the insulation is covered with drywall.

Proper Attic Ventilation to Prevent Ice Dams

While insulation is essential, proper attic ventilation is equally important in preventing ice dams. Good ventilation helps maintain a consistent temperature in your attic space, reducing the likelihood of snow melting and refreezing at the eaves.

Types of Attic Ventilation

There are several types of attic ventilation systems:

• Soffit vents
• Ridge vents
• Gable vents
• Attic fans

A combination of these ventilation methods can create an effective system for maintaining proper attic temperature and moisture levels.

Importance of Balanced Ventilation

It’s essential to have a balanced ventilation system with both intake and exhaust vents. This allows for proper air circulation, helping to keep your attic at a more constant temperature. Proper ventilation also helps extend the life of your roof by reducing moisture buildup and preventing shingle damage.

Air Sealing Your Attic to prevent Ice Dams

Air sealing is another critical step in preventing ice dams. By sealing gaps and cracks in your attic floor, you can prevent warm air from the living space below from entering the attic and causing snow to melt on the roof. Unlike applying spray foam insulation or creating a new roof ventilation system, this is a step you can take yourself.

Common Air Leak Areas

Some common areas where air leaks occur include:

• Around electrical wires and plumbing pipes
• Chimney chases
• Attic hatches or pull-down stairs
• Recessed lighting fixtures
• Wall top plates

Air Sealing Methods

There are several effective methods for air sealing your attic based on where the leak occurs:

• Using caulk for small gaps and cracks
• Applying expanding foam for larger openings
• Installing weatherstripping around attic hatches
• Using fire-rated materials around chimneys and flues

Silva emphasizes the importance of air sealing in the video, demonstrating how to seal gaps around wiring penetrations using spray foam.

Professional Ice Dam Prevention Services

While some ice dam prevention measures like air sealing can be DIY projects, others are best left to professionals. Professional services can provide comprehensive solutions to prevent ice dams and ensure your home is properly protected.

Services Offered by Professionals

Professional ice dam prevention services may include:

• Attic insulation assessment and upgrades
• Ventilation system installation or improvements
• Air sealing services
• Roof inspection and repair
• Installation of heat cables or ice belts

When To Call the Pros

Consider calling a professional if:

• You want to install spray foam insulation
• You’re experiencing recurring ice dam problems
• Your attic is difficult to access or navigate
• You’re unsure about the current state of your insulation or ventilation
• You want to ensure a comprehensive, long-term solution

Professional services can provide peace of mind and often result in more effective, long-lasting ice dam prevention.

Additional Ice Dam Prevention Measures

While proper insulation, ventilation, and air sealing are the primary methods for preventing ice dams, there are additional measures you can take to further protect your home.

Roof Raking

Regularly removing snow from your roof can help prevent ice dams from forming. Use a roof rake with a long handle to safely remove snow from the ground—never climb up on the roof or even a ladder for this job. Focus on the first 3–4 feet from the eaves, where ice dams typically form. For roof areas you can’t reach from the ground, call a snow removal professional.

Heat Cables

Heat cables, also known as heat tape or de-icing cables, can be installed along the eaves of your roof. These cables heat up to melt snow and ice, creating channels for water to drain off the roof. While they can be effective, they should be used in conjunction with other prevention methods for best results.

Proper Gutter Maintenance

Keeping your gutters clean and in good repair can help prevent ice dams. Clogged gutters can cause water to back up and freeze, contributing to ice dam formation. Regular gutter cleaning and maintenance can help ensure proper water drainage. Make sure to remove fall debris before the winter sets in.

Routine Roof Inspection

Regular roof inspection can help you avoid the conditions that are likely to cause ice dams. Check your roof at least twice a year and after major storms, first from the ground to ensure that the roof looks stable enough to walk on. Pay attention to potential trouble spots where ice may form.

• Look for loose or missing shingles or granules.
• Inspect roof valleys.
• Check the flashing around chimneys and other penetrations.
• Look for signs of wear and tear.

Consider having a professional roof inspection done once a year. A pro will be able to catch early signs of damage you might miss, stopping a leak before it becomes widespread damage.

Strategic Landscaping

Landscaping can play an unexpected role in preventing ice dams. Trees overhanging your roof can drop leaves and branches that clog gutters, leading to ice formation. Proper tree maintenance and strategic planting can minimize these risks. Here are some strategies to consider:

• Reduced debris: Removing leaves and branches keeps gutters clear.
• Shade management: Properly placed trees can provide shade in summer, reducing cooling costs. In winter, this lets sunlight reach the roof, melting excess snow.
• Windbreaks: Planting shrubs and trees as windbreaks can reduce snowdrift on roofs and lower the overall snow load.

Our Conclusion

Preventing ice dams helps protect your home from water damage and maintain its structural integrity. By focusing on proper attic insulation, ventilation, and air sealing, you can significantly reduce the risk of ice dam formation. Closed-cell spray foam insulation is a highly effective long-term solution, but you’ll need to have it installed by professionals. However, there are a number of other maintenance tasks you can perform yourself.