Winter Roofing Prep: How to Protect Your Attic and Shingles from Ice Dams

Published: October 15, 2025 | By Principal Roofing Editorial Team

Here in York Region and Simcoe County, our roofs endure some of the harshest seasonal changes in Canada. While modern shingles are designed to resist high winds and heavy precipitation, the combination of thick snow accumulation and interior home heat can create a destructive phenomenon known as ice damming.

What is an Ice Dam and Why Does It Form?

An ice dam forms when heat escaping from your living space warms the roof deck, melting the snow above it. The melted water runs down the slope until it reaches the cold eaves (overhangs), which are not warmed by the attic. When the water hits this freezing edge, it solidifies into a ridge of ice.

As the cycle continues, more melted water pools behind this ridge. Eventually, the standing water backs up under the shingles, bypassing the natural water-shedding system and leaking into the attic, wall cavities, and ceiling drywall.

Step 1: Check Your Attic Insulation Levels

The first defense against ice dams is maintaining a cold roof deck. To achieve this, you must keep your indoor heat inside the living spaces. In Ontario, building codes recommend an insulation value of at least R-60 (roughly 16 to 18 inches of blown-in fiberglass or cellulose). If your home was built before 2010, there's a strong chance your attic is under-insulated.

Step 2: Ensure Proper Intake and Exhaust Ventilation

Insulation stops heat, but any warm air that does escape must be quickly flushed out of the attic space. This is where the combination of soffit vents (intake) and ridge vents (exhaust) becomes critical.

• Soffit Vents: Located under the eaves, these allow cool outdoor air to enter the bottom of the attic space.
• Ridge or Roof Vents: Installed at the peak of the roof, these let warm, moist air escape naturally.

If your soffit vents are blocked by loose insulation or your roof vents are covered, the warm air stays trapped, heating the roof deck and promoting snow melt.

Step 3: Clean and Clear Your Eavestroughs

Clogged eavestroughs (gutters) trap autumn leaves and debris. When winter arrives, the trapped moisture freezes solid, creating a foundation of ice that accelerates ice dam formation. Ensure your eavestroughs and downspouts are fully cleaned out in late autumn to allow clear passage for meltwater.

Step 4: Inspect the Ice and Water Shield

When having a new roof installed, make sure your roofing contractor installs a high-quality self-adhering ice and water shield membrane along all eaves, valleys, and around penetrations (skylights, chimneys). This waterproof barrier adheres directly to the wood decking, preventing water from penetrating even if it backs up under the shingles.