Why Proper Roof Underlayment and Ice & Water Protection Matter in Victoria, BC

By The Great Canadian Roof Doctor Inc.

When it comes to protecting your home, what’s under your roof covering is just as important—if not more important—than what you see on the surface. In Victoria, BC, where we live in a coastal rainforest and increasingly experience atmospheric river events, proper roof underlayment and ice & water protection are essential.

At The Great Canadian Roof Doctor Inc., we routinely find roof systems that fail not because of defective shingles, but because of improper, insufficient, or completely missing underlayment. This article explains why correct underlayment, ice & water protection, and proper detailing around roof penetrations are critical in Victoria’s climate.

Asphalt Shingles Are Designed to Shed Water — Not Stop It

Asphalt shingles are engineered to shed water, not act as a waterproof barrier. They rely on gravity and slope to direct water off the roof surface.

In normal conditions, this works well. However, in prolonged rain events, wind-driven rain, and atmospheric rivers, water can:

Be driven beneath shingles
Back up in valleys and eaves
Travel laterally due to wind pressure

When this happens, the roof’s underlayment becomes the last line of defense.

In Victoria’s rainforest climate, roofs often fail below the shingles, not because the shingles themselves have failed.

The Role of Roof Underlayment

Roof underlayment is installed directly over the roof deck and beneath the finished roofing material. Its purpose is to provide secondary moisture protection when water bypasses the roof covering.

Proper underlayment helps protect against:

Wind-driven rain
Prolonged saturation during heavy storms
Minor leaks and condensation
Moisture intrusion at vulnerable points

Without correct underlayment, even a new roof can fail prematurely.

Ice & Water Protection Is Not Optional in Victoria, BC

Ice & water protection is a self-adhering membrane designed to seal around fasteners and protect the most vulnerable areas of a roof.

In Victoria, ice & water protection is:

Strongly recommended due to climate conditions
Required by RCABC roofing standards and best practices
Essential during atmospheric river events

Ice & Water Protection Should Be Installed At:

All eaves
All valleys
Roof edges
Transitions and roof-to-wall connections

These areas experience the highest water volume and pressure.

Lower-Slope Roofs Require Additional Protection

Roof slope plays a critical role in how water moves across a roofing system.

Roofs Over 4/12 Pitch

Steeper slopes shed water more efficiently and typically require standard ice & water protection at eaves and valleys.

Roofs Below 4/12 Pitch

Steeper slopes shed water more efficiently and typically require standard ice & water protection at eaves and valleys.

Increased water pooling
Lateral water movement
Greater risk of wind-driven intrusion

For this reason, roofs below a 4/12 pitch require additional underlayment and ice & water protection beyond what steeper roofs need. This is a critical consideration that is often overlooked during installation.

Protecting Valleys, Eaves, and Roof Edges

Valleys

Valleys collect and concentrate large volumes of water. Without ice & water protection, even minor installation flaws can lead to leaks.

Eaves

Eaves are highly vulnerable to water backup during heavy rain. Ice & water protection helps prevent moisture from reaching the roof deck.

Roof Edges

Wind-driven rain can push water beneath roofing materials at edges, making proper membrane installation essential.

Wrapping Skylights, Chimneys, and Roof Penetrations

Roof penetrations are among the most common sources of leaks.

Skylights

Skylights must be fully wrapped with ice & water membrane and properly integrated with flashing systems. Partial protection often leads to delayed leaks.

Chimneys

Chimneys require careful membrane wrapping and layered flashing. Failure here can allow water to enter behind the flashing and into the roof structure.

Vent Pipes and Flashing

All vent penetrations must be wrapped with ice & water protection and sealed correctly. Exposed or poorly installed vent flashing is a frequent cause of leaks in Victoria homes.

Common Underlayment Failures We See in Victoria, BC

At The Great Canadian Roof Doctor Inc., we commonly find:

Ice & water protection missing at eaves or valleys
Inadequate membrane coverage on low-slope roofs
Improper wrapping of skylights and chimneys
Poorly sealed vent flashing
Underlayment systems not matched to roof slope

These failures often remain hidden until significant damage has already occurred.

Underlayment Matters More Than Ever in a Rainforest Climate

With the increase in extreme weather events and atmospheric rivers, underlayment is no longer a secondary consideration—it is a critical system component.

Even high-quality roofing materials cannot compensate for:

Missing underlayment
Insufficient ice & water protection
Improper installation techniques

A roof is only as strong as its weakest layer.

Professional Roofing Standards in Victoria, BC

At The Great Canadian Roof Doctor Inc., we build and evaluate roofing systems from the deck up. That means prioritizing:

Correct underlayment selection
RCABC-compliant ice & water protection
Slope-appropriate installation practices
Proper wrapping of all penetrations

Our inspection-first approach helps homeowners understand how their roof truly performs—not just how it looks.

📞 Contact us today to schedule a professional roof inspection and ensure your roof is properly protected for Victoria’s climate.