What Is an Ice and Water Shield on a Roof?

ice and water shield on roof to help with ice dams and water buildup

Building or Replacing a Roof? Don’t Skip the Ice and Water Shield

When Minnesota winters hit, your roof becomes your home’s first line of defense. One of the most important layers in that defense is called an ice and water shield, a self-adhering waterproof membrane designed to protect vulnerable areas of the roof from water infiltration caused by ice dams and wind-driven rain.

Required by building code for all new roofs in Minnesota, let’s break down what an ice and water shield is, how it works, where it goes, and why it’s such a critical part of your roofing system.

What is an Ice and Water Shield?

An ice and water shield (sometimes referred to as an ice and water protector) is a self-adhering, waterproof underlayment installed beneath your shingles. Unlike traditional roofing felt or synthetic underlayment, this membrane creates a tight seal directly on your roof deck. It’s made from polymer-modified bitumen, which gives it flexibility, strong adhesion, and the ability to seal around nails.

That self-sealing quality is what makes it so effective. When water backs up under shingles because of ice dams or heavy rain, it can’t sneak past the membrane and soak into the wood below. Instead, water hits a waterproof barrier designed to keep your home protected from the inside out.

Why Ice Dams Are a Serious Problem

Ice dams are one of the main reasons ice and water shields exist. They form when snow melts on a warm section of your roof, usually higher up, then refreezes near the eaves where the roof is colder. Over time, this creates a literal dam of ice at the roof’s edge, blocking melting snow from draining properly.

That trapped water has to go somewhere, and it often ends up under your shingles, working its way into your attic, ceilings, and walls. The damage can be extensive, from stained drywall to warped wood and mold growth.

Ice and water shields help prevent ice dam-related water damage by creating a watertight seal underneath the shingle layer, especially in areas where water is most likely to collect or back up.

What Causes Ice Dams:

Daytime temperatures above freezing followed by freezing nights
Poor attic insulation or ventilation
Roof pitches that encourage snow accumulation
Clogged gutters that prevent proper runoff

Without a proper barrier in place, ice dams can lead to significant and expensive water damage. This is why Minnesota’s building code mandates the use of ice and water shield for new roofs.

What’s Required By the Minnesota Building Code

Minnesota follows the International Residential Code (IRC) with specific requirements for cold climates. According to the state’s building code, ice and water shield is mandatory on all new residential roofs in areas prone to ice damming.

Here’s what’s required of your ice and water shield:

The membrane must extend at least 24 inches past the warm side of the exterior wall (measured horizontally).
It must cover all eaves where ice dams are likely to form.
The product must be a self-adhering polymer-modified bitumen sheet or two layers of cemented underlayment.

In practice, this means most homes need 3 to 6 feet of ice and water shield from the edge of the roof up the slope. If your overhang is longer than average, you may need more coverage to meet code.

Where Ice and Water Shields Get Installed

An ice and water shield isn’t meant to cover the entire roof, just the areas most vulnerable to water intrusion. A professional installer will usually apply it in the following places:

Eaves

This is the most common area for ice dams, so the code requires an ice and water shield to be applied here. They’re typically used in strips running horizontally from the edge of the roof up the slope.

Valleys

When two roof slopes meet, they form a valley: a natural channel for water runoff. Because valleys carry more water, they’re especially prone to leaks. An ice and water shield should be applied here for added protection.

Around Roof Openings

Skylights, chimneys, vents, and pipes are all common entry points for water. Ice and water shields are cut and shaped to wrap around these penetrations, sealing off potential gaps.

Low-Slope Roof Sections

Roofs with a shallow pitch (typically under 4:12) may not shed water as effectively, making them more susceptible to leaks. In these cases, a wider area, or even the full roof deck, might be covered with an ice and water shield.

Rake Edges (Optional)

While not required by code, some contractors install ice and water shield along rake edges as added insurance against wind-driven rain or snow intrusion.

Types of Ice and Water Shields

Not all membranes are built the same. Choosing the right one depends on your roof structure, budget, and the conditions your home faces.

Granular or Sand-Surfaced

A thicker, textured surface that’s more slip-resistant. It’s often used in valleys or under metal roofs, but can be harder to work with around corners and roof penetrations.

Smooth Surface

This version is more flexible and easier to mold around details like chimneys, skylights, and vents. It’s often used in more intricate roof areas where a tighter seal is needed.

High-Temperature Membrane

Ideal for metal roofs or south-facing slopes where temperatures get high. These products are specially formulated to resist heat without melting or breaking down over time.

Benefits of Ice and Water Shields

Aside from meeting building code, there are real advantages to installing ice and water shield on your roof.

Water Protection Where It Matters Most

Ice and water shields seal tightly against the roof deck and around nails, creating a barrier even when shingles alone aren’t enough.

Insurance Against Costly Leaks

By stopping water infiltration at key points, you’re helping prevent damage that could lead to expensive repairs.

Better Long-Term Performance

A roof with proper underlayment lasts longer, performs better, and gives you more peace of mind, especially through Minnesota winters.

Increased Home Value

Buyers in cold-weather regions often look for homes with modern, code-compliant roofing systems. This upgrade could be a selling point when it’s time to move.

Common Mistakes to Watch Out For

Even with the right materials, a poor installation job can still lead to problems. Here are a few common issues to avoid:

Not covering enough area: If the membrane of your shield doesn’t extend 24 inches past the warm side of the wall, it won’t meet code, and it won’t protect your home effectively.
Incorrect overlap: Each strip of membrane should overlap the next by several inches. Gaps or misaligned seams can allow water to seep in.
Installing over dust, frost, or moisture: These can prevent the membrane from sticking properly. Roof decks should be clean and dry before application.
Wrinkling or bubbling: Air pockets can cause weak spots that compromise the seal and let water sneak through.

If you’re not sure your contractor is following best practices, don’t hesitate to ask questions or request photos of the work as it’s being completed.

Need Your New Roof to Be Up to Code? We’ve Got It Covered.

In Minnesota, an ice and water shield isn’t optional; it’s code.

If you’re planning a roof replacement or new build, All Craftsmen Exteriors makes sure every detail meets local requirements, including the ice dam protection your home needs.