Ice and Water Shield for Roofs: Do You Need It?

Ice and water shield is a self-adhering waterproof membrane installed directly on the roof deck before your shingles go on. It costs $0.50 to $1.50 per square foot for materials and is required by South Carolina building code at eaves, valleys, and around all roof penetrations. For a typical 2,000-square-foot roof, standard installation at code-required locations adds $500 to $1,500 to your roof replacement cost.

Here is the quick answer most homeowners want: if you are getting a new roof in Myrtle Beach or anywhere along the South Carolina coast, yes, you need ice and water shield. It is not optional — building code requires it in specific locations. The real question is whether you should go beyond code minimums and install it across your entire roof deck.

This guide covers exactly what ice and water shield is, where it gets installed, what it costs, how it compares to synthetic underlayment, what South Carolina building codes require, and whether full-roof coverage makes sense for your home. Thinking about a roof replacement? Request a free roof replacement consultation to discuss the right underlayment approach for your home.

What Is Ice and Water Shield?

Ice and water shield (also called ice barrier, ice and water membrane, or self-adhering underlayment) is a rubberized asphalt membrane with a sticky backing that bonds directly to the roof deck. Unlike other underlayment products that just lay on top of the plywood, ice and water shield forms a permanent adhesive bond to the wood surface.

The critical feature that makes ice and water shield different from every other underlayment product is its self-sealing ability around nail penetrations. When a roofing nail is driven through the membrane, the rubberized asphalt material compresses and seals tightly around the nail shaft. This means that even when thousands of nails puncture the membrane during shingle installation, every single nail hole remains watertight.

Standard felt paper and synthetic underlayment cannot do this. When a nail goes through felt or synthetic, it creates a hole. Water that gets past the shingles can follow the nail down through the underlayment and into the roof deck. Ice and water shield eliminates that pathway entirely.

The product typically consists of two layers: a rubberized asphalt adhesive layer on the bottom (which bonds to the deck and seals around nails) and a polyethylene film layer on top (which provides a smooth surface for shingle installation). Most products are approximately 40 mils thick and come in 36-inch-wide rolls that are 65 to 75 feet long. Major brands include GAF StormGuard, Owens Corning WeatherLock, CertainTeed WinterGuard, and Grace Ice & Water Shield (the original product that gave the category its name).

Where Ice and Water Shield Gets Installed on a Roof

Ice and water shield goes in the places where water intrusion is most likely to happen. These are the areas where water pools, changes direction, or gets driven under shingles by wind.

Eaves (Along the Roof Edge)

The eaves are the bottom edge of the roof where it overhangs the exterior wall. Building code requires ice and water shield to extend from the eave edge to at least 24 inches past the interior wall line. On most homes, this means 3 to 4 feet of coverage up from the edge.

Why here? The eaves are where ice dams form. When heat escapes through the attic, it melts snow on the upper portion of the roof. That meltwater flows down to the colder eave overhang, refreezes, and creates a dam. Water pools behind the dam and backs up under the shingles. Without ice and water shield, that pooled water soaks through the nail holes and into the attic. In coastal South Carolina, ice dams are less common, but wind-driven rain creates the same effect — water pushes up and under shingles at the eave line.

Valleys

Roof valleys are where two sloping roof planes meet and create a channel for water runoff. During a heavy rain, valleys carry enormous volumes of water. The concentration of water flow, combined with debris accumulation and the angles where shingles meet, makes valleys one of the most common leak points on any roof.

Code requires ice and water shield to cover the full length of every valley, extending at least 24 inches on each side of the valley centerline. For a typical valley, that means a 48-inch-wide strip of continuous waterproof protection running from eave to ridge.

Roof Penetrations

Every hole in your roof is a potential leak point. Plumbing vents, exhaust fans, chimneys, skylights, satellite dish mounts, and any other penetration through the roof deck gets a collar of ice and water shield extending at least 12 to 18 inches in all directions from the penetration.

Chimney flashings are particularly important. The intersection between a chimney and the roof surface involves complex geometry — step flashing along the sides, counterflashing into the masonry, a cricket or saddle on the uphill side. Ice and water shield at every chimney joint provides backup waterproofing if the metal flashing ever fails.

Low-Slope Areas

Any section of your roof with a pitch below 4:12 (meaning the roof rises less than 4 inches for every 12 inches of horizontal run) is considered low-slope. Water moves slower on low-slope surfaces, which means it has more time to find its way under shingles and through nail holes.

Most roofing manufacturers require ice and water shield on the entire surface of any roof section below 4:12 to maintain their shingle warranty. If your roof has a porch overhang, a dormer transition, or a garage extension with a lower pitch than the main roof, those areas need full ice and water shield coverage.

Sidewalls and Headwalls

Where a roof plane meets a vertical wall (sidewall) or runs into a wall (headwall), wind-driven rain can push water up and behind the flashing. Ice and water shield at these transitions provides a second line of defense behind the step flashing or kick-out flashing.

When You Need Ice and Water Shield: Code Requirements and High-Risk Situations

South Carolina Building Code Requirements

South Carolina adopts the International Residential Code (IRC) with state-specific amendments. For Myrtle Beach and the entire coastal region, you are building in Wind Zone III, which has the strictest underlayment requirements in the state.

The IRC requires ice and water shield (or equivalent self-adhering polymer-modified bitumen membrane) at:

• Eaves: A minimum of one layer extending from the eave edge to at least 24 inches inside the exterior wall line of the building
• Valleys: One layer centered in the valley extending 24 inches on each side
• Penetrations: Self-adhering membrane around all roof penetrations
• Wind Zone III areas: Enhanced underlayment requirements including two layers of underlayment or one layer of self-adhering membrane for the entire roof in the highest wind zones

The Horry County building department (which covers Myrtle Beach) enforces these requirements during roof replacement inspections. If your roofer skips ice and water shield at required locations, the inspection will fail and the work will need to be redone.

Beyond Code: When You Should Install More

Building code sets the minimum standard. For coastal Myrtle Beach homes, there are situations where going beyond code minimums makes sense:

• Hurricane-prone areas: During a Category 2+ hurricane, wind-driven rain gets under shingles across entire roof surfaces, not just at eaves and valleys
• Complex roof geometry: The more hips, valleys, dormers, and transitions your roof has, the more potential leak points exist
• Low-slope sections: Any pitch below 4:12 should get full ice and water shield, not just underlayment
• Homes near the ocean: Salt air accelerates fastener corrosion, and storm surge flooding can push water into unexpected places
• Previous leak history: If your old roof leaked at specific locations, ice and water shield those areas regardless of what code requires

For most Myrtle Beach homeowners, the sweet spot is ice and water shield at all code-required locations plus full coverage on any roof section below 6:12 pitch and any section facing the prevailing storm direction (typically southeast for coastal SC hurricanes).

Ice and Water Shield vs Synthetic Underlayment: What Is the Difference?

This is the comparison most homeowners ask about. Both products go on the roof deck before shingles, but they serve fundamentally different purposes.

Most roofs use both products together. Ice and water shield goes at the high-risk locations where true waterproofing is needed — eaves, valleys, penetrations, and low-slope areas. Synthetic underlayment covers the remaining field of the roof where water resistance (not full waterproofing) is sufficient.

One important note about breathability: Ice and water shield is a vapor barrier. That means moisture in the attic cannot pass through it. On a roof with full ice and water shield coverage, proper attic ventilation becomes critical. Without adequate ridge and soffit vents, trapped moisture can cause condensation problems on the underside of the roof deck. This is one reason why full-roof ice and water shield is not always the best approach — it requires the ventilation system to handle all moisture removal.

For detailed protection against wind-driven rain during hurricanes, ice and water shield is the single most effective underlayment product. Synthetic underlayment sheds water that flows over it, but it cannot stop water that is being pushed upward by 100+ mph winds.

Ice and Water Shield Cost: What You Will Pay

Ice and water shield material costs $0.50 to $1.50 per square foot depending on the brand and product grade. Here is what that looks like for a typical 2,000-square-foot roof:

Labor cost is minimal because ice and water shield is installed as part of the normal roof replacement process. Your roofer applies it to the deck before installing synthetic underlayment and shingles. The added labor for ice and water shield at code-required locations is typically included in the roof replacement quote. Full-roof coverage adds modest additional labor (1 to 2 hours for a crew) because the self-adhering rolls are somewhat slower to install than synthetic underlayment.

Compared to the total cost of a roof replacement in Myrtle Beach — typically $8,000 to $15,000 for asphalt shingles on a 2,000-square-foot home — ice and water shield adds 3% to 10% to the total project cost depending on coverage level. That is a small premium for a product that can prevent tens of thousands of dollars in water damage.

Cost by Brand

Your contractor typically sources the ice and water shield brand that matches their shingle system. If you are installing GAF shingles, your roofer will likely use GAF StormGuard. Owens Corning shingles pair with WeatherLock. Using matching brands from the same manufacturer is important for warranty coverage — most shingle manufacturers require their own underlayment products to honor the full system warranty.

Full-Roof Ice and Water Shield: Pros and Cons

Some homeowners — especially in hurricane-prone areas like Myrtle Beach — ask about covering the entire roof deck with ice and water shield. Here is an honest assessment:

Pros of Full-Roof Coverage

• Maximum waterproofing: Every square foot of roof deck is sealed against water intrusion, even if shingles are torn off during a hurricane
• Complete protection against wind-driven rain: No gaps in the waterproof layer where water can penetrate
• Secondary roof function: If shingles are blown off, the ice and water shield alone can protect the structure from water damage for weeks or months until repairs happen
• Insurance value: Some carriers offer additional premium reductions for homes with full waterproof underlayment, particularly in hurricane zones
• Peace of mind: Knowing your roof deck is completely sealed is worth something, especially during hurricane season

Cons of Full-Roof Coverage

• Cost premium: Adds $1,000 to $3,000 versus code-minimum coverage
• Vapor barrier concerns: Full coverage creates a complete vapor barrier that traps moisture below the deck. Adequate attic ventilation is absolutely critical — without it, condensation can damage the underside of the deck
• Deck adhesion permanence: Once applied, ice and water shield bonds permanently to the plywood. If you need to replace deck boards in the future, removing the membrane is difficult and time-consuming
• Heat absorption: The dark membrane absorbs more heat than synthetic underlayment, which can contribute to slightly higher attic temperatures in summer (though this effect is minimal once shingles are installed)
• Overkill for simple roofs: A straightforward gable roof with adequate slope, no valleys, and few penetrations gets limited additional benefit from full coverage

Our Recommendation for Myrtle Beach Homes

For most Myrtle Beach homeowners, we recommend enhanced coverage rather than full-roof or code-minimum. This means ice and water shield at all code-required locations (eaves, valleys, penetrations) plus all roof sections below 6:12 pitch and any roof planes facing the prevailing storm direction. This provides roughly 60% to 70% of the protection of full-roof coverage at about half the added cost. For homes within 2 miles of the ocean or homes that have experienced hurricane damage before, full-roof coverage is worth the investment.

South Carolina Building Code: Ice and Water Shield Requirements

South Carolina uses the International Residential Code (IRC) as its foundation, with state-specific amendments that reflect the coastal hurricane risk. Here is what the code requires for Myrtle Beach and coastal SC:

Wind Zone III Requirements

Myrtle Beach, North Myrtle Beach, Surfside Beach, Pawleys Island, and most of Horry and Georgetown counties fall within Wind Zone III, which means ultimate design wind speeds of 150 mph or higher. The code requirements for this zone include:

• Ice and water shield at all eaves extending at least 24 inches past the interior wall line
• Ice and water shield in all valleys, full length, minimum 36 inches wide (18 inches each side of centerline)
• Ice and water shield around all roof penetrations
• Enhanced underlayment requirements for the field of the roof (two layers of ASTM D226 Type II felt or one layer of self-adhering membrane meeting ASTM D1970)
• Shingles rated for 110+ mph wind resistance (ASTM D3161 Class F or D7158 Class H)

The enhanced underlayment requirement for Wind Zone III is significant. Many coastal SC contractors use ice and water shield for the first 6 feet from the eave (double the minimum) plus all valleys and penetrations, with a high-quality synthetic underlayment on the field. This approach meets and exceeds code requirements while keeping costs reasonable.

Permit and Inspection Requirements

Horry County and the City of Myrtle Beach require a building permit for any roof replacement. The inspection process includes verification that ice and water shield is installed at all code-required locations before shingles go on. Your contractor must schedule an underlayment inspection after the deck prep is complete and before shingle installation begins. If the inspector finds missing or improperly installed ice and water shield, the work stops until corrections are made.

Frequently Asked Questions About Ice and Water Shield

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