Roofing Felt vs Ice and Water Shield: Key Differences and Applications
In roofing projects, selecting the right underlayment material is essential for protecting your home from water damage and weather elements. Two common options are roofing felt and ice and water shield. While both serve as a moisture barrier, they have distinct characteristics and applications that affect their performance. This article explores the differences between roofing felt and ice and water shield, helping homeowners and contractors make informed decisions for roofing projects.
| Feature | Roofing Felt | Ice and Water Shield |
|---|---|---|
| Material | Fiberglass or organic felt saturated with asphalt | Rubberized asphalt with a sticky adhesive backing |
| Thickness | Typically 15 or 30 pounds weight per roll | Thicker, more pliable membrane |
| Water Resistance | Water-resistant but not waterproof | Fully waterproof and self-sealing |
| Primary Use | General underlayment under shingles | Critical areas prone to leaks (eaves, valleys, chimneys) |
| Installation | Rolled out and nailed or stapled | Peel-and-stick adhesive application |
| Cost | Less expensive | Higher cost due to enhanced protection |
What Is Roofing Felt?
Roofing felt, also known as tar paper, is a traditional underlayment material composed of either organic fibers or fiberglass mats saturated with asphalt. It is available in various weights, primarily 15-pound and 30-pound varieties, which indicate thickness and durability. This felt acts as a secondary barrier against wind-driven rain and protects the wooden roof deck during shingle installation.
Though roofing felt offers water resistance, it is not fully waterproof. Its primary function is to provide a layer between the roof deck and shingles, offering moderate protection against moisture. It also helps improve shingle adhesion and reduces blistering caused by trapped moisture beneath asphalt shingles.
Understanding Ice and Water Shield
Ice and water shield is a peel-and-stick waterproof membrane made from rubberized asphalt with a tough polyethylene film on top. This product is designed to create a fully sealed barrier in vulnerable areas, such as roof edges, valleys, chimneys, skylights, and around vent pipes. The self-adhesive nature of the membrane allows it to bond tightly with the roof deck, providing superior protection against water infiltration.
Ice and water shield is especially important in cold climates where ice dams can form, causing water to back up under shingles and leading to leaks. Because of its unique properties, this membrane is recognized as a critical component in moisture control during harsh winter months or intense storms.
Comparing Roofing Felt and Ice and Water Shield by Application
Water Protection Capabilities
While both roofing felt and ice and water shield serve to protect the roof deck from moisture, their effectiveness varies significantly. Roofing felt is only water-resistant and relies heavily on the shingles to keep most water out.
In contrast, ice and water shield is waterproof. It seals tightly to the roof deck and self-seals around nails and fasteners, preventing leaked water from penetrating the structure.
Recommended Uses
- Roofing Felt: Used as general underlayment beneath asphalt, wood, or composite shingles. It covers the entire roof deck, providing an economical moisture barrier.
- Ice and Water Shield: Installed in specific, vulnerable zones such as eaves, rakes, valleys, dormers, flashing areas, chimneys, skylights, and chimneys. It helps prevent leaks caused by ice dams, wind-driven rain, or flashing failures.
Installation Techniques
Roofing felt is unrolled across the roof deck and fastened mechanically using nails or staples. This requires overlapping seams and careful alignment to prevent water entry. It is fairly straightforward but requires skilled installation to avoid wrinkling or gaps.
Ice and water shield involves peeling a release film and adhering the membrane directly onto the roof decking or previously applied underlayment. This self-adhering process simplifies installation in complex roof areas, ensures coverage in tight spaces, and eliminates potential weak points around fasteners.
Cost Considerations
Generally, roofing felt is less expensive, making it a popular choice for entire roof coverage. Ice and water shield costs considerably more but provides higher-level protection in leak-prone zones. Combining both materials is often the most cost-effective and performance-optimized strategy.
Durability and Lifespan
Roofing felt, depending on its grade, lasts approximately 20 to 30 years, but its performance declines with prolonged UV exposure or moisture intrusion. Ice and water shield membranes are designed to last as long as the roof itself due to their resistance to tearing, water penetration, and temperature fluctuations.
Because ice and water shield tightly bonds with the roof deck, it also helps reinforce structural integrity in freeze-thaw cycles by reducing water damage and rot.
Building Code Requirements and Industry Standards
Many local building codes in the US mandate the use of ice and water shield in critical areas susceptible to ice dams and water intrusion, especially in colder climates. For example, the International Residential Code (IRC) requires a minimum 36-inch wide waterproof membrane at eaves and valleys.
On the other hand, roofing felt is universally accepted as standard underlayment but must be complemented by ice and water shield or similar products where specified. Compliance with standards ensures optimal roof performance and longevity.
Environmental and Safety Aspects
Roofing felt production involves asphalt and petroleum products, while some organic felts may include wood fibers. It is typically recyclable but may not be biodegradable.
Ice and water shield uses rubberized asphalt and synthetic materials, providing a durable option with minimal environmental degradation when properly disposed of. Both materials should be handled carefully due to asphalt compounds, following safety recommendations during installation.
Choosing Between Roofing Felt and Ice and Water Shield for Your Project
Here are key considerations for selecting the right underlayment:
- Climate: In regions with regular ice dam formation or heavy rain, prioritize ice and water shield in vulnerable zones.
- Roof Design: Complex roofs with numerous penetrations and valleys benefit from the self-sealing properties of ice and water shield.
- Budget: Use roofing felt for broad coverage and invest in ice and water shield selectively to balance cost with performance.
- Local Codes: Verify specific requirements to ensure compliance with building regulations.
Summary Table: Roofing Felt vs Ice and Water Shield
| Aspect | Roofing Felt | Ice and Water Shield |
|---|---|---|
| Material Type | Fiberglass/organic felt saturated with asphalt | Rubberized asphalt with adhesive backing |
| Water Resistance | Resistant but not waterproof | Fully waterproof and self-sealing |
| Installation | Rolled out and mechanically fastened | Peel-and-stick adhesive application |
| Common Uses | Full roof underlayment | Vulnerable areas: eaves, valleys, around penetrations |
| Cost | Lower upfront cost | Higher cost, higher protection |
| Lifespan | 20–30 years | As long as roofing system |
| Building Code | Standard underlayment | Required in areas prone to ice dams and leaks |