What Is Roofing Felt: A Comprehensive Guide to Roofing Underlayment

Roofing felt, commonly known as tar paper or underlayment, is a protective layer installed beneath roofing materials to shield a structure from moisture, wind, and temperature changes. In modern construction, felt remains a critical option for many homes, even as synthetic underlayments gain popularity. Understanding what roofing felt is, how it works, and where it fits in the roofing system helps homeowners and builders choose the right protection for durability, energy efficiency, and cost.

What Roofing Felt Is

Roofing felt is a sheet material applied over roof sheathing as an underlayment. Traditionally made from a base paper saturated with asphalt or tar, it provides a temporary, weather-resistant barrier during installation and beyond. In many regions, roofing felt is sold in rolls and comes in varying weights, typically described as 15-pound or 30-pound felt, indicating the weight of asphalt-saturated felt per square. Modern products also include synthetic felts made from polyethylene or polypropylene fibers, offering enhanced strength and tear resistance.

Types Of Roofing Felt

• Asphalt-Saturated Felt (Traditional Tar Paper): The classic option, relatively inexpensive, and widely used on felt-belt roofs. It dries and seals as the roof is installed, but may degrade under prolonged UV exposure or extreme temperatures.
• Synthetic Roofing Felt: Made from polymer-based fibers, these felts are lightweight, tear-resistant, and more resistant to moisture. They often provide superior dimensional stability and longer service life.
• Rubberized Asphalt Felt: A variant designed for improved water resistance, commonly used in areas with heavy rainfall or where additional protection is desired against leaks.

Functions And Benefits

• Moisture Barrier: Roofing felt slows water infiltration during rain or snow and provides a secondary defense if shingles are damaged before sealing.
• Wind Resistance: A continuous underlayment helps stabilize the roof deck and minimizes wind-driven moisture intrusion.
• Nail Sealant: Felt helps obscure nail heads and creates a surface that supports shingles during installation, reducing the risk of lifting.
• Temporary Weather Protection: During construction, felt remains in place to protect the deck from precipitation until the final roofing material is installed.
• Ventilation And Breathability: Some modern felts are designed to allow limited vapor diffusion, aiding in moisture management when paired with proper attic ventilation.

When And How To Install

Timing and method depend on the roofing system and climate. Installation generally occurs after sheathing is in place and the roof outline is complete. The following practices help ensure effective performance:

• Weather Considerations: Install underlayment when temperatures are moderate and there is no rain forecast for at least 24 hours to prevent premature deterioration.
• Overlap And Fastening: Felt is usually laid in courses with horizontal overlaps of about 2 to 4 inches, depending on product instructions. Fasten with corrosion-resistant nails or staples, ensuring a snug fit with no excessive wrinkles.
• Ventilated Roofs: In vented roof assemblies, underlayment must be compatible with roof ventilation requirements to prevent moisture buildup beneath the felt.
• Seam Protection: For colder climates or exposed regions, some roof designs require additional protection at seams and vulnerable edges to minimize water seepage.

Usage notes:

• Follow Manufacturer Guidelines: Always read the product label for application temperature ranges, overlapping requirements, and fastening patterns.
• Compatibility With Shingles: Ensure the underlayment is compatible with the chosen roofing material to maintain warranty coverage.
• Deck Dryness: The roof deck should be dry and clean before applying underlayment to maximize adhesion and performance.

Roofing Felt vs Other Underlayments

Choosing between felt and other underlayments depends on climate, budget, and expected roof wear. Key considerations include:

• Cost And Availability: Asphalt-saturated felt is typically less expensive than synthetic underlayments, making it a common choice for budget-conscious projects.
• Durability: Synthetic felts generally offer higher tear resistance and longer service life, especially in hot or UV-heavy environments.
• Water Resistance: Rubberized asphalt and premium synthetic felts can provide superior moisture protection in heavy rainfall regions or areas prone to leaks.
• Installation Speed: Synthetic underlayments are often lighter and easier to handle, potentially speeding up installation.
• Warranty Implications: Some roofing manufacturers specify underlayment requirements for warranty validity; compliance is essential to maintain coverage.

Maintenance And Lifespan

Proper installation largely determines the lifespan of roofing felt. While felt itself is not a structural component, its performance can affect roof longevity. Consider these points:

• Visible Signs Of Wear: Inspect for curling, tearing, or detachment after major storms or temperature fluctuations. Damaged areas should be repaired promptly.
• UV Exposure: Prolonged sun exposure can degrade traditional asphalt-saturated felt; synthetic felts offer improved UV resistance.
• Weather Events: In areas with frequent hail or heavy rainfall, regular roof inspections help detect blistering or punctures in the underlayment before leaks develop.
• Seasonal Maintenance: After severe weather, check attic ventilation and ensure no moisture intrusion has occurred beneath the underlayment.

Common Questions About Roofing Felt

1. Is roofing felt required by code? Requirements vary by region and building code. Some jurisdictions permit synthetic underlayment as an alternative, while others may require or recommend felt as part of the roofing system.
2. How long does roofing felt last? Traditional asphalt-saturated felt may last 15–20 years under favorable conditions, while synthetic felts often reach 25 years or more, depending on climate and installation quality.
3. Can I install shingles directly over damaged felt? No. Damaged underlayment should be repaired or replaced to maintain waterproofing and warranty compliance.
4. Which underlayment should I choose? A balance of cost, climate, roof type, and warranty requirements guides the choice between asphalt-saturated, synthetic, or rubberized options.