Roofing felt, also known as underlayment, plays a critical role in protecting the roof deck from moisture before and after shingles are installed. This guide explains the main types, what to consider when choosing felt, and practical installation tips to maximize performance and longevity across different U.S. climates and building codes.
Understanding Roofing Felt
Roofing felt is a layer installed between the roof deck and the final shingles. It provides a secondary waterproof barrier, reduces wind-driven rain intrusion, and helps with shingle placement during installation. Traditional asphalt felt is measured in pounds per 100 square feet, commonly 15-lb and 30-lb. Heavier felt offers greater tear resistance and longer-term protection, but comes with more handling complexity. Modern homes often use synthetic underlayment, which delivers higher tear resistance and lower shrinkage, especially in cold weather.
Asphalt Felt Versus Synthetic Underlayment
Asphalt felt, sometimes called tar paper, has a long track record for reliability and cost-effectiveness. It remains a solid option in many roofing projects, especially with asphalt shingles. However, it is heavier, can absorb moisture, and may suffer from deterioration in prolonged wet conditions. Synthetic underlayment is made from polypropylene or polyethylene blends. It tends to be lighter, more tear-resistant, and performs well in high winds and cold temperatures. Some synthetics are self-adhering, which helps seal around nails and resist wind uplift more effectively.
- Pros of Asphalt Felt: Low cost, easy to source, familiar installation methods, works with most traditional shingles.
- Cons of Asphalt Felt: Heavier, slower to dry after moisture exposure, shorter lifespan in prolonged wet conditions.
- Pros of Synthetic Underlayment: Higher tear strength, lighter, better in extreme temperatures, often mildew resistant.
- Cons of Synthetic Underlayment: Higher upfront cost, some products have steep learning curves for proper installation.
Choosing The Right Felt For Climate And Roofing Type
Climate and roof design determine which underlayment performs best. In humid or rainy regions, a robust water barrier and fast-drying properties are valuable. In cold climates with ice dam risk, look for self-adhesive or laminated underlayments that seal tightly around nails and minimize moisture intrusion. For metal roofs or tile roofs, a more puncture-resistant underlayment is beneficial to prevent damage during installation and weather events. Shingle type also matters: asphalt shingles pair well with asphalt felt, while synthetic underlayments are often preferred beneath premium roofing materials and in high-wasters areas where wind-driven rain is common.
- Climate considerations: High rainfall or humidity favors synthetics with superior tear resistance and moisture handling.
- Roof pitch: Steeper roofs benefit from underlayment that resists shifting and tearing during installation.
- Shingle compatibility: Check manufacturer guidance for compatibility between underlayment and shingle products.
Installation Best Practices
Proper installation maximizes the protective value of roofing felt. Start with clean, dry deck surfaces and follow local code requirements. Roll out felt with manufacturer-recommended direction and overlaps. For asphalt felt, typical overlaps are 2-4 inches horizontally and 4 inches vertically, but always verify product instructions. When using self-adhering underlayment, roll slowly to avoid wrinkles and ensure full adhesive contact; use appropriate آnail caps or fasteners where required by the product.
- Nailing and fasteners: Place nails in the center of each tab on sloped roofs; ensure nails are driven fully and do not tear the underlayment.
- Flashing and penetrations: Seal around chimneys, vents, and skylights with compatible sealants and flashing to create a continuous barrier.
- Ventilation consideration: Ensure roof ventilation remains intact and does not trap moisture behind the underlayment.
- Exposure and weather: Do not install in rain or high humidity; allow underlayment to acclimate in temperature-friendly conditions when possible.
Longevity, Durability, And Maintenance
Underlayment life depends on material, exposure, and climate. Asphalt felt tends to last 15-25 years under typical conditions but can degrade faster with repeated moisture exposure. Synthetic underlayment often offers 30 years or more in favorable climates and is less prone to cracking in extreme cold. Regular roof inspections after heavy storms help identify wrinkles, tears, or punctures in the felt. If damage is found, patching or full replacement of the underlayment in affected areas preserves the roof’s integrity until it’s time for a full roof replacement.
- Inspection cues: Torn edges, wrinkled sections, or obvious moisture staining indicate potential failure points.
- Repair approach: Small tears can be patched with compatible underlayment patches or sealant recommended by the manufacturer; larger damage may require reinstallation.
Environmental And Safety Considerations
Choosing roofing felt also involves environmental considerations. Synthetic underlayment often contains fewer volatile organic compounds and can be more recyclable than some asphalt-based products. Some manufacturers offer recycled-content options with improved sustainability profiles. Safety on the jobsite includes proper handling to avoid tears, skin contact with adhesives, and ensuring proper fall protection for workers. Local building codes may require specific underlayment standards, especially for wood-shingle roofs or areas with stricter wind and moisture provisions.
- Sustainability trends: Look for products labeled as recycled-content or with reduced environmental impact.
- Code compliance: Verify underlayment type, thickness, and application methods meet local IRC or jurisdictional requirements.
Practical Recommendations For Homeowners
For most U.S. residential projects, synthetic underlayment is a strong, durable choice that works well with modern shingles and in diverse climates. If budget is a primary constraint or if working with traditional asphalt shingles, 15-lb or 30-lb asphalt felt remains a viable option. In regions with heavy rainfall, high winds, or ice-damming risk, consider self-adhering or laminated synthetic underlayment for superior protection. Always follow the roofing manufacturer’s installation guidelines for underlayment compatibility with shingles and flashing components.
- Budget vs. performance: Weigh initial cost against long-term protection and ease of installation.
- Product selection: Choose underlayment compatible with your roofing system and climate.
- Professional guidance: When in doubt, consult a licensed roofer to confirm the best underlayment solution for the home’s design and local conditions.