Roofing Felt Uses, Types, and Installation Guide

Roofing felt, also known as underlayment, is a protective layer installed between roof sheathing and shingles or other final roofing materials. It helps shield the roof from moisture, wind-driven rain, and temperature fluctuations while providing a workable surface for installing shingles. This guide explains what roofing felt is, the different types available, how it functions, and best practices for installation and maintenance to ensure long-lasting roof performance.

What Is Roofing Felt

Roofing felt is a paper or synthetic sheet designed to act as a secondary barrier against water intrusion. Traditional felt is made from asphalt-saturated paper, while modern options include synthetic underlayments that blend polypropylene or fiberglass with asphalt. The underlayment lies directly on the roof deck and under the final roof covering, such as shingles or metal panels. Its placement and material affect drought resistance, wind uplift protection, and overall roof durability.

Types Of Roofing Felt

Choosing the right underlayment depends on climate, roof type, and local building codes. The main categories are:

• Traditional Asphalt-Saturated Felt: Also called tar paper, this budget-friendly option offers basic moisture protection. It is lightweight and easy to install but can deteriorate in high heat and UV exposure.
• Synthetic Underlayment: Made from polypropylene or fiberglass, synthetic underlayment provides superior tear resistance, moisture resistance, and longevity. It performs well in hot climates and windy areas.
• Self-Adhering Underlayment: A peel-and-stick variant with an adhesive backing that creates a seamless moisture barrier. It protects against wind-driven rain and is effective on complex roof shapes.
• Roofing Membranes For Specific Applications: In some roofs, fluid-applied membranes or innovative high-performance underlayments are used for additional water control, especially in areas with heavy rainfall or complex flashing details.

Key Functions Of Roofing Felt

The underlayment serves several critical roles in roof performance:

• Moisture Protection: Acts as a secondary barrier to prevent water from reaching the plywood or OSB deck during storms, shingle installation, or temporary exposure.
• Wind-Driven Rain Defense: Helps resist wind-driven moisture that can penetrate gaps around nails or fasteners.
• Nailing Surface: Provides a stable surface for installing shingles, helping prevent tear-out and misalignment during wind events.
• Ventilation And Drying: In some designs, the underlayment allows for micro-ventilation beneath shingles, aiding in deck drying after wet conditions.
• Fire And Thermal Resistance: Depending on the material, some underlayments contribute to a roof’s fire resistance rating and thermal barrier performance.

When To Use Roofing Felt

Underlayment is typically required on most residential roofs, though the exact rules vary by region and code. It is commonly installed in the following scenarios:

• New Roof Installations: Underlayment is installed over clean, dry roof decking before shingles or metal panels.
• Roof Repairs And Replacements: When replacing shingles, underlayment is often removed and replaced to restore moisture protection.
• In Areas With High Rain Or Snow: Climate-driven codes may require a higher-performance underlayment to guard against water intrusion during storms or rapid temperature changes.
• Complex Roof Geometries: Roofs with many valleys, hips, or penetrations benefit from a reliable underlayment to manage moisture at joints and flashing.

installation Basics

Proper installation is crucial for underlayment effectiveness. The following guidelines help ensure a durable outcome:

• Surface Preparation: Ensure the roof deck is clean, dry, and smooth. Remove dust, nails, and protrusions that could compromise coverage.
• Overlap And Fastening: Overlap courses according to product instructions, typically 2 to 4 inches on each layer. Fasten with corrosion-resistant nails or staples, spacing per manufacturer guidelines.
• Seam Handling: For self-adhering underlayments, remove the release film and press firmly to create a tight seal, avoiding air pockets around fasteners.
• Edge And Penetration Details: Pay careful attention to eaves, rakes, and around skylights, vents, and chimneys. Use flashing where required and seal joints properly.
• Climate Considerations: Warm, sunny days facilitate easier handling; extreme cold can make materials brittle, requiring adjusted methods.

Common Issues And Maintenance

Even when properly installed, some issues can arise over time. Regular inspection helps detect and address problems early:

• Punctures And Tears: Deterioration from foot traffic or debris can create openings for moisture. Prompt repair or replacement is advisable.
• Loose Or Peeling Sections: Poor adhesion or wind uplift can cause loose areas that require re-fastening or resealing.
• Ventilation Gaps: Inadequate ventilation can cause decking to trap moisture, promoting mold or rot. Ensure proper attic or roof deck ventilation.
• Compatibility With Final Roof: Some shingles or metal systems require specific underlayment types. Mismatches can affect warranty and performance.

Maintenance And Replacement Considerations

Maintenance routines extend the life of the roof system. Consider these practices:

• Inspections After Severe Weather: Check for visible punctures, tears, or lifting after storms, hail, or high winds.
• Seasonal Checks: Inspect eave edges and roof penetrations for signs of wear or moisture accumulation.
• Replacement Timelines: Underlayment typically lasts 15 to 30 years depending on material and climate. Signs of aging include brittleness, thinning, or loss of adhesion.
• Warranty And Codes: Follow local building codes and product warranties. Some regions mandate synthetic or self-adhering underlayments for specific roof types.

Environmental Considerations

Material choices may impact environmental performance. Synthetic underlayments often offer better durability and longer life, reducing waste over time. Some products are designed for lower emissions during manufacturing, and many can be recycled after use in compliant facilities. When selecting underlayment, consider life-cycle impacts, local availability, and compatibility with the chosen final roof covering.

Frequently Asked Questions

What is roofing felt used for? It provides a moisture barrier, wind protection, and a stable nailing surface under the final roof covering. How long does roofing felt last? Durability depends on material and climate, typically 15 to 30 years for modern products. Is underlayment required by code? In many areas, yes, but the requirement varies by region and roof type. How do you install underlayment on a roof? Prepare the deck, lay or adhere the underlayment per manufacturer instructions, and secure with fasteners, ensuring proper overlaps and detailing at edges and penetrations.