What Roof Felt Is Made Of: Materials, Types, and Uses

Roof felt, or roofing underlayment, serves as a protective barrier beneath shingles and roofing materials. It helps shed moisture, provides a temporary weather seal, and reduces potential damage from condensation and wind-driven rain. Modern roof felt comes in a range of base materials and reinforcements, each offering different levels of durability, permeability, and ease of installation. Understanding what roof felt is made of helps homeowners choose the right product for climate, roof design, and budget.

Common Base Materials

The base material, often referred to as the carrier, forms the backbone of roof felt. The most common options in the United States are asphalt-impregnated paper and synthetic underlayments. Each has distinct advantages depending on installation conditions and roof type.

• Asphalt-impregnated paper: A traditional option that blends asphalt with fiberglass or cellulose fibers. It is inexpensive and provides decent water resistance, making it suitable for many asphalt shingle installations. It is less tear-resistant than synthetic options and can be damaged by prolonged exposure to sunlight before shingles are applied.
• Synthetic underlayments: Made from polymer-based fibers such as polypropylene or polyethylene. They are lighter, more durable, and have higher tear resistance than asphalt felt. Synthetic underlayments perform well in a variety of climates and tend to resist water and moisture more effectively.
• Fiberglass or cloth facings: Some underlayments use a fiberglass mat or non-woven cloth as a support structure. These facings improve tear resistance and allow for faster installation with better grip and traction.

Reinforcements And Facings

In addition to the base material, roof felt often includes a reinforcement layer that enhances strength and durability. Reinforcement can impact durability in windy, rainy, or icy conditions and can influence installers’ traction and protection during application.

• Fiberglass reinforcement: Common in asphalt or synthetic underlayments, fiberglass increases dimensional stability and tear resistance. It stands up well to heat and helps prevent stretching or sagging.
• Polypropylene or polyester fabrics: Synthetic fabrics provide excellent strength-to-weight ratios and improved resistance to tearing and abrasion. They’re particularly common in high-performance underlayments for steeper roofs and cold climates.
• Nonwoven textiles: Some synthetic underlayments use nonwoven fabrics that balance flexibility with puncture resistance, reducing the risk of damage during installation.

Asphalt Felt Classifications

When homeowners hear the term “roof felt,” they often refer to asphalt-based products. These come in several classifications that indicate thickness, weight, and performance characteristics.

• Standard asphalt felt: Typically labeled with weights like 15-pound or 30-pound per 1000 square feet. Heavier weights offer better moisture resistance and durability but may be stiffer to handle.
• Interleaved or laminated felt: A combination of layers that improve tear resistance and puncture protection. Laminated felt is more resilient in wind-driven rain conditions.
• Self-sealing or self-adhering variants: These incorporate adhesive properties to improve installation when fasteners are hard to place or when wind uplift is a concern. They can provide an extra layer of protection until shingles are installed.

Synthetic Roofing Underlayment Options

Synthetic underlayments have become widely adopted due to durability, water-performance, and lighter weight. They are available in various forms to suit different roofing systems and climates.

• Unfaced synthetic underlayment: A bare, non-slip surface that dries quickly. It’s popular for modern roofs with advanced drainage and ventilation systems.
• Self-adhering synthetic underlayment: Features a pressure-sensitive adhesive on one side for faster, weather-tight installation. It reduces the need for nailing in high-wind areas and improves overall waterproofing.
• Underlayment with mineral surface: Some products have a mineral surface to improve walkability and UV resistance during the installation window.

Pros And Cons Of Each Material

Choosing the right roof felt involves weighing protection, durability, installation, and cost. The following summary highlights typical pros and cons.

• Asphalt felt (paper-based): Low cost, easy to source, familiar for many contractors. Cons include lower tear resistance, reduced performance in prolonged sun exposure, and heavier weight compared to synthetics.
• Asphalt + fiberglass: Moderate durability with improved heat resistance. Can tolerate some moisture but is not ideal for areas with heavy rainfall or prolonged exposure before shingling.
• Fiberglass-reinforced asphalt: Better tear and puncture resistance; mid-range price. Susceptible to heat damage if left exposed for extended periods.
• Synthetic underlayments: High durability, excellent tear strength, and better performance in cold and wet climates. Higher initial cost but longer lifespan and easier installation.
• Self-adhering underlayments: Superior seal against wind and moisture, quick installation in difficult conditions. Requires careful surface preparation and can be pricier.

Installation Considerations

Proper installation is crucial for roof felt to perform as intended. Climate, roof pitch, and roofing material influence the choice and method.

• Climate and weather windows: In rainy or snowy regions, a synthetic or self-adhering underlayment offers better protection during construction. In dry climates, standard asphalt felt may suffice if installed promptly.
• Roof pitch and exposure: Steeper roofs can benefit from tougher underlayments with higher tear resistance. Low-slope roofs often require more robust moisture barriers.
• Ventilation and condensation: Underlayments work with roof ventilation to manage moisture. Proper attic ventilation reduces the risk of condensation that can degrade roofing materials beneath.
• Nailing patterns and fasteners: Follow manufacturer guidelines for fastener type, length, and spacing. Some self-adhering products use fewer fasteners due to adhesive strength.
• UV exposure: Some underlayments are designed to withstand short-term UV exposure. Prolonged exposure can reduce the life of traditional asphalt felt, making synthetic options more favorable for longer delays before shingling.

Durability, Longevity, And Maintenance Considerations

The long-term performance of roof felt depends on material quality and how it is protected from damage during construction and use. Synthetics generally offer extended lifespans and better resistance to weather exposure, while asphalt-based products are cost-effective for standard applications.

• Durability: Synthetic underlayments typically resist tearing, punctures, and abrasion better than asphalt felt, especially in harsher climates.
• Moisture management: High-quality underlayments provide reliable water shedding and resist moisture saturation. Self-adhering variants add an extra layer of protection against leaks during installation.
• Maintenance: Roof felt is usually a one-time installation layer, but damaged sections should be replaced during roof maintenance to prevent water intrusion and structural damage.

Choosing The Right Material For A U.S. Roof

Selecting roof felt hinges on climate, roof type, and budget. For coastal or rainy regions, synthetic underlayments with self-sealing capabilities offer robust protection. In milder inland areas, standard asphalt felt often meets performance needs at a lower cost. Homeowners should consult local building codes and contractor recommendations to ensure compatibility with shingle types and roof design.