What Is Roof Felt Made Of

Roof felt, also known as underlayment or tar paper, serves as a protective layer beneath shingles or other roofing materials. It helps shield the structure from moisture, wind, and minor weather exposures during construction and after installation. Understanding what roof felt is made of reveals why it behaves differently under varying climates and roof types. This article outlines the key components, the main product types, how it’s manufactured, and how to choose the right roof felt for a home in the United States.

What Roof Felt Is Made Of

Traditional roof felt is a composite material made from a reinforcing layer, saturated or coated with asphalt or bitumen. The reinforcing layer can be organic paper, fiberglass, or polyester, each offering different strength and moisture characteristics. The asphalt or bitumen component provides water resistance and flexibility, enabling the felt to bend with roof contours and temperature fluctuations. Some products feature a granular or smooth surface finish that improves durability and, in some cases, helps with UV protection before shingles are installed.

Types Of Roof Felt

Roof felt generally falls into two broad categories: organic felt and synthetic felt. Each category includes variations, such as fiberglass-reinforced and polyester-reinforced products, and can be saturated or coated with asphalt for enhanced waterproofing.

• Organic Felt (Paper-Based): Made from wood pulp or cellulose reinforced with a paper layer. It is then saturated with asphalt to improve water resistance. Organic felt has a long history in roof underlayment but can break down more quickly in persistent moisture and high heat.
• Asphalt-Saturated Felt: A traditional option where a paper or organic base is impregnated with asphalt. This increases impermeability but may be less durable in extreme temperatures compared with synthetic options.
• Fiberglass Felt: A fiberglass mat provides greater tear resistance and dimensional stability. When asphalt-saturated, it forms a robust barrier against moisture while remaining pliable.
• Synthetic Felt: Made from polymer fibers such as polyethylene or polypropylene, often reinforced with polyester. Synthetic felts offer superior tear resistance, dimensional stability, and faster drying times, especially in humid environments.
• Self-Adhered Underlayment: A variant that uses a rubberized or asphaltic adhesive backing for easier installation and superior seal at overlaps and around roof penetrations.

Common Materials In Roof Felt

Key materials found in roof felts include:

• Reinforcing Layer: Fiberglass, polyester, or organic paper. This layer gives tear resistance and helps maintain integrity when exposed to weather during construction.
• Waterproofing Binder: Asphalt, bitumen, or other polymer coatings that provide the primary moisture barrier. The binder also contributes to flexibility at low temperatures.
• Surface Finish: Granulated mineral surfaces or smooth, polymer-coated faces. Granules protect the felt surface and can provide some weathering protection before shingles are installed.
• Adhesives: Some products include self-adhesive backing or additional tackifiers to improve sealing at seams and around roof details.

How Roof Felt Is Manufactured

The manufacturing process starts with selecting a reinforcing substrate, such as fiberglass or a cellulose-based paper. The substrate is then coated or saturated with asphalt or a bitumen blend. For synthetic felts, polymeric fibers are integrated before coating. In some cases, a granule surface is added during production to enhance durability and UV resistance. The finished product is rolled into large sheets and coated with protective films or backings for storage and transport. Quality standards typically govern tear strength, permeability, and resistance to weathering and aging.

Choosing The Right Roof Felt For Your Home

Selecting an appropriate underlayment depends on climate, roof pitch, and local building codes. In regions with heavy rainfall or snow, a high-quality synthetic or asphalt-saturated underlayment with strong tear resistance and good waterproofing properties is beneficial. For steeper pitches, a lighter-weight organic or asphalt-saturated option may suffice, provided it offers adequate protection during installation. Local building codes may specify a minimum underlayment performance, such as a water resistance rating or vapor permeance threshold. Consider these factors:

• Weather and Climate: Colder regions favor materials that remain flexible in low temperatures, while hot, sunny climates demand UV stability and resistance to aging.
• Roof Type And Slope: Steeper roofs reduce long-term water exposure but require reliable seam sealing and compatibility with shingles.
• Installation Time: Self-adhesive or peel-and-stick options can speed up installation and improve airtightness during construction.
• Durability And Longevity: Synthetic felts generally outperform organic options in terms of tear resistance and lifespan, especially in humid environments.
• Compatibility With Shingles: Underlayment should be compatible with the chosen roofing material to ensure proper adhesion and performance.

Installation And Durability Considerations

Proper installation is essential to maximize the performance of roof felt. Overlaps should follow manufacturer guidance to prevent water intrusion at seams. Fasteners, nails, or staples must be placed per code and product instructions to avoid compromising the felt. In regions with heavy wind, extra attention to edge fastenings and ridge coverage enhances durability. During construction, felt should be installed in dry conditions to prevent moisture entrapment, which can degrade the material or encourage mold growth. After shingles are installed, underlayment continues to act as a moisture buffer and secondary barrier if the outer roof layer is compromised.

Maintenance, Lifespan, And Replacement

Roof felt is a preventive measure rather than a primary waterproofing layer. Its lifespan varies by material and climate, but typical synthetic or asphalt-saturated felts can perform well for 15 to 30 years under normal conditions. Over time, exposure to UV light, temperature swings, and precipitation can cause brittleness or delamination. Homeowners should inspect attics, crawl spaces, and roof edges for signs of moisture intrusion or deterioration in the felt after severe weather. Replacement becomes necessary when leaks or significant wear appear, often coinciding with roof replacement projects.

Frequently Asked Questions

Is roof felt waterproof? Roof felt provides a waterproof barrier, but it is primarily an underlayment that complements the primary roofing material. It protects the roof deck during construction and offers secondary protection during weather events.

What materials are used in roof felt? Materials include asphalt-saturated organic paper, fiberglass or cellulose-reinforced felt, and synthetic felts with polymer reinforcements. Some products are self-adhering for easier installation.

Do modern roofs still use felt? Many modern roofs use synthetic or self-adhered underlayments that offer superior durability and easier handling, though traditional asphalt-saturated felt remains in use in many projects for cost or code reasons.

Can I install roof felt myself? Installation is feasible for skilled DIYers with proper safety measures and adherence to local codes. Complex roof shapes or high wind areas may benefit from professional installation.

Understanding what roof felt is made of helps homeowners assess durability, expected performance, and installation needs. By considering climate, roof design, and local regulations, homeowners can select the most appropriate underlayment to protect the roof structure and extend the life of the entire roofing system.