Glossary > #Asphalt Felt

Asphalt Felt

What is Asphalt Felt?

Asphalt felt, also known as roofing felt or tar paper, is a key component of roofing systems, widely recognized for its protective properties. It is a type of roof underlayment that is applied between the roof structure (usually made of wood or other structural materials) and the final roofing material, such as shingles, metal sheets, or tiles. This layer functions as protection against water penetration, moisture accumulation, and external damage, ensuring durability and long lifespan of the roof.

Asphalt felt is typically made from a base material, either organic (cellulose from wood) or synthetic (fiberglass or polyester). This base is then saturated or coated with asphalt (bitumen), which is a waterproofing substance. The asphalt coating not only repels water but also allows the material to “breathe,” thereby preventing condensation and moisture-related problems under the roofing.

Purpose of Asphalt Felt in Roofing Systems

1. Waterproofing and Moisture Protection

Asphalt felt serves as an additional water barrier that prevents water from penetrating the roof structure. This is especially important during heavy rains, snow, or storms. By repelling water, it protects the structure from damage, mold formation, and wood rot.

2. Secondary Protection

In cases where the primary roofing material (such as shingles or tiles) is damaged or removed, asphalt felt acts as a secondary defense. It temporarily prevents water from penetrating the structure until repairs are made.

3. Resistance to Ice and Snow

In colder climates, ice dams and snow accumulation can be a significant problem. Asphalt felt helps mitigate these issues by preventing ice dam formation, which occurs when melted snow at the roof edge refreezes, causing water to penetrate under the roofing.

4. Fire Resistance

In combination with certain roofing materials, asphalt felt can achieve a Class A fire resistance rating, which is the highest level of fire resistance. This increases building safety and can reduce insurance costs.

5. Protection During Construction

During the construction phase, the roof structure is often exposed to weather conditions. Asphalt felt provides temporary weather protection, protecting structural materials from moisture and damage until final roofing materials are installed.

6. Improved Aesthetic and Functional Performance

Asphalt felt creates a smooth and even surface that facilitates proper adhesion of shingles or other roofing materials. This prevents visible imperfections, such as “pattern telegraphing,” where the pattern of the underlying structure becomes visible through the final roofing.

Types of Asphalt Felt

1. Traditional Asphalt Felt

  • Composition: Made from organic materials, such as cellulose from wood, or synthetic fibers, coated with asphalt.
  • Weights: Available in two main weights:
    • 15 lb felt: Lightweight and affordable, suitable for less demanding environments.
    • 30 lb felt: Thicker and more durable, ideal for areas with demanding climate conditions.
  • Use: Commonly used in both residential and commercial roofing projects.

2. Synthetic Underlayment

  • Composition: Made from modern synthetic materials, such as polypropylene or polyethylene.
  • Advantages:
    • Lightweight and easy to handle.
    • Excellent resistance to tearing, crushing, and UV degradation.
    • Superior water-repellent properties that surpass traditional felt.
  • Use: Ideal for high-performance roofing systems or areas with extreme weather conditions.

Benefits of Using Asphalt Felt

1. Durability

Asphalt felt significantly extends the lifespan of roofing systems by providing an additional protective barrier against environmental stress factors.

2. Cost-Effectiveness

Its availability and effectiveness make it a practical choice for improving roof performance while minimizing potential repair costs.

3. Versatility

Compatible with various roofing materials, including asphalt shingles, metal sheets, wood shingles, and slate tiles.

4. Easy Installation

Both traditional and synthetic underlayments are user-friendly and can be installed using standard tools, such as nails or staples. Synthetic options may require the use of nails with washers for optimal installation.

5. Environmental Aspects

Modern asphalt felt products are increasingly designed with environmental considerations in mind, with options for recycling or use of sustainable components.

Common Uses of Asphalt Felt

1. Residential Roofs

Asphalt felt is a fundamental element of residential roofs, providing a reliable moisture barrier under asphalt shingles or other materials.

2. Commercial Roofs

In larger commercial projects, it forms an important part of multi-layer roofing systems that offer increased protection and longevity.

3. Temporary Roofs – for example, roofs on assemblies from shipping containers

During construction or renovation, asphalt felt serves as temporary roofing, protecting the structure until permanent materials are installed.

Frequently Asked Questions (FAQ)

1. Is asphalt felt necessary for all roofs?

Yes, it is strongly recommended by organizations such as the National Roofing Contractors Association (NRCA), and is often required by building codes.

2. Can asphalt felt be used in all climate conditions?

Yes, with options such as synthetic underlayments, it is suitable for a wide range of conditions, from humid to extremely cold climates.

3. How long does asphalt felt last?

With proper installation and protection, it can last as long as the roof itself – typically 20–30 years or more.

4. Can asphalt felt be left uncovered?

Traditional felt is not designed for long-term exposure. However, synthetic underlayments offer better UV resistance and can remain uncovered for longer periods.

5. What is the difference between 15 lb and 30 lb felt?

The difference lies in thickness and durability. 30 lb felt is more robust and suitable for more demanding conditions, while 15 lb felt is lighter and more economical.

Alternatives to Asphalt Felt

  • Rubber Asphalt Membranes: Self-adhesive and highly waterproof, ideal for areas prone to ice dam formation.
  • Synthetic Underlayments: Durable, lightweight, and resistant to UV degradation, increasingly popular in modern roofing systems.

Asphalt felt is indispensable in the construction of durable and weather-resistant roofing systems. Its ability to repel water, provide secondary protection, and increase fire resistance makes it an invaluable component of both residential and commercial projects. Whether you choose traditional asphalt felt or modern synthetic underlayments, investing in asphalt felt will ensure a safer and more durable roof.