How Thick Is Roofing Felt and How to Choose the Right Thickness
Roofing felt is an essential underlayment material used in many roofing systems, providing waterproofing and protection. Knowing how thick roofing felt is helps homeowners and contractors make informed decisions on installation and durability. This article explores typical thicknesses, types, and the factors influencing the choice of roofing felt thickness.
| Type of Roofing Felt | Typical Thickness Range | Common Uses |
|---|---|---|
| 15 lb (Pound) Felt | Approximately 0.3 to 0.4 millimeters (12 to 16 mils) | Single-layer underlayment for standard residential roofs |
| 30 lb Felt | Approximately 0.5 to 0.7 millimeters (20 to 28 mils) | Heavier, more durable underlayment; often used for increased protection |
| Synthetic Felt | 0.25 to 0.45 millimeters (10 to 18 mils), varies by brand | Lighter, stronger, moisture-resistant alternative to traditional felts |
What Is Roofing Felt?
Roofing felt, sometimes called tar paper, is a protective layer laid between the roof deck and shingles. It acts as a moisture barrier and adds an extra layer of protection against weather damage. Traditionally made from organic materials saturated with asphalt, modern felts also include synthetic varieties that offer enhanced durability and water resistance.
Standard Thickness of Roofing Felt
Roofing felt thickness is typically measured in pounds per 100 square feet (lbs/100 sq ft), with two common weights:
- 15 lb felt: This thinner felt generally measures around 0.3 to 0.4 millimeters thick. It provides basic protection and is common on residential roofs.
- 30 lb felt: Thicker and more robust, this felt ranges from 0.5 to 0.7 millimeters in thickness, offering better durability and tear resistance.
While the pound rating traditionally indicated weight, it correlates with the material’s thickness and density, enhancing waterproofing capabilities.
Thickness Comparison: Organic Vs. Synthetic Roofing Felt
Organic felt thickness can vary slightly due to natural fiber composition. It is generally heavier and thicker but less resistant to tearing.
Synthetic felt, made from polymeric materials, is lighter and often thinner but stronger. It typically ranges between 10 and 18 mils (0.25 to 0.45 mm) in thickness, depending on manufacturer specifications.
How Thickness Affects Roofing Felt Performance
The thickness of roofing felt influences several performance factors:
- Durability: Thicker felt tends to be more resilient to punctures, tears, and foot traffic during installation.
- Water Resistance: Increased thickness usually translates to better waterproofing protection.
- Weight: Thicker felt is heavier, which may slightly affect roof structure loading though generally minimal.
Choosing the right thickness balances these factors with budget and roofing type.
Industry Standards and Building Code Requirements
Building codes often specify minimum roofing felt requirements, for example:
- The International Residential Code (IRC) references the use of minimum 15 lb roofing felt as underlayment.
- In regions with severe weather or steep roofs, 30 lb felt or synthetic alternatives might be mandated.
Local building codes should always be consulted to determine applicable roofing felt thickness and type standards.
Tips for Choosing the Right Roofing Felt Thickness
Considerations for selecting roofing felt thickness include:
- Climate: Heavier felts or synthetic options are better suited for wet or snowy conditions.
- Roof Slope: Steeper roofs may need thicker felt for enhanced protection.
- Budget: 15 lb felt is less expensive, whereas 30 lb and synthetic felts are higher quality but cost more.
- Installation: Thicker felt may be more cumbersome to work with but provides superior durability.
Common Misconceptions About Roofing Felt Thickness
Several misunderstandings exist regarding roofing felt thickness:
- More thickness does not always equal better waterproofing if the material quality is low.
- Thicker felt is not always necessary—modern synthetic options can outperform heavier organic felts despite being thinner.
- Weight ratings refer to traditional manufacturing standards and do not directly translate to thickness measurements.
Installation Considerations Based on Felt Thickness
Thicker felts offer better protection during installation but can be heavier and less flexible, affecting handling. Synthetic felts, though thinner, offer ease of installation due to lightweight properties and increased tear resistance.
Proper installation is critical regardless of felt thickness to ensure optimal performance and roof longevity.
Future Trends in Roofing Felt Thickness and Materials
Technological advances drive the evolution of roofing underlayment materials:
- Synthetic felts continue to gain popularity for being thinner, lighter, and stronger.
- Multi-layer membranes provide enhanced waterproofing with less material thickness.
- Smart roofing materials that incorporate moisture sensing and improved weather resistance are emerging.
These trends suggest traditional thickness standards for organic felt may evolve as new materials dominate.