What Roofing Felt Is Used for and Why It Matters

Roofing felt, commonly known as underlayment, plays a critical role in protecting homes from moisture, wind, and weather-related damage. It serves as a secondary barrier beneath shingles or other roofing materials, improving durability and installation quality. Understanding its purpose, types, and installation helps homeowners and builders choose the right product for climate, roof pitch, and design.

What Roofing Felt Is

Roofing felt is a paper-like or fiberglass-reinforced sheet that is installed on the roof deck before the final roofing layer. It acts as a moisture barrier, guiding water away from the sheathing and into gutters. Felt also provides temporary weather protection during construction and offers a smooth surface for shingles to adhere to. The material is typically sold in rolls and comes in various weights and compositions to suit different roofs.

Types Of Roofing Felt

• Oil-Saturated Felt: An affordable option made from paper saturated with oil. It provides basic moisture resistance but is less durable in UV exposure.
• Fiberglass-Backed Felt: A stronger underlayment with a fiberglass mat backing. It resists tearing and typically handles higher temperatures well.
• Polyester-Backed Felt: Similar to fiberglass but with improved tear resistance and dimensional stability, often used in higher wind zones.
• Self-Adhering (Liquid-Applied) Felt: A peel-and-stick version that offers superior water seal, especially at penetrations and valleys. It provides strong wind uplift protection but can be more costly.

Materials chosen affect tear resistance, nail pull-through, and longevity. Climate, roof pitch, and local building codes influence the best choice for a project.

Common Uses And Benefits

• Moisture Barrier: The primary function is to prevent water from seeping into the roof deck during rain or snow melts.
• Temporary Weather Protection: It shields unfinished roofs from wind-driven rain during construction until final roofing is installed.
• Slip Surface: Provides a smooth, uniform surface to help shingles lay correctly and align, improving overall installation quality.
• Enhanced Wind Resistance: Some underlayments improve wind uplift resistance when used with compatible roofing systems.

Installation Considerations

• Exposure And Coverage: Follow manufacturer guidelines for exposure—the portion of the underlayment exposed to the elements. Overexposure can reduce protection, while underexposure can affect shingles’ alignment.
• Nailing Pattern: Nail lines should be placed according to the product specifications to prevent tearing and ensure a secure bond.
• Seams And Penetrations: Seal seams with compatible tape or adhesive where required, and properly flash around chimneys, vents, and skylights to prevent leaks.
• Climate and Roof Type: In hot climates, heat resistance and UV durability are crucial. In cold or snowy regions, vapor permeability and moisture handling matter more.

Benefits And Limitations

• Benefits: Cost-effective moisture protection, additional weather barrier during construction, compatibility with most roofing systems, and ease of installation.
• Limitations: Some felt types are sensitive to UV exposure, may degrade over time if left exposed, and not all options provide the same level of water resistance as modern synthetic underlayments.

Environmental And Safety Considerations

Manufacturers increasingly offer low-VOC emissions and recyclable packaging. When disposing of old felt, follow local guidelines for asphalt-impregnated materials. From a safety perspective, wear gloves and eye protection during handling to avoid skin and eye contact with adhesives or fibers. Proper storage away from moisture maintains product integrity before installation.

Alternatives And Complementary Systems

• Synthetic Underlayments: Made from polyethylene or polypropylene, these underlayments offer higher tear resistance, lighter weight, and better longevity in UV exposure.
• Self-Adhering Roof Underlayments: Combine moisture sealing with convenience, especially on complex roof lines or areas prone to leaks.
• Ice And Water Shield: A specialized underlayment used at eaves and around penetrations to prevent ice dams and leaks in freezing conditions.
• Ventilation Considerations: Adequate attic ventilation reduces moisture buildup behind the underlayment, improving overall roof health.

Best Practices For Homeowners

• Consult Local Codes: Some regions require specific underlayment types or wind-rated products for code compliance.
• Match With Roofing Material: Ensure the underlayment is compatible with the chosen shingles or metal roofing to optimize performance.
• Inspect During Installation: Check that seams are properly sealed and that the underlayment lies flat with no wrinkles or gaps.
• Performance In Different Climates: For coastal areas, opt for moisture and salt-resistant products; for mountain regions, prioritize wind resistance and UV durability.