What Is Roofing Paper: A Practical Guide for Homeowners

Roofing paper, commonly known as roofing felt or tar paper, is a crucial underlayment layer installed beneath shingles or other roofing materials. It acts as a secondary barrier against moisture, wind, and vapor and helps protect the roof deck during construction and in service. Understanding what roofing paper does, the different types available, and how it is installed can help homeowners make informed decisions about roof performance, durability, and value.

What Roofing Paper Is

Roofing paper is a sheet material designed to provide temporary and, in some cases, long-term protection for the roof structure. Most traditional roofing paper is made from asphalt-saturated felt or a synthetic alternative. The primary function is to create a moisture barrier that reduces the risk of water penetrating the roof deck if shingles are damaged or wind-driven rain occurs. In some climates, roofing paper also serves as a starting point for vapor control, helping manage condensation inside the roof assembly.

Types Of Roofing Paper

Roofing paper comes in several varieties, each with distinct properties and best-use scenarios. The main categories are:

• Asphalt-Saturated Felt (Tar Paper): The classic option, typically available in 15-pound (33 g/m²) and 30-pound (67 g/m²) weights. It provides basic moisture protection and is common on many older and mid-range roofs.
• Synthetic Roofing Underlayment: Made from polymers such as polypropylene or polyethylene, these underlayments offer superior durability, resistance to tearing, and often better water shedding. They are lighter and can be more weather-resistant than felt.
• Self-Adhering Underlayment: A peel-and-stick variant with an adhesive backing. It provides excellent wind and moisture resistance, reducing the risk of wrinkles and gaps during installation.
• Ice and Water Shield: A specialty underlayment with a self-adhesive, waterproof membrane designed to protect vulnerable areas like eaves, roof valleys, and around chimneys where ice damming can occur.
• Breathable vs. Non-Breathable: Some underlayments are semi-permeable to allow vapor to escape, while others are designed to be fully waterproof. The choice depends on local climate and roof design.

Uses And Applications

Roofing paper serves multiple purposes across different roof systems. Key applications include:

• Weather Barrier During Construction: It protects the plywood or OSB roof deck from rain before shingles are installed, preserving the structural integrity of the roof framing.
• Moisture Control After Installation: It provides a secondary layer of protection if shingles are damaged or blown off, preventing water from directly soaking the deck.
• Vapor Management: In some assemblies, underlayment helps control moisture movement within the roof, reducing the risk of mold and rot in colder, more humid environments.
• Wind-Driven Rain Protection: A high-quality underlayment can improve performance in windy regions, reducing the chance of water infiltration through gaps around fasteners.

Benefits And Limitations

Understanding the benefits and limitations helps homeowners select the right product for their roof and climate.

• Benefits: Provides an extra moisture barrier, protects the roof deck during construction, enhances wind resistance when installed correctly, and can improve roof longevity when combined with proper flashing and drip edge details.
• Limitations: Some traditional felts can tear or degrade in extreme heat, and older asphalt-based products may shrink or wrinkle if not installed properly. Synthetic and self-adhering options generally cost more but offer superior durability and easier installation.

Installation Considerations

Proper installation is critical to the performance of roofing paper. Consider these guidelines:

• Climate-Driven Choice: In wet or freeze-thaw climates, premium underlayments (synthetic or self-adhering) provide better protection against moisture intrusion and wind uplift.
• Overlap And Alignment: Typical practice is to overlap courses by 2 to 4 inches horizontally and 4 to 6 inches vertically, ensuring continuous coverage and preventing water intrusion at seams.
• Nailing And Fasteners: When using felt, fasten with corrosion-resistant nails or staples as recommended by the manufacturer. With self-adhering products, follow the adhesive guidelines and ensure a clean, dry surface for reliable adhesion.
• Flashing Integration: Roofing paper works in coordination with flashing around chimneys, vents, and valleys. Proper flashing installation is essential to prevent leaks where layers meet other roof components.
• Ventilation: Adequate attic ventilation reduces moisture buildup, which can affect underlayment performance and overall roof health.

Choosing The Right Roofing Paper

Selecting the right underlayment involves climate, roof type, and budget considerations. Key factors include:

• Climate And Weather: Wet or icy regions benefit from self-adhering or ice-and-water shield products at critical points such as eaves and valleys.
• Roof Type: Asphalt shingles commonly use standard felt or synthetic underlayment, while metal roofs may require breathable membranes designed for metal fasteners.
• Installation Surface: Dry, clean OSB or plywood supports better adhesion for self-adhering products and reduces the risk of gaps or wrinkles.
• Warranty And Code Requirements: Local building codes may specify minimum underlayment requirements; manufacturer warranties vary by product and installation method.
• Budget: Synthetic and self-adhering underlayments typically cost more upfront but can offer longer-term durability and faster installation.

Maintenance And Longevity

Roofing paper’s performance hinges on correct installation and subsequent roof care. Consider these maintenance tips:

• Inspection After Severe Weather: Check for punctures, tears, or exposed edges, especially after storms. Damaged sections should be repaired or replaced promptly.
• Avoid Early Exposure: Prolonged sun exposure before shingle installation can degrade some felt products. Follow manufacturer guidelines for exposure times.
• Combine With Proper Shingle Installation: Underlayment is part of an overall system. Ensure shingles are installed with proper nailing patterns and flashing to maximize longevity.
• Seasonal Checks: In climates with freeze-thaw cycles, inspect for ice dam-related issues and ensure ice and water shield coverage remains intact in critical areas.

Common Misconceptions

Several myths about roofing paper can mislead homeowners. Debunking these helps with informed decisions:

• All Underlayments Are the Same: Performance varies widely by material, thickness, and installation method. Higher quality underlayments often provide better protection and ease of use.
• Underlayment Is Optional: In many regions, building codes require a functional underlayment. Skipping it can void warranties and increase leak risk during heavy rainfall or construction delays.
• More Thickness Always Means Better: Thickness matters, but the product type and integrity of installation are equally important. A high-quality synthetic product can outperform a cheaper felt with proper installation.

Roofing paper remains a foundational element of a durable roof assembly. By selecting the right type, adhering to installation best practices, and integrating it with flashing, insulation, and ventilation, homeowners can enhance moisture resistance, improve longevity, and protect the roof deck through the life of the roof.