Tar Paper on Roof: Understanding Its Purpose

Tar paper, commonly known as roofing felt, serves as an essential layer in many roofing assemblies. This underlayment sits between the roof decking and the final shingles or tiles, offering a moisture barrier, temporary protection during construction, and a smoother surface for shingle installation. While modern roofs increasingly use synthetic underlayments, traditional asphalt-saturated felt remains widely used for its cost effectiveness and proven performance in varied climates. Understanding its purpose helps homeowners and builders choose the right products and installation strategies for long-lasting roofs.

What Is Tar Paper On Roof?

Tar paper is a heavy, paper-like material saturated with asphalt or bitumen. It is designed to be laid over roof decking before the final roofing material is installed. The term “roofing felt” covers both asphalt-saturated felts and newer synthetic alternatives, though tar paper specifically notes the traditional asphalt composition. In many markets, you will see a weight rating (for example, 15-pound, 30-pound) indicating the material’s strength and tear resistance. The primary role is to act as an underlayment that accompanies the roof’s waterproofing strategy.

How It Works As Roofing Underlayment

Tar paper functions as a secondary moisture barrier. It is not meant to replace a roof’s primary waterproofing system but to complement it. When installed correctly, the underlayment helps seal minor gaps and provides a path for incidental moisture to escape rather than penetrating the attic space. It also adds a forgiving surface for shingles, reducing the risk of fastener misplacement and helping to prevent wind-driven water from reaching the decking during storms. In cooler climates, the warmth of the underlayment can aid in sealing shingles during installation, improving performance for the finished roof.

Key Benefits Of Tar Paper

• Moisture Protection: Acts as a secondary barrier against water that bypasses the outer roofing layer, such as ice dams or wind-driven rain.
• Decking Protection: Shields the roof deck from exposure to humidity and temperature fluctuations during construction and after installation.
• Surface For Fastener Guidance: Provides a stable surface for nail and staple placement, reducing deck splintering and aiding proper shingle seating.
• Temporary Weather Barrier: Offers limited protection during wet weather before final roof materials are fully sealed.
• Cost-Effective Option: Provides a budget-friendly underlayment solution in many traditional roofing systems.

When To Use Tar Paper

Tar paper is commonly installed in traditional asphalt shingle roofs, wood shingle systems, and some metal roof assemblies that require a conventional underlayment. It remains prevalent in renovations or repairs where existing roofing structures expect a familiar, proven component. Local building codes may permit or require specific underlayment types based on climate, slope, or roof design. In regions with heavy snowfall or frequent freeze-thaw cycles, an adequately rated underlayment becomes crucial to manage moisture and protect interior spaces during winter months.

Common Myths And Misconceptions

Several myths surround tar paper that can influence installation decisions. One misconception is that tar paper alone guarantees waterproofing; in reality, it is a secondary layer and relies on the outer roofing material to provide primary protection. Another myth is that all underlayments are the same; in truth, there is a spectrum from traditional asphalt-saturated felts to modern synthetic underlayments, each with distinct performance characteristics. Finally, some assume underlayment is optional in dry climates, but proper installation can still improve deck longevity and provide a buffer against wind-driven rain or hail damage.

Installation Considerations And Alternatives

Proper installation is critical for tar paper to deliver its intended benefits. The underlayment should be laid with a deliberate pattern that ensures overlapping seams, typically with a headlap to prevent water infiltration. Fasteners must be secured per manufacturer specifications to minimize wind uplift, especially on vented or flat roof sections. Ventilation and attic insulation play a complementary role, reducing condensation that can originate from within the roof assembly.

Alternatives to traditional tar paper include synthetic underlayment products, which often offer superior tear resistance, lighter weight, and better performance in extreme temperatures. Some builders prefer metal or rubberized underlayment in highly exposed locations, while others integrate multiple layers, such as a self-adhering membrane at eaves and green areas to combat ice dam formation. The choice depends on climate, roof pitch, exposure, and the contractor’s experience.

Key installation tips include inspecting the roof deck for damage before laying underlayment, ensuring clean and dry surfaces, and using compatible accessories for flashing and edge details. Periodic inspection after severe weather can catch issues early, such as blistering or punctures, allowing timely repairs to maintain roof integrity.

Why Tar Paper Remains Relevant In U.S. Roofing

In many parts of the United States, tar paper provides a reliable, time-tested solution that aligns with budget constraints and local building traditions. It also serves as a bridge between older roofs and modern upgrades, allowing homeowners to maintain effective protection without a full system overhaul. When combined with proper ventilation, accurate slope calculations, and appropriate flashing details, tar paper can contribute to a durable roof that stands up to seasonal shifts and moisture challenges.

For homeowners considering roof upgrades, it is essential to consult local codes and a qualified contractor. They can assess whether asphalt-saturated felt, a synthetic underlayment, or a hybrid approach best fits climate, roof design, and expected service life. Regular maintenance—such as clearing debris, inspecting for punctures, and ensuring proper drainage—helps preserve the underlayment’s performance over time.

In summary, tar paper on the roof serves several practical roles: it supplements waterproofing, protects the decking during construction, aids shingle installation, and provides an economical layer that enhances overall roof durability. Understanding its purpose helps ensure proper selection, installation, and long-term performance of the roofing system.