Tar paper, also known as roofing felt, is a traditional underlayment used during roof construction and repairs. This article explains how tar paper behaves in rainy conditions, its protective capabilities, and how it fits with modern roofing systems. By understanding its role, homeowners can make informed decisions about underlayment choices, installation practices, and potential weather-related risks.
What Tar Paper Is And What It Does
Tar paper is a layered sheet of paper saturated with asphalt or bitumen, designed to provide a secondary barrier against moisture. Its primary function is to prevent water infiltration from entering the attic space or interior structure during installation and between roofing layers. On many roofs, tar paper sits beneath shingles, tiles, or metal panels and above the roof deck, serving as a deck protection and moisture barrier. While it helps reduce water intrusion, tar paper is not a stand-alone roof waterproofing solution and should be used in conjunction with proper flashing, sealing, and ventilation.
Tar Paper In Rainy Conditions: What To Expect
Tar paper can resist some moisture when dry or slightly damp, but prolonged exposure to rain challenges its performance. Classic asphalt-saturated felt swells and tears more easily when wet, and heavy rainfall can cause it to lose flexibility and strength. If tar paper becomes saturated, it can become heavier and may sag, potentially creating gaps under the shingles. In addition, repeated wetting and drying cycles can lead to wear over time. The takeaway is that tar paper offers temporary protection during construction or emergency conditions, but it is not a durable waterproof barrier in sustained rain.
When Tar Paper Is Most Effective
Tar paper shines in three scenarios: during installation, as a temporary shield when a roof is open, and as a secondary backup in certain climate zones. During installation, tar paper protects the roof deck from wind-driven rain before shingles are laid. In emergencies, if weather shifts and a roof deck is exposed, tar paper can help minimize direct water contact. In some traditional or budget-friendly projects, it provides an extra layer of moisture control below the final roofing material. However, its long-term effectiveness relies on timely completion of the final roofing system and proper detailing at joints and penetrations.
Limitations Of Tar Paper As A Rain Barrier
- Not Waterproof By Itself: Tar paper is a moisture barrier, not a fully waterproof membrane. It can allow slow leakage under sustained rain or wind-driven moisture.
- Vulnerability To Damage: Wind, foot traffic, and improper handling can tear or puncture tar paper, creating weak spots.
- Degradation Over Time: Exposure to sun, heat, and weather accelerates wear; older tar paper loses flexibility and resilience.
- Compatibility With Modern Materials: Synthetic underlayments have largely replaced traditional tar paper due to superior waterproofing and durability.
Modern Alternatives And Best Practices
Today, many roof assemblies use synthetic underlayment or self-adhering membranes that provide better waterproofing, durability, and ease of installation. These materials perform well in rain, resist tearing, and maintain weather protection during installation. When choosing underlayment, consider climate, roof slope, roof pitch, and local building codes. If tar paper is used, it should be installed with care and paired with high-quality flashing and sealants to minimize water entry points.
Best Practices For Using Tar Paper On A Roof
- Ensure the roof deck is dry, clean, and free of protrusions before installing tar paper.
- Install underlayment during dry conditions if possible; avoid prolonged exposure to heavy rain before the final roof covering is installed.
- Follow manufacturer guidelines for nailing or stapling patterns and ensure edges overlap adequately to minimize gaps.
- Pay extra attention to around chimneys, vent pipes, and roof valleys; use appropriate flashing and sealant to reduce water entry paths.
- Limit Handling Time: Minimize foot traffic on tar paper to prevent tearing; use planks or temporary walkways when working on the roof.
- Plan For Replacement: If tar paper is part of a temporary setup, schedule the final roofing material installation promptly to avoid long-term exposure.
How Tar Paper Fits Into A Complete Roofing System
In a complete roofing system, tar paper is typically the layer immediately above the roof deck and beneath the final roofing material. It works in concert with underlayment fasteners, waterproof flashing, ridge caps, and valley protections. The final roofing material—shingles, tiles, or metal—provides the primary waterproof barrier, while the underlayment adds a secondary defense against moisture intrusion. In regions with heavy rain, snow, or freeze-thaw cycles, a more robust underlayment is often recommended.
Safety Considerations And Maintenance
Roof work requires safety measures to prevent injury. Use fall protection, stable ladders, and proper footwear. If tar paper becomes wet during installation, avoid stepping on it until it dries or is covered by the final roof material. After installation, inspect for exposed edges, gaps, or damaged sections, especially after storms. Regular maintenance should focus on ensuring flashing remains intact and that water channels are clear of debris to keep moisture from seeping under the underlayment.
Conclusion: Is Tar Paper Still Worth It?
Tar paper can provide valuable temporary protection during roof installation and serve as a secondary moisture barrier in certain contexts. However, it is not a substitute for modern, high-performance underlayments designed to perform in rain and long-term weather exposure. For best results, consider synthetic underlayment or self-adhering membranes for new roofs, particularly in areas with frequent rain or severe weather. If tar paper is used, follow proper installation practices and pair it with robust flashing and timely completion of the final roof covering to minimize water intrusion risks.