Tar paper, also known as asphalt-saturated felt, remains a foundational weather barrier in many exterior wall assemblies. This guide explains how to install tar paper on exterior walls correctly, highlighting best practices for durability, moisture management, and compatibility with siding and flashing. By understanding the purpose, materials, and step-by-step process, homeowners and contractors can ensure a robust wall system resistant to rain, wind, and temperature fluctuations.
Before beginning, identify the project scope and local building codes. Tar paper is typically used behind durable claddings or as a secondary barrier in conjunction with other weather-resistive barriers. While newer synthetic membranes have gained popularity, tar paper offers cost-effective protection when installed with proper overlaps, fasteners, and flashing details. The focus here is on exterior walls, where proper layering and edge treatment are essential for long-term performance.
What Is Tar Paper And Why Use It?
Tar paper is an asphalt-saturated felt product designed to shed water and provide a breathable yet water-resistant layer. It functions as a secondary weather barrier behind siding or brick, helping to prevent moisture intrusion from exterior rainfall. Tar paper differs from roofing felt in thickness and application patterns, and it should be installed per manufacturer guidelines and local code requirements.
Key benefits include a simple, familiar installation process, crack-bridging capability, and compatibility with traditional wood or fiber-cement siding. Poor installation can lead to trapped moisture, mold growth, and wood rot, underscoring the need for proper overlaps, fastener spacing, and corner/edge protection. When used correctly, tar paper contributes to a durable, rot-resistant wall assembly.
Tools And Materials Needed
Assemble a complete set of tools and materials before starting. This reduces interruptions and ensures consistent installation. Essential items include a sharp utility knife, siding nails or staples, a chalk line, measuring tape, straightedge, a hammer, a utility knife, and waterproof construction adhesive as needed. Materials should include tar paper or asphalt-saturated felt, appropriate fasteners for the wall substrate, corner and edge flashing, and compatible sealant for seams and penetrations.
Choose tar paper with a weather-resistant backing and ensure it is rated for exterior use. The product should specify compatible sheathing or siding types and acceptable exposure times. For regions with high wind exposure or heavy precipitation, consider heavy-duty tar paper or a builder-approved alternative with enhanced tear resistance and longer life expectancy.
Preparing The Wall Surface
Proper wall preparation is essential for tar paper performance. Clear debris, repair any damaged sheathing, and ensure a clean, dry surface. Remove loose paint and protrusions that could snag the tar paper. If the wall has existing moisture damage, address it before installation by fixing leaks and allowing sufficient drying time.
Inspect windows, doors, and penetrations for proper flashing and sealant compatibility. Install any required moisture barriers or drainage channels according to local code and manufacturer guidelines. A clean, dry base promotes adhesion and reduces the risk of blistering or tearing once tar paper is laid.
Installing Tar Paper On Exterior Walls
Start at one corner of the wall and work horizontally or vertically according to the wall design and siding type. Place the tar paper with the asphalt side facing outward and the felt surface against the sheathing. Overlap adjacent sheets by a minimum amount specified by the manufacturer, typically 2 to 4 inches, to ensure effective water shedding.
Secure tar paper with corrosion-resistant fasteners appropriate for the substrate, spacing fasteners per the product instructions. Avoid over-tightening, which can cause tearing or wrinkling. As sheets are applied, keep them flat and wrinkle-free to prevent moisture pockets. Cut precisely around windows, doors, and other openings to maintain a tight seal.
When wrapping around corners or edges, use corner flashing or pre-formed corner pieces to maintain continuous protection. At seam intersections, maintain a consistent overlap direction and ensure the seals are protected by siding or flashing components. If additional layers of weather barrier are necessary due to code or manufacturer requirements, install them in the correct sequence to avoid trapping moisture.
Sealing And Edges
Seams and edges require careful sealing to prevent wind-driven rain infiltration. Apply a compatible sealant or flashing tape over exposed seams at critical locations, especially around penetrations and along door and window frames. Ensure that sealants are compatible with tar paper, siding, and flashing materials to avoid chemical reactions or deterioration.
For all penetrations, run flashing under the tar paper and over the sealant to create a continuous drainage path. Maintain a slight slope or drainage plane away from the wall plane to direct moisture toward the exterior. Avoid overlapped seams that create tight gaps where water can accumulate; instead, maintain consistent overlap to promote shedding.
Integrating With Siding And Flashing
Tar paper installation should be integrated with the chosen exterior cladding. When installing siding, ensure the siding’s starter strips and fasteners do not compromise the tar paper layer. Flashing at windows, doors, and roof lines should be designed so that water flows over the tar paper rather than behind it. The use of continuous flashing at changes in plane reduces the risk of moisture intrusion.
In some siding systems, a drainage plane or rainscreen may be installed in front of the tar paper to improve air circulation and moisture management. When combining tar paper with such systems, follow both the tar paper manufacturer’s guidelines and the cladding manufacturer’s installation instructions to avoid warranty issues and ensure long-term performance.
Maintenance And Common Issues
Tar paper installations should be inspected periodically for signs of damage, such as tears, blistering, or loosening at edges. Address any damage promptly to prevent moisture intrusion. If the wall has sustained hail or high winds, check for punctures or peeled edges and re-seal as needed. Periodic maintenance can extend the life of the weather barrier and protect the interior from moisture-related problems.
Common issues include improper overlaps, insufficient fastener counts, and poor edge treatment. In warmer climates, excessive heat can cause tar paper to become brittle or warp; in colder climates, it may stiffen and crack. Choosing the right type and thickness for the climate, plus correct installation, mitigates these risks.
Safety Considerations
Follow standard construction safety practices when handling tar paper and installing on exterior walls. Use gloves to protect hands from sharp edges, eye protection when cutting, and a sturdy ladder or scaffold for elevated work. Ensure the work area remains weather-safe, and postpone tasks during high winds or heavy rain to prevent accidents and improper installation.
Dispose of waste materials according to local regulations. Store tar paper and flashing components in a dry, protected area to prevent degradation before use. Adhere to manufacturer instructions for any waterproofing products, sealants, or flashing specifics to maintain warranty coverage and performance.
Key Takeaways: Tar paper provides an economical secondary weather barrier when installed with proper overlaps, edge flashing, and compatible cladding. Preparing the wall, selecting the right product, and integrating with flashing details are essential for durable exterior walls. Regular inspection and timely maintenance help ensure long-lasting protection against moisture and weather.