How to Lay Tar Paper: A Step by Step Guide

Tar paper, also known as roofing felt or asphalt-saturated felt, is a traditional underlayment used to provide a moisture barrier and improve roof durability. Properly laying tar paper helps prevent leaks, extends shingle life, and creates a more stable roof deck. This guide presents a clear, step-by-step approach for homeowners and professionals, with practical tips for different roof types and climates. The instructions emphasize safety, correct material selection, and best practices to ensure a durable, long-lasting roof.

What Is Tar Paper And Why It Matters

Tar paper is a heavy, paper-based underlayment treated with asphalt to resist moisture. It sits between the roof deck and shingles, acting as a secondary barrier against wind-driven rain and minor leaks. Tar paper also helps to seal small gaps and provides a smooth surface for shingle installation. In modern construction, synthetic underlayments are common, but traditional tar paper remains a cost-effective option in many regions. Understanding its role clarifies why proper installation is essential for roof longevity.

Tools And Materials You Will Need

Assemble the following before starting work to maintain a steady workflow:

• Tar paper rolls (roofing felt) in the correct weight for your climate (15-lb, 30-lb, or 40-mil synthetic options where applicable)
• Measuring tape and chalk line
• Roofing nails or staples, plus a hammer or nail gun
• Utility knife or shears
• Roofing nails with plastic caps or corrosion-resistant fasteners
• Chimney or vent flashing, cap flashing, and sealant
• Ladder, harness, and fall protection equipment as required
• Broom or blower for deck cleanliness

Choosing the right tar paper weight and type depends on local building codes and climate. In colder regions, a higher weight underlayment reduces the risk of tearing, while in hot climates, select a product rated for heat exposure to prevent warping.

Prepare The Roof Deck

Preparation is critical for a successful tar paper installation. Start by ensuring the roof deck is clean, dry, and free of protruding nails or debris. Lightly sweep the surface, remove any moss or dust, and fix any warped or damaged deck boards. If there are gaps or irregularities, plan to address them before applying underlayment to prevent wrinkles and tears. A smooth, dry deck reduces the likelihood of air pockets beneath the tar paper and improves adhesion of future shingles.

Measure And Plan For Coverage

Tar paper is typically installed in strips to cover the roof deck with an overlap that prevents moisture intrusion. Plan for an overlap of about 19 to 24 inches along the horizontal runs and 2 to 4 inches at vertical joints, depending on the product and local code. Mark lines with a chalk line to ensure straight placement across the roof. For rakes, start at the bottom edge and work upward to maintain proper orientation and wind alignment.

Apply The First Layer And Secure Properly

Begin at the eave with the first row, placing tar paper so the bottom edge overlaps the fascia and any drip edge. Secure the edge with nails or staples every 6 to 8 inches along the horizontal run, ensuring fasteners are driven perpendicular to the deck. Do not drive fasteners too deeply, which can tear the paper, or too shallow, which can cause loosening in wind. Keep the sheet flat with no major wrinkles, and avoid stretching the paper during placement.

Overlap And Seam Techniques

Each subsequent strip should overlap the previous one by the recommended amount. For asphalt-saturated tar paper, typical overlaps range from 2 to 4 inches along vertical seams. If weather conditions are windy or rainy, temporarily secure with a few starter nails while you align the next sheet. Ensure seams are staggered if multiple sheets are used, which strengthens the overall layer and reduces the risk of leaks at joints.

Flashing And Penetrations

Flashing around chimneys, vents, and skylights is essential for a watertight roof. Install tar paper up to the underflashing area, then apply metal or flexible flashing over the underlayment. Seal all edges with roofing sealant designed for tar paper compatibility. For roof penetrations, cut slits in the tar paper to fit flashing pieces and secure them with nails or sealant. Ensure a smooth transition between underlayment and flashing to prevent moisture pockets.

Special Considerations For Roof Type

Pitch and roof design influence tar paper installation. Low-slope roofs (<2:12 pitch) may require additional waterproof membranes or a higher weight underlayment to mitigate potential leakage. Steeper roofs require careful handling to avoid tearing during installation and wind uplift. In areas with heavy snowfall or rain, additional overlaps and secure fasteners reduce the risk of wind-driven edges peeling away. Always follow local building codes and manufacturer guidelines for your specific roof type.

Ventilation, Safety And Maintenance

Safety is essential when working on roofs. Use proper fall protection, stable ladders, and non-slip footwear. Work on dry days to prevent slipping and to ensure tar paper adheres properly. After installation, inspect for loose edges or ridges after severe weather. Periodic maintenance includes clearing debris, checking flashing seals, and replacing damaged sections to maintain the integrity of the underlayment over time. Keeping the deck clean and dry extends the life of both the tar paper and the roof system.

Common Mistakes To Avoid

• Skimping on overlaps or improper seam alignment
• Installing on a damp or dirty deck, which reduces adhesion
• Driving fasteners too deeply or too shallowly
• Neglecting flashing integration with the underlayment
• Using tar paper past its service life or unsuitable for climate conditions

Avoiding these pitfalls improves the underlayment’s performance and helps prevent leaks during heavy rain or wind. When in doubt, consult a professional roofer for evaluation and installation guidance.

Maintenance And Longevity Of Tar Paper

Tar paper underlayment is designed to protect the roof deck for a limited period, typically until the final shingle layer is installed. Its lifespan depends on climate, exposure, and installation quality. Routine inspections after storms should check for wrinkles, tears, or lifted edges. If damage is detected, replace the affected section promptly to maintain a continuous moisture barrier. In newer homes, synthetic underlayments may offer longer life and easier handling, but tar paper remains a cost-effective option in many builds when installed correctly.

References And Best Practices

Effective tar paper installation aligns with manufacturing instructions and local building codes. Best practices include keeping the deck dry, using proper overlaps, ensuring secure fasteners, and integrating flashing correctly. For homeowners, starting with a clean slate and following step-by-step measurements reduces errors. Always verify that the chosen tar paper weight and type meet climate-specific requirements and roof slope guidelines.