Tar paper, or roofing felt, is a foundational layer used under shingles to provide moisture protection, insulation, and a stable base for roofing materials. This guide explains how to choose the right felt, prepare the roof, and apply tar paper correctly to extend roof life. It covers safety considerations, common mistakes, and maintenance tips, with practical, step-by-step instructions tailored to American homes.
Preparation And Materials
Effective tar paper installation starts with proper preparation and the right materials. Homeowners should choose the correct felt weight for their climate and roof pitch. Common options include:
- Standard felt (15-pound or 30-pound) for most asphalt shingle installations.
- Heavyweight felt (30-pound or higher) for steeper pitches or areas with high wind exposure.
- Organic or fiberglass-backed felt with good tear resistance and dimensional stability.
Before laying tar paper, inspect the roof deck for damage, loose boards, or protruding nails. All gaps and rot should be repaired. Clean debris, ensure the underlayment is dry, and remove any old roofing remnants that could interfere with adhesion. Weather conditions influence timing: install when dry and calm to prevent moisture trapping beneath the felt.
Tools And Materials
Having the right tools reduces installation errors and speeds up the process. Essential items include:
- Roofing nails with wide heads and plastic caps to prevent pull-through.
- Nail bar or roofing nailer for consistent nail placement (optional but efficient).
- Utility knife for trimming and cutting the felt
- Tape measure and chalk line for straight alignment
- Roofing felt starter strips to begin the first row
- Lath or battens if required by local code or roof type
- Adhesive or sealant for edging and flashing seams (where applicable)
- Scaffolding or stable ladder and appropriate fall protection for safety
Safety Considerations
Roof work can be hazardous. Wear non-slip footwear, use fall protection, and check weather forecasts to avoid wet or windy conditions. Keep tools secure to prevent slipping or dropping hazards. If the roof is steep or you are uncomfortable with heights, consider hiring a professional roofer.
Step‑By‑Step Application Process
The following steps outline a typical installation for asphalt shingles with tar paper as underlayment. Always follow local building codes and manufacturer guidelines.
- Lay starter strips: Begin along the eaves with starter strips that extend slightly over the drip edge. This creates a clean starting line and helps seal the first row of shingles.
- Roll out the felt: Unroll felt from the lower edge up the roof. Overlap each subsequent strip by about 2 to 4 inches (5 to 10 cm) to ensure water shedding. Maintain tension to prevent wrinkles.
- Align and secure: Position the felt so it covers the entire deck with the edge aligned to the eave. Use nails about every 12 to 18 inches (30 to 45 cm) along the top and bottom edges and in the field, ensuring the nail heads lie flat and flush.
- Stagger seams: When starting a new roll, offset seams from the previous row by at least 4 inches (10 cm) to reduce leak risk. Subsequent rows should maintain this staggered pattern.
- Seal edges and fasten: Secure the edges by driving nails at the edges through the felt. Avoid over-nailing near the edges to prevent tearing.
- Check for wrinkles and bubbles: If any air pockets form under the felt, gently lift and reseat the material to prevent improper drainage.
Overlapping And Nailing Pattern
The overlap and nail pattern are critical for long‑term performance. A common practice is to overlap 2 to 4 inches (5 to 10 cm) horizontally and vertically. Nails should penetrate the sheathing by at least 3/4 inch (2 cm) and be driven straight. Start with nails at the upper edge, then place nails along the center of each strip to secure the seam. Excessively long edges may require extra nails at ends to resist wind uplift.
Sealing Edges, Seams, And Flashing
Proper sealing around edges, hips, valleys, and flashing is essential to prevent water intrusion. Apply tar paper over flashing where applicable, ensuring the paper sits flush against vertical surfaces. For valleys, consider installing additional protection such as valley metal—but if using felt, lay the paper with extra careful overlap and secure with nails along both sides. Seams should be tight, with no gaps that could trap moisture. For roof penetrations, seal underlayment around pipes, vents, and chimneys using compatible sealants or flashing membranes as specified by the underlayment and roofing material manufacturers.
Common Mistakes And Troubleshooting
- Wrinkles and air pockets: These create weak spots and potential leaks. Reseal by lifting the affected area and retying the felt flat.
- Inadequate overlaps: Too little overlap can allow water intrusion at seams. Re‑lay affected strips if necessary.
- Over‑nailing or tearing near edges: Keep nails at a consistent distance from edges to avoid tearing the felt.
- Installing on wet or frosty days: Moisture reduces adhesion and can lead to mold or delamination. Wait for dry conditions.
- Ignoring code specifics: Some regions require separate self‑adhering underlayment or additional layers under certain roof types. Always verify local building codes.
Maintenance And Longevity
Tar paper underlayment contributes to roof longevity when installed correctly and maintained. Inspect the roof seasonally for torn edges, loose nails, or moisture signs. Clear debris from the roof and ensure gutters and downspouts are free of obstructions to prevent water backup. If the roof deck shows signs of moisture damage, treat or replace damaged sections promptly. Periodic re‑inspections after severe weather help catch issues before they become costly repairs.
Tips For American Homes
- Match felt weight to climate and roof pitch; steeper roofs and windy regions benefit from heavier felt.
- Always follow manufacturer instructions for underlayment and shingles, as some products require self‑sealing tapes or membranes along seams.
- Prioritize dry, calm days for installation to ensure proper adhesion and a clean finish.
- Consider a self‑adhering membrane in areas with high wind or frequent rain for additional protection.