How to Install Tar Paper for Roofing: A Step-by-Step Guide

Tar paper, or asphalt-saturated roofing underlayment, provides a moisture barrier between the roof deck and shingles. Installing it correctly protects the roof from leaks and helps extend the life of the shingles. This guide covers materials, preparation, and a clear step-by-step process to install tar paper on standard residential roofs in the United States. Follow local building codes and manufacturer recommendations for best results.

Materials And Tools

Having the right supplies on hand keeps the project moving smoothly. The following list covers common needs for applying tar paper on a typical pitched roof.

• Tar paper or asphalt-saturated roofing felt: 15-pound or 30-pound felt is common; 30-pound offers greater tear resistance.
• Roofing nails with caps or cap nails: Choose corrosion-resistant nails long enough to penetrate the decking by 3/4 inch.
• Stapler (optional): Some installers use a cap staple for lighter underlayment; confirm compatibility with your product.
• Nail apron or roofing hat: Keeps nails organized and reduces trips up the ladder.
• Chalk line, measuring tape, and markers: For straight, consistent laps.
• Utility knife: For trimming tar paper to fit around vents, chimneys, and edges.
• Roofing felt stripper or putty knife (optional): Useful for aligning edges and smoothing laps.
• Ladder and fall protection: Proper harnesses, guard rails, or stabilizers per local codes.
• Plywood or roof deck repairs (if needed): Patching damaged areas before underlayment.

Safety And Preparation

Preparation and safety are essential. Tar paper can be slippery when wet, and roof work carries fall risks. Follow these precautions before starting.

• Check weather: Install on dry, calm days. Do not apply tar paper in rain, snow, or when dew is present.
• Inspect the roof deck: Look for damaged, warped, or rotten boards. Replace or repair as needed.
• Secure the work area: Use proper fall protection and keep the area clear of debris.
• Plan the starting edge: Eaves are typically the starting edge; confirm any local variation.
• Measure and plan laps: Standard overlaps are 2 inches horizontally and 4 inches vertically for single-layer applications; follow manufacturer instructions if different.

Preparation Of The Roof Deck

A clean, dry deck ensures the tar paper adheres and lies flat. Prepare as follows.

• Remove debris: Clear dust, nails, and loose fibers from the deck.
• Dry fit and trim: Dry-fit the first row of tar paper sections to ensure proper width and alignment.
• Install any necessary flashing: If roof penetrations exist, install flashing or step-flash around vents, chimneys, and skylights before laying underlayment.
• Start at the eaves: Ensure the deck is dry and free of moisture to maximize adhesion.

Step By Step: Installing Tar Paper

The following steps outline a standard method for applying tar paper on a pitched roof. Adapt to your roof slope and product instructions.

1. Position the first row: Start at the eaves with the treated side (the side impregnated with asphalt) facing down toward the deck. Unroll a section and align it along the gutter line.
2. Overlap levels: Overlap the top edge by 2 inches over the bottom edge of the previous section, maintaining a uniform seam pattern across the roof.
3. Nail pattern and fasteners: Place nails about 6-8 inches apart along the edges and every 12-18 inches along the center, ensuring fasteners penetrate into the deck by at least 3/4 inch. Avoid driving nails too close to the edge to prevent tearing.
4. Lay subsequent rows: Roll out the next strip, aligning with the first row and maintaining a consistent 2-inch horizontal overlap and a 4-inch vertical offset, if required by the product guidelines.
5. Cut around penetrations: Use a utility knife to trim around vents, chimneys, and other protrusions. Leave adequate clearance for flashing details.
6. Check for air pockets: Smooth each section from the bottom up to prevent bubbles and wrinkles that can trap moisture.
7. Edge alignment: Ensure the side laps run over the previous sheet and are fully embedded in place before nailing down.

Overlaps, Seams, And Nailing

Efficient overlaps and secure fastening protect against wind-driven moisture. Keep these practices in mind.

• Horizontal overlaps: Ensure each row overlaps by 2 inches at the top seam to prevent leaks along the seams.
• Vertical seams: Offset vertical seams between courses to reduce potential leak lines, similar to standard shingle layouts.
• Nail coverage: Space nails along the edges and centers as recommended by the manufacturer. Check for uniform nail depth to prevent tearing.
• Edge protection: When installing along eaves and rakes, maintain a consistent edge line to simplify shingle installation afterward.

Common Mistakes To Avoid

Avoid typical issues that compromise the underlayment’s effectiveness and roof longevity.

• Using wrong underlayment type: Do not substitute roofing felt with a different underlayment type without confirming compatibility with shingles and adhesives.
• Inadequate overlaps: Skipping required overlaps increases the risk of leaks in heavy rain or wind.
• Prolonged exposure: Prolonged exposure to sunlight on underlayment without protection can cause deterioration; work efficiently and cover exposed edges promptly if needed.
• Improper fasteners: Use the wrong length or material can lead to loosening in windy conditions.

Maintenance And Inspection Tips

Routine checks help maintain roof integrity between major repairs or replacements.

• Seasonal inspection: Inspect after major storms or seasonal wind events for loose edges or lifted seams.
• Repair promptly: Replace damaged sections or re-nail edges to prevent moisture intrusion.
• Ventilation checks: Ensure roof ventilation remains unobstructed, which supports the effectiveness of underlayment and shingles.
• Compatibility reminder: If adding insulation or changing roofing materials later, confirm underlayment compatibility to avoid conflicts.