Tar paper, also known as roofing felt or building paper, serves as a moisture barrier beneath shingles, siding, or other exterior finishes. Proper installation protects structures from water intrusion, improves insulation performance, and extends roof or wall life. This guide provides a clear, step‑by‑step approach to installing tar paper, covering material choices, tools, safety, and best practices for both roofing and wall applications.
Understand Tar Paper And Its Uses
Tar paper comes in several weights and grades, typically measured by pounds per square (lb) or by thickness. Heavier felt, such as 15‑lb or 30‑lb, offers greater tear resistance and durability during installation. Modern synthetic alternatives provide improved longevity and moisture resistance, but traditional asphalt‑based tar paper remains common in many projects. For roofing, tar paper acts as a secondary barrier against wind-driven rain, helping prevent leaks if shingles are damaged. On walls, it provides a vapor barrier and a surface for siding to grip.
Choose The Right Material
Key considerations include climate, roof pitch, and the type of exterior finish. In colder climates or areas with heavy rainfall, a more durable underlayment—such as a heavy‑weight felt or a synthetic option—is advisable. For wood shingles or shakes, tar paper underlayment must be compatible with flashing details around chimneys, vent pipes, and valleys. When using asphalt‑based tar paper, verify that the backing is rated for roof exposure and that the product is designed for roof or wall applications as appropriate.
Gather Essential Tools And Materials
- Tar paper in the appropriate weight and width
- Roofing nails or staples (galvanized or aluminum, depending on the substrate)
- Nail gun or hammer
- Utility knife with sharpened blade
- Measuring tape and chalk line
- Roofing felt roller or brush (optional for flat installations)
- Lubricant or release agent for smooth overlaps (optional)
- Lint free wipe or rags for cleaning
- Safety gear: gloves, hard hat, non‑slip footwear, fall protection as required
Prepare The Surface
A clean, dry substrate is essential for tar paper adhesion. Inspect the roof decking or wall sheathing for damage and repair as needed. Remove dirt, dust, and protruding nails that could snag the felt. For roofs, ensure the roof is dry and free of standing water or snow. For walls, ensure siding or sheathing is compatible with underlayment and flashing details. Proper preparation reduces wrinkles, air pockets, and blistering after installation.
Install Tar Paper On A Roof
- Start at the eave and unroll the first strip so the upper edge overlaps the drip edge. Maintain a slight overhang beyond the edge to shed water.
- Roll out the tar paper across the roof deck toward the ridge, aligning with rafter lines. Avoid bunching or tearing the material.
- Sustain a consistent 19–21 inch overlap between adjacent strips for most residential applications, or follow manufacturer specifications. Maintain a straight orientation using chalk lines.
- Nail the tar paper every 4–6 inches along the edges with corrosion‑resistant roofing nails. Place fasteners within 1 inch of the edge to prevent wrinkling, but not so close as to tear the material.
- Overlap the second strip with the same alignment, ensuring the nailing strip sits on the lower sheet’s upper edge to avoid exposed nails on the surface.
- Continue working up the roof, periodically checking for air pockets or wrinkles. If found, gently smooth them out with a gloved hand or a roller designed for underlayment.
- At hips, ridges, and around protrusions, cut the tar paper to fit, maintaining the required overlaps and proper flashing procedures around vents and chimneys.
- Edge treatment: Extend tar paper a bit over eaves and underlayment flashing to direct water away from the fascia and into gutters. Secure with nails along the edges, ensuring clean lines and proper wind‑driven rain protection.
Install Tar Paper On A Wall Or Sheathing
- Begin at the bottom of the wall, aligning the first sheet with the base plate or starter strip as specified by the manufacturer.
- Unroll horizontally or vertically depending on weather exposure, ensuring consistent overlaps of 2–4 inches between sheets. The overlap direction should prevent wind-driven water from penetrating the seams.
- Nail the sheets along the edges at regular intervals, avoiding excessive nailing that could crack the sheathing. Use corrosion‑resistant nails or staples recommended by the tar paper manufacturer.
- Overlap and secure each subsequent sheet, maintaining a taut, wrinkle‑free surface. For exterior walls, consider installing a drainage plane behind the tar paper if the siding requires it.
- Cut around openings such as windows and doors with a utility knife, leaving generous clearance for flashing and sealants to maintain a water barrier.
Flashing And Seals: Critical Details
Flashing is essential where tar paper meets roof edges, chimneys, vents, dormers, and transitions to different materials. Install flashing first where possible, then cover with tar paper. At joints, use appropriate tape or sealant as recommended by the tar paper manufacturer to seal seams and prevent air infiltration. Proper sealing around vents and penetrations reduces the risk of leaks and improves long‑term performance.
Safety Considerations
Handle tar paper with care to avoid skin irritation from asphalt materials. Use gloves and eye protection when cutting. For roofing projects, employ fall protection and stable ladders. Work in dry weather to prevent slippery surfaces. Dispose of damaged or waste tar paper according to local regulations. Ensure that scaffolding, ladder access, and job site cleanup comply with safety standards to prevent injuries.
Quality Assurance And Maintenance
After installation, inspect the entire surface for gaps, wrinkles, or loose nails. Touch up any exposed fasteners and reseal edges as needed. Periodically check the underlayment from within the attic or crawl space after significant weather events to identify potential water intrusion early. If roof or siding is replaced or updated, confirm compatibility with existing tar paper and flashing to preserve the moisture barrier.
Common Mistakes To Avoid
- Overlapping Too Little: Insufficient overlaps can allow water infiltration at seams. Maintain the recommended overlap per product guidelines.
- Dirty Substrates: Installing over dust or debris can prevent proper adhesion and fastener seating. Clean surfaces before application.
- Inconsistent Fastening: Uneven nails or staples create wrinkles and gaps. Space fasteners evenly along edges and seams.
- Improper Ventilation: Inadequate ventilation increases moisture buildup. Pair tar paper with appropriate ventilation strategies for roof and wall assemblies.