Tar paper, or roofing felt, remains a common underlayment choice for many U.S. roofs due to its water resistance, ease of installation, and cost effectiveness. Understanding tar paper roll size helps homeowners and contractors estimate material needs, plan waste, and ensure the chosen underlayment meets local building codes and climate demands. This guide breaks down typical widths, lengths, and weight ratings, and explains how these factors translate into coverage, installation considerations, and selection tips.
Common Tar Paper Roll Widths
Width is one of the most visible tar paper characteristics. The majority of roofing felt rolls sold in the United States are 36 inches wide, which lines up well with standard rafter spacing and shingle layouts. Some specialty or higher-end underlayments may come in wider formats to reduce the number of seams on larger roofs, but 36 inches remains the default for most projects.
In addition to width, some manufacturers offer custom or regional products that may be slightly narrower or broader. When selecting a width, consider the roof slope and the desire to minimize seam crossings. Wider rolls can reduce labor time but may require different waste calculations for peculiar roof shapes.
Roll Lengths And Coverage
Roll length determines total coverage per roll, but coverage also depends on the precise roll width and the waste factor during installation. Typical tar paper roll lengths range from about 70 to 100 feet. For example, a common 36-inch-wide roll might cover roughly 210 to 240 square feet per roll under standard installation practices, before accounting for waste.
Calculation tips:
- Area per roll = (roll width in feet) × (roll length in feet).
- Use a waste factor of 5–10% for sloped roofs, odd shapes, and adjustments at eaves and rakes.
- Always verify product specifications on the packaging, as some regional products differ slightly in length.
Understanding these numbers helps ensure you purchase enough material in advance, minimizing on-site shortages or excess. For complex roof geometries, estimating by area rather than by rolls can reduce waste and simplify ordering.
Weight And Coverage Metrics
Tar paper underlayment is rated by weight, which reflects its reinforcement and durability. The two most common categories in residential roofing are:
- 15 lb per 100 sq ft (per ply): Traditional lighter felt used on many single-layer installations. It offers basic protection against moisture during construction and when paired with a primary roofing layer.
- 30 lb per 100 sq ft (per ply): The standard for many new-build roofs and re-roofs. Heavier felt provides greater tear resistance and better performance under wind-driven rain, especially on steeper pitches.
Older or specialized projects may reference heavier or lighter grades, but 15 lb and 30 lb are the most widely encountered in today’s residential market. When choosing, consider roof slope, climate, and local code requirements. In regions with heavy winds or frequent storms, a 30 lb or higher underlayment may reduce leak risk during construction and after installation.
Choosing The Right Tar Paper Size For Projects
Selecting the appropriate tar paper roll size involves balancing width, length, and weight with project scope and local building practices. Consider these factors:
- : Large, simple roofs benefit from wider panels to reduce seams, but ensure the width matches the installation method and any fastener requirements.
- : Steeper pitches may require more waste allowances and careful seam placement; heavier weight can improve tear resistance during installation on challenging surfaces.
- : Regions with frequent rain, wind, or hail may benefit from 30 lb felt for enhanced protection during construction and weather exposure before final roofing is installed.
- : Some jurisdictions have minimum underlayment standards; confirm with the local building department before purchase.
- : If the roof is later covered with a self-adhealing or synthetic underlayment, you may opt for lighter felt or a different product class, but ensure compatibility with the final roofing system.
Practical planning steps:
- Measure the roof plan to determine total square footage. One roofing square equals 100 square feet; divide total area by 100 to estimate required rolls, applying a waste factor of 5–10% for cuts and waste.
- Choose a width that aligns with common shingle layouts and minimizes the number of seams crossing critical roof areas like ridges and hips.
- Verify that the selected weight aligns with anticipated weather exposure and laddering or installation dynamics on the roof.
Installation Considerations And Practical Tips
Beyond size, proper installation ensures tar paper performs as intended. Here are practical tips to maximize performance:
- lid alignment: Start at the eaves, unrolling and aligning the felt so that overlaps follow the manufacturer’s guidelines, typically 2 to 4 inches per course, to prevent wind-driven moisture intrusion.
- fastening: Use staples or nails per the product’s instructions and local code. Ensure fasteners do not damage underlying roof decking and are spaced consistently along the seams.
- seam management: Overlap seams in the recommended direction and maintain continuous coverage up the roof plane to simplify future shingle or compliant underlayment installation.
- storage: Store unused rolls in a dry area to prevent deterioration of the asphalt core, which can compromise performance if exposed to moisture over time.
- compatibility: When paired with asphalt shingles, synthetic underlayment options, or rubberized barrier products, ensure the tar paper is compatible with the final roofing system to avoid delamination or poor adhesion.
Common Questions About Tar Paper Roll Size
- Are there cheaper alternatives to tar paper? Yes, synthetic underlayment options exist that offer higher tear resistance and longer life. They often come in similar widths but vary in weight rating and permeability.
- Can I mix sizes on a single roof? It’s common to mix underlayments if specific roof areas require different performance profiles, but confirm with local codes and the manufacturer’s guidelines.
- How much tar paper should I buy for a typical home? For a standard house with a simple gable roof, calculating by square footage with a 5–10% waste factor usually yields an accurate estimate for rolls of 36 inches wide and 70–100 feet long.
Understanding tar paper roll size helps optimize material purchases, installation efficiency, and overall roof performance. By focusing on width, length, and weight, homeowners and contractors can select the right underlayment for a durable, weather-resistant roof underlayment system.