Roofing felt underlayment, often called roofing felt or tar paper, forms a water-shedding layer beneath shingles or other roofing materials. A correct nailing pattern ensures the felt stays flat, resists wind uplift, and seals properly at seams. This article outlines common nailing patterns, weight considerations, and practical tips to help builders and homeowners apply underlayment correctly, safely, and in compliance with manufacturer guidelines and local code requirements.
What Is The Roofing Felt Nailing Pattern
The roofing felt nailing pattern refers to how and where fasteners—nails or staples—are placed along the felt sheets to secure them to the roof deck. Proper patterning minimizes movement, prevents peeling at edges and seams, and reduces the risk of leaks. The pattern varies with felt weight, roof pitch, climate, and manufacturer instructions, but generally follows consistent spacing at edges and across the field.
Felt Weight And Pattern Variations
Roofing felt commonly comes in 15-pound and 30-pound weights, with specific requirements often provided by the manufacturer. In many installations, a consistent baseline pattern is used, then adjusted for high-wind areas or steeper pitches. Key distinctions include:
- 15-pound felt: A common pattern is nails or staples every 6 inches along the long edges and every 12 inches across the field of the sheet. Seams typically require fasteners per manufacturer guidance, often with staples not exceeding the recommended length.
- 30-pound felt: Heavier felt may tolerate similar edge spacing (6 inches) but sometimes uses tighter field spacing (12 inches) or, in windy regions, closer edge spacing to counter uplift. Always consult the product spec sheet for exact distances.
- High-wind or steep-pitch roofs: Some installations require additional fasteners at lap joints and along rakes, sometimes every 6 inches at the edges and along seams to prevent billowing during wind events.
Nails, Fasteners, And Sealant Considerations
Choosing the right fasteners is critical to performance and durability. Roofing nails, typically corrosion-resistant and with wide heads, are standard, but in some climates staples are acceptable under certain felt products and codes. Common guidance includes:
- Nails: Typically corrosion-resistant steel roofing nails, about 1-1/4 inch to 1-1/2 inch in length, driven per manufacturer recommendations. For built-up or synthetic underlayments, some installers use larger head nails for better holding power.
- Staples: Used in some regions or for lighter felt, but not universally accepted. Check local code and the felt’s instructions.
- Sealant/adhesive at seams: In addition to fasteners, some installations require seam tapes or roofing cement at butt joints for extra waterproofing, especially on wood decks with a potential for moisture exposure.
Installation Steps By Pattern
Following a clear sequence helps ensure a uniform pattern and a durable roof deck. The steps below reflect typical practice, but always verify with the felt manufacturer and local codes.
- Prepare the deck: Clean and dry the roof surface; ensure plywood or OSB is in good condition and free of protrusions that could damage the felt.
- Roll alignment: Start at the bottom edge of the roof, unroll the felt squarely over the deck, letting it overhang the eave by a small amount as directed by the manufacturer (commonly 1/4 inch to 1/2 inch).
- Edge fasteners: Place nails or staples along the eaves and rakes at 6-inch intervals, ensuring the fastener heads are flush or slightly below the surface to prevent snagging.
- Field fasteners: Move across the sheet, placing fasteners every 12 inches in the field. Maintain a straight line and consistent spacing to avoid ridges or buckling.
- Seams: Align the next sheet with a proper lap, typically 19 inches for standard laps, and fasten according to the pattern. At all seams, add fasteners as per manufacturer guidelines and seal as required.
- Second layer (if required): In some installations, a second layer of felt is installed, offsetting seams between layers and appying new fasteners per pattern for the top layer, creating a stronger weather barrier.
Common Mistakes And How To Avoid Them
Even experienced roofers can err when applying felt. Awareness of frequent pitfalls helps maintain an effective underlayment.
- Inconsistent fastener spacing: Use a layout line or chalk lines to keep rows straight and evenly spaced, preventing buckling and uneven edges.
- Driving nails too deep: Keep nails flush with the surface to avoid tearing the felt upon compression or during shingling.
- Not following manufacturer guidelines: Always check product literature for exact nail counts, spacing, and acceptable fastener types for the specific felt roll.
- Ignoring climate considerations: Wind, rain, and temperature can affect underlayment behavior; adapt the pattern to conditions and use locking tapes or sealants where recommended.
Tools And Materials For The Job
A successful installation depends on having the right tools and supplies handy. A typical toolkit:
- Measuring tape, chalk line, and straightedge
- Roofing nails or staples as specified by the felt Manufacturer
- Hammer or pneumatic nail gun with appropriate fasteners
- Utility knife for trimming edges
- Roofing cement or seam tape for optional sealant at seams
- Weather-appropriate PPE and fall protection equipment
Tips For Long-Term Performance
To maximize the life of roofing felt, consider these practical tips.
- Install in dry conditions to avoid moisture entrapment under the felt, which can cause warping or mold growth.
- Ensure the deck is dry before applying a second layer or finishing with shingles.
- Keep a clean, straight edge for consistent laps; misalignment can create minor water entry points over time.
- Follow local building codes and product documentation for any wind-rated or region-specific requirements.