Nails for Roof Felt: A Comprehensive Guide for Durable, Weather‑resistant Underlayment Installation

The installation of roof felt, or underlayment, relies on the right nails to ensure a secure, durable base for shingles and protecting the roof deck from moisture. This article explains the best nail types, materials, sizes, and installation practices for various climates and roof assemblies in the United States. It covers compatibility with felt thickness, deck material, and wind uplift considerations, helping homeowners and professionals achieve a long-lasting roof underlayment.

Understanding Roof Felt And Its Fastening Needs

Roof felt provides a secondary weather barrier beneath roofing shingles. It helps seal gaps, reduces wind-driven moisture, and adds an extra layer of protection during installation. The fastener must penetrate enough to hold the felt without tearing the material, resist corrosion, and perform well under temperature fluctuations and moisture exposure. Factors shaping nail choice include felt weight (commonly 15‑pound or 30‑pound), roof deck material (wood, plywood, or oriented strand board), climate (humid, coastal, or desert), and local building codes.

Key Nail Types For Roof Felt

Choosing the right nail involves balancing material compatibility, head design, and shank style. The following options are commonly used with roof felt in residential construction.

• Galvanized Roofing Nails – Zinc-coated steel nails with a wide, flat head. Suitable for standard felt installations on wood decks. In coastal or high-humidity areas, hot-dip galvanizing or stainless options may be preferred to resist corrosion.
• Stainless Steel Roofing Nails – Highly corrosion-resistant, ideal for coastal or salt‑exposed environments. Typically more expensive, but offer superior longevity in harsh conditions.
• Copper Roofing Nails – Excellent corrosion resistance and long life, often used on premium projects or historic restorations. They can be softer than steel, so proper driving is important to avoid bending.
• Polymer-Coated Nails – Steel nails with polymer coatings reduce friction during driving and improve corrosion resistance, suitable for various climates.
• Ring-Shnken Nails – Feature ridges along the shank that create additional grip and resistance to pull-out, beneficial in windy areas or when decks experience swelling and contraction.
• Smooth-Shank Nails – Traditional option for lighter underlayment; adequate in calm climates but offer less grip in high wind or expansive wood.

Materials And Coatings To Consider

Material and coating influence longevity and performance. In the United States, common choices include:

• Plain Steel – Inexpensive but more prone to corrosion in humid or coastal climates unless galvanized.
• Galvanized Steel – Provides a protective zinc coating that reduces rust and staining, widely used for standard felt installations.
• Stainless Steel – Best durability, ideal for harsh environments and long-term performance, especially in beach towns or regions with salt spray.
• Copper – High durability and aesthetic appeal for certain applications, but higher cost and softer metal quality require careful handling.

Nail Size, Length, And Shank Style

The correct size and length ensure adequate embedment into the roof deck without tearing the felt. Typical guidelines include:

• Length – For most 15‑pound or 30‑pound felt installations over wood decking, 1 inch to 1 1/4 inch nails are common when used with a roofing staple system. If fasteners must penetrate into the decking for wind resistance, 1 1/2 inch to 1 3/4 inch nails may be recommended depending on deck thickness.
• Diameter – A standard 0.102 inch to 0.128 inch diameter provides sufficient strength for felt without excessive splitting of the decking.
• Shank Style – Ring-shank nails offer better withdrawal resistance and hold in swollen wood, which can be advantageous in regions with high humidity or prone to moisture gain.
• Head Design – A broad, flat head reduces pull-through risk and helps seat the felt evenly. Some nails feature washer heads to distribute loading and minimize tears in the felt.

Installation Best Practices For Roof Felt Nails

Proper installation improves performance and longevity. Adhere to these practices for consistent results.

• Pre-Drilling Not Usually Required – Do not pre-drill when using standard roofing nails on typical plywood or OSB decks; it may cause decking damage or misalignment.
• Angle And Depth – Drive nails perpendicular to the deck to ensure full penetration and proper seat of the head. Do not over-drive, which can tear felt; under-driving can lead to lift and leaks.
• Spacing – Space nails according to manufacturer recommendations (often about 6 to 8 inches along the edges and 12 to 18 inches on the field for large panels). Ensure nails align evenly for a neat, uniform appearance.
• Sealant Considerations – Some installers apply a compatible asphalt-based sealant or roofing cement at exposed edges or penetrations where strips of felt overlap to improve moisture resistance, though this is not always necessary with wind‑rated underlayment.
• Wind Uplift – In high-wind areas, ensure nails provide sufficient withdrawal resistance. Ring-shank or galvanized nails with larger heads can improve performance under uplift forces.

Climate And Local Code Considerations

Regional differences influence fastener choices. For coastal regions with high salinity, stainless or copper nails reduce corrosion risk. In areas with freeze-thaw cycles, corrosion resistance and proper embedment are critical to avoid rust migration and deck damage. Local building codes may specify acceptable materials, coatings, and nail lengths for roof underlayment. Consulting the latest code provisions and manufacturer guidelines helps ensure compliance and optimal performance.

Compatibility With Different Roof Decks

Deck material affects nail selection. Wood decks like dimensional lumber respond well to standard roofing nails. Plywood and OSB decks may require different nail lengths to ensure penetration through the deck and into the framing. In some installations, additional fasteners or mechanical fixings are used to meet wind-resistance requirements. Always verify that the chosen nails are rated for the specific deck and underlayment type in use.

Common Mistakes To Avoid

• Using the Wrong Length – Nails that are too short fail to secure the felt, while overly long nails can damage the deck or shingles.
• Choosing Non‑Corrosion‑Resistant Materials – In humid or coastal environments, non-galvanized nails corrode quickly and stain or compromise the felt.
• Over-Tightening Or Skipping Nails – Inadequate fastening can cause lift, while overtightening may tear the felt or degrade the head.
• Ignoring Manufacturer Guidelines – Different underlayment brands may have specific nail requirements; follow their instructions for best results.

Summary Of Practical Recommendations

For most U.S. residential felt installations, use galvanized roofing nails or stainless steel nails for coastal regions. Choose ring-shank nails when wind uplift and deck movement are concerns. Select nail lengths that ensure adequate penetration into the deck without tearing the felt, and maintain proper spacing per manufacturer guidelines. Consider coatings or stainless options for high-corrosion environments, while copper is reserved for premium or historic projects. Always align with local codes and felt manufacturer specifications to optimize durability and performance.

Practical Quick Reference

Material: Galvanized steel or stainless steel; Coatings: polymer-coated options available; Shank: Ring-shank for wind zones; Head: Wide, flat washer-style; Length: 1 inch to 1 3/4 inch depending on deck thickness; Spacing: 6–8 inches at edges, 12–18 inches in field; Climate considerations: coastal/high humidity favor corrosion-resistant materials; Deck compatibility: adjust length for plywood/OSB vs. solid wood.