Best Roofing Nail Size for Two Layers of Shingles

Choosing the right roofing nail size for two layers of shingles ensures secure fastening, code compliance, and longer shingle life. This article explains recommended nail lengths and types, nailing patterns, code considerations, installation tips, and when to re-roof instead of overlaying.

Situation	Recommended Nail	Notes
Two Layers Of Asphalt Dimensional Shingles	1-1/2″ Ring Or Common Shank	Penetrate Roof Deck By At Least 3/8″ To 1/2″
Two Layers Over Ply Sheathing Or Solid Deck	1-3/4″ Ring Shank	Better Holding Power For Thicker Substrate
High Wind Zones	Ring Shank 1-1/2″ To 1-3/4″	Follow Local Code For Wind Ratings

How Nail Length Affects Two-Layer Shingle Roofs

The nail must pass through both shingle layers and penetrate the roof deck sufficiently; otherwise fastener pullout and blow-offs occur. Correct nail length ensures structural holding power and wind resistance while minimizing deck damage and splitting.

Recommended Nail Sizes For Two Layers Of Shingles

For typical two-layer asphalt shingle overlays, 1-1/2 inch nails are the most commonly recommended length when using 7/16″ or 1/2″ roof decking because they achieve adequate deck penetration. Where thicker decking or double sheathing exists, 1-3/4 inch nails provide extra grip.

Nail Type And Shank Options

Ring shank nails offer far better withdrawal resistance than smooth shank (common) nails; therefore ring shank or spiral shank nails are preferred for two-layer installations, especially in high wind areas. Use hot-dipped galvanized or stainless steel nails to avoid corrosion with modern shingles.

Material And Corrosion Resistance

Roofing fasteners must resist corrosion from weather and asphalt contact. Hot-dipped galvanized nails meet most standard requirements; use stainless steel nails in coastal or corrosive environments to prevent staining and failure.

Penetration Depth And Holding Power

Building codes and manufacturer instructions typically require the nail to penetrate the roof sheathing by at least 3/8 inch to 1/2 inch. For two-layer roofs, ensure the nail does more than just bite the top layer; it must reach and anchor into the deck below for reliable holding power.

Local Building Codes And Manufacturer Requirements

Local codes and shingle manufacturer warranties often restrict overlaying more than two layers and specify nail type and length. Always consult local building codes and the shingle manufacturer’s installation instructions because improper fasteners can void warranties and fail inspections.

Nailing Pattern, Spacing, And Placement

Follow the shingle manufacturer’s specified nailing pattern and placement. Typically, birds-mouth or starter-course rules still apply, and use four to six nails per shingle depending on wind zone. Ensure nails are placed in the designated nail line for proper sealing and to avoid misalignment.

Wind Zones And Fastener Quantity

High wind zones may require six nails per shingle and ring shank fasteners to achieve the rated uplift resistance. Increase fastener quantity and use ring shanks in regions with higher wind speeds, and follow local codes for uplift performance.

When To Remove The Existing Layer Instead Of Overlaying

Overlaying two layers is allowed in many places, but structural capacity, deck condition, and flashing details matter. Remove old shingles when the deck is warped, plywood is damaged, or flashing conditions are compromised to prevent leaks and ensure long-term performance.

Estimating Nail Quantity And Fastener Calculation

Calculate nails by squares (1 square = 100 sq ft). With four nails per shingle and approximately 29 shingles per square for a 3-tab, expect about 116 nails per square; for architectural shingles, count shingles per square and multiply by required nails. Add 10% waste for overlaps and misfires when using a nail gun.

Tools And Best Installation Practices

Use a properly calibrated roofing nailer or hand nail with a roofing hammer to avoid overdriving or underdriving. Set pneumatic nailers to seat the head flush without tearing the shingle mat. Verify random fastened tests to confirm correct depth and placement.

Common Mistakes To Avoid

• Using Nails That Are Too Short: Leads To Pullout And Blow-Offs.
• Using Smooth Shank Nails In High Wind Areas: Poor Withdrawal Resistance.
• Overdriving Nails: Damages Shingle Sealant And Reduces Holding.
• Ignoring Deck Condition: Rotten Or Spongy Decking Cannot Hold Fasteners.

Inspection, Warranty, And Insurance Considerations

Overlaying with incorrect nails can void shingle warranties and affect insurance claims after storm damage. Document nail type and length, and follow manufacturer and local code requirements to maintain warranty and coverage eligibility.

Practical Examples And Scenarios

Example 1: A homeowner with two asphalt layers over 1/2″ plywood in a moderate wind zone should use 1-1/2″ hot-dip galvanized ring shank nails, four to six nails per shingle. Example 2: In a coastal high-wind area, choose 1-3/4″ stainless ring shank nails and six nails per shingle per manufacturer’s high-wind instructions.

When To Consult A Professional

If roof decking thickness is uncertain, rafters are undersized, or local codes are strict, consult a licensed roofing contractor or building official. Professional evaluation avoids structural overload, improper fastening, and future failures.

Summary Of Key Recommendations

For two layers of shingles, the practical default is 1-1/2 inch ring shank galvanized nails for typical 7/16″ to 1/2″ sheathing; use 1-3/4 inch for thicker decking or high-wind demands, prefer ring or spiral shanks, and always follow local code and shingle manufacturer instructions.