Why Tongue & Groove Decking Fails Modern Roofs — and What Florida Homeowners Should Do Instead

Image: Courtesy of Earl W. Johnston Roofing, LLC

What’s the Problem with Tongue & Groove Decking?

If your home has a tongue and groove (T&G) deck, you might be sitting on a leak risk, even if your roof looks fine on the surface.

At Earl W. Johnston Roofing, we’ve seen this issue countless times during GAF warranty inspections, and it’s a growing concern. Why? Because T&G decking, once common in older homes, simply doesn’t meet the needs of modern roofing systems or current building codes.

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Image: Courtesy of Earl W. Johnston Roofing, LLC

Top Reasons Tongue & Groove Decks Fail Today

1. Too Many Nail Holes

Over time, multiple reroofs leave T&G decks riddled with nail holes. This weakens the structure and opens the door to water intrusion.

2. Nails Miss the Mark

Due to the narrow joints in T&G boards, nails often land between boards, which provides little holding strength and becomes a source of loose nails and leaks.

3. Gaps Between Boards

T&G relies on tight seams, but after years of wear, the boards separate, leaving gaps and uneven surfaces beneath your roof.

4. It’s Not Code-Compliant

According to the Florida Building Code, tongue and groove decking is no longer permitted for most roof installations. If you’re in a region like Broward or Miami-Dade (HVHZ), this can put your project out of code and at risk of failing inspection.

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Image: Courtesy of Earl W. Johnston Roofing, LLC

What We Recommend Instead: Full Resheathing

To properly install a new roofing system, we recommend resheathing over the T&G decking using 1/2″ or 3/8″ CDX plywood.

This gives you:

• A solid, reliable base for roofing fasteners

• Compliance with the Florida Building Code

• Better long-term performance and wind uplift resistance

• Protection against future leaks and costly repairs

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Image: Courtesy of Earl W. Johnston Roofing, LLC

Why It Matters for Your GAF Warranty

As a GAF Master Elite® Contractor, Earl W. Johnston Roofing is frequently called to assess roofs covered under the GAF Golden Pledge® Warranty. In many cases, the leaks aren’t caused by the roofing system — they’re caused by the deck beneath.

If T&G decking isn’t addressed, it can lead to warranty issues and unexpected repairs.

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Image: Courtesy of Earl W. Johnston Roofing, LLC

Final Thoughts

When replacing your roof, don’t stop at the surface. If you have tongue and groove decking, ask about resheathing. It’s an investment that protects your home, warranty, and peace of mind — especially in storm-prone South Florida.

Side Note:
This issue primarily affects shingle roofs, where thousands of nails must be driven into the decking. Unlike tile roofs, which are typically installed using foam adhesive (except in rare mechanically fastened cases), shingle systems rely heavily on a solid nail base, making weak or jointed decks like tongue & groove especially vulnerable to future leaks and fastener failure.

Need an Expert Roof Evaluation?

Call 1-800-940-LEAK or visit johnstonroofing.com to schedule a free estimate with Earl W. Johnston Roofing — proudly serving Broward, Miami-Dade, Lee, and Palm Beach Counties since 1986.