How to Determine the Right Size Nail for Your Roof

Lydia Schapiro
Written by Lydia Schapiro
Updated December 21, 2021
A gray suburban house
Photo: Ursula Page / Adobe Stock

Highlights

  • Having properly sized roofing nails helps your roof stay securely intact.

  • Choosing improperly sized nails may lead to roof cracks or mildew growth. 

  • By understanding how to calculate the dimensions of roof nails, you can help prevent roof issues.

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While nails may seem like a small part of your roof, they’re actually a big deal because they hold together the whole operation. And for roofing nails to stay securely in place and give your home a fully functional, protective cover, they need to be properly sized. 

Selecting just-right roofing nails requires examining the thickness of other materials on your roof—the decking and shingles. Here’s an overview of how these parts influence nail selection, what can happen when your roof has wrong-size nails, and what you can do about it.

Roofing Nail Dimensions

The standard dimensions for roofing nails are gauge (diameter) and length. Roofing nails are usually somewhere between 1 to 2 inches long, while the gauge is often between 10 and 12

Nail gauge refers to the thickness of the nail, and the higher the gauge number, the thinner the nail. Thus, the smaller the gauge size, the stronger the nail. Typically, the minimum gauge number is 12

Decking and Shingle Thickness

The thickness of other roofing materials—specifically, decking and shingles—heavily influences roofing nail selection. While most shingles typically have similar thickness, the thickness of your decking—what connects the roof to the house—–can vary based on your preference. The thickest decking in modern roofing is usually a little under an inch, while most decking is roughly 3/4 of an inch thick.

For most decking materials, such as solid wood, plywood, OSB (oriented strand board), and non-veneer wood, roofing nails should be around 19 mm long and penetrate the decking at least 3/4 of an inch. Ideally, they’ll puncture the decking entirely, meaning that the whole tip goes past the decking. 

If you have thicker shingles, your roofer will likely use nails that are 30 mm long. If they’re installing an additional layer of shingles (double layers), they’ll use nails that are at least 35 mm long.

Consequences of Wrong-Size Roofing Nails

Roofer worker using air or pneumatic nail gun
Photo: visoot / Adobe Stock

One consequence of improperly drilled nails is splintering in your wood/timber, which can lead to gaps and cracks. These gaps leave potential for things to pass through, which means your roof isn’t doing its job. Additionally, when gaps form, moisture can form and give way to mold. 

Overdriven nails (nails drilled in too much) can also cause cracks—sometimes, the nails loosen and even come out, which can make the shingles break. On the contrary, underdriven nails (nails not drilled in enough) can give way to air bubbles, which make your roof more vulnerable to wind damage.

What to Do When You Have Improperly Sized Roofing Nails

If you think your roof is holding the wrong size nails, it’s important to take action. 

Because most roofing-related projects can be dangerous, your best bet is to work with a professional roofing inspector who can meticulously evaluate your roof and help you identify next steps.

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