Your roof is arguably the most important defense your home has against the weather. Wind, snow, hail, rain, and even sunshine can wreak havoc on a roof that's not up to the task. The quality of your roofing material may only be as good as how it's fastened to the house. To make the grade and avoid premature roofing material failure, the length of nails used to install your roof must be correct. Learn what you need to know about roofing nail length, whether you're tackling roof repairs or installing a new one.
Asphalt Shingle Nail Length
There are competing rules regarding the correct nail length for asphalt shingles. The discrepancy comes from variations in local building code regulations. Shingle manufacturers' guidelines for asphalt roofing nail lengths fall between 1 1/4 and 2 inches. But that's only part of the story.
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Roofing nails holding asphalt shingles in place should protrude at least 1/4 inch beyond the underside of the roof deck material according to most local building codes and manufacturer requirements where the roof decking is less than 3/4 inch thick. However, some locations may only require that the nail penetrates 3/4 inch into the decking material regardless of the thickness of the decking. Check your local code rules to be sure.
Most often, that means installing a single layer of asphalt shingles onto 1/2- to 3/4-inch-thick roof decking requires nails that are 1 1/4 inches long to meet the manufacturers' requirements and the building code. For ridge shingles that overlap the top row of roofing material, the nails must penetrate two layers of shingles and reach the appropriate depth into the sheathing, which may mean using 2-inch nails for installation.
Roof Overlay Nail Length
Often, an existing asphalt roof doesn't need to be removed before installing new shingles. The method is called a roof overlay and has its own regulations to govern installation. What doesn't change during an overlay roofing project are the roofing nail requirements. They still need to penetrate the decking to the same depth, which means using 2-inch nails for installing the second layer of shingles is necessary. Ridge shingles may even require nails longer than 2 inches.
Cedar Shake Roofing Nail Length
Cedar shake shingles use box nails instead of common roof nails for installation. However, the requirements for their length are similar to those for asphalt roofing. The nails that affix the cedar shakes to the decking must penetrate 3/4 inch into the substrate material or go all the way through. The thickness of the shingles you're installing will determine the length of nails necessary, from 1 1/4 to over 2 inches.