How long should roofing nails be, and can they be too long?
How the rule plays out
Most houses here have 7/16 inch OSB or 1/2 inch plywood decking. Because that is thinner than 3/4 inch, the nail has to pass all the way through it, which is why you see rows of nail tips when you look up in the attic. That is normal and expected, not a sign of a bad roof.
Too short causes real problems
- Less grip in the wood, so shingles pull loose in strong wind.
- Nails that back out over time and push up through the shingle above, known as nail pops.
- Installation that does not follow the manufacturer's instructions, which can affect the shingle warranty.
When nails can be too long
Length is rarely a problem over an attic, but it matters at open eaves and porch ceilings where the underside of the deck is finished and visible, often tongue and groove boards. Long nails there leave points sticking through the ceiling. Installers handle it with shorter nails in that zone that still meet the penetration rule, or with a thicker deck at the overhang. Overly long nails in a cold attic can also collect frost and drip in winter, which is uncommon in most of Georgia but does happen in the mountains.
Gauge and head size matter too
The code also sets a minimum 12 gauge shank and a 3/8 inch head, made of galvanized steel, stainless, aluminum or copper. A long nail with a small head still fails if the head pulls through the shingle.