A nail pop is a roofing nail that has backed partway out of the decking, pushing up the shingle above it into a small visible bump. It usually happens from improper nailing, wood shrinkage, or the deck flexing with temperature changes, and it leaves a raised nail head that can wear through the shingle above it or work its way further out over time. Nail pops are common and usually an easy, inexpensive repair, especially when caught before the exposed nail head causes a leak.
Every shingle is held down by a handful of nails driven through it into the decking below, and a properly set nail sits flush, with its head firmly seated against the shingle so the seal above it stays flat.
A nail pop is what happens when one of those nails does not stay put. It backs partway out of the wood, usually because it missed solid framing, was driven at an angle, or simply worked loose as the decking expanded and contracted with the seasons.
As the nail rises, it pushes up on the shingle directly above it, creating a small, visible bump or ridge on the roof surface right over the nail location.
That raised bump does two things over time. It concentrates foot and weather wear right at that one point, and it can eventually punch a small hole through the shingle above it or simply keep working its way further out of the deck.
Either outcome creates a tiny, direct opening for water right where the nail sits, which is a common, very localized cause of a small ceiling stain that seems to appear out of nowhere with no obvious source on the roof itself.
Nail pops are one of the more forgiving problems a roof can have. Spotted early, from the ground or during a routine inspection, a popped nail is usually a quick, low-cost fix: resetting or replacing the popped nail and resealing the shingle above it before it ever gets the real chance to leak.
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