Nail Pops on a Roof: Why Nails Back Out and How They Are Fixed

Every asphalt shingle is held down by roofing nails driven through the shingle and into the wood deck below. The industry minimum for most strip shingles is four nails per shingle, and many manufacturers call for more in their enhanced or high-wind patterns. The nail head is supposed to sit flush and tight on the shingle surface, under the course above, where you never see it.

A pop is that nail rising out of its hole. As it rises, the head pushes up on the overlying shingle. On a three-tab or architectural roof you may see a small dome or a tab corner that stands proud of its neighbors. In bad cases the head pokes right through. Shingle maker IKO describes exactly that progression in its raised-nail bulletin: first small bumps in the roof, and in extreme cases nails that poke through and let water in.

A pop is different from a nail placed too high or too close to a seam on day one. Those leak because of where the nail is. A pop leaks because the nail moved.

"Many times" can be put in numbers. NOAA's 1991 to 2020 climate normals for the Grand Rapids airport count about 133 days a year when the low drops to 32°F or below, but only about 50 days when the high stays at or below freezing. Subtracting one from the other, roughly 80 days a year swing across the freezing mark. March is the worst single month: about 23 freezing nights but fewer than 5 days that stay frozen, so most March days thaw and refreeze. November and April add more than a dozen and about nine such days respectively. Each swing is another chance for water around a loose shank to freeze, expand and lift the nail a little further.

The 2015 Michigan Residential Code, still the code in force for houses, sets the nail itself. Section R905.2.5 requires galvanized steel, stainless steel, aluminum or copper roofing nails with at least a 12-gage (0.105 inch) shank and a 3/8-inch head, complying with ASTM F1667, long enough to go through the roofing and at least 3/4 inch into the sheathing, or all the way through sheathing thinner than 3/4 inch. Section R905.2.6 sets the count: the number the shingle manufacturer requires, and never fewer than four per strip shingle.

That second clause matters on older Michigan houses. Most plywood and OSB roof decks are thinner than 3/4 inch, and the code's own table for board sheathing on rafters 24 inches apart calls for 5/8-inch net boards, so on most roofs the nail is supposed to come through the deck. Nail tips in the attic are expected; it is a nail that has lifted from the shingle side that signals a problem. When a pop is repaired, the replacement nails are new work, and Section R102.7.1 says repairs must meet the requirements for new work, so the new fastener should meet R905.2.5 even if the original nails did not.

The attic tells you a lot, but it is easy to misread. When roofers use nails of the correct length, the nail points come through the underside of the deck. ARMA says this is expected. A forest of nail tips over your head is normal, not a defect.

What matters is what is happening at those tips. In winter, frost on the nail tips or water droplets hanging from them means warm, humid house air is reaching the cold deck and condensing. That moisture is one of the forces that works nails loose, and it is not a roof leak in the usual sense. Rust stains around many tips point to the same thing, repeated over many winters.

A shiner is a different thing. It is a nail, usually one holding the deck to the framing, that missed the rafter or truss and sticks out beside it into open air. A few are common. Rows of them mean the deck panels may not be fastened tightly to the framing, which lets the deck flex and pumps the shingle nails above. That is worth pointing out to whoever inspects the roof.

A single wet spot or a drip on one nail during a rain, with a dry deck around it, is more likely a true leak at that nail. Mark it with tape or a marker and note the weather, because water can also travel along the deck before it drips.

One or two pops on an older roof are ordinary wear and an easy repair. A slope covered in them is telling you something about the deck or the attic, and pulling nails one by one will not keep up.

If the deck is going through big moisture swings, the long-term fix is in the attic: balanced intake and exhaust ventilation, and sealing the air leaks that push warm, wet air up from the house. If nails were too short across the whole roof, or the deck itself is soft, delaminated or rotted, the repair is in the wood. That can mean replacing a section of decking, which is a bigger job than resetting nails.