Roof Leak caused by Nail Pops

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We often get the call… “Help! My roof is leaking!”
While a roof seems to be a simple matter, finding the source of a leak can be challenging.  One cause of leaks can be ‘nail pops.’ With age, and cold/hot cycles, roofing nails can work their way OUT of the roof. When they do, they push up the shingles above them. This can be seen when you know what to look for.

What are Roof Nail Pops?

When doing a roof inspection to repair a roof leak, nail pops are a common culprit.  These are nails that work their way out of the decking.  This type of roof problem happens when the roofing nails have been forced back and out of the roof sheathing.  Hot/cold changes cause this to happen because of the pressure exerted on the nail by the surrounding wood.

What causes Roof Nail Pops?

Wood roof sheathing (plywood, OSB, wood plank) swells with increased humidity and high temperatures. When it cools and dries out, it contracts. Repetitive hot/cold cycles reduces the ability of the wood to hold the nail. This causes the nail to loosen.  Each and every time the wood swells it pushes the nail out of the hole a little bit more. Eventually, this leads to visible roof nail pops, with lifted or punctured asphalt roof shingles.

Poor attic ventilation

Roof nail pops tend to be a common issue when the roof has a poorly-ventilated attic, where extreme overheating of the roof occurs, as well as on roofs that were installed while the roof sheathing was not dry. Nailing into damp wood prevents the nails from being properly held in place by the wood right from the start.

Multiple layers of roof shingles

Another situation where roof leaks occur, is when roof nail pops occur is on roofs where a second layer of shingles has been installed over an existing layer of asphalt shingles. In this case, a common issue is the use of roofing nails that are too short to properly penetrate the sheathing. Nails should fully penetrate the sheathing and extend at least 3/8 inch beyond the underside of the roof sheathing.  When they don’t, they are particularly susceptible to back-out due to the shape of the nail. If the tapered section of the nail shank is left embedded in the sheathing instead of being hammered all the way through, you can expect problems.

Why Roof Nail Pops cause leaks?

Roof nail pops are unattractive, for one thing. Your roof will have bumps and humps and out-of-place shadows. So, they are an aesthetic eyesore.

Nail Pops lift roof shingles

The serious issue with roof nail pops is performance-related. When they force the shingles up, it creates a path for wind-driven rain to reach the roof sheathing and to enter your house causing a roof leak. In the image below you can see a nail that has lifted a shingle and broken the seal.  The seal has been broken long enough for the nail to rust.

Nail Pops puncture roof shingles

By forcing the shingles up, the backed-out nails break the bond between shingles created by the shingles’ self-sealing strip or any added roof cement. This will greatly increase the chance of wind damage to your roof. Wind agitation of the shingles can lead to cracked, torn, or broken shingles, and probably punctures at the location of the roof nail pops themselves causing a roof leak.

If the bond between the shingles is strong enough to resist the pressure from below, the nail heads will simply puncture the shingle (See Above Image).  This gives rain a direct path into your house, through the hole in the shingle and down the nail hole below.  All roof leaks need to be repaired.

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