I noticed a few nail pops (lifted shingles) on your roof during my annual roofing inspection. My concern is the lifted shingle may get blown up during a wind event and cause a roof leak, or worse.
A nail pop is a bump or slightly raised area on the roof’s surface that leaves the roof susceptible to water intrusion. There are multiple reasons for this condition.
Poorly fastened roof decking could be the culprit. Most builders in the US use a type of engineered wood similar to particleboard, called oriented strand board (OSB), for roof decking. Unfortunately, the plywood has installation requirements that often aren’t followed. One of the most common installation mistakes is poor or improper fastening. During the day, attic temperatures increase and cause the plywood decking to expand. At night it contracts. If not properly fastened, these natural forces can slowly lift the plywood, and its nails, lose. As a result, the shingles are pushed upward.
According to the International Residential Code (IRC) R905.2.5: “Fasteners for asphalt shingles shall be galvanized steel, stainless steel, aluminum or copper roofing nails, minimum 12-gage [0.105 inches (3 mm)] shank with a minimum 3/8-inch-diameter (9.5 mm) head, complying with ASTM F1667, of a length to penetrate through the roofing materials and not less than 3/4 inch
(19.1 mm) into the roof sheathing. Where the roof sheathing is less than 3/4 inch (19.1 mm) thick, the fasteners shall penetrate through the sheathing.”
The above-referenced code addresses the gauge of the nail. However, it doesn’t address the shank design or “type.”
Ring shank nails have small grooves cut around the shank. Due to this unique shape, the nails have approximately twice the withdrawal resistance of smooth shank nails with the same diameter.
Nail length and shank design are important and can lead to nail pops.
Pneumatic nailers are another piece of the puzzle. Often, gun nails are driven in at an angle, or the gun isn’t set properly and overdrives or underdrives the nail. Some roofing contractors use staples. Staples can easily tear through the shingle. Most shingle manufacturers recommend using nails rather than staples.
Shingles also have a minimum required nailing pattern. If not followed, it can easily move or slip. See video >>>
When the nails have a smooth shank and don’t penetrate the decking properly, they don’t grip the sheathing very well. Again – poorly fastened shingles lead to nail pops.
Soft Roof Decking
Another cause for a nail pope is subsurface fastening. If your roof is installed over thin or soft decking, the fasteners could slip pull up. That’s why it’s best to monitor your deck from inside the attic. Regular inspections help lower maintenance cost.
The prescription for preventing nail pops varies. My concern is that a wind event might blow the shingle up and cause more damage.
Repairing Nail Pops
Now that you’ve identified and corrected the most probable cause for the nail pop, you’re ready to repair it. However, there is a specific protocol for hand sealing asphalt shingles.
- Use asphalt roofing cement that conforms to ASTM D4586. DAP® DYNAFLEX® 4586 Flexible Roof Asphalt Sealant is often used to seal leaks or for repairing loose shingles. It resists cracking and sagging and provides excellent adhesion, even on wet surfaces.
- Two cement spots about the size of a quarter are typically placed under each tab on three-tab shingles.
- Use four spots of asphalt roofing cement on laminated shingles.
- One spot may be placed one to two inches from each end of the tab and near the bottom, but not so close to the bottom that it is squeezed out from under the tab as the tab is pressed into the cement.
- It’s always best to consult the individual shingle manufacturer’s recommendations for specific hand sealing instructions.
One important thing to keep in mind when repairing a nail pop. Don’t just drive the roofing nail back down into the same hole. Lift it out and move over about an inch or so and drive a ring shank nail into a new section of decking.
Here’s my best advice for hand sealing asphalt shingles: Consult the individual shingle manufacturer’s recommendations for specific hand sealing instructions.
I recommend a roofing contractor or other professional experienced with roofing installation review the condition and repair as deemed necessary.Gary Smith – Construction Coach – Professional Home Inspector
You nailed it!