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What causes roof shingles to curl up at corners?
Thursday, June 14, 2018
Usually A Sign of Age
Shingles curl as they reach the end of their serviceable lifespan. It’s one of several signs of that an older roof is approaching time for replacement. Other indications are areas of missing surface granules and loose tab adhesion, which makes the front of the shingle lift easily. The photo above shows the first stage of curl, while the one below is an example of more advanced curl.
Three Reasons For Premature Shingle Curl
Curl can also happen prematurely on a newer roof. Three reasons for premature curl are:
- Poor attic ventilation - Roofs get hotter and have excessive moisture rising up under the sheathing when there is inadequate air flow. It should come in through the soffit and and rise out of vents at the ridge of a roof. The overheating speeds up normal deterioration of the shingles.
- Multiple roof layers - The building code allows a second layer of shingles to be laid over the original one—but no more than two total layers. This eliminates the labor and dump fees for removal of an older roof, but speeds up the deterioration of the new one. The new roof gets laid over an uneven surface, nailing through the old shingles is less secure, and the original roof continues to age and move under the new one. So early curl is more likely. See our blog post How can I tell if a roof has more than one layer of shingles? for more on this.
- Sloppy installation - If the shingles are not secured with enough nails, the nails located poorly, or the shingles are not aligned accurately, early curl can occur.
Unfortunately, premature curl can become an issue when you apply for a new homeowner’s insurance policy. For an overview of the signs that your roof is ready to be replaced, see our blog post How can I tell if the house needs a new roof?
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To learn more about roofs and attics, see these other blog posts:
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