lateral surface cracks on 3 tab

[Jerry Lozier]

I see 'spider' cracking on Pabco Horizon shingles from time to time, these 3 tab are different. Not a real old roof and all are stuck down good. Weird cause it looks like they continue from one shingle to the next.

Could it be something from possible high heat in attic? Sufficient gable vents, no soffit venting????

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[Mike Lamb]

It's likely a shingle defect. Thermal splitting.

http://inspectapedia.com/roof/SplittingShingles.htm

[John Kogel]

The cracks correspond with the top edges of the shingles two rows down.

[Jerry Lozier]

thanks guys