help Identify these marks

[George Hallaron]

To start with, I wish the photo was better, but unfortunately I had a camera malfunction while on the roof so I had to take photos with my phone and forgot to reformat the camera setting. This was the only photo I could get to upload. Now to the issue. The roof I was on had uniform dark lines across the middle of some shingles. It appeared to be granule loss but I'm not sure if it is by design, a defect, or part of the normal aging process. The roof is a 15 to 20 yr. Roof and was installed 9 to 10 yrs ago. It is on both the north and south facing slopes. Any comments or suggestions would be appreciated.

I figured out how to add another Photo! Any suggestions would be helpful...

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[JeffGHooper]

Appears to be marks left by shingle jacks used for scaffold. Roof does not appear to be so steep they needed to use them though.

Here is one type.

How To Install Roof Jacks - Work Safely On A Steep Roof With Proper Roof Scaffolding (http://www.hammerzone.com/archives/roof/access/steep_9/using-roof-jacks-to-repair-shingles.htm)

[Lon Henderson]

If there is granular loss on the stripes, then I lean toward manufacturer's defect.

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If there is granular loss on the stripes, then I lean toward manufacturer's defect.

[Jim Luttrall]

Manufacturers defect randomly distributed as they blended bundles during installation. It may have just been one or two bundles of shingles but the roofer did a good job of "shuffling" to blend but he missed the strip or the granules washed off after installation.