The roof of my house has many vertical "streaks" in the asphalt
shingles, evidently caused by the removal of the light-colored granular
material from the shingles which exposes the darker matrix. The streaks
start in a small region then spread downward and outward for about a
foot - sort of like the splat of a juicy insect against a windshield.
Much of the granular material ends up in the gutters. This has mostly
occurred within the last year.

Is this normal wear-and-tear, or an indication that the shingles are
overly worn? The re-roof job is about 10 years old.

This is often an indication that the shingles are getting hard and
brittle. If it's just spots and streaks, but otherwise the roof
looks OK, I wouldn't worry about it just yet.

But I also wouldn't suggest waiting for signs of actual leakage to
replace the roof -- that can end up with an emergency re-roof in
nasty winter weather, or a homeowners insurance claim for lots of
water damage. When the aggregate loss gets more widespread, or the
shingles start curling up at the corners, I'd go for a planned re-
roof before it's an emergency.

Also, if the existing roof is failing well before its planned life,
I'd check on ventilation -- is the roof getting too hot, shortening
the shingles' life?

--
is Joshua Putnam
http://www.phred.org/~josh/
Updated Infrared Photography Books List:
http://www.phred.org/~josh/photo/irbooks.html