How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What are the dark lines running parallel to shingles on my roof?
Saturday, August 4, 2018
If it looks like the photo above, then your shingle roof has lost its tab adhesion at the leading edge and is flapping up in high winds. The dark line is a crease created when the shingles repeatedly hinge up under wind pressure.
Shown below is a wider view of a roof with this problem, along with an example of a broken shingle that you will find blown up the roof or laying on the ground after they start to snap at that hinge line.
Another sign of this problem is leaf debris trapped under the shingle.
Also, see our blog posts What causes roof shingles to curl up at corners? and What causes shingles to buckle along a line on the roof?
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To learn more about roofs and attics, see these other blog posts:
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