Wavy looking roof shignles

The roof is 20-25 years old with one layer, vented by soffit/ridge. The waviest looking side is Southern exposed. My question is why or what is cause the shingle to have a wavy look with some buckling. If the underlayment roofing paper got wet before installation could that be cause?

google produces 1,200,000 results
pick any & you may find an answer to your ?

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As a home inspector, just write up what you see and recommend further evaluation by a roofer. It may be underlayment, but that pattern is different than I typically see with thermal expansion of the underlayment.


My opinion, it looks like the shingles were butted too tight. There should be a nominal gap for expansion.

That said, it’s not the only explanation. As @lhenderson2 and @badair stated, don’t box yourself in.

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Morning, Shay. Hope this post finds you well.
Observations: Composition shingles.
Wavy, lifted shingles.
Installation deficiency.
Suspect: Fish mouthing. *Note: Fish mouthing occurs when the moisture tries to escape through the decking, it can reach the underside of the shingles, which is the least waterproof part of an asphalt shingle. The moisture and exposure to the weather can cause fishmouthing, particularly at points where the edges of shingles meet.
Recommendation: Recommend a licensed roofing contractor service the roof within 1 physical year or prior the onset of winter, whichever comes first.
Act upon referrals offered.
Limitation: Inspected from the roof.
Good linked article on fishmouthing. Covers new and old shingle roof coverings.

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Or why not asks this legitimate question to a group of your peers instead of wasting time searching through millions of Google results that includes “opinions” from individuals who know absolutely nothing about the subject.