What would cause this on shingles?
Improper installation, and possibly “nail pops” both.
Poor installation practices.
California Cut Valley.
Shingle not flat. Bulging Shingles. Poor sealing.
Likely the composition shingles were laid when it was cold and the packs were stacked poorly and the installers did not give a chance to warm up the bundles so the strips were stiff and not pliable when laid.
Any images further back?
Imo, the courses were butted together too tight leaving no room for expansion. The result is buckling. I say this with caution because I was not there.
Was it just in this one area or the entire roof? Multiple layers maybe?
Multiple areas, one layer.
Possibly stored not flat before installation.
maybe installed over wet felt paper underlayment…
I agree with Robert
I’ve seen that on recently installed shingles during a cold time of year when it warms up rapidly. It was on a new build. The strange thing is the way it would come and go (I went out and looked several times - largely just due to curiosity). Something was expanding/contracting but I was never sure what. I didn’t think the actual shingles would change that much or we’d be seeing it all over the place. Temps in my area of Oregon vary by roughly 100 degrees throughout the year.
Bundles compressed into the slats at the bottom of the pallet.
Everything looked good from inside the attic, Todd? Insulation/ventilation, roof structure, etc?
Attic and structure looked fine. My best guess is expansion. I’ll note what I see in my report and recommend further evaluation.
It will also most likely void any manufacturer’s warranty.
Looks like defective shingles and or improper installation, either way you’re doing the right thing writing it up.
I am surprised nobody said wrinkled underlayment. That would be my guess, James mentioned it could have been wet, which is the likely culprit to wrinkles. Tar paper underlayment should not be rained on before shingle installation. Synthetic underlayment wouldnt matter.
Its funny you posted this, because I had the same thing today, and I was going to post a question about how serious it would be. I could physically push all the wrinkles down pretty easily.
I think the biggest issue is that it would just lead to faster wear at those spots., and maybe wind driven rain intrusion in your case.
I think Jim was meaning that when he posted this:
Which is why I mentioned him in the comment
Sorry. I didn’t read far enough…my bad.
When my time is limited, I do that sometimes…I’ll try to watch more closely.