Has Anyone Seen This Before?

This is a new one for me… looks to be a defect of some kind, but I haven’t seen it before. Maybe caused during storage?

What do you guys think?

O ya, 20-year 3 tab in relatively good shape otherwise. There was only one small section (under a tree) affected and then two other small areas in valleys. Condition was present on probably around 5% of the roof surface. Soffit vents present, but blocked by insulation… gable vents, and ridge vents present.

Thanks in advance for any ideas.

South Valley.JPG

Affected Area.jpg

Close Up.JPG


As asphalt shingles age, large bubble-like blisters may appear on the surface, some as large as a quarter. They may be open, exposing the asphalt, or closed. Blisters are more likely to appear when there is inadequate ventilation, or in areas where tree sap drips onto the shingles. Small “rash” blisters do not affect the performance of the shingles.

Hi Barry - That was my first thought, but the condition was present on the other side of the roof as well… far from any trees. The last picture, labeled South Valley was the one that made me wonder if it was a defect of some kind. The blistering / bubbling was in a perfect rectangular shape and there were no trees anywhere in the area.
Anyway, thanks for the repsonse.


The images 2 and 3 look very typical for blistering. The two shingle in image 4 are atypical with a small rectangle of intense blistering on each tab and nothing outside the margin of the rectangle. Was there something under those tabs?

Ya Chuck, it was the fourth picture that was odd to me, too. There was nothing unusual beneath, just metal valley flashing that is seen every day. Soffit vents in the area were blocked, so maybe that contributed… lowest part of the space, no air and whatnot.

Thanks for the responses, I’ll file it in my brain as uncommonly common…

During manufacturing the last step is a top coating of adhesive asphalt is applied and ceramic granules are then embedded.
Pour manufacturing.
That is a low grade shingle.
Recommend yearly observation.