07/20/2026
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Shingle blistering refers to raised, bubble-like bumps on asphalt shingles, typically caused by manufacturing defects (residual hydrocarbons in the asphalt) or poor attic ventilation that traps extreme heat. If the blisters remain intact, they are largely a cosmetic issue, but once they pop, they expose the shingle's matting to UV rays and moisture, accelerating roof erosion and granule loss.
What Causes Shingle Blistering?
Shingle blisters primarily appear on asphalt and fiberglass composition shingles. The main causes include:
*Poor Attic Ventilation: When attics lack proper intake and exhaust, trapped heat causes the asphalt in the shingles to overheat and bubble. This kind of blistering is often isolated to south- or west-facing slopes that receive the most intense sunlight.
*Manufacturing Defects: Bitumen (the tar byproduct used to coat shingles) can sometimes contain residual hydrocarbons. When heated by the sun, these compounds can undergo micro-explosions that kick protective granules off the top of the shingle.
*Trapped Moisture: Moisture trapped inside the shingle during the manufacturing process can turn to steam when the sun heats the roof, pushing the surface material up.
Are Blistered Shingles a Problem?
*Closed/Intact Blisters: If the blisters haven't popped and are just raised bumps, they usually do not cause immediate leaking.
*Popped Blisters: When the blisters break, they leave behind small pockmarks with rigid sides. Once popped, the exposed areas rapidly lose protective granules, leaving the roof vulnerable to water damage and severe wear.
How to Identify and Differentiate
*Blistering is often mistaken for hail damage, which causes concave bruising rather than a rigid-sided bubble with lost granules. Blisters also generally show up within the first year after a roof installation