Hail Damage vs Blistering on Shingles: How to Tell the Difference

Understanding the Two Conditions

Hail damage and blistering are the two most commonly confused conditions on asphalt shingle roofs. Both can cause granule loss and visible marks on the shingle surface, but they originate from completely different causes and have distinct characteristics. Hail damage results from the physical impact of ice stones striking the roof during a storm. Blistering results from moisture or volatile compounds trapped within the shingle expanding under heat, creating a bubble that eventually pops and leaves a mark.

The distinction matters enormously for insurance claims. Hail damage is a covered peril under virtually all homeowner policies. Blistering is a material defect or wear issue that falls outside the scope of storm damage claims. When a carrier denies a hail claim by attributing damage to blistering, the homeowner or contractor needs to know how to document the differences and dispute the finding.

Visual and Physical Differences

Hail strikes create depressions in the shingle surface. The impact pushes the granules aside and compresses the mat beneath them. When viewed from the side or felt by hand, hail damage feels like a dent or soft spot. The surrounding granules may be cracked or displaced outward from the center of impact. The mark has a concave profile.

Blisters have the opposite profile. A blister forms when trapped gas or moisture expands beneath the shingle surface, pushing upward and creating a raised bubble. When the blister pops, it leaves a crater with a convex rim around the edges and exposed mat in the center. The granules around a popped blister are pushed outward and upward, while hail damage pushes them downward and outward. This difference in profile is visible in close-up photographs and is one of the most reliable ways to distinguish the two.

Using Collateral Evidence

The strongest evidence for distinguishing hail from blistering comes from metal components on and around the roof. Hailstorms leave dents on aluminum and galvanized steel surfaces including vents, flashing, gutters, downspouts, and HVAC equipment. Blistering is a shingle-specific condition and does not affect metal at all. If the roof has marks on shingles and dents on metal, the marks are consistent with hail. If the shingles show marks but no metal surfaces are dented, blistering or another non-impact cause is more likely.

Pattern distribution provides additional evidence. Hail damage is random because hailstones fall erratically. Blistering concentrates on south and west-facing slopes that receive the most direct sunlight and heat, because heat accelerates the blistering process. A roof where marks appear only on the hottest slopes and not on shaded north-facing planes is exhibiting a blistering pattern rather than a hail pattern.

Handling Disputes with the Carrier

If an insurance carrier denies a hail claim by attributing the damage to blistering, the policyholder has options. Requesting a re-inspection with a different adjuster is the first step. Providing comparison photos showing both the shingle marks and collateral metal dents strengthens the case. If the dispute continues, hiring a public adjuster or an independent forensic engineer to examine the roof and issue a report is a recognized path for resolving disagreements. The appraisal clause in most homeowner policies provides a formal mechanism for settling disputes over the amount of loss when the cause is not in question.