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

Hail damage and blistering both cause granule loss on asphalt shingles, which is why they are frequently confused during roof inspections. The distinction matters because hail damage is a covered peril under standard homeowner insurance policies, while blistering is considered a maintenance or manufacturing issue and is typically excluded from coverage. Adjusters, contractors, and public adjusters who can accurately tell the difference between the two are in a stronger position to either approve or challenge a claim determination.

What Causes Each Condition

Hail damage is caused by the physical impact of ice falling onto the shingle surface. The hailstone displaces granules at the point of contact, fractures the asphalt mat fibers underneath, and leaves a depression or bruise. The damage is immediate, caused by a specific storm event, and distributed randomly across exposed roof surfaces.

Blistering is caused by trapped moisture or volatile compounds within the shingle that expand when heated by the sun. As the gases expand, they push the asphalt upward, creating a raised bubble on the shingle surface. Over time, the blister may pop, exposing the mat underneath and shedding the granules that covered the bubble. Blistering develops gradually over months or years. It is caused by manufacturing conditions, poor attic ventilation that traps heat, or improper installation over wet decking.

Visual Differences: Side by Side

Characteristic	Hail Damage	Blistering
Shape	Round or oval depression	Round raised bubble or crater with a raised rim
Granule pattern	Granules displaced outward from impact center	Granules missing from the bubble surface; surrounding area intact
Mat condition	Mat fractured or bruised beneath the surface; feels soft on compression	Mat intact but exposed when blister pops; no bruising underneath
Distribution	Random across the roof; more concentrated on windward slopes	Can appear anywhere; often clusters in areas of poor ventilation or on south-facing slopes
Collateral evidence	Dented gutters, vents, and other soft metals	No collateral damage to surrounding materials
Edge profile	Flat or slightly concave at the strike point	Raised rim around the exposed area

The collateral evidence test is often the most conclusive. If gutters, vents, and other metal surfaces show hail dents, the granule loss on the shingles is far more likely hail-related. Blistering does not produce any damage to anything except the shingle itself.

The Tactile Test

One of the most reliable field methods for distinguishing hail from blistering is the tactile (touch) test. Press your thumb firmly on a suspected hail strike. If the spot feels soft, spongy, or gives way slightly compared to the surrounding shingle, the mat fibers beneath are fractured from impact. That is hail damage.

A popped blister, by contrast, exposes the mat but does not fracture it. The mat underneath a blister site feels firm, the same as the surrounding material. The granule loss looks similar visually, but the structural integrity of the mat is intact.

This test works best on shingles that are at a moderate temperature. Cold shingles are stiffer overall, and very hot shingles feel soft everywhere. Mid-morning on a mild day provides the best conditions for tactile evaluation.

How This Affects Insurance Claims

When an adjuster inspects a roof and finds granule loss, their determination of hail damage versus blistering drives the entire claim outcome. If they call it blistering, the claim is denied. If they call it hail, it proceeds to scoping and payment.

The most common dispute scenario involves a roof that has both conditions. Older roofs in hot climates frequently develop blisters over time. When a hailstorm hits the same roof, both types of granule loss are present. An adjuster looking for reasons to limit the claim may attribute some or all of the damage to pre-existing blistering.

If you disagree with the adjuster's determination, your options include requesting a re-inspection with a different adjuster, hiring a public adjuster to conduct an independent evaluation, or invoking the appraisal clause in the insurance policy. In all cases, detailed photo documentation with close-ups showing the flat depression profile (hail) versus the raised rim profile (blister) is your strongest evidence.

Preventing and Addressing Blistering

Since blistering is primarily a ventilation and manufacturing issue, preventing it starts with proper attic airflow. Building code typically requires 1 square foot of net free ventilation area for every 150 square feet of attic floor space (or 1:300 with balanced intake and exhaust). Inadequate ventilation traps heat against the underside of the roof deck, accelerating blister formation.

If blistering appears on a relatively new roof (under 5 years), it may be a manufacturing defect covered under the shingle manufacturer's warranty. Document the blistering with photos and contact the manufacturer's warranty department. If it appears on an older roof, improving attic ventilation can slow the progression but will not reverse existing blisters.

For contractors and adjusters who need to build a supplement on a hail claim where the carrier is attributing damage to blistering, having the adjuster's estimate in Xactimate format is essential for a line-by-line review. CapOut converts the carrier's PDF estimate into your Xactimate account in minutes, not hours so you can review the scope and build your argument with the actual data.

Related Guides

• What Does Hail Damage Look Like on a Roof?
• How to Tell If Your Roof Has Hail Damage
• How Much Hail Damage Is Needed to Replace a Roof?
• Hail Damage Roof Insurance Claims Guide