Identifying Hail Damage to Asphalt Shingle Roofs

Hail events are common in many parts of the United States during spring and summer but can occur throughout the year. In fact, there were 3,762 hail events documented in 2021 alone, according to the National Oceanic and Atmospheric Administration’s National Water Service Storm Prediction Center, with more than half of those events in the states commonly referred to as “Hail Alley.” Each year, thousands of property owners experience hailstorms and report damaged roof shingles. It’s critical to know what to look for to verify hail damage. 

Map Hail Alley 608 59 Pm

The states marked in red are in an area called Hail Alley, known for its frequency of hail events.

Why Are Reports of Hail Damage so Common?

Hail is a result of raindrops being carried upward into thunderstorm updrafts, which is why hailstorms most commonly take place in seasons when thunderstorms are most likely. These raindrops reach a point in the atmosphere cold enough to freeze them, then grow as more raindrops freeze to the surface of the ice. By the time these balls of ice become heavy enough to fall, they can be of sufficient size to damage buildings and vehicles, and even harm people and animals. 

While hailfall may be disconcerting, not every hail impact causes functional hail damage. For asphalt shingle roofs in particular, functional hail damage occurs when hail has measurably reduced the functionality of a shingle that was sound prior to the impact.

Hail is a natural weather phenomenon, and roofs subjected to hailstorms can still provide years of protection with no intervention, or could require varying degrees of repair or replacement. That’s why it is vital to know what to look for when diagnosing hail damage. 


Collateral Indicators

Hail studies don’t always start on the roof. Collateral indicators of hail impact are as important as what’s on the shingles. Collateral damages to things like downspouts, vent covers, and weathered surfaces provide clear and tangible clues about the nature of the hailstorm, specifically the size (diameter), direction, and density of the hailstones.

Soft metal components such as those mentioned above, gutters, and HVAC condensing unit fins are typically the first surfaces to exhibit signs of hail impact. Dents in these collaterals can be up to two times the size of the hail that fell and are good indicators of the direction of the hail.

Vent Cover 608 58 Pm

Hail can frequently damage soft metals, such as this vent cover.


Clean spots, also called “spatter marks” or “splash marks,” occur when hail strikes a weather-stained surface, including wood, metal, shingles, or even concrete. When hail impacts such a surface, it cleans away the discoloration. The hail leaves a spatter mark trailing after this clean spot, which indicates the directionality of the hail. 

If hail has functionally damaged the roof, the shingle blemishes will match the size, direction, and density determined by damage to the collateral indicators.


Hail Damage to Asphalt Roof Shingles

On the roof itself, the most vulnerable asphalt shingles are those that face incoming hailstones and those that are not firmly backed. These include the shingles along the edges of the eaves and rakes, as well as in the valleys and ridges where the shingles are bent. Hail damage in the field of the roof will be found randomly throughout each slope. 

Shingles 608 58 Pm

Hail impacts are common along the ridgeline where shingles are bent. 


Hail size is often described in comparison to familiar objects. Damage to three-tab asphalt and dimensional-style shingles, the most widely used roofing materials, requires a hailstone size of 1 to 1 ¼ inches – or quarter- to golf ball-sized hail. Impact marks smaller than ¾ inch are very rarely functional hail damage.

Hail Size3

The size of a hailstone can be described in comparison to the size of everyday objects.


Hail strikes often leave the granules in place at the center of the blemish and cause an indentation on the back side of the shingle. An indentation is a good indication of a fracture in the shingle mat, which is a thin layer of fiberglass meant to reinforce the shingle. Mat fracture is a common result of damaging hail impact. 


Diagnosing Hail Damage

Though hail is a common cause of loss, several other elements that affect many roofs can look like hail damage. These include man-made damage, bird damage, moss and lichen growth, granule loss due to natural weathering, heat blistering, and nail pops. The nuances between true hail damage and blemishes due to other perils make expert inspection and documentation a must when diagnosing roof damage. 

To learn how a Donan expert can answer questions about the cause and origin of damage to a roof, or provide other mechanical, electrical, and structural solutions, contact us today.