What hail actually does to an asphalt shingle

An architectural asphalt shingle is a sandwich. In the middle is a fibreglass mat, which is the structure and the thing that holds a nail. Over it is asphalt, which is the waterproofing. Over that is a layer of ceramic-coated mineral granules, which are the colour, the fire rating, and above all the sunscreen: they exist to keep ultraviolet light off the asphalt, because ultraviolet light is what turns asphalt from a flexible waterproof membrane into something with the consistency of a cracker.

Hail attacks that sandwich in three different ways, and they behave completely differently.

One: granule loss

The commonest outcome, and the least dramatic to look at. A stone lands, and the impact knocks the granules off in a rough circle somewhere between the size of a pea and the size of a half dollar. Underneath, the asphalt shows as a darker patch. On a roof that has already weathered fifteen years the contrast is subtle, which is why granule loss from hail gets confused with granule loss from age.

The distinction an inspector is drawing is about pattern. Age sheds granules gradually and everywhere, heaviest where water concentrates and where the sun is hardest. Hail sheds them in discrete circular spots, randomly scattered, with a density that changes slope by slope depending on which face the storm hit. A gutter full of granules after a storm is a clue but not a finding, because gutters accumulate granules constantly.

Two: bruising, which is the real damage

A bruise is a fracture in the fibreglass mat underneath a surface that may look almost normal. You find it by touch as much as by eye: pressed with a thumb, a bruised spot gives slightly, the way a soft patch on an apple does, because the mat under it is no longer continuous. Some inspectors call it a soft hit. It is the finding that matters most and the one an untrained eye essentially never sees.

A bruise does not leak. It has no immediate consequence at all. What it does is create a line of weakness that thermal cycling then works on. St. Louis gives a roof roughly a hundred freeze and thaw crossings a year and a summer deck temperature that can pass 150 degrees. The fracture opens, the asphalt around it, already stripped of granules by the same impact, gets brittle, and eventually the shingle cracks through along the line that the stone drew years earlier.

Three: mechanical damage

At the top of the size range hail stops bruising and starts breaking. Stones from roughly an inch and a half upward can split a shingle outright, tear the tab, break the sealant strip that holds each course down against wind, or punch through an older brittle shingle entirely. NOAA logged stones up to two and a half inches in St. Louis County across 2020 to 2025, which is tennis ball size and firmly in this territory.

Broken sealant strips deserve their own mention because they are almost never noticed. Once the strip is broken the tab above it is loose, and the next serious wind lifts it. A roof can therefore fail from the wind event in August because of the hail event in April, and the wind gets the blame.

What it is not, which matters just as much

• Blistering. Small raised bubbles that pop and leave a crater, caused by moisture or volatiles in the asphalt, not by impact. Craters from blisters have raised rims and a sharper edge. They are a manufacturing or ventilation issue.
• Foot traffic. Scuffing and granule displacement in a walkable line, usually running toward a chimney or a satellite mount. Directional, not random.
• Mechanical marks. Tool drops, ladder scrapes, and the tell-tale row of dimples where somebody set a boot on a ridge.
• Normal aging. Uniform, everywhere, worst on the south and west faces, accompanied by curling at the tab edges and a chalky look.

A competent inspection is at least as much about ruling these out as about finding hail, because an adjuster who has seen a thousand roofs will rule them out immediately and a report that confuses them is a report that gets discounted.

The one that gets argued about: cosmetic

On metal roofing, metal accessories, and to a lesser extent on some shingle claims, the argument is not whether the hail hit but whether the result is functional or cosmetic. A dent in a standing seam panel almost never affects the panel's ability to shed water. Many policies now carry a cosmetic damage exclusion or a separate cosmetic endorsement that explicitly says so. If you have metal anywhere on the house, that clause is the one to read on your declarations page, before you do anything else.