Granules are the tiny mineral pebbles bonded to the surface of an asphalt shingle. They give the shingle its color and, more importantly, shield the asphalt underneath from the sun's ultraviolet rays. As long as the granules stay put, the shingle is protected. When they wear off or get knocked loose by hail or age, the bare asphalt is exposed, dries out, and the shingle starts to fail. Granule loss is one of the clearest signs a roof is aging or storm-damaged.
Look closely at an asphalt shingle and you will see it is covered in fine, sandy granules. These are not just for color.
They form a protective coating over the asphalt layer that does the actual waterproofing. Asphalt left bare in the sun dries out, hardens, and cracks, so the granules act like sunscreen, taking the ultraviolet punishment year after year so the asphalt underneath stays flexible and intact.
Granules come off slowly over a roof's whole life, which is normal. What is not normal is sudden or heavy loss.
Hail knocks granules off in small dark spots where the impact lands, exposing the asphalt mat beneath. An aging roof sheds them broadly as the bond weakens.
Either way, the loose granules wash down the slopes and collect in the gutters, which is why a pile of grit in the gutters or a gritty black wash at the downspouts is a telltale clue.
For a homeowner, granules are an easy roof-health gauge you can check from the ground. After a storm, granules in the gutters can point to hail or wind stress.
On an older roof, widespread bald, shiny patches mean the protection is wearing thin and the shingles are entering their final years. Either pattern is worth a documented inspection to learn how much life the roof has left.
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