One gap after a storm is not the same problem as a line of them. What the underlayment does and does not protect, and what to check from below.
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Reading asphalt shingles from the ground
Asphalt shingles fail visibly and fairly predictably, which is unusually helpful. Most of what you need to know can be seen with binoculars from the yard.
What the roof looks like tells you how much life is left
Asphalt shingles are the most common roof covering in the United States by a very wide margin, and they have one genuinely useful property: they tell you how they are doing. Unlike a hidden failure in a flashing detail, shingle wear is visible, and the different kinds of wear mean different things.
A missing shingle is usually a wind event, and the question is not really the shingle — it is whether the ones around it are still sealed. Shingles rely on a strip of adhesive that bonds each course to the one below; once that seal breaks, a shingle can look perfectly fine and still lift in the next storm. That is why one missing shingle in the middle of an otherwise sound roof means something different from three missing in a line along the rake edge.
Curling and cupping are age and heat, usually from the long side, and they tend to show up first on the slope that gets the most sun. Cracking is the mat itself becoming brittle. Granule loss — the sandy grit collecting in the gutters — is the shingle losing the layer that shields the asphalt from ultraviolet light, which is what actually kills it. A little after a new roof is normal and expected. A lot, years in, with bald dark patches visible from the ground, is not.
Then there is the cosmetic layer that worries people far more than it should. Those dark streaks running down a north-facing slope are algae, not decay, and they do not shorten the life of the roof. Moss is a different matter: it holds water against the shingle and lifts the edges as it grows, so it does cause damage, but the common instinct — get up there and pressure wash it — strips the granules off and does far more harm than the moss ever would.
Everything in this section is written to be checked from the ground with a pair of binoculars, from a ladder set at the eaves, or from inside the attic. We do not give step-by-step instructions for replacing shingles, and that is a deliberate choice rather than an oversight. Nearly every other page you will find on these searches does, and we think the honest version of this advice is the one that tells you what you are looking at and what it means — not the one that puts you on a slope.
Shingles guides
Three different failures with three different timelines. Which ones mean years left and which mean you should start planning.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.