What This Tells You: The roof has a leak, which can be tricky to pinpoint. "A slow leak is harder to find than a big leak," says Joan Crowe, director of technical services for the National Roofing Contractors Association (NRCA). "If it's just a couple of drips, it can be hard to find."
What This Tells You: The step flashing where the roof meets a wall is loose, rusted, or otherwise damaged.
What This Tells You: The shingles are deteriorating or reaching the end of their lifespan.
What This Tells You: The granules have probably worn off, allowing the shingles to become brittle. They probably need to be replaced.
Cracking shingles are another symptom of the same disease. Perhaps you didn't notice the granules washing away, but if you see signs of cracking in your shingles, then it probably means they are being exposed to direct sunlight and are wearing out. "The shingles are approaching the end of their service life," Crowe says. "Asphalt shingles don't like heat."
What This Tells You: The attic may not be properly vented, and you might need to reshingle.
When shingles get old and worn out, the ends sometimes start to cup — the corners turn up or the shingles look wavy. An attic that's not vented properly can exacerbate this problem. If the attic gets too hot, it can heat up the roof, which consequently heats up the underside of the shingles. The heat can cause the shingles to age faster and start to cup. Eventually, that can allow wind-blown rain to work its way under the shingles and leak into the house.
What This Tells You: You might have a critter getting on your roof, or the sealant strip under the shingles may have been damaged.
What This Tells You: You probably have ice dams. Ice dams are caused by freeze-and-thaw cycles that allow ice to build up on the roof and block melting snow from draining off. That backed-up water can get under the shingles and leak inside. Ice dams can form in as little as 1 or 2 inches of snow.
What This Tells You: There are algae growing on the shingles.