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House roofs fail at details far more often than they fail as systems. Knowing the difference is the difference between a repair bill and a replacement bill.
Flashing failures
The most common leak source on any house.
Chimney flashing, wall and step flashing where a roof meets a vertical surface, valley flashing where two slopes meet, and skylight flashing. All are junctions, and junctions move.
Sealant applied over failed flashing is a temporary measure that hides the problem. Correct flashing is mechanical.
Pipe boot failure
The rubber or neoprene collar around each plumbing vent splits under years of ultraviolet exposure.
It is cheap to replace, predictable in timing, and responsible for a surprising share of ceiling stains.
Missing, lifted or creased shingles
Wind damage starts at edges and corners. A creased shingle has been lifted and dropped and will not reseal, even though it is still in place.
Missing tabs after a storm are obvious. Creasing is not, and it matters just as much.
Granule loss
Granules protect the asphalt beneath from sunlight. Losing them accelerates everything.
Some loss is normal, especially from a new roof. A gutter full of granules on an older roof is a countdown.
Cracked, slipped or broken tile
On a tile roof, damaged tiles are a symptom and rarely the actual leak. Tile sheds water; the underlayment beneath keeps it out.
A tile roof that leaks with intact tiles usually has failed underlayment, which is a different job and a much larger one.
Valley failure
Valleys carry more water than anything else on the roof. Debris collects there, holds moisture and eventually diverts water sideways under the covering.
Nail pops and backed out fasteners
Fasteners work loose through thermal movement. A raised nail lifts the material above it and creates a path.
Ventilation problems presenting as leaks
Condensation in the attic drips onto insulation and ceilings and is regularly reported as a roof leak. It appears in cold weather rather than during rain, and across an area rather than at a point.
Ice damming, in cold climates
Melt water refreezing at the eave backs water under the covering. It shows near exterior walls, in winter, on the sunny side.
How to tell detail failure from system failure
One identifiable point, on a roof with life left, is a repair.
Failures appearing in several unrelated places within a short period, on a covering at or near the end of its life, is a system telling you it has finished.
