Flashing failure
A roof almost never gives out in the open field. It gives out at the transitions, where shingle meets chimney, wall or vent, because those joints depend on metal flashing and sealant, and the Piedmont works both: summer heat expands and contracts the metal daily, and the humidity never gives the sealant a dry season to rest in.
- 1 Ridge caps. Thin, hot, and the first course to loosen on a Piedmont summer roof.
- 2 The field. Streaks first, then real age. The two are not the same problem.
- 3 Valleys. Pine straw mats where two slopes drain as one, and holds the water there.
- 4 Flashing. The chimney, and the line where the garage roof meets the wall.
- 5 The vent boot. Usually cracked by its teens, long before the field around it is.
- 6 Eaves. Where gutter overflow lands, and where the fascia goes soft first.
Why the joints go first here
Metal moves more than the shingle around it, and a Southern summer moves it every single day: a chimney flashing can cycle through thousands of expansions in a covering’s life, each one working the sealant a little. Meanwhile the sealant itself ages in heat and humidity, hardening and cracking years before the shingles fail. On the region’s renovation-era housing there is a second version: the joint where an addition’s new roof meets original framing, two generations of construction held together by one flashing line, reliably the first place that house leaks.
The leak that follows rarely shows up under the failure: water travels along framing before it drips, so the stain appears a room away from the open joint. This is why “the roof leaks” and “the roof is worn out” are different diagnoses: a failed step flashing on a mid-life roof is a flashing job; the same failure on a streaked, granule-bare covering is the roof telling you its age. Distinguishing the two is most of what a good inspection is for.
Two joints the Piedmont builds into almost every house
Brick veneer is the first. Done properly, the counter-flashing above a roof-to-wall junction is let into a mortar joint and turned down over the step flashing beneath it, so water running down the brick is thrown back out. Done quickly, it is a bead of caulk laid against the face of the brick, which looks identical from the ground and lasts about as long as caulk lasts. Brick is not waterproof and never was; it absorbs and passes water through to the cavity behind it, and everything depends on the metal catching that water and sending it back out at the roof. On a house where the porch or garage roof meets a veneer wall, that line is worth asking about by name.
The second is the chimney chase: the framed and sided box, common on houses built from the eighties onward, that holds a metal flue rather than masonry. Its cap is a sheet of metal on top, and a flat sheet of metal holds water. Standing rain works the seams and rusts the pan from the inside, the collar sealed around the flue dries out and shrinks, and what runs in goes straight down inside the chase, where nobody looks until the ceiling below marks. A chase cover is an inexpensive thing to replace and an expensive thing to ignore, and it does not show up on a walk around the yard.