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 on the Sound they spend eight months of the year wet, under debris, without a real chance to dry.
- 1 Ridge caps. The first pieces to lift, and the ones the weather gets underneath.
- 2 The field. Moss on the damp slopes holds water where the covering wants to dry.
- 3 Valleys. Needles mat where two slopes drain as one, and stay wet for months.
- 4 Flashing. The chimney, and where an addition meets the original roof.
- 5 The vent boot. Rubber perishes quietly under a canopy that never lets it dry out.
- 6 Eaves. The last part of the roof to dry, and the first to go soft.
Why the joints go first here
Sealant ages fastest where it stays damp, and a joint under needle litter or moss edge is damp from October to May. Near the water, salt air adds its own tax: flashings, vent caps and fasteners corrode years ahead of their inland twins, so a shoreline roof can have a healthy covering and failing metal at the same time. And on the region’s remodel-heavy older stock, the joint between an original roof and a later addition is the most failure-prone line on the house: two roof generations, one bead of sealant holding the meeting.
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 the honest reason “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 moss-eaten, edge-soft covering is the roof telling you its age. Distinguishing the two is most of what a good inspection is for.
Skylights, and the leak that is not a leak
This region puts skylights in houses the way drier ones put in windows, for the obvious reason, and every one of them is a hole in the roof with metal folded around it. How it was mounted matters more than the brand. A curb-mounted unit sits on a built-up frame with step flashing woven up the sides and a head flashing over the top, which is the arrangement that survives; a deck-mounted unit lies closer to the plane of the roof and depends on its flashing kit and its perimeter gasket, and gaskets have a working life of their own, generally shorter than the roof they sit in. On a covering being evaluated for age, the skylights get their own verdict.
Before assuming a wet skylight is leaking, though, check the weather it happens in. Glass is the coldest surface in the room, the air in a Northwest house in February is full of moisture, and the two meet along the bottom of the light well. Condensation runs clear, arrives on cold clear mornings as readily as on wet ones, and marks the low edge rather than the corners. A genuine leak shows up during or just after rain and usually stains one corner where the flashing turns. Sorting out which one you have decides whether the answer is on the roof or in the bathroom fan.