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 Front Range the daily temperature swing works every one of those joints season after season.
- 1 Ridge caps. Worked loose by a temperature swing that happens every single day.
- 2 The field. High-altitude sun dries the covering out from above, faster than the calendar says.
- 3 Valleys. Where two slopes drain as one, and where meltwater runs longest.
- 4 Flashing. Chimney joints, and the line where the garage roof meets the house.
- 5 The vent boot. Rubber cracks early at this altitude, well before the shingles do.
- 6 Eaves. Ice builds at the edge wherever the attic is leaking heat into the roof.
Why the joints go first
Metal expands and contracts more than the shingle around it, so every hard swing between warm afternoon and freezing night shifts the flashing a fraction against its sealant. The sealant, meanwhile, is aging in the same altitude sun that ages the shingles. The joint that was watertight for fifteen years opens a hairline, and the leak that follows shows up indoors somewhere else entirely, water travels along framing before it drips.
This is also 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 problem; the same failure on a covering that is brittle and granule-bare is the roof telling you its age. Distinguishing the two is most of what a good inspection is for.
The joints that give out here, roughly in order
Chimneys lead, because masonry and a wood-framed roof move independently and the flashing has to absorb the difference for decades. The counter-flashing mortared into the brick is usually what lets go first, and on a wide chimney the cricket, that small ridged saddle behind it, is either there or the snow sits against the brick until April. Sidewall step flashing comes next, and it matters more here than the average because of how the post-war subdivisions were drawn: split-levels and two-story plans put a lower roof into a wall constantly, and every course of that junction needs its own piece of metal woven up behind the siding.
Then there is the joint that is close to a Front Range signature. A great many homes in the metro run a rooftop evaporative cooler, or ran one and had it taken off, and either way there is a curb cut through the deck with metal folded around it. A working unit drips onto that curb all summer and has a water line run to it. A removed one leaves an opening closed up by whoever hauled the box away, sometimes properly, sometimes with a sheet of tin and a tube of caulk that is now ten years old. An evaluation that walks past the curb without looking into it has skipped the likeliest hole in the roof.