Flashing in a cold climate
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 and sealant, and in this climate the metal moves every day and the sealant spends four months frozen and five months in the sun.
- 1 Ridge caps. Fatigued by an annual swing few other climates ask of a roof.
- 2 The field. Snow load and age together, not one or the other.
- 3 Valleys. Meltwater runs under the snowpack here, out of sight.
- 4 Flashing. The chimney, and where a lower roof meets a wall.
- 5 The vent boot. Cold makes the rubber brittle, then a thaw opens the crack.
- 6 Eaves and ice dams. Ice builds at the edge wherever attic heat is escaping.
Why the joints go first here
Metal expands and contracts far more than the shingle around it, and a Twin Cities year asks it to travel through sixty degrees of range plus a daily freeze-thaw all winter. Every cycle shifts the flashing a fraction against its sealant; the sealant hardens with age and cracks. Meanwhile the specific geometry of Minnesota housing concentrates the damage: split-entries, walkouts and attached garages all create a lower roof meeting an upper wall, and that junction receives the meltwater of the entire slope above it, all winter, every winter.
Two shortcuts are worth recognizing in a quote. Reusing existing step flashing and sealing over it is fast and it is the most common reason a new roof leaks in its first year. And counter-flashing that is surface-caulked to masonry rather than cut into a mortar joint will fail in this climate, the freeze cycle finds the seam. Ask which of the two you are being sold.
Reading the symptom
A leak rarely appears under the failure: water travels along framing before it drips, so the stain shows up in a room away from the open joint. This is also the honest reason “the roof leaks” and “the roof is worn out” are different diagnoses.
A failed wall flashing on a mid-life roof is a flashing job; the same failure on a granule-bare covering with loose ridge caps is the roof telling you its age. Distinguishing between the two is most of what a good inspection is for, and in February, when meltwater is finding every weakness at once, it is worth having someone who can tell the difference.