Where North Shore leaks actually start
Water travels along the underside of the roof deck or across a ceiling joist before it finds its way through drywall, so the stain and the leak are often several feet apart. We start in the attic where we can, tracing dark staining and damp insulation back along the rafters to the point where the deck itself is wet. On roofs we cannot access from inside, we get up on the slope in dry weather and look for the usual suspects.
The most common failure points on the roofs we see here are flashing around skylights and chimneys, valleys where two roof planes meet, and shingles that have lifted after sitting under wet moss for a season. Each one has a different fix, and going up and patching directly above a ceiling stain without finding the real source almost never solves the problem.
Flashing and valley repairs
Flashing does the actual work of keeping water out at every place a roof plane meets something else, a wall, a skylight curb, a chimney. On older North Shore homes it was often installed once decades ago and never replaced, and the sealant around it has usually failed long before the metal itself has. We replace the flashing rather than resealing over the top of a failure, because a bead of new sealant on a bent or corroded flashing buys a season at most.
Valleys take more water volume than any other part of a roof, since two slopes drain into one channel. On the heavier rain events we get here, a valley with worn or improperly lapped shingles will show a leak faster than almost anywhere else on the roof. We rebuild valleys with proper underlayment and metal where the existing detail has failed.
Skylights and moss related damage
Skylights are a frequent call, particularly on the split level homes common around Lynn Valley and Edgemont where a skylight sits over a stairwell or a sunken living room. Most skylight leaks come from failed perimeter flashing rather than the glazing unit itself, and we check both before recommending a fix.
Where moss has been left to grow thick, it holds water against the shingle surface for days after a storm, and the granules underneath wear away faster than on a clean roof. That damage shows up as a soft, worn patch rather than a single obvious hole, and it is one of the more common repair calls we get on shaded, tree covered lots.
When a repair is not the honest answer
If we get up on a roof and find widespread granule loss, brittle shingles across most of the slope, and more than one active leak point, we say so directly rather than patching a roof that needs to be replaced. A repair on a roof in that condition buys a short window at best, and we would rather tell you that up front than have you call us again after the next heavy rain.