Ninety percent of roof leaks trace back to one culprit: failed flashing. Those thin metal strips that seal transitions and penetrations take constant abuse from sun, rain, and temperature swings. In San Diego, where UV exposure accelerates deterioration, flashing problems show up sooner than homeowners expect.
Understanding Where Flashing Fails
Flashing appears wherever your roof meets something else. Around chimneys, along walls, at skylights, in valleys where roof planes intersect—these are the vulnerable spots that demand attention.
Chimney flashing fails most often. The joint between masonry and roofing material moves constantly as temperatures change. San Diego's temperature swings—from cool mornings to hot afternoons—work that joint repeatedly. The caulk cracks, the metal corrodes, and water finds its way in.
Step flashing along walls is equally vulnerable. These L-shaped pieces overlap like shingles, directing water away from the wall. When one piece corrodes or slips out of position, water runs behind your siding and into the wall cavity. The damage often goes unnoticed until interior paint starts bubbling or mold develops.
Valley flashing handles the heaviest water flow on your roof. During San Diego's winter rains, gallons of water funnel through these channels. Debris accumulation, corrosion, or improper installation creates leaks that can damage multiple areas of your home.
The inspection process matters. From the ground, flashing problems are nearly invisible. Getting on the roof (or hiring someone who will) reveals lifted edges, rust spots, dried-out sealant, and gaps that explain those mysterious water stains on your ceiling.
Water doesn't always leak directly below the problem spot. It travels along rafters and sheathing, appearing far from the actual entry point. That stain in your living room ceiling might trace back to flashing failure twenty feet away.
Repair approaches depend on the extent of damage. Minor issues—dried caulk, small rust spots, slightly lifted edges—respond well to cleaning, treatment, and resealing. More significant damage requires partial or complete flashing replacement.
Matching materials matters for longevity. Galvanized steel, aluminum, and copper all serve as flashing materials. Mixing metals creates galvanic corrosion, where one metal deteriorates faster due to electrochemical reaction. Quality repairs use the same metal as the existing flashing or completely replace the section.
Sealant selection affects durability. The wrong product fails within a year. Polyurethane sealants handle roof movement and temperature extremes better than standard caulk. They cost more but save money by lasting longer between applications.
Prevention starts with annual inspections. Catching flashing problems early—before they cause interior damage—keeps repair costs manageable. Schedule inspections in spring after winter rains and in fall before the wet season returns.
Quality installation makes the biggest difference. Flashing that's properly stepped, adequately overlapped, and correctly sealed rarely causes problems within its expected lifespan. Poor workmanship creates leaks from day one.
