When a homeowner calls about a leaking roof, the conversation almost always starts with the shingles. Are they worn? Are they cracked? Do they need to be replaced? These are reasonable questions — but they're usually the wrong ones. In our experience, the majority of residential roof leaks in Southern California originate not at the field of the roof, but at the transitions: where the roof meets a wall, where a chimney penetrates the plane, where two slopes converge in a valley.

These transitions are managed by flashing — thin metal (typically galvanized steel, aluminum, or copper) formed and installed to direct water away from vulnerable joints. Flashing is not glamorous. It doesn't appear in manufacturer marketing materials. It's rarely discussed in contractor proposals. And it's almost never replaced when a roof is re-roofed, because replacing it adds cost and complexity that most contractors — and most homeowners — prefer to avoid.

The problem is that flashing has a finite service life, and that service life is often shorter than the roofing material it protects. Galvanized steel flashing begins to corrode within 15–20 years in coastal Southern California environments. Aluminum flashing is susceptible to galvanic corrosion where it contacts dissimilar metals. Improperly lapped or sealed flashing can fail within a few years of installation, regardless of material.

When we assess a roof, we document every flashing condition — not just the ones that are visibly failing. We look at step flashing along walls, counter flashing at chimneys, valley flashing at slope intersections, and boot flashing at pipe penetrations. We photograph each condition and note its severity. In our experience, roughly 60% of the roofs we assess have at least one flashing condition that will cause a leak within five years — regardless of the condition of the roofing material itself.

The practical implication for homeowners is this: when you're evaluating a roofing proposal, ask specifically about the flashing. Will it be replaced? If not, why not? What is its current condition? A contractor who can't answer these questions in detail hasn't looked closely enough at your roof.