Ask a roofer where roofs leak, and the answer is almost always the same: the flashing. It is the least glamorous part of any roof, a bit of metal you rarely notice, and it does the single hardest job up there. Understanding what flashing is and why it matters explains most roof leaks and helps you tell a careful roofing job from a sloppy one.
A roof sheds water easily across its flat, open surface. The problem is everywhere that surface is interrupted, at a chimney, a wall, a valley where two roof planes meet, a skylight, or a vent. At each of those spots, water has to be steered around the interruption and back onto the roof. Flashing is the metal, usually galvanized steel, aluminum, or copper, that does that steering, layered and tucked so water flows over it and away rather than into the gap.
Because flashing lives at the hardest-working spots on a roof, it is what fails most. The metal flexes with the daily heating and cooling, catches wind, and corrodes over the years. Very often, the real failure is that someone, a previous owner or a careless contractor, tried to seal a flashing joint with caulk instead of proper metal, and caulk dries and cracks within a season or two. Once flashing lifts or fails, water pours into the joint it was meant to seal, which is covered on our page on flashing failures.
| Location | What the flashing does |
|---|---|
| Chimney | Seals the joint around the masonry |
| Walls and dormers | Seals where roof meets vertical wall |
| Valleys | Carries water where two roof planes meet |
| Skylights and vents | Seals around each penetration |
| Eaves (drip edge) | Directs water into the gutter |
This is the key lesson. Caulk has its place as a supplement, but it is not a substitute for proper flashing. A bead of caulk over a failed flashing joint hides the problem for a season and then leaks again, which is why the lasting fix for a flashing leak is to reflash the joint correctly, not to add more sealant. Our flashing repair is built around doing it the right way.
When you get a reroof or replacement, the flashing is one of the most important, and most easily skipped, parts of the job. A cheap bid may reuse old flashing to save money, which is a leak waiting to happen. New flashing at every penetration is worth paying for, which is why it is a line to check on any estimate, covered on our page on reading a roofing estimate. Good flashing is quiet, invisible, and the difference between a roof that stays dry and one that does not.
Because flashing is behind most leaks, a stain near a chimney, skylight, or wall points to it first. If you see one, our pages on chimney leaks and flashing around chimneys, vents, and valleys go deeper, and a roof inspection confirms the source so the right repair goes in.
We reflash properly, not with caulk. Call (310) 806-5959 or request an estimate below.
Tell us where the stain shows and we will trace it and give you a written price for a lasting fix, with no obligation.