How to Fix Roof Flashing Leaks

Flashing is the thin metal barrier that bridges the gap between your roof and anything punching through it—chimneys, vent pipes, skylights, valleys. When flashing fails, water doesn't run off anymore. It pools, seeps into the gap, and starts rotting the roof deck beneath. A flashing leak is one of those problems that looks small from inside the attic but spreads fast once it finds wood. The good news: most flashing leaks are fixable without a full roof replacement. You're replacing a seal, not the whole roof. Done right, new flashing will outlast the surrounding shingles by years.

1. Find the Leak Entry Point. Go into the attic and locate the wet spot. Mark it with a pencil or tape so you can find it from the roof. Then go outside and inspect the roof above that mark. Look for rust streaks running down the flashing, visible gaps between flashing and shingles, missing caulk, or standing water pooling on the flashing surface. Take photos from ground level before climbing.
2. Strip Away the Old Metal. Use a flat pry bar to gently lift the shingles above and around the flashing. Work slowly—you're not trying to salvage these shingles, but you don't want to tear them more than necessary. Once shingles are lifted, unbend or cut the nails holding the flashing down. Slide the old flashing out carefully. If it's rusted or corroded, it will likely break apart—that's fine. Remove all old nails and any remaining debris.
3. Replace Any Rotted Wood. Look at the wood underneath where the flashing was. If it's solid, dry, and shows no soft spots when you press a screwdriver into it, you're good. If there's rot—dark staining, soft wood, or spongy feel—cut out the damaged section with a reciprocating saw and replace it with new plywood cut to fit. Nail or screw it flush. Let any wet wood dry completely before installing new flashing.
4. Seat the New Flashing. Slide the new flashing piece under the shingles above it and over the shingles below. The overlap should be at least 4 inches on all sides. Position it so water will flow down and away from the vent or chimney, not toward it. The bottom edge of the flashing should be on top of the shingles below, not underneath them. Secure the top edge with galvanized roofing nails, one nail per corner and one every 6 inches along the top edge.
5. Cement the Edges First. Apply a continuous bead of roofing cement or sealant caulk under the lifted shingles where they now sit on the new flashing. Also run a bead along the top edge of the flashing where it meets the shingles. Use a caulking gun and keep the bead about 1/4 inch thick. Smooth it with a wet finger if you want a cleaner finish, but thick is better than thin—gaps let water in.
6. Nail Down the Shingles. Once the cement is tacky (5-10 minutes), press the lifted shingles back down onto the flashing. Drive new roofing nails through each shingle into the flashing or roof deck below, spacing them 6 inches apart. Use galvanized nails long enough to penetrate the deck but not so long they stick through. This holds the shingles down and keeps water from running up under them.
7. Lock Down the Tabs. Once shingles are nailed, cover each nail head with a dab of roofing cement. Apply a small bead of cement under the edge of each shingle tab to lock them down and prevent wind lift. Let all cement cure for 24 hours before walking on the roof again or exposing it to rain.
8. Test Under Real Rain. Go back into the attic during or shortly after the next rainstorm and look at that marked spot. You should see no new water. If there's still moisture, the leak may be coming from a different angle or the wood may not have dried fully. Mark the new leak location and plan a follow-up repair.