How to Replace Damaged Roof Flashing

Flashing is the unsung hero of your roof, acting as the primary defense against water intrusion at the most vulnerable points: chimneys, vents, and roof-to-wall joints. Over time, metal corrodes, nails back out, and caulk cracks, turning a small, ignored gap into a major interior leak. A roof that is 'done well' doesn't just look flush; it creates a redundant system where shingles overlap the flashing, and sealant acts only as a secondary backup. Taking on this project requires a head for heights and an eye for detail. You are essentially rebuilding a drainage path, so every piece must be installed in the correct sequence to ensure water flows over the metal rather than under it. If you keep the lap order logical and use the right materials, you will stop leaks at their source and add years of life to your roof deck.

  1. Pry Shingles Without Breaking. Carefully pry up the shingles covering the existing flashing using a flat pry bar. Work slowly to avoid cracking the shingles, as you will need to reuse them.
  2. Strip Out the Old Metal. Pull the old nails holding the flashing in place and slide the damaged metal out. Clean any remaining old sealant, rust, or debris from the underlayment and wood sheathing.
  3. Test for Hidden Rot. Check the roof sheathing for signs of rot or water damage while the area is exposed. If the wood is soft or crumbly, cut out the section and install a matching piece of plywood before proceeding.
  4. Lock Flashing in Place. Slide the new flashing into place, ensuring it tucks under the shingles above. Secure it using roofing nails placed only in the top edge where they will be covered by the next layer of shingles.
  5. Seal Without Trapping Water. Apply a bead of roofing cement under the edges of the flashing and along the nail heads. Fold the shingles back down and apply a dab of cement under each shingle corner to hold them flat.
  6. Sweep and Secure All Edges. Inspect the work area to ensure all nails are driven flush and no metal edges are exposed to catch wind or debris. Collect all old metal scraps and nails from the ground below.