How to Repair Window Frame Flashing

Sienna Condy

If you have a window that leaks around the frame, the window flashing probably needs to be repaired or replaced. A type of peel-and-stick membrane, window flashing prevents water from leaking around the window and into the house. Over time, siding or other exterior elements cut or wear away the flashing, creating a need to replace it. In some cases, such as with a double-hung window, homeowners place additional pan flashing along the bottom edge of the hole for the window before a window is installed to prevent leakage.

Window flashing is commonly used around windows in homes with siding, which can leak.
  1. Remove the old window from the window frame per the manufacturer's instructions. Remove any screws or nails from the trim. Pry the trim off with a pry bar.

  2. Remove any other nails and screws around the window, if necessary. Peel back the old flashing and remove it from the window if necessary. Remove the old window out of the window hole. In some cases, you may have to peel back the siding slightly to remove the window.

  3. Remove the pan flashing if the leak is occurring around the bottom of the window. Use the old piece of pan flashing as a guide. Cut a new piece of pan flashing with a utility knife. Install the pan flashing where the old pan flashing was. Peel the back of the pan flashing off slowly as you install it. The bottom piece should overlap the window jamb by at least a few inches and should run over the edge of the outside sill by at least an inch or two.

  4. Measure the height of the window. Add approximately 6 to 12 inches to the measurement. Cut flashing to length for both sides of the window with a utility knife. Apply flashing to the sides of the window. Overlap the jamb a few inches on each side. Both the bottom and top of the membrane should run past the bottom and top of the window. Try to extend the top and bottom of the flashing at least 3 to 4 inches longer than the window if possible. This precaution will help keep water from getting in the window. Use the utility knife to remove any excess.

  5. Measure the inside, bottom corners of the window. Cut a piece of flashing membrane to fit into each corner. Apply the flashing in each corner over the seam where the larger pieces of flashing meet. The flashing patches should overlap the other pieces. This process will help reduce the chance of leakage.

  6. Measure the width of the window. Add 6 to 12 inches to the measurement. Cut a piece of flashing to length using a utility knife. Apply the flashing to the top of the window. The flashing should overlap both sides. Cut the flashing in the corners. Fold the membrane over until it sticks to the inside of the window frame.

  7. Install the window per the manufacturer's instructions.