How to Replace the Flashing Around a Dormer Window

Properly sealing a window is important because it prevents drafts and leaks from occurring. There are several layers of protection around the windows, including flashing. Flashing consists of metal strips that are placed around the joint where two different surfaces meet, such as along a chimney or around doors and windows. When you're replacing a dormer window, you could damage the old flashing, which means it has to be replaced.

Tape measure
Aluminum flashing
Gloves
Tin snips
Hammer
Galvanized roofing nails
Work gloves

Instructions

- 1
  Measure the height and width of the window. Add four inches to each measurement, and cut four strips of aluminum flashing to match. Adding the extra four inches provides extra protection against leaks.
- 2
  Install the flashing along the bottom edge of the window by sliding the top of the flashing underneath the bottom flange of the window. Position the flashing so that it extends two inches past each side of the window. Drive galvanized roofing nails through the flange and the flashing, and into the siding.
- 3
  Slide one of the flashing strips underneath the flange on one side of the window, centering it so that two inches of the flange extends past the top and bottom of the window. Overlap the bottom of the flange with the side piece, which prevents water from seeping down underneath the bottom flashing. Nail the flashing into place.
- 4
  Install the flashing on the other side of the window, following the same process you used for the first side.
- 5
  Slide the flashing for the top of the window underneath the flange along the top edge. Center the flashing over the window, with two inches extending past each side of the window, and overlap the side flashing. Nail it into position with galvanized roofing nails.

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