Installing Flanged Windows – Part 4: Final Flashing and Head Flashing

This is part of a video series on installing replacement windows, covering the flashing steps that keep water out around a new window. After the window is fastened in place, the next step is taping the seams along the sides and across the top with flashing tape, a self-adhesive strip that seals the gap between the window frame and the wall. If a small wrinkle or gap shows up in the tape, it can be covered with another strip of tape or sealed with liquid flashing, a paintable sealant that bridges tricky spots.

The last piece is head flashing, a strip installed above the window that sheds water away from the top edge. It needs to cover both sides of the window and slope slightly downward so water runs off rather than pooling. The flashing gets nailed in with corrosion-resistant roofing nails, taped along the top for a watertight seal, and tied into the wall's structural sheathing behind the siding. One tricky spot, called a reverse lap, is where an overlap runs the wrong way and could let water in; it gets cleaned and sealed with liquid flashing to close that gap.

For a homeowner, this level of detail matters most if you're planning a window replacement, since sloppy flashing is a common cause of water damage and rot around windows years down the road. It's not something you'd typically inspect yourself, but knowing these steps exist can help you ask good questions if you're getting new windows installed.