Seal the Opening
An innovative special flashing system was used to seal and protect the window from leaking for this particular project. Apply this double-sided adhesive along the surface of the window frame, starting along the top. Overlap the next strip at the corner (Image 1), making sure there are no gaps, and press into place.
Lay pan flashing down on the sill using flashing tape. You can create this pan flashing with window tape. Start the flashing on the sill on one side of the window and extend it to the other side (Image 2). Then make two cuts so you can fold the flashing over the top of the sill. The adhesive creates a watertight seal and helps protect the sill from condensation or leaks, which should prevent any future rotting.
Note: The outside of the tape has a polyethylene film that helps keep the water out. Add a second layer of flashing over the first layer. Cut the outside edges so this layer can lay flat against the sheathing.
This is a very sticky asphalt based product that will create a positive seal once the window goes in. It's pliable.