Self-adhesive flashing tape is used in the installation of windows and doors to seal the seams and prevent moisture damage. Flashing needs to be properly installed to keep water from getting into the walls. Self-adhesive flashing tape will stick to most building materials and seal around holes made by nails and screws. Flashing tape typically comes in rolls that are four inches, six inches or nine inches wide. Flashing tape is installed after the sill pan flashing and window has been set into the rough opening.
Cut the corners of the house wrap--the plastic sheeting that goes underneath the house siding--above the top ledge of the window at a 45-degree angle to make a flap. Fold the flap up and tape it up to temporarily keep it out of the way.
Cut flashing to fit along the sides of the window with a sharp utility knife. Cut the flashing so that it is long enough to overlap the sill pan flashing and so that it extends two inches above the top of the window. The sill pan lining is the rigid fling that is installed under the window before setting it into the rough opening.
Affix the side flashing. Starting at the top, set the tape against the side of the window and gradually work your way downward. Remove the backing from the tape as you go. Use your hand to smooth down and adhere the tape as you go. Make sure at the bottom ends of the sides, the flashing overlaps the sill pan lining.
Cut the header flashing; make sure it is long enough to overlap the extended ends of side flashing.
Affix the header flashing. If your window has a drip cap, this should be installed beforehand so that it can also be sealed by the flashing. Make sure that the ends of the header flashing are completely overlapping the top ends of the side flashing.
Make sure that all of the flashing tape is laying flat and that there are no gaps or bubbles by going over it with a J roller.
Pull the house wrap flap from above the window down and over the flashing.