How to: Door Flashing

Remove the exterior door. It's best to install flashing before installing the door. If your door is already installed, however, remove it is necessary.

Unscrew and remove the metal threshold if one is present.

Measure the base of the door frame. Cut three strips of self-adhesive membrane flashing 4 inches longer than the door frame.

Position one strip of flashing about halfway across the width of the wooden threshold with 2 extra inches of flashing on each end at the door frame. Make excess flashing face the home's interior. Peel off the flashing's paper to reveal the adhesive portion. Apply the flashing to the wooden threshold. It must cover one-half of the threshold and 2 inches of the door frame on both sides. Tuck excess flashing around the interior side of the wooden threshold.

Apply one piece of flashing over the exposed half of the wooden threshold. Arrange this piece of flashing so that it slightly overlaps the first strip of flashing, but extend it at least 1 inch beyond the exterior portion of the threshold. Remove the flashing's paper, and put the flashing in place. Tuck its excess around the exterior part of the threshold.

Apply the third strip of flashing along the seam created by overlapping the previous two pieces flashing. The third piece won't overhang the threshold, but, like the first two strips, it must cover the threshold and 2 inches of the door frame on each side.

Cut two strips of self-adhesive membrane flashing about 4 inches wide. Peel off their backing. Align each piece of flashing with the threshold's exterior corners, and apply the flashing in those locations. Cut a diagonal line in the loose flashing with scissors. Fold the resulting corners over the threshold and door frame.

Cut and apply additional strips of flashing to cover all exposed wood remaining on the threshold.