The invention pertains to a novel method for flashing a door, window, ductwork or other rough opening in a building surface. The method involves the use of a tape strip having a continuous, non-perforated, machine-direction-splittable plastic release sheet liner which is selectively removed in controlled portions without the need for cutting strings. Anisotropic tear-resistance properties of the release liner facilitate a careful, controlled, and progressive installation of the tape strip while avoiding unwanted transverse tearing that could block or foul the adhesive.