The answer to 'what is flashing' is flashing is a critical component of a roof system that helps prevent water leaks. Flashing is a thin, impermeable material, usually made of galvanized steel, aluminum, or plastic, that is installed at roof joints, edges, and penetrations to divert water away from vulnerable areas and prevent it from entering the home.
Flashing is typically installed around chimneys, skylights, vents, and other roof protrusions, as well as along the edges of the roof, such as the eaves and rakes. It is designed to create a watertight seal and redirect water runoff, ensuring that moisture does not penetrate the roof and cause damage to the underlying structure or interior of the home.