The answer to 'what causes flashing' is flashing is a thin metal or plastic strip used to prevent water leaks in areas where the roof meets another surface, like a wall or chimney. Flashing is installed to create a waterproof barrier and divert water away from critical areas on the roof. It is an essential component of a properly installed roof system.
Flashing can fail for a few common reasons: age and wear, improper installation, damage from weather or impact, or poor sealant around the edges. Over time, flashing can crack, rust, or become dislodged, allowing water to seep in and potentially cause leaks and damage to the roof and home interior.