Which component serves to redirect rainwater from a roof to the ground or a drainage system?

The component that effectively redirects rainwater from a roof to the ground or a drainage system is the gutter. Gutters are specifically designed to collect rainwater that runs off the roof and channel it away, preventing potential water damage to the building's foundation or landscape. By directing this water efficiently, gutters help manage the flow of rainwater and minimize erosion and flooding in areas surrounding the structure.

The fascia is a board that runs along the lower edge of the roof, primarily serving as a support for the gutter system and enhancing the aesthetics of the building, but it does not perform the function of redirecting water. A parapet is a low wall along the edge of a rooftop, which can offer some protection and aesthetic value but is not intended for water drainage. A ridge vent is used for ventilation purposes, allowing air to escape from the attic space, but it does not play a role in directing rainwater. Hence, gutters are essential for the effective management of rainwater from rooftops.