What is base flashing?

Base flashing refers to the type of flashing that is installed at the intersection of a vertical wall and a horizontal surface, such as a roof. Its primary purpose is to redirect water away from the wall and prevent it from penetrating into the building structure. When flashing is turned up on a vertical surface, it creates a barrier that helps channel water away from vulnerable areas, thus protecting against water intrusion and potential damage.

Choosing the option that states flashing turned up on a vertical surface accurately captures the functionality of base flashing. This design allows for proper drainage and minimizes the risks associated with water pooling or running down the wall, which could lead to leaks and structural issues.

The other choices misinterpret the function or positioning of base flashing. For instance, flashing on horizontal surfaces alone lacks the vertical protection needed in this scenario. Flashing turned down on a vertical surface would not serve the intended purpose of preventing water from running behind the flashing. Lastly, flashing installed primarily for aesthetic purposes neglects the critical role that base flashing plays in safeguarding the integrity of the building envelope.