What structural element is necessary to change the shape or direction of a chimney?

The correct choice is corbel, as it serves as a structural support element in chimneys where the flue needs to change direction or shape. Corbels are projections that extend outward from a wall, helping to distribute the weight of the chimney and ensure stability when it moves from a vertical direction to an angle or when it transitions into a different shape.

In chimney design, corbels can often be seen at the base where the flue meets the surrounding structure. This capability to change direction is essential for the efficient and effective operation of the chimney, allowing for proper venting of smoke and gases.

While flues, crickets, and flashing are components associated with chimney systems, they do not primarily function to change the shape or direction of the chimney. Flues are the inner ducts that carry smoke and gases; crickets are used to direct water away from the chimney but do not alter its structural shape; flashing prevents water intrusion and thus protects the chimney but does not impact its direction or shape either. Therefore, the corbel plays a vital role in the architectural integrity and functionality of a chimney.