What structural elements span the distance from one side of a foundation to the other?

Girders are the correct choice because they are large beams that support the structure of a building by spanning the distance across the foundation from one side to the other. Their primary role is to carry the load of the structure above and distribute that load to the foundation, ensuring stability. Girders are typically found in larger constructions, providing the necessary strength and support for beams or joists that are laid across them.

Headers are generally horizontal support elements used above openings like doors and windows, rather than spanning the entire foundation. Footings refer to the base that supports a foundation, serving as a structural element that distributes the weight of the building to the ground but does not span across the distance itself. Joists are smaller structural members that run between beams, providing support for floors, but they do not span the entire width of a foundation. Thus, girders are specifically designed for that role, making them the right answer.