The substructure refers to the parts of a building below ground level, such as foundations and basements, which transfer loads safely into the ground. The superstructure includes all elements above ground level, such as walls, floors, beams, columns and roofs. Structural engineers design both to work together safely and efficiently. A well-designed substructure is critical to preventing settlement and movement, while a robust superstructure ensures the building performs as intended throughout its lifespan.