Foundation walls are constructed on top of which of these items?

Foundation walls are constructed on top of footings because footings are designed to support the weight of the walls and distribute that weight over a larger area of soil. Properly designed footings help to prevent the foundation from settling unevenly or shifting over time, which can lead to structural issues. Footings are typically made of concrete and are often placed below the frost line to reduce the risk of heaving due to temperature changes. This foundational principle ensures that the home or structure above remains stable and secure.

In contrast, a slab refers to a concrete floor that sits directly on the ground and does not involve foundation walls supported by footings. Baseboards are decorative moldings that cover the joint between walls and floors, while columns are vertical structural elements that may support beams or roofs but are not foundational elements upon which walls are built. Thus, footings are essential for the proper construction of foundation walls, making this choice the correct answer.