A _______________ consists of plywood placed on top of floor joists to make the area walkable.

A subfloor is the appropriate term used to refer to the structural layer placed on top of floor joists, providing a solid, stable base for the flooring material above. The subfloor typically consists of plywood or oriented strand board (OSB), ensuring that the area is walkable and supports both the weight of the finished flooring and any loads that may be applied to it. This construction component is critical for creating a level and durable surface in residential and commercial buildings.

The other terms, while related to construction, do not capture the specific function of providing a walkable layer over floor joists. A deck generally refers to an outdoor floor structure supported by posts but is distinct from interior flooring. A waffle system typically involves a type of concrete slab that provides support through molded patterns, rather than plywood on joists. A platform can refer to a raised surface but lacks the specificity and structural functionality associated with a subfloor in flooring systems.