What area of a building is defined as having its floor subgrade on all sides?

The area of a building that is defined as having its floor subgrade on all sides is known as a basement. A basement typically refers to a portion of a building that is entirely below the ground level, making it distinct from a cellar, which may have partial exposure to the outside.

Basements are often used for various purposes, such as storage, living space, or utilities, and their floor being subgrade on all sides allows for features like windows that may be above ground level. Understanding this distinction is crucial in property assessments, real estate listings, and various zoning codes, where the terminology can indicate specific compliance and design requirements.

The other areas listed do not encompass this definition: a cellar could be partially above grade; an attic is located above the uppermost floor of the building; and the ground floor is the lowest floor that typically has a direct exit to the outside, not completely subgrade. Therefore, basements are uniquely characterized by their complete subgrade positioning.