How is the gross floor area of a building defined?

The definition of the gross floor area of a building is accurately represented by the choice that describes it as the sum area of all floors measured from the outside walls. This measurement includes the total area across all levels of the building, encompassing both the usable and non-usable spaces, and is calculated by measuring from the exterior walls.

This definition is crucial because it provides a comprehensive understanding of the space within a building, which is essential for various applications such as zoning, taxation, and assessing the market value of properties. By measuring from the outside walls, gross floor area accounts for features such as walls, corridors, and structural elements that contribute to the building's overall footprint.

The other options present narrower or incomplete perspectives on what gross floor area entails, leading to inadequate definitions that do not align with standard practices in real estate and architecture. Understanding gross floor area is vital for real estate professionals, as it impacts everything from property appraisals to investment analyses.