The following definitions are common in commercial and nonmedical construction and are particularly useful for the purpose of rental agreements:

Gross building area. The sum of all floor areas of a building measured between outside faces of the building, including all horizontal and vertical circulation, service and mechanical areas. Any architectural features that project out of a building, such as pilasters, awnings, cornices and buttresses, are excluded.

Net building area. The sum of all areas enclosed by the walls measured within the inside faces. The sum of all usable area that is either assigned to or currently available for assigning to occupants, or a function or use that was defined as net usable square feet.

Assignable building area. The total area assigned to or able to be assigned to occupants or to a specific function. It does not include the wall thickness, but includes any circulation space that is part of the space or a suite of spaces.

Non-assignable building area. Contrary to the assignable building area, the sum of all areas that are not assigned to or are not available to be assigned to occupants or to a specific function or use is known as non-assignable building area. The sum of assignable and non-assignable areas provides the net building area. When the total net building area is deducted from the total gross building area, the remainder is called the total structural area.