In a building inventory, it is important to be able to determine the amount of space that can be assigned to people or programs. However, buildings necessarily contain other types of space as well. Technical definitions and examples of types of space are provided in chapter 4.
The amount of space that can be used for people or programs is known as the Net Assignable Area.2 The area of an Assignable space is the area measured within its interior walls. The Net Assignable Area of a building (or all buildings in an inventory) is the sum of the space allocated to the 10 major assignable space use categories: classrooms, laboratories, offices, study areas, special use space, general use areas, support rooms, health care, residential, and unclassified space. These categories are further described below.
Net Assignable Area = Sum of the 10 Major Space Use Categories of Assignable Space
The amount of space within a building that is essential to the operation of the building but not assigned directly to people or programs is known as the Nonassignable Area. The area of a Nonassignable space is the area measured within its interior walls. The Nonassignable Area of a building (or all buildings in an inventory) is the sum of the space allocated to the three major nonassignable space use categories: building service area, Circulation Area, and mechanical area. These categories are further described below.
Nonassignable Area = Sum of the Three Major Space Use Categories of Nonassignable Space
Figure 3-1. Conceptual framework for analyzing building space
The aggregate interior area of a building, known as the Net Usable Area,3 is the sum of Assignable Area and Nonassignable Area.
Net Usable Area = Assignable Area + Nonassignable Area
It is also important to know that the gross area4 of a building is the floor area of a structure within the outside faces of the exterior walls. This value is either physically measured or scaled from as-built drawings. Figures illustrating all of these areas are provided later in the chapter.
The difference between the exterior or gross area and the interior or Net Usable Area is the Structural Area, the floor area upon which the exterior and interior walls sit and the unusable areas in attics and excavated basements. Structural Area is calculated as the difference between the gross area of a building and the Net Usable Area of that building.
Structural Area = gross area - Net Usable Area