In this method, the total area that can be occupied in an office suit is measured to help the tenant decide on the furniture and number of personnel to assign to that space. Over a long period of time, however, this area may vary due to remodeling of floors, expansion and contraction of corridors. Usable area is measured from the side of the office space and corridors with a permanent wall or finished surfaces to the partitions' centers. These are what separate adjacent usable areas from the inner surface of the outside walls of the building.
The rentable area of a building refers to the total portion of the floor owned by the tenant. It is measured from the inner finished surface of the outer walls of the building, disregarding any corridor walls or structures within the given area. It is possible, however, to convert rentable area to usable area and vice versa using the common area factor.
The building common area refers to those sections of the building that are not included in the office area but are still used to provide service to the office tenants. The common area applied to the floor rentable area gives the gross rentable area of the building.
The common area factor is the ratio of the rentable area to the usable area of the office space. It expresses the total area that cannot be used in the office area and can be expressed as a percentage of the total usable area. It is also referred to as the load factor or loss factor brought about by using the following formula: R/U ratio - 1, where "R" and "U" mean rentable and usable areas.