A Summary of the Building Owners And Managers Association (BOMA) Guidelines
BOMA has defined standard methods for measuring office space, in both old and new buildings.
This method measures the area of a floor or an office suite occupied by a tenant. The tenant uses this space for any necessary staff and furniture. The "Usable Area" of an office is based on the inside-office walls for hallways, corridors and exterior walls. It is measured from the finished surface on the office side of corridor and other permanent walls, or to the center of the partitions that separate the office from adjoining Usable Areas, and to the inside finished surface of the permanent outer building walls, with no deduction is made for structural columns or wall protrusions. Often the Usable Area is converted to Rentable Area by the use of a conversion factor. The Usable Area (adding up the individual tenant Usable Areas) on a multi-tenant floor can vary as corridors and floors are remodeled and shifted.
This method measures the area of the entire office floor, deducting for building elements that penetrate several floors, like stairs and elevators (but not structural columns). The "Rentable Area" of floor area is measured to the inside finished surface of the permanent outer building walls. The Rentable Area of a building is unaffected by changes in corridor or office configuration, and is used for measuring the total income-producing area of a building.
The "R/U Ratio" is the factor that is the division of the Rentable Area for a floor by the Usable Area of that floor.
Common Area Factor
The "Common Area Factor" is the percentage of space on a floor that is not usable, expressed as a percent of Usable Area. This is used to calculate the portion of a building's maintenance costs applied to a tenant's actual Usable Area.