Victoria Measuring Floor Area in Office Buildings

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.

Usable Area
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.

Rentable Area
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.

Common Formulas

  • Common Area Factor (Load) = 1.0 - R/U Ratio
  • R/U Ratio = Rentable Area Usable Area
  • Rentable Area = Usable Area x R/U Ratio
  • Usable Area = Rentable Area R/U Ratio
  • Rentable Area = Usable Area x (1 + Load)
Definitions Used Above
Finished Surface
A wall, ceiling or floor surface (including glass) as prepared for tenant use, excluding the thickness of any special surfacing materials such as paneling or carpet.
Dominant Portion
That portion of the inside finished surface of the permanent outer building wall which is 50% or more of the vertical floor to ceiling dimension. If there is no dominant portion, or if the dominant portion is not vertical, the measurement is done where the inside finished surface of the permanent outer building wall intersects the finished floor.
Major Vertical Penetrations
Stairs, elevator shafts, flues, pipe shafts, vertical ducts, and the like, and their enclosing walls, which serve more than one floor of the building, but shall not include stairs, dumb-waiters, lifts, and the like, exclusively serving a tenant occupying offices on more than one floor.
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