Calculating Office Building Areas

August 11, 2014

office buildingAs an architect who specializes in commercial office space, I am often asked to help interpret the areas of buildings. Unfortunately, many of these requests come after a purchase has already been made based on gross figures. While the gross area is valid and useful, “rentable” area per BOMA (Building Owners and Managers Association International) standards is the most widely accepted. 

A savvy buyer or renter may request rates based on the rentable area, which is always smaller than the gross area. Here are some terms and concepts related to BOMA standards that businesses should consider before buying or renting.

Although the calculations can be quite complex, three basic terms are “Rentable Square Feet” or RSF, “Usable Square Feet” or USF, and “Building R/U Factor” which is commonly referred to as a “Core Factor.” The Rentable area is essentially the interior of the building without vertical penetrations (usually stairs, elevators, and mechanical shafts).

The Usable Area for a tenant suite is typically what they can put furniture in. USF is measured from the dominant face of the exterior wall (often times measured to the interior glass pane if it is the majority of the vertical face) to the inside face of common walls and to the center line of the demising wall (the wall the tenant shares with neighbors). Structural members, such as columns, are always included as part of the USF.

To get the “Core Factor” the public elements such as corridors, elevator lobbies, bathrooms, janitor’s closets, mechanical rooms, even shared conference rooms and fitness centers, are measured and then sorted into floor common and building common categories. These figures form ratios in a complex formula that eventually produces a building factor, or “core factor,” to be multiplied against a tenant USF to charge each occupant their portion of the common amenities. These days, when an office building development is being considered, these numbers should always be calculated early in the design of the building. The area calculations can influence decisions such as using a certain window manufacturer that has the glass surface closer to the exterior or changing the corridor paths to eliminate the need for a third stairwell. Both increase the rentable area, which maximizes the profit of the developer.

The gross area, or footprint of the building, must also be given to the municipalities on a building’s documentation. It is different than RSF because it includes the thickness of the exterior walls and the vertical penetrations, therefore it is a larger number than the RSF. The gross area is a real number and often, the property taxes are paid on this number (although I have seen clients negotiate a lower tax rate when they prove they can only generate income on the rentable area).

Often, the gross number is how the building is marketed for purchase later. We recommend that clients who are considering a purchase include BOMA calculations as part of their due diligence study. If someone chooses to convert a building that is documented only in gross square feet to the BOMA standard, the building “shrinks,” which never makes investors happy. If the numbers are converted to BOMA standards, the rates must increase to keep the property successful and of course, the rates need to be evaluated for competitiveness in today’s market.

To learn more about this common and complicated issue, visit

The author, Jennifer Keaton, is a registered Architect and Interior Designer and Owner of the firm Red Design Studios. Learn more about her work at She can be reached at or 512-207-0141.

Topics: Business Operations, Featured

Jennifer Keaton

Red Design Studios

Jennifer Keaton is a registered Architect and Interior Designer and has practiced all around the country in such metropolitan areas as Boston, Atlanta, Portland, and Raleigh/Durham. Throughout her 22 year career, Jennifer has produced award-winning, nationally-recognized, and locally-admired work. When she moved to Austin in late 2007, she knew that she had everything necessary to start her own firm: the experience, the talent, and the charisma; and thus, Red Design Studios was born. Red Design Studios analyzes every budget, space, schedule, preferences, and company philosophy. Jennifer personally ensures that these needs are successfully interpreted into an efficient physical environment that projects the client’s desired image. Jennifer is well versed in every aspect of interior projects from property searches, programming needs, design, material and fixture selections, documentation, project management, and construction observation. She finds that documenting the design herself allows for better coordination resulting in a more complete set of detailed documents for the contractor and therefore, a harmonized environment for the client at a conclusive price. The name, Red Design Studios, stems from the red hair Jennifer inherited from her great Aunt Clairol. The logo was designed with sparks to symbolize her passion for lighting design and the recognition she has had in that field. Jennifer loves the challenge of renovations but also the evolution of shell buildings and spaces. She specializes in corporate interiors but has also designed, documented, and managed several restaurants, medical-office suites, retail tenants, furniture specifications and bid packages, corporate cafeterias, shell buildings, and hospitality spaces.
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