Circulation factor refers to spaces in a building that are necessary to allow occupants to circulate, but do not comprise part of the usable square footage. This becomes a particular concern in commercial buildings, where property owners usually want to maximize the amount of space they can rent or lease to tenants. Good design can reduce the amount of circulation factor necessary in a building, but only so far, and a certain amount may be required by law for safety reasons.
Hallways are an example of areas covered under circulation factor. Offices and other commercial spaces need halls to allow occupants to move between spaces in the building, but the halls don't have any additional purpose. They cannot be used for display or storage, for example. Other corridors and spaces intended to permit transit from one space to another, like walkways over an atrium, are also part of the circulation factor.
In a commercial building, there may also be public hallways and lobbies. These are not part of the circulation factor, which only includes halls and access directly used by a specific tenant. It is possible to estimate total square footage, including circulation factor, with a simple formula multiplying usable square footage by 1.35. If the circulation factor is too low, it may be difficult to navigate an office environment. This would limit efficiency and may also be a safety risk, as personnel could have difficulty evacuating safely in the event of a fire or similar emergency.
Houses may also have a certain amount of non-usable space for circulation, depending on layout and design preferences. Usually less space is necessary for circulation in a home because of the lower volume of traffic. Unlike businesses and offices, homes do not see hundreds or thousands of people every day, and emergency evacuations typically involve a small number of people who do not need particularly large hallways to get out safely.
The circulation factor must be built in during the design phase. Architects and contractors can estimate how much space will need to be made available for circulation and will add it to the plans. Since every bit of space matters in construction, care is taken to keep costs down by laying buildings out efficiently and effectively. Configurable walls and other components that tenants can adjust as needed can be helpful, as they will allow tenants to rearrange to suit their requirements without having to make substantial remodels.