Floor area ratio

Floor area ratio (FAR) is the ratio of a building's total floor area (zoning floor area) to the size of the piece of land upon which it is built. The terms can also refer to limits imposed on such a ratio.

As a formula: Floor area ratio = (total amount of usable floor area that a building has, zoning floor area) / (area of the plot)

One of the purposes of the 1916 zoning ordinance of New York City was to prevent tall buildings from obstructing too much light and air. The 1916 zoning ordinance sought to control building size by regulating height and setback requirements for towers. In 1961, a revision to the zoning ordinance introduced the concept of floor area ratio (FAR). Buildings built before 1961 often have FARs that would be unachievable today, such as the Empire State Building which has an FAR of 25 - meaning that it earns considerably greater rent than a newer building on the same land could hope for.

The floor area ratio (FAR) can be used in zoning to limit the number of people that a building can hold instead of controlling a building's external shape.

For example, if lot must adhere to a 0.10 FAR, then the total area of all floors in all buildings on the lot must be no more than one-tenth the area of the parcel itself. (In other words, if the lot was 10,000 sq. ft, then the total floor area of all floors in all buildings mustn't exceed 1,000 sq. ft.)

Common exclusions to the total calculation of square footage for the purpose of floor area ratio (FAR) include unoccupied areas such as mechanical equipment floors, basements, stair towers, elevator shafts, and parking garages.

An architect can plan for either a single-story building consuming the entire allowable area in one floor, or a multi-story building that rises higher above the plane of the land, but which must consequently result in a smaller footprint than would a single-story building of the same total floor area. By combining the horizontal and vertical limits into a single figure, some flexibility is permitted in building design, while achieving a hard limit on at least one measure of overall size. One advantage to fixing this parameter, as opposed to others such as height, width, or length, is that floor area correlates well with other considerations relevant to zoning regulation, such as total parking that would be required for an office building, total number of units that might be available for residential use, total load on municipal services, etc. The amounts of these things tend to be constant for a given total floor area, regardless of how that area is distributed horizontally and vertically. Thus, many jurisdictions have found it unnecessary to include hard height limitations when using floor area ratio calculations.

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