Floor area ratio
Floor area ratio (FAR), floor space ratio (FSR), floor space index (FSI), site ratio and plot ratio are all terms for the ratio of a building's total floor area (Gross 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 covered area on all floors of all buildings on a certain plot, Gross Floor Area) / (area of the plot)
Thus, an FSI of 2.0 would indicate that the total floor area of a building is two times the gross area of the plot on which it is constructed, as would be found in a multiple-story building.
The terms most commonly used for this measurement vary from one country or region to the next.
In Singapore the terms "plot ratio" or "gross plot ratio (GPR)" are more commonly used.
Use in zoning
Floor area ratios are used as a measure of the intensity of the site being developed. The ratio is generated by dividing the building area by the parcel area, being sure to use the same units.
The floor area ratio can be used in zoning to limit the amount of construction in a certain area. For example, if the relevant zoning ordinance permits construction on a parcel, and if construction must adhere to a 0.10 FAR, then the total area of all floors in all buildings constructed on the parcel must be no more than one-tenth the area of the parcel itself.
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.
Impact on land value
Edward Ptacek, 2009, noted that the allowable FAR has a major impact on the value of the land. Higher allowable FAR yields higher land value.
Andres Duany, 2000, notes:
- Abdicating to floor area ratios (market forces) is the opposite of aiming a community toward something more than the sum of its parts.
- FAR, a poor predictor of physical form, should not be used when the objective is to conserve and enhance neighborhood character. Whereas traditional design standards (height, lot coverage and setbacks or build-to lines) enable anyone to make reasonably accurate predictions, recognize violations, and feel secure in their investment decisions.
- If FAR is carelessly combined with traditional setbacks, assembled lots have a considerable advantage over individual lots, which has a negative effect on fine grained cities and the diversity of ownership.
Japan has extensively adopted the floor area ratio in the zoning system since 1970. The evaluation of the adoption is, however, controversial: some say that it has deteriorated the skylines and building lines in Japanese cities; others[who?] claim that it has protected the residential environments.
- NSW Department of Planning, retrieved 19 August 2010
- Quick Start Guide to Town Planning in the City of South Perth , retrieved 19 August 2010
- India Environment Portal, retrieved 19 August 2010
- http://www.townplanning.in/database_show.asp?id=124, retrieved 30 December 2010
- University of Dundee: Town and Regional planning, retrieved 19 August 2010
- Kerr, Alex. Dogs and Demons. New York: Hill and Wang, 2001. pp190-197ff.
- Meriam, Dwight (2004). The Complete Guide to Zoning. McGraw-Hill. ISBN 0-07-144379-7