Architectural Theory, Building Design, Calculations, Design Guide, Design Theory

Floor Area Ratio (FAR) Formula and Calculation Guide

When starting a site analysis, it’s important to look into the local building by-laws of the city or location. The Floor Area Ratio (FAR) differs for each site on the basis of its location, population, road widths, and so on. 

The floor area ratio or more commonly, FAR, is the ratio of a building’s total floor area to the size of the entire piece of land. In simpler terms, it is the building floor-to-plot area ratio. 

In India, FAR is sometimes also known as FSR (floor space ratio) or represented as FSI (floor space index). The difference between FAR and FSI is that while the first is represented as a ratio, the latter is a percentage. Thus a FAR of 1 is represented as an FSI of 100%.

Floor Area Ratio Purpose

FAR determines the total capacity of structure on a piece of land. Depending on the type of land, the structure has a limited capacity of taking its load, and fundamentally, it is not advisable to put additional stress beyond this capacity. Simply, it decides the height of a building and the respective number of floors that will be built in the project. Every municipality and authority allows the construction of a property up to a set FAR which thus, depends on the nature of the land.

Building area constraints

FAR can also be considered as the limits imposed on a building’s construction. It is also used to determine other measures like floor area, building height, plot coverage, and several other aspects. 

Volume and density

Higher the FAR, the greater the building volume and the greater the density of construction. 

It is often used to express the development intensity of the different land uses for the site and integrated into a community’s zoning and other land development controls.

Impact on the surroundings

FAR can be used to either limit the intensity of land use so as to lessen the environmental impacts of development or to control the mass and scale of development.

FAR as a tool

By calculating the rough number of users and vehicles per square foot of building space, FARs can estimate the potential impact the construction will have on the situation. FAR is sometimes used as an analytical tool for projecting the impact of different land use and development intensity scenarios.

Floor Area Ratio (FAR) Formula

FAR is expressed as a numerical (in decimals), and is calculated by dividing the total area of the building by the total area of the plot (building area ÷ plot area).

The formula for FAR = gross floor area/area of the plot

Floor Area Ratio for common FAR values
FAR = gross floor area/area of the plot

Steps to Calculate Floor Area Ratio (FAR)

  1. Calculate the total land area for building:

The buildable part of a plot is the part where construction can legally take place after taking into account all parts of it. Taking measurements of the plot area is one of the first steps in the construction process. 

  1. Calculate the floor area of each floor of the building

The part of each story above the ground surface, between the exterior walls is measured, prior to any further construction or manipulation. 

  1. Determine the total floor area of the building

Total or gross floor area is the sum of the floor area of each of the stories. 

Total Floor Area = Area of 1st floor + Area of 2nd floor… 

  1. Determine the ratio

Using the formula mentioned above, divide the total floor area by the total buildable area of the plot. The result obtained is the floor area ratio.

  1. Calculate the FSI if needed

Convert the ratio to percentage or index if needed. 

The importance of Floor Area Ratio (FAR) to different groups involved in construction

FAR is very important for the designers as well as the end-users. The proposed FAR lays the terms and conditions for the construction process. Therefore, it is important to understand how it affects the different groups. 

Buyer and user:

As a person taking up the project for a certain land, it is important to find out FAR because it gives an initial idea about the density, volume, and zoning of the project. Higher FAR means sharing the benefits like lifts, pool, parking, parks, etc. A low FAR means a shorter building and for a high-rise building, FAR has a big impact on its cost. Increasing the value of FAR provides room for further construction or development if permitted. 

Designer:

As per the permissible FAR, the people involved in construction have to get approval for the heights and floor area for their buildings. Hence, higher FAR leads to the vertical expansion of a project. An increase in FAR would help developers with adding extra floors and in meeting the gap of demand and supply in the modern world. 

It’s important to understand that FAR only decides the height and floor area of a building, not control its layout. Hence, to avoid FAR violations, one should always make sure to inspect the site and its restriction before taking any decision.

You might also like:

Leave a Reply

Your email address will not be published.