What is Floor Space Index (FSI)?

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The floor space index (FSI) or floor area ratio (FAR) is the ratio of the total usable floor area of a building to the plot area. In simple words, FSI is the maximum amount of permissible area that can be used for construction in the given plot of land. It is also termed as floor space ratio.

Floor space index can be further defined as the maximum area to construct on a piece of land or a plot. It varies from one city or even locality to another.

Importance of Floor Space Index

1. The floor space index plays a significant role in controlling urban density. 
2. FSI value directly limits the number of buildings within a land or plot, and any use of land exceeding FSI value can create unwanted pressure on the city. 
3. Unauthorized and illegal construction will increase in the absence of FSI rules.
4. The floor space index also impacts the land value in an area. 
5. Proper utilization of FSI rules in building plans will help in early approvals of building permits and NOCs.

Factors Affecting Floor Space Index Value

FSI/FAR value is determined by the local municipal corporations. The permissible floor space index ratio value depends upon:

1. Population density
2. Size of the plot
3. Availability of open spaces
4. Availability of power, water, sewer lines
5. Building type
6. Environmental impact of the project
7. Preparedness in the event of a natural disaster

Calculation of Floor Space Index

The floor area ratio is used to calculate the total built-up area for a plot and calculate the number of floors the building can have.

FSI is given by: 

Total built-up area= FSI ✕ Area of plot

Example: To calculate the total built-up area, one needs to know the type of building that is being planned to construct. Generally, different buildings have different FSI regardless of the location.

If the area of plot being used for a project is 800 sq ft and the FSI determined for that particular city/locality is 1.5, then the built-up area that can be constructed will be 1200 sq ft (500×1.5). The maximum space available on the ground floor is 800 sq ft and the remaining built-up area of 400 sq ft can be constructed on the first floor. Thus, considering the plot area and the floor space index applicable in that particular locality, a developer would be permitted to construct a one-story building.

Advantages of Floor Space Index

The floor area ratio has the following advantages in a city or a place where construction is progressing at a fast pace.

1. FSI maintains the ratio of open space to built-up space.
2. It controls the skyline of the city.
3. It ensures development in urban areas.
4. It ensures efficient use of resources in the city.
5. It eliminates illegal and unauthorized construction.
6. It helps government authorities in the proper planning of the city.
7. It ensures the proper layout of the city.
8. It controls pollution.

What is Premium Floor Space Index?

The premium floor space index is an extra floor space index ratio allocated by the government by paying the premium fee by the developer. To avail premium floor space index ratio, the width of the road adjacent to the land must be at least 30 feet. The premium floor space index ratio value varies, as shown in the table below:

Road width	Premium FSI
30-40 ft	20%
40-60 ft	30%
Over 60 ft	40%

Exceptions to Floor Space Index

The following shall not be counted for computation of floor space index:

1. The open area under a building constructed on stilts and specifically used as parking space.
2. Parking space open to the sky.
3. Ramps running towards the parking area.
4. Building projection to the extent of 0.6 m.
5. Area covered by fountains, septic tank, manholes, water tank, and overhead tank.
6. Stair-cabin, ramp-cabin, lift cabin with machine room constructed on the terrace.

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