FSI refers to Floor Space Index, the ratio of the permissible built-up area to the plot area. The standard FSI in the city is 1.33. For the suburbs, the base FSI has traditionally been 1.

In a city where land is at a premium, developers have perennially been petitioning the state to raise the vertical limits for constructions. And in recent months, the government sanctioned over a dozen proposals to increase the FSI for private hospitals and hotels to slums and even cattle-shed plots.

To begin with, the base FSI for the suburbs was proposed to be raised to 1.33. The right of the urban poor to live in bigger flats led to raising FSI for the controversial Slum Rehabilitation Authority scheme to 4. Then came the rights of the original residents of the city. The FSI was increased for redevelopment of chawls on mill lands, gaothans, cluster redevelopment of old buildings in the island city and redevelopment of MHADA colonies. The need for creating rental housing stock was quoted for granting an FSI of 4 as an incentive to private land owners willing to hand over 1 FSI of the total built-up area for rental housing.

“Today, an FSI increase is not confined to urban renewal, say for old and dilapidated buildings. The subtle process of increasing FSI is just an instrument for creation of wealth,” said Professor R N Sharma, who heads Urban Studies at the Tata Institute of Social Sciences.

He demolishes the reasoning of developers that Mumbai has one of the lowest FSI among international cities. “If foreign cities can sustain development with a high FSI it is because unlike India such countries do not plan for merely eight cities resulting in en masse migration to cities,” said Sharma.

Some planners say that as existing norms were tweaked to accommodate the FSI hike, flawed principles of urban planning were put into practice. In case of MHADA, one of the prime reasons for increasing the FSI this year was that MHADA would get some of the incentive area from the developer for public housing. But the Urban Development Department has now allowed developers to keep even the share meant for public housing on payment of a premium.

“FSI increase is not aimed at increasing housing stock even if that is the reason given. Once the FSI is increased for a project, only areas that ensure maximum profit are dealt with. FSI as a tool has to be followed up by infrastructures and social amenities,” said Pankaj Joshi, a conservation architect at the Urban Development and Research Institute.

But builders say that there are few options in a city so crowded and the question of prices would be tackled by supply. “FSI has to be the product of population, especially in a city like Mumbai where the land mass is restricted,” said Vimal Shah MD of Akruti Nirman developers and vice president of the Maharashtra Chamber of Housing Industry.

Shah said in 1967, when the population of Mumbai was a third of today’s, the FSI was 1.67. “In 1991 it was reduced to 1 with the same argument that a higher FSI would increase population density. But if every existing family in Mumbai were to have a house of at least 500 sq ft, we need a FSI of 15. Once supply is plenty, prices will become affordable and there will be homes available for people from every stratum of society,” he said.