Does Mumbai need more FSI or less?
As of early 2015, there is a lot of debate in Mumbai about the new draft Development Plan which has allowed for increased FSI in some areas of the city. This article discusses FSI at a fundamental level and talks about its implications for the city.
What is FSI?
FSI or floor space index is the maximum built space you may construct on a given plot. It is the ratio of building area to the plot area. For example, on a 10,000 square foot plot which has an FSI of 2, you may construct a building with up to a maximum of 20,000 square feet of area, and no more. On the same plot, with an FSI of 3, you could construct 30,000 square feet of built space.
We have just seen that FSI sets a maximum limit on how much construction can be done on a plot. More FSI means more construction area. So is more FSI better for the city? To answer this question, we need to understand the concept of population density, most often just called density. Density is simply the number of people per unit area, for example, 10,000 people per square kilometer, or say 1,000 people per hectare. A hectare is 10,000 square meters.
A city needs to have an optimum population density. If the density is too high (too many people per hectare), then everyone suffers - there are not enough roads, not enough pavements for them to walk on, not enough public transport, not enough parks, garbage dumps, schools, shops, barber shops, internet cafes, and so on. Many areas of Mumbai currently suffer from this problem. Dharavi is a classic example, but almost all areas of Mumbai are overstretched in some ways.
If the density is too low, this is bad for residents and for the city, as transport is expensive, and it is difficult to provide amenities. Luckily, very few or no cities in India suffer from this problem. This could occur in bankrupt or dying cities like Detroit in the USA.
Let us return to our starting point, which is FSI. What is the ideal way of deciding how much FSI should be given on a plot? One way to look at it is:
FSI area = number of people who will live on the plot X built up area per person
Now, Mumbai regulations make no mention of how many people will live on a plot, and this is where the problem arises. Let us take our 10,000 square foot plot, and develop it in two different ways: firstly, in luxury apartments, and secondly, in low income housing. We will assume an FSI of 2 on the plot.
With an FSI of 2, we can construct a building with 20,000 square feet of space. Consider option 1, in which we build a luxury apartment building with 2,000 square foot flats. We can therefore fit in 10 flats, and each flat will house about 3 people on average. High income families tend to have fewer people at home. The plot will house a total of 20 x 3 = 60 people, and each person will occupy an area of 2,000 / 3 = 660 square feet. This figure is called the built up area per person.
Now consider the second option, in which we build low income housing on the same plot. We know we can construct 20,000 square feet of space. However, each of these units is only about 400 square feet, so we can have 20,000 / 400 = 50 apartments on the plot. Low income families are larger, with about 5.5 people per apartment. So the plot will have 50 x 5.5 = 275 people. The built up area per person is 400 / 5.5 = 73 square feet per person.
Let us compare the two. In the first option, the plot will house 60 people, and in the second, 275 people. This is a massive difference! To get a feel for this at a larger scale, consider a small street with 10 plots on each side, with a total of 20 plots. If all of them were developed as per option 1, there would be 60 x 20 = 1200 people living on the street. If all of the plots were developed as per option 2, there are 275 x 20 = 5,500 people living in the street. This is a very wide range of densities.
So the fundamental problem with Mumbai's regulations is that they do not really deal with or control the number of people in a particular area, and this is why the quality of life for most Mumbaikars is quite poor. Most of us are accustomed to having no green spaces, very few playgrounds, and barely enough footpaths to walk on. It is very difficult to provide amenities such as police stations, hospitals, and schools, if we do not know how many people will live in an area.
Mumbai's planners must find a way to work out how many people can live in a certain area, and then create building regulations that respect this limit. FSI is too blunt a tool with which to carve out Mumbai's future.
Q: Some residential areas of Manhattan have an FSI of 20. Why cannot Mumbai have the same?
A: We need to link FSI to population density. In Manhattan, large apartments are apartments that are about 6,000 square feet or more. Most of these apartments house 3 people on average. Therefore, the built up area per person in Manhattan is 2,000 square feet per person. Let us take our previous plot of 10,000 square feet. With an FSI of 20, we can construct a 2,00,000 square foot building on the plot. If each person takes up 2,000 square feet, the building will house only 100 people. So in Manhattan, this massive building will not load the city excessively, and not cause excessive "street crowding". In Mumbai, this building will house many more people, as the built up area per person is much higher. This overcrowding causes great pressure on the areas surrounding the plot. Therefore, it makes no sense to compare FSI in Manhattan with FSI in Mumbai, because the built up areas per person differ massively.
So to answer our question - does Mumbai need more FSI or less - the answer is: FSI is just one tool to control development. Unfortunately, FSI is the one and only tool in Mumbai's building regulations. In Mumbai, we need to create additional mechanisms to ensure that areas do not become overcrowded. The new DP has proposed different FSI for different areas of the city, which is a welcome step. But this will not ensure healthy development for the city. Mumbai needs to bring in additional regulations along with FSI, or scrap the FSI system entirely and use alternate methods to govern construction in the city, which is certainly possible.
What is FSI?
FSI or floor space index is the maximum built space you may construct on a given plot. It is the ratio of building area to the plot area. For example, on a 10,000 square foot plot which has an FSI of 2, you may construct a building with up to a maximum of 20,000 square feet of area, and no more. On the same plot, with an FSI of 3, you could construct 30,000 square feet of built space.
We have just seen that FSI sets a maximum limit on how much construction can be done on a plot. More FSI means more construction area. So is more FSI better for the city? To answer this question, we need to understand the concept of population density, most often just called density. Density is simply the number of people per unit area, for example, 10,000 people per square kilometer, or say 1,000 people per hectare. A hectare is 10,000 square meters.
A city needs to have an optimum population density. If the density is too high (too many people per hectare), then everyone suffers - there are not enough roads, not enough pavements for them to walk on, not enough public transport, not enough parks, garbage dumps, schools, shops, barber shops, internet cafes, and so on. Many areas of Mumbai currently suffer from this problem. Dharavi is a classic example, but almost all areas of Mumbai are overstretched in some ways.
If the density is too low, this is bad for residents and for the city, as transport is expensive, and it is difficult to provide amenities. Luckily, very few or no cities in India suffer from this problem. This could occur in bankrupt or dying cities like Detroit in the USA.
Let us return to our starting point, which is FSI. What is the ideal way of deciding how much FSI should be given on a plot? One way to look at it is:
FSI area = number of people who will live on the plot X built up area per person
Now, Mumbai regulations make no mention of how many people will live on a plot, and this is where the problem arises. Let us take our 10,000 square foot plot, and develop it in two different ways: firstly, in luxury apartments, and secondly, in low income housing. We will assume an FSI of 2 on the plot.
With an FSI of 2, we can construct a building with 20,000 square feet of space. Consider option 1, in which we build a luxury apartment building with 2,000 square foot flats. We can therefore fit in 10 flats, and each flat will house about 3 people on average. High income families tend to have fewer people at home. The plot will house a total of 20 x 3 = 60 people, and each person will occupy an area of 2,000 / 3 = 660 square feet. This figure is called the built up area per person.
Now consider the second option, in which we build low income housing on the same plot. We know we can construct 20,000 square feet of space. However, each of these units is only about 400 square feet, so we can have 20,000 / 400 = 50 apartments on the plot. Low income families are larger, with about 5.5 people per apartment. So the plot will have 50 x 5.5 = 275 people. The built up area per person is 400 / 5.5 = 73 square feet per person.
Let us compare the two. In the first option, the plot will house 60 people, and in the second, 275 people. This is a massive difference! To get a feel for this at a larger scale, consider a small street with 10 plots on each side, with a total of 20 plots. If all of them were developed as per option 1, there would be 60 x 20 = 1200 people living on the street. If all of the plots were developed as per option 2, there are 275 x 20 = 5,500 people living in the street. This is a very wide range of densities.
So the fundamental problem with Mumbai's regulations is that they do not really deal with or control the number of people in a particular area, and this is why the quality of life for most Mumbaikars is quite poor. Most of us are accustomed to having no green spaces, very few playgrounds, and barely enough footpaths to walk on. It is very difficult to provide amenities such as police stations, hospitals, and schools, if we do not know how many people will live in an area.
Mumbai's planners must find a way to work out how many people can live in a certain area, and then create building regulations that respect this limit. FSI is too blunt a tool with which to carve out Mumbai's future.
Q: Some residential areas of Manhattan have an FSI of 20. Why cannot Mumbai have the same?
A: We need to link FSI to population density. In Manhattan, large apartments are apartments that are about 6,000 square feet or more. Most of these apartments house 3 people on average. Therefore, the built up area per person in Manhattan is 2,000 square feet per person. Let us take our previous plot of 10,000 square feet. With an FSI of 20, we can construct a 2,00,000 square foot building on the plot. If each person takes up 2,000 square feet, the building will house only 100 people. So in Manhattan, this massive building will not load the city excessively, and not cause excessive "street crowding". In Mumbai, this building will house many more people, as the built up area per person is much higher. This overcrowding causes great pressure on the areas surrounding the plot. Therefore, it makes no sense to compare FSI in Manhattan with FSI in Mumbai, because the built up areas per person differ massively.
So to answer our question - does Mumbai need more FSI or less - the answer is: FSI is just one tool to control development. Unfortunately, FSI is the one and only tool in Mumbai's building regulations. In Mumbai, we need to create additional mechanisms to ensure that areas do not become overcrowded. The new DP has proposed different FSI for different areas of the city, which is a welcome step. But this will not ensure healthy development for the city. Mumbai needs to bring in additional regulations along with FSI, or scrap the FSI system entirely and use alternate methods to govern construction in the city, which is certainly possible.
