Plot coverage and set back rules
The setback spaces ensure sufficient light, air and privacy, writes SURESH KUPPUSWAMY
The maximum permissible FSI for a Special building whether it is intended for residential or commercial use is 1.5 which means that the maximum extent of construction in any plot cannot exceed one and half times the area of the said plot.
The factors that are related to achieving the prescribed FSI are the Plot Coverage and Set Back Rules.
Plot coverage is the extent of plot covered by the building(s) or structure and this is expressed in terms of percentage. It is actually a ratio of the built-up area over plot area.
As per the rules of CMDA, for Special building, the maximum Plot Coverage permissible is 65%. It means that the plinth area of the construction proposed should not exceed 65% of the plot area.
By this, it is implied that at least 35% of the plot area is to be left open to the sky permanently.
The concept behind imposing a ceiling on the footprint of the proposed construction is to ensure that every plot gets sufficient sunlight, air and receives rainwater.
It will facilitate recharge of aquifer and help in promoting greenery around.
The Plot Coverage is computed by taking into account all the projections at upper levels.
Broadly speaking it is the area of the shadow of the proposed building at noon, which is expressed in percentage of the plot area.
It is to be noted that the Plot Coverage restriction has no bearing on the profile of a building.
For a special building there are mandatory regulations in terms of the spaces to be left between the proposed construction and the boundary of the plot.
They are known as Set Back Rules.
The setback spaces ensure sufficient light, air and privacy not only for the occupants of the proposed building but also to the immediate neighbours.
They also facilitate movement of vehicles around the building including fire tenders in case of an emergency. Besides, they provide spaces for parking vehicles.
In some cases, they promote landscaping around the building. In addition, sewer lines with necessary inspection chambers are normally laid out in the open spaces around the building.
As per DC rules of CMDA the Set Backs are classified as Front Set Backs, Rear Set Backs and Side Set Backs.
The required minimum Front Set Back for different widths of roads is as follows:
The Rear Set Back is the space to be left at the rear of a plot.
|Abutting road width||Front Set Back
|Above 10M (33')
but less than 15M (50')
|Above 15M (50')
but less than 30M (100')
|Above 30M (100')|| 6M
Strangely, it is related to the depth of the plot. The minimum Rear Set Back are as follows:
|Depth of plot||Rear Set Back
|15M (50') below ||3.5M (11'6")
|Above 15M (50') and up to 30M (100') ||4.0M (13'0")
|Above 30M (100')||4.5M (14'9")
Side Set Backs are spaces to be left at the sides of a building and are governed by the height of a building proposed. The rules stipulate that they shall be a minimum of one-third the height of the building subject to a minimum of 3.5M. The Side Set Back need not be necessarily the same on both sides. CMDA permits a minimum of 3.5m on any one side provided the remainder of the total two-third of the building is left on the other side. For instance, for a building of 15M height, the side Set Back can be 3.5M on one side and 6.5M on the other side. By this option, a developer would be able to accommodate vehicles parking on the side having more width.
Set Back space is computed by taking into account the space left between the outer surface of the building proposed and the edge of the plot boundary.
However, unsupported sunshades and wardrobes up to 0.6M and non-continuous balconies up to 1.0M projection are permitted in the Set Backs.
The author is Professor, School of Architecture and Planning, Anna University, Chennai.
THE AUTHOR IS PROFESSOR, SCHOOL OF ARCHITECTURE AND PLANNING, ANNA UNIVERSITY, CHENNAI.
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