Lesson A1·06 · FAR / FSI
FAR / FSI — the math that decides if your floor is legal
5 min read · 4 terms · 1 formula
The trap, first
A family buys the fourth floor of a builder floor in Delhi — best price in the building, ₹10 lakh under the others. Two years later, the municipal notice arrives: the plot's FAR permitted three floors of construction. The fourth was never sanctioned. It gets sealed. The floors below stay legal. Theirs doesn't.
The seller knew. The math was public. The buyers never ran it — because nobody told them a floor's legality is arithmetic, not paperwork vibes. Here's the arithmetic.
The four terms
The same number with two names (North India says FAR, Mumbai says FSI): how much total construction a plot allows, as a multiple of the plot's size. FAR 2 on a 1,000 sq m plot = 2,000 sq m of building, counted across all floors together. Set by the local development authority; varies by city, zone, and road width.
The maximum share of the plot the building's footprint may occupy — e.g. 40% coverage on 1,000 sq m means the structure can sit on at most 400 sq m of ground. FAR decides how much you can build; coverage decides how much land stays open. Together they force buildings upward.
Mandatory open strips between the building and the plot boundaries — front, rear, sides. They exist for fire access, light, and ventilation. A structure built into its setbacks is unauthorised even if the total FAR is fine. That "extra room" jutting to the boundary wall in a resale house? Check it against the sanctioned plan.
The advanced one, basics only: when the government takes part of someone's land (road widening, public projects), it can compensate with a certificate of buildable area usable on another plot — or sellable to a developer. TDR is why some projects build beyond the zone's base FAR legally. If a project claims extra height "via TDR," that claim is verifiable in its sanctioned plan.
The formula, worked
1,000 sq m plot × FAR 2.5 = 2,500 sq m total construction
Now stack the constraints. Same plot, 40% ground coverage → each floor plate maxes at 400 sq m. So 2,500 ÷ 400 ≈ 6 full floors is the legal envelope. If a builder on that plot is selling a 9th floor, either TDR/extra-FAR was legally purchased and sits in the sanctioned plan — or you're being sold the family's fourth floor from the trap above.
The analyst's cut
Test yourself — 5 questions before the next lesson
1. A plot is 1,200 sq m with FAR 1.75. Maximum total construction allowed:
Plot × FAR = 1,200 × 1.75 = 2,100 sq m, counted across all floors combined.
2. Ground coverage of 40% on a 1,000 sq m plot means:
Coverage caps the footprint; FAR caps total construction. Together they push buildings up instead of out.
3. Same plot: FAR 2.5 (2,500 sq m buildable), 40% coverage (400 sq m per floor). Roughly how many full floors are legal?
2,500 ÷ 400 ≈ 6.25 → about 6 full floors. Anything above that needs legally acquired extra FAR/TDR — visible in the sanctioned plan.
4. A structure within its FAR limit but built right up to the plot boundary is:
Setbacks are independent requirements for fire access, light and air. FAR compliance doesn't excuse building into mandatory open space.
5. A 4th-floor builder floor is ₹10L cheaper than the identical 2nd floor in the same building. The first document to demand is:
In low-rise construction, the cheap top floor is the classic unsanctioned floor. The sanctioned plan answers it in two minutes; a sealing notice answers it in two years.
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