FSI, TDR and fungible FSI: the three letters that decide your redevelopment
Almost every redevelopment number flows from FSI, TDR and fungible FSI. Here's a plain-English explanation of what they are and why they decide how much extra flat you get.
If you understand only one technical idea in redevelopment, make it this one. FSI — and its cousins TDR and fungible FSI — determine how much can be built on your plot, which determines the developer's surplus, which determines how much extra flat your members can get. Everything else is downstream.
FSI: how much you can build
FSI (Floor Space Index), sometimes called FAR, is the ratio of total built-up floor area permitted to the area of the plot. An FSI of 1 on a 1,000 sq m plot means roughly 1,000 sq m of construction is allowed; an FSI of 2 means about 2,000 sq m.
Your old building probably used only a fraction of today's permissible FSI. Redevelopment unlocks the difference: the gap between what is built and what is now permitted is the raw material for everyone's gain — bigger flats for members and saleable flats for the developer.
TDR: importing extra FSI
TDR (Transferable Development Rights) lets development potential generated elsewhere be used on your plot. When a landowner surrenders land for a public purpose (a road, an amenity), they may receive development rights as compensation — rights that can be sold and "loaded" onto another plot, subject to the rules for that zone.
For your redevelopment, loading TDR can increase the buildable area beyond the base FSI, within limits. More buildable area means more saleable flats, which means more room to negotiate member benefit.
Fungible FSI: the flexible top-up
Fungible FSI is an additional, compensatory FSI that can be availed by paying a premium, used to regularise areas like flower beds, voids and balconies that earlier sat outside the FSI count. In practice it adds usable area and gives flexibility in planning the new building.
Why members must care about all three
Here is the chain that decides your deal:
Permissible FSI + TDR + fungible FSI − what's needed to rehouse members = the developer's saleable surplus.
The larger that surplus, the more the developer can afford to give members and still profit. So when a builder says "this is the best we can offer," the real question is: what is the total buildable potential of this plot, and how is the surplus being split?
A society that knows its plot's FSI potential negotiates from facts. A society that doesn't, negotiates from hope.
The carpet-area translation
All of this eventually shows up as one number members feel: the new carpet area of their flat. Use our Carpet Area Gain Calculator to turn a builder's percentage offer into real new carpet — measured on RERA carpet, never built-up.
What to do at feasibility
- Commission a feasibility study that states the plot's permissible FSI, the TDR that can be loaded, and the realistic buildable area.
- Ask for the surplus split — how much of the saleable area funds member benefit versus developer profit.
- Compare offers on the same basis — total buildable potential, not just the headline percentage.
Rules on FSI, TDR and premiums vary by location and change over time. But the principle is permanent: the more clearly your society understands the buildable potential of its own land, the fairer the deal it can strike.
Educational overview only. FSI, TDR and fungible FSI rules vary by municipality and change; rely on a current professional feasibility study for your plot.
Editorial, not legal or financial advice. Consult your own advisors before deciding.
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