Buildable area is the plot extent multiplied by the permitted Floor Space Index. Under the Tamil Nadu Combined Development and Building Rules 2019, FSI is the total covered area on all floors divided by the plot area; base FSI is generally 2.0, rising to up to 2.5 along notified metro corridors.
The permitted figure depends on the abutting road width, land use and building height, which is why a buildability assessment confirms it for the specific site rather than assuming it.
Premium FSI is additional floor area beyond the base entitlement, granted on payment of a charge linked to guideline value. Properties within 500 metres of a metro corridor receive a discount on that charge. Whether the extra area justifies its cost is a project-level decision.
Approvals run through CMDA for much of the Chennai Metropolitan Area and DTCP for areas outside it, alongside the local body, with planning permission and building sanction in sequence. Road width, setbacks, parking and OSR requirements then shape what the parcel can hold.
Mapping the route and its clearances before design avoids the rework that stalls projects.
Common blockers are an unconverted or misclassified parcel, insufficient abutting road width for the intended height, a water body or OSR buffer, or a clouded title in a multi-parcel layout. Each is checked at source so it surfaces before, not after, capital is committed.