It's not mandatory to offer extra area to Society, however as per the provisions of prevailing D. C. regulation, fungible compensatory floor Space Index (FSI) of the existing building shall not be used for free sale, depending upon the feasibility of the project extra area is offered. In suburbs builder get admissible FSI of the plot, TDR ( depending upon the road on which the plot of the society situated) and fungible compensatory FSI not exceeding 35% for residential development and 20% for the Industrial/commercial development.