GST exemption for residential construction using TDR/FSI permits proportionate exemption with reverse charge liability for unbooked units. The notification adds exempt entries for transfer of development rights (TDR) or FSI and for upfront amounts for long term land leases used for construction of residential apartments for sale, providing that the GST exemption shall be apportioned to residential apartments by the ratio of residential carpet area to total carpet area. Promoters bear a reverse charge liability for the proportion of value attributable to residential apartments remaining un booked on issuance of the completion certificate or first occupation, calculated by reference to un booked residential carpet area and subject to specified caps; valuation of transferred rights and un booked apartments is to follow promoter sale values nearest the relevant date.