The Department's attempt to trigger Rule 42 reversal by treating the statutory 1/3rd land abatement as an "exempt supply" is a jurisdictional error that confuses a valuation measure with a taxable event. Under the Govind Saran mandate (1985 (4) TMI 65), the 1/3rd deduction is a legal fiction used solely to determine the "Measure" of the taxable construction service, not to vivisect an indivisible composite supply into a separate sale of land.
Since the "Consideration" is paid in respect of a taxable residential unit and all inputs are physically consumed to create that unit-not the earth beneath it-there is no "dual use" of inputs. Judicially, following the logic in Munjaal Manishbhai Bhatt (Gujarat HC) (2022 (5) TMI 397), the land component is incidental to the taxable supply of construction; thus, a valuation mechanism cannot be used to manufacture an "exempt supply" reality where none exists.
You may effectively defend on this legal position.