Section 13(1)(b) in Tamil Nadu Inam Estates (Abolition and Conversion into Ryotwari) Rules, 1965
(b)The net annual rent of the building shall be ascertained by deducting, from the gross annual rent for the building,-(i)the taxes and land revenue charges payable annually in respect of the building; and(ii)one month's rent towards the annual cost of ordinary repairs to the building.