Section 298(1) in The Mumbai Municipal Corporation Act, 1888
(1)If any part of a building abutting on a public street is within the regular line of such street, the Commissioner may, whenever it is proposed -(a)to rebuild such building or to take down such building to an extent exceeding one-half thereof above the ground level, such half to be measured in cubic feet; or(b)to remove, reconstruct or make any addition to any portion of such building which is within the regular line of the street,in any order which he issues, under section 345 or 346, concerning the rebuilding, alteration or repair of such building require such building to be set back to the regular line of the street.
