(1)If any part of a building abutting on a public street is within the regular tine of that street, the Board of Councilors may, whenever it is proposed -(a)to repair, rebuilt or construct such building or to pull down such building to an extent measured in cubic metre exceeding one-half thereof above the ground level, or(b)to repair, remove, construct or reconstruct or make any additions to, or structural alterations of, any portion of such building which is within the regular line of the street,by an order, as respects the additions to or rebuilding, construction, repair or alteration of such building, require such building to be set back to the regular line of such street,
