(1)No portion of any building or boundary wall shall be erected or added to within such street alignment as the Board of Councilors may determine by regulation under section 172 :Provided that the Board of Councilors may, in its discretion, permit additions to a building to be made within a street alignment, if such additions merely add to the height of, and rest upon, an existing building or wall, upon the owner of the building executing an agreement binding himself and his successors in interest-(a)not to claim compensation in the event of the Board of Councilors at any time thereafter calling upon him or such successors, by written notice, to remove any addition made to any building in pursuance of such permission, or any portion thereof, and(b)to pay the expenses of such removal.
