Materials. All building(s) or addition(s) thereto shall be of masonry construction. No such building(s) or addition(s) shall be covered with sheet aluminum, iron or steel, or corrugated aluminum, asbestos or iron, except when such materials form an integral part of a standard modular curtain wall panel or insulated sandwich wall as defined by the modular industry. In the event that any such buildings or additions thereto shall be constructed with concrete, concrete blocks, tile blocks or tile brick, the outside face of the wall(s) thereof which are exposed to the street, shall be finished with face brick, insulated curtain wall, insulated sandwich wall, their equivalent or better; and, in addition, the outside face of walls abutting such walls exposed to streets shall be so finished to a minimum depth of 15 feet.