The exterior of a two-family dwelling (or duplex) shall be designed, constructed and maintained in a manner that provides the appearance of a single-family dwelling as specified by Sec. 1162.07 (Single-Family Dwellings, Detached). The addition of a separate exterior door on the front facade is prohibited. The primary entrance for the second dwelling unit may be located on a side wall, or both units may share a common entrance on the front facade.