Open porches, balconies, overhangs, breezeways, terraces and carports attached to single- and two-family dwellings shall be considered as part of the principal structure and may project into any required yard area, provided that:
(a) Not more than 80 square feet of said structure shall project into the required yard area; and
(b) No portion of any such structure shall be closer than five feet to any property line as measured horizontally.