In R1, R2, R3, R4-1 and R4A Districts within lower density growth management areas, the provisions of this Section shall apply to any zoning lot with two or more buildings, where at least 75 percent of the floor area of one building is located beyond 50 feet of a street line and the private road provisions do not apply. For the purposes of this Section, any building containing residences with no building containing residences located between it and the street line so that lines drawn perpendicular to the street line do not intersect any other building containing residences shall be considered a “front building,” and any building containing residences with at least 75 percent of its floor area located beyond the rear wall line, or prolongation thereof, of a “front building” shall be considered a “rear building”. An open area with a minimum width of 15 feet shall be provided between any such “rear building” and the side lot line of an adjoining zoning lot, and an open area with a minimum width of 30 feet shall be provided between any such “rear building” and the rear lot line of an adjoining zoning lot. The permitted obstruction provisions of Section 23-44 for side yards shall apply where such open areas adjoin a side lot line, and the permitted obstruction provisions of Section 23-44 for rear yards shall apply where such open areas adjoin a rear lot line.