There shall be no minimum front, side or rear yard setback requirements for lots interior to the planned commercial center site; however, the interior yard setback requirements shown in an application for a planned commercial center shall be subject to approval by the Board of Commissioners, following recommendation of the Planning Commission, provided adequate provisions are made to guarantee the public health, safety and welfare and the requested yards promote a harmonious, efficient and attractive development. In any event, where parallel walls of detached buildings adjoin each other, whether on the same lot or on adjoining lots, a minimum of 20 feet shall be provided between those parallel building walls. Attached buildings, as defined herein, may be subdivided by a common property line along or between common vertical walls.