No row of attached townhouses shall exceed a total of eight attached units or 160 feet. No more than three abutting townhouses shall have the same front and rear setbacks. At each required change in setback distance, the minimum offset shall be three feet. A common solid fence or equivalent shall be constructed between each townhouse along the rear side lot lines for a distance at least equal to the width of each unit, in order to provide a privacy area, such fence to be at least six feet in height.