Where an outside off-street parking area for four or more vehicles, or a loading and unloading area, abuts a residential zone or a lot which was developed for residential use prior to initiation of the nonresidential use on the subject property, a buffer strip, in accordance with applicable buffer requirements of this chapter, shall be provided between the parking area and the adjoining property. Said buffer shall be a minimum of six feet in height at the time of planting. This required buffer shall also be required for outside parking areas for four or more cars which serve single-family dwellings.