Front setback: seven feet, but where a building, structure or accessory building or structure exceeds one story in height, each story above the first shall be progressively set back from the property line five feet greater than the story below it. Alternatively, a building may be set back uniformly, without regard to the number of stories, 10 feet from any property line abutting a street. Where a proposed county street widening encroaches into or beyond such required setback area, the required setback area shall be measured from the proposed county widening line. In any circumstance, this setback shall be planted and maintained with low-growing evergreen shrubs spaced at not more than five feet apart.