Detached accessory buildings. No detached accessory building shall occupy any portion of the required front yard setback, and no detached accessory building or buildings shall occupy more than 30% of the required rear yard or be located within five feet of any other accessory building or principal building. A three-foot minimum setback measured to the building wall, with a building overhang not to exceed two feet, shall be maintained from rear and side lot lines, except that where an accessory building has an entrance on an alley, such entrance shall be located not less than 10 feet from the nearest alley line.