An accessory building or a private parking area shall not be located in any required front yard space, except that nothing shall prohibit an owner of a home from counting his driveway as one parking space per dwelling unit and except further that any driveway in excess of 10% slope shall not be considered as off-street parking. If erected on a corner lot, it shall be set back from the side street to comply with the setback line applying to the principal building for that side street.