Side yards. There shall be two side yards, except in the case of a corner lot, each of which shall be not less than 15 feet, within which no buildings, parking, display or impervious coverage shall be located, provided that when authorized by the Board of Supervisors as a conditional use, structures, exclusive of buildings, such as curbs and retaining walls, may be permitted in the side yard, subject to the applicant's compliance with the minimum landscape requirements of § 122-46C.