Within thirty (30) days of approval of a historic district by the city council, property owners located within the district may elect to exempt their property from the requirements of the historic district by providing written notice of the self-exemption to the preservation staff. In the event of a contract sale of real property, both the owner of record and party or parties holding an equitable interest in the property must consent to the exemption. The property shall automatically convert to the historic overlay zoning district upon sale of the property, including a contract sale.