“Building site” means the land occupied or to be occupied by a building and its accessory buildings, or by a dwelling group and its accessory buildings, together with such open spaces as may be required under the provisions of this Title, having not less than the minimum area required under this Title for a building site in the zone in which such lot is situated, and having its principal frontage on a street. An existing lot of record constituting a legal building site as of the effective date of the ordinance codified in this Title is deemed to be a legal building site. (Ord. 89-1 § 1, 1989.)