Every building site shall have an effective lot frontage equal to or greater than one-half the median lot width required in the district, and in no case shall the effective lot frontage be less than twenty-five (25) feet. Whenever a new building site is hereinafter created by division of an existing lot, the effective frontage of each such new building site shall be equal to one-half of either the required or the actual median lot width thereof, whichever is greater. Each such new building site shall be recorded forthwith as a lot in the office of the county recorder. (Prior gen. code § 8-60.13)