No building permit shall be issued and no dwelling or building shall be constructed on any lot in any zone where the lot does not have the minimum area, minimum frontage, and the minimum average width required for the zone in which it is situated, unless the lot has at least the minimum area, minimum average width, and minimum frontage required by the Zoning Ordinance in effect at the time an official subdivision map showing it as bounded by established lot lines was on file with the Marin County Recorder, or at the time the deed describing the lot was on record in the office of the Marin County Recorder. (Ord. 89-1 § 1, 1989.)