There shall be a front yard having a minimum depth of forty feet, except:
(a) Where a uniform setback line has been established or observed on one side of a street between two intersecting streets or for a distance of 600 feet on both sides of the lot in question at the time of the effective date of Ordinance 24-66 passed April 5, 1966, no building hereafter erected or structurally altered shall project beyond such setback line; and
(b) Where twenty-five percent or more of all the property, according to front feet, abutting upon one side of a street between two intersecting streets or for a distance of 600 feet on both sides of the lot in question is built up with buildings having an average setback of more or less than forty feet, no building hereafter erected or structurally altered shall project beyond the average setback line so established. (Ord. 29-69. Passed4-29-69.)