The minimum width of a court shall be 30 feet for one-story buildings, 40 feet for two-story buildings and 60 feet for four-story buildings. For every five feet of height over 40 feet, the width of such a court shall be increased by two feet, provided that open unenclosed porches may project into a required court not more than 25 percent of the width of such court. Nominal insets in the building facade of six feet or less shall be exempt from this section.