No two-story dwelling shall be erected upon a plot having a frontage of less than 50 feet upon a public street, and such fifty-foot width shall continue for a depth of 100 feet or to the rear line of the dwelling, whichever is greater, except that where a plot in single and separate ownership on, and continuing since, June 4, 1940, has a frontage upon a public street of not less than 40 feet, one detached dwelling may be erected thereon, provided that all other requirements of this Code of Ordinances have been fulfilled. A certified title report issued by a recognized title company and a current survey certified by a duly licensed surveyor demonstrating such single and separate ownership shall be submitted to the Superintendent of the Building Department, prior to the issuance of a building permit.