Any lot of record forty feet or wider existing at the effective date of this Zoning Ordinance in an "SR" or "R" District may be used for the erection of a single-family dwelling even though its area and width are less than the minimum requirements set forth herein. Each side yard shall be a minimum of five feet. Where two adjacent lots of record with less than the required area and width are held by one owner, the Board may require that the lot be combined and used for one main building. In either case, the prevailing setback shall be met. Where three or more contiguous unimproved lots of record with less than the required area and width are held by one owner, the Board may require replatting to fewer lots to permit compliance with minimum yard requirements.