An undeveloped, nonconforming lot may continue to exist indefinitely, unless it is less than 70% of the applicable minimum lot size and is or becomes under the same ownership as an adjoining lot, whether or not that adjoining lot is nonconforming. When common ownership occurs, the two adjoining lots shall be considered a single lot. Upon any Town official or board determining that such condition exists, the official or board shall notify, in writing, the owner, Tax Assessor, Zoning Officer, Board of Selectmen and Planning Board. The act of combining the lots shall be considered a decision of the Zoning Officer, and appeals shall follow the provisions of RSA Ch. 677.