Merged lots. Except as otherwise provided herein, lawfully nonconforming lots that are adjoining and held in common ownership, or under the control of the same owner, shall be treated so as to conform so far as possible with the minimum area requirement of the zoning district in which they are located. No lot so merged, or portion thereof, may be changed or transferred in any manner that will increase the degree of nonconformity unless a special permit has first been obtained from the Zoning Board of Appeals. No such special permit may create any additional buildable lot(s).