Any lot or parcel of land containing an area or width less than that prescribed in the district in which such lot is located, which lot or parcel of record was under one ownership on the date of adoption of this Planning and Zoning Code, which owner owned no adjoining land, may be used for any purpose permitted within the district, provided, however, that in districts where side yards are required, a side yard dimension of not less than five feet shall be maintained for any principal building.