A DWELLING UNIT consists of one or more ROOMS in a RESIDENTIAL BUILDING, RESIDENTIAL portion of a BUILDING, or NON-PROFIT HOSPITAL STAFF DWELLING, which are arranged, designed, used or intended for use by one or more persons living together and maintaining a common household, and which include lawful cooking space and lawful sanitary facilities reserved for the occupants thereof. In counting the number of ROOMS in a DWELLING UNIT for the purpose of determining the LOT AREA requirements, no ROOMING UNIT shall be counted as part of the DWELLING UNIT.