For the purpose of computing the gross parking area for required off-street parking, 350 square feet of unobstructed net standing, maneuvering or access area shall be considered as one parking space. However a lesser area may be considered as one parking space if the Code Enforcement Officer certifies that the layout and design of the parking area are adequate to permit convenient access and maneuvering. In any event, each allocated parking space shall be at least 20 feet long and 10 feet wide, exclusive of access or maneuvering area.