Private garages, provided that no business, service or industry is conducted therefrom or therein. Not more than one motor vehicle for each 5,000 square feet of lot area or fraction thereof up to a limit of five vehicles per lot shall be permitted. Space for motor vehicles shall not be used, leased or rented for commercial vehicles. No commercial vehicles shall be parked on a lot in the open. These space regulations shall apply to vehicles regularly left on the lot, whether housed or in the open. The presence of more than one unregistered vehicle is prohibited.