A single-family residence existing on a lot of fifty feet or more in width at the time of the enactment of this Zoning Code may be altered or enlarged for multiple-family occupancy, provided that existing conforming yards shall not be diminished to a depth or width less than is required by this Zoning Code for RL-3 Residential Districts, except that such yards, when of less depth or width than is required for RL-3 Residential Districts, shall not be further reduced in depth or width, provided however, that the minimum floor area and lot area requirements are fulfilled. (Ord. 29-69. Passed 4-29-69.)