In any residential zoning district where the owner of a lot existing at the time of the adoption of this Ordinance, or his successor in title thereto, does not own sufficient land to enable him to conform to the minimum lot area or frontage requirements of this Ordinance, such lot may be used for a one-family dwelling provided that minimum yard and building setback requirements for the zoning district in which said lot is located are maintained.

If two or more adjoining and vacant lots with continuous frontage are in a single ownership at any time after the adoption of this Ordinance and such lots individually are less than the lot width requirements for the zoning district in which they are located, such groups of lots shall together be considered as a single lot or shall be grouped into several lots of minimum permitted size and the resulting lot or lots shall be subject to the dimensional requirements of this Ordinance.

The building setback requirements of this Ordinance for dwellings shall not apply to any lot where the average existing building setback line on lots located wholly or in part within two hundred feet on each side of such lot, within the same block and in the same zoning district, and fronting on the same side of the street as such lot, is less than the minimum required building setback. In such cases the minimum building setback on said lot may be equal to the average of the existing setbacks on the aforementioned lots, or not less than ten feet from the street right-of-way, whichever is greater.

More than one dwelling, institutional, commercial, or industrial building may be located upon a lot in a zoning district where such a use would be permitted, but no such building shall encroach upon the front, side, or rear yards required for any other building site. For dwellings the open space between buildings shall not be less than 20 feet for one-story buildings, 30 feet when either building is a two-story building and 40 feet when either building is a three-story building, and 40 feet plus and additional 10 feet for each story over three stories when either building is over three stories in height. The minimum dimension for the yard upon which any entrance or exit of a dwelling faces shall be 20 feet, and such space shall not be counted as a yard for any other building.