Location of Dwellings and Buildings. Only one main building for one-family and two-family use with permitted accessory buildings may be located upon a lot or unplatted tract. Every one-family or two-family dwelling shall face or front upon a public street, other than an alley. Where a lot is used for multiple-family dwelling, retail, commercial, industrial purposes, or a combination of same, more than one (1) main building may be located upon the lot, but only when such buildings conform to all the open space, parking and density requirements applicable to the uses and districts and when all such main buildings face upon a public street, other than an alley. Whenever two (2) or more main buildings, or portions thereof, are placed upon a single lot or tract and such buildings will not face upon a public street, the same may be permitted when the site plan for such development is approved by the Planning and Zoning Commission. No parking area, storage area, or required open space for one building shall be computed as being the open space, yard or area requirements for any other dwelling or other use. This paragraph shall not be used to limit or restrict development according to approved site plan in a Planned Development District (PD) or in a Public Lands and Institutions District (PLI).