(a) Increases. Each side yard, where required, shall be increased in width by two inches for each foot by which the length of the side wall of the building, adjacent to the side yard, exceeds forty feet.
(b) Varied; Wall Not Parallel. Side yard width may be varied where the side wall of a building is not parallel with the side lot line or is broken or otherwise irregular. In such case the average width of the side yard shall not be less than otherwise required least width; provided however, that such side yard shall not be narrower at any point than one-half the otherwise required least width, or narrower than three feet in any case.
(c) One Side Yard Reduced. Width of one side yard may be reduced when authorized by the Board of Zoning Appeals, in the case of a one-family or two-family dwelling, to a width not less than three feet; provided the sum of the widths of the two side yards is not less than the required minimum, and provided the distance between the proposed dwelling and another dwelling, existing or proposed, on an adjacent lot is not less than the required minimum sum of the widths of two side yards. Such reductions may be authorized only when the Board finds it to be warranted by the location of existing buildings or conductive to the desirable development of two or more lots.
(d) Corner Lots. A side yard along the side street lot line of a corner lot, which lot abuts in the rear, either directly or across an alley, the side lot line of another lot in an R District, shall have a width of not less than one-half the required depth of the front yard on such other lot fronting the side street.