(a)        In R4 Districts, except R4-1, R4A and R4B Districts, and in R5 Districts other than R5B Districts, for an existing single- or two-family residence with a non-complying front yard, an enlargement involving a vertical extension of existing building walls facing such non-complying front yard is permitted, provided the following conditions are met:

(1)        the portion of the building which is being vertically extended complies with the height and setback regulations specified for the district in which it is located; and

(2)        the non-complying front yard where the building wall is being vertically extended is at least 10 feet in depth.

Notwithstanding the above, the provisions of this paragraph (a) shall also be applicable in R4A Districts in lower density growth management areas.

(b)        In all districts, for an existing single- or two-family residence with a non-complying side yard, an enlargement involving a vertical extension of existing building walls facing such non-complying side yard is permitted, provided the following conditions are met:

(1)        the portion of the building which is being vertically extended complies with the height and setback regulations applicable to an R3-2 District;

(2)        the non-complying side yard where the building wall is being vertically extended is at least three feet in width and the minimum distance between such building wall and the nearest building wall or vertical prolongation thereof on an adjoining zoning lot across the common side lot line is eight feet;

(3)        the enlarged building does not contain more than two dwelling units;

(4)        there is no encroachment on the existing non-complying side yard, except as set forth in this Section; and

(5)        the enlargement does not otherwise result in the creation of a new non-compliance or in an increase in the degree of non-compliance.

Notwithstanding the provisions set forth in paragraphs (a)(1) and (b)(1) of this Section, when an existing building has added qualifying exterior wall thickness pursuant to Section 23-44 (Permitted Obstructions in Required Yards or Rear Yard Equivalents), such vertical extensions may align with the location of the finished exterior building wall of the existing building.