In M1-1D, M1-2D, M1-3D, M1-4D and M1-5D Districts, a building containing conforming or non-conforming residential uses may be enlarged and the residential uses extended thereby, provided that no non-residential uses exist above the level of the first story ceiling.

Such enlargement is subject to all of the following regulations:

(a)        There shall be no increase in the number of dwelling units in the building beyond the lawful number in existence on December 21, 1989.

(b)        The total amount of residential floor area in the building shall not exceed 500 square feet additional to the residential floor area in existence on December 21, 1989, or a floor area ratio of 1.65, whichever is less.

(c)        No residential enlargement shall be permitted within 30 feet of the rear lot line.

(d)        No enlarged portion shall exceed a height of 32 feet above curb level.

(e)        No side yards shall be required. However, if any open area extending along a side lot line is provided at any level it shall have a width of not less than eight feet. However, enlargements of single-family or two-family residences existing as of June 20, 1988 shall be exempt from this requirement, provided such enlarged building does not exceed a height of two stories.

Enlargements in excess of those permitted in this Section, and enlargements that create additional dwelling units may be permitted by authorization of the City Planning Commission, pursuant to the regulations of Sections 42-321 (Residential uses in M1-1D through M1-5D Districts) and 42-322 (Use regulations in M1-6D Districts).