Notwithstanding the other provisions of this Chapter, in all districts, for buildings where 75 percent or more of the existing floor space is allocated to residential uses, an enlargement, extension, conversion, change of use or other alteration to such building may create a new non-compliance or increase the degree of a non-compliance, provided that:

1. increases to existing non-compliances, or the creation of new non-compliances, with regard to maximum residential floor area ratio shall be limited in size to floor space existing with the volume of a building or other structure on the zoning lot. For multiple dwelling residences, such allowance shall be limited to buildings existing on December 5, 2024;
2. increases to existing non-compliances with regard to required open space, yards, rear yard equivalents, or courts, as applicable, shall not diminish the area of the existing open area by more than 20 percent and no further encroachment to a non-complying yard shall be closer to a lot line than an existing building on the zoning lot; and
3. increases to existing non-compliances, or the creation of new non-compliances, with regard to the permitted height and setback of a building or other structure, or the height of a permitted obstruction, shall be limited to one story or 15 feet, whichever is less.

Allowances for permitted obstructions may be applied to an existing building, including as modified pursuant to the provisions of this Section.