For buildings existing on December 31, 1990, the City Planning Commission may authorize an enlargement, extension, conversion, change of use or other alteration to a building that includes or will include residences that would create a new non-compliance or increase the degree of an existing non-compliance, with the applicable bulk regulations, provided that the conditions of paragraph (a) and the findings of paragraph (b) are met.

1. Conditions
   
   The following conditions shall be met:
   1. Where maximum building height limitations apply, the proposed height modifications shall not result in an increase that exceeds 25 percent of the height permitted by the applicable district regulations, or the height of the existing building, whichever is greater; and
   2. Where floor area ratio modifications are proposed, no increase in residential floor area shall exceed the maximum floor area permitted by the applicable district regulations by more than 20 percent.
2. Findings
   
   In order to grant such authorization, the Commission shall find that:
   1. the configuration of the existing building, proximity to other buildings, or other site conditions create practical difficulties that would adversely affect the configuration of residences or the building site plan;
   2. for enlargements, where applicable:
      1. the proposed modifications will not unduly obstruct access to light and air to adjoining properties or streets;
      2. the proposed scale and placement relates harmoniously with the surrounding area; and
   3. the requested modification is the least amount necessary to relieve such practical difficulties.

The Commission may prescribe appropriate conditions and safeguards to minimize adverse effects on the character of the surrounding area.