N.Y.C. Admin. Code § EBC D303: D303 Changes from 1 class or kind (MDL 9(3), 9(4)).

A dwelling, of 1 class or kind, altered or converted to another class or kind, shall comply with the requirements of Sections D303.1 and D303.2 and shall be classified as HAEA (2008+) or HAEB (2008+).

Exceptions:

1. The conversion from a one- or two-family dwelling to a converted dwelling to the extent otherwise provided for in Sections D603 or D604 (MDL 9(3)).

2. The change of a converted dwelling from Class B to Class A to the extent otherwise provided for in Chapter D6 (MDL 9(3)).

3. The change of a tenement to single room occupancy to the extent otherwise provided for Sections D303.3 and D704 (MDL 9(8)).

4. The reconversions to tenements to the extent otherwise provided for Section D701.1 (MDL 9(6)).

5. The change from HEXB to a HEXA to the extent the application of Sections D303.1 and D303.2 would require changes to the egress systems, yards, or courts, provided that the entire dwelling is of fireproof construction and provided the room sizes comply with the minimum requirements in the New York City Building Code for dwelling units in a group R-2 occupancy (MDL 9(4)).

D303.1 Applicable provisions other than height, bulk, open spaces (MDL 9(3), 9(4), 9(6), 9(8)).

A dwelling of 1 class or kind, altered or converted to another class or kind, shall thereupon comply with the applicable provisions of this code, including Chapter D3.

D303.2 Height, bulk, open spaces (MDL 9(3), 26).

A dwelling of 1 class or kind, altered or converted to another class or kind, shall thereupon comply with all applicable requirements for yards and courts under the New York City Zoning Resolution and shall thereupon comply with the floor area ratio provisions of Section 26(3) of the MDL. For the purposes of this section:

1. Alterations or conversions that are allowed by the New York City Zoning Resolution to retain existing non-complying yards and courts shall, at a minimum, meet the light and air requirements of Section 277 of the MDL. Existing courts or yards constructed in accordance with Article 7 of the MDL shall not be reduced below the dimension prescribed in Chapter D7.

2. For buildings altered or converted to multiple dwellings classified as commercial uses under the New York City Zoning Resolution, including but not limited to transient hotels as such term is defined in the New York City Zoning Resolution, any courts with required windows opening thereon shall comply with Section D305.1.

3. Buildings granted a lawful variance, authorization, or special permit modifying the requirements of the New York City Zoning Resolution with respect to yards and courts by the board of standards and appeals or the city planning commission shall be deemed in compliance with this section.

D303.3 Conversion to single room occupancy (MDL 9(8)).

Any dwelling unit in any Class A multiple dwelling may be occupied for single room occupancy only if such dwelling complies with the provisions of Section D704 and all other provisions of this code applicable to such dwelling.

D303.4 Class A use in Class B multiple dwelling (MDL 9(7)).

In any Class B multiple dwelling, except a rooming house or lodging house, any dwelling unit may be occupied as a dwelling unit in a Class A multiple dwelling, provided such dwelling unit has both lawful sanitary and cooking facilities for the sole use of the 1 family residing therein and complies with all the requirements for dwelling units in Class A multiple dwellings erected after April 18, 1929, including that such occupancy conforms to any applicable provisions of the New York City Zoning Resolution including location of uses within buildings and a new or amended certificate of occupancy is obtained where required by law. However, where such dwelling unit does not have both lawful sanitary and cooking facilities for the sole use of the 1 family residing therein, the creation thereby of any rooming unit must be authorized pursuant to Section 27-2077 of the New York City Housing Maintenance Code. In any rooming house or lodging house, 1 dwelling unit may be occupied as a dwelling unit in a Class A multiple dwelling, provided such dwelling unit is occupied solely by the owner, janitor, superintendent, or caretaker.