N.Y.C. Admin. Code § BC U201: Section BC U201: Above Grade ADU Within a One-Family Primary Dwelling

U201.1 Scope.

An ADU located entirely above the grade plane and adjoining or within the same building of the one-family dwelling shall be constructed in accordance with Section U103 and Sections U201.2 through U201.4.

Exception: ADUs constructed in accordance with this section, other than ADUs constructed in an attic, shall not be required to comply with Section U103.6.1.

U201.2 Occupancy classification.

Where the ADU is adjoining or within the same building as a one-family dwelling, both the ADU and the primary dwelling unit shall be classified as Group R-3 occupancy and shall comply with all applicable requirements of Group R-3 occupancy in this code.

U201.3 Fire separation.

The ADU shall be separated from the primary dwelling by a fire barrier having at least a one-hour fire-resistance rating meeting the requirements of Section 420.

U201.4 Exit stairway.

The exit stair required by Section 1006.3.2 may be constructed as an interior or exterior stair serving a Group R-3 occupancy in accordance with Chapter 10. Where an interior stair is provided, such interior stair shall be enclosed in accordance with Section 1023. Where an exterior stair is provided, such exterior stair shall be permitted to be constructed of combustible materials where all of the following conditions are met:

1. The stair is at least 10 feet away from any lot line or wall of any other building on the same tax lot;

2. Sprinklers are provided throughout the ADU in accordance with Section U103.6.1;

3. The building is lawfully constructed as Type V construction; and

4. The stair is constructed in accordance with Section 1011.7.2.

(L.L. 2024/127, 12/18/2024, eff. 6/16/2025)