N.Y.C. Admin. Code § BC U202: Section BC U202: ADU in a Basement or Cellar

U202.1 Scope.

An ADU located in a basement or cellar of an existing one- or two-family dwelling shall be constructed in accordance with Section U103 and Sections U202.2 through U202.12, as required by this section.

U202.2 Definitions.

The following words and terms shall, for the purposes of this section, have the meanings shown herein:

10-YEAR RAINFALL FLOOD RISK AREA. Shall have the same definition as such term is defined in Section 24-809 of the Administrative Code.

COASTAL FLOOD RISK AREA. Shall have the same definition as such term is defined in Section 24-809 of the Administrative Code.

COMMUNITY DISTRICT. A community district established pursuant to chapter 69 of the New York City Charter.

ELIGIBLE BASEMENT OR CELLAR RESIDENCE. A basement or cellar in an existing dwelling within the program area, unlawfully arranged to be occupied as an apartment and with kitchen and sanitation facilities acceptable to the department, and which apartment was in existence prior to April 20, 2024.

PROGRAM AREA. As permitted by Section 289 of the New York State Multiple Dwelling Law, Bronx community district 9; Bronx community district 10; Bronx community district 11; Bronx community district 12; Brooklyn community district 4; Brooklyn community district 10; Brooklyn community district 11; Brooklyn community district 17; Manhattan community district 2; Manhattan community district 3; Manhattan community district 9; Manhattan community district 10; Manhattan community district 11; Manhattan community district 12; and Queens community district 2 and such other community districts as may be authorized pursuant to such section.

U202.3 Prohibited locations.

An ADU shall not be permitted in a basement or cellar of a building in the following locations, except as otherwise provided pursuant to the New York City Zoning Resolution:

1. Within the special flood hazard area in accordance with Appendix G.

2. Within the 10-year rainfall flood risk area.

3. Within the coastal flood risk area.

U202.3.1 Identification of flood hazard areas.

Where an ADU is permitted in accordance with Section U202.3, the construction documents for the ADU shall include a statement to certify that the premises are not located in any one of the following flood hazard areas:

1. Special flood hazard area, in accordance with Section G201.

1.1. Coastal A-zone.

1.2. Coastal high-hazard area.

1.3. A-zone.

2. 10-year rainfall flood risk area.

3. Coastal flood risk area.

Each such statement shall be accompanied with the applicable flood area map.

U202.4 Applicability.

Where permitted by this code, a basement or cellar ADU may be permitted if 1 of the following conditions is met:

1. In the program area, eligible basement or cellar residences may be made habitable in accordance with Article 507 of Chapter 5 of Title 28 of the Administrative Code and Section U202.12.

2. An existing basement or cellar space in a one-family dwelling may be converted to 1 ADU in accordance with Sections U202.5 through U202.11.

3. An existing basement or cellar space in a two-family dwelling may be converted to 1 ADU in accordance with all applicable requirements of the New York State Multiple Dwelling Law. Such ADU shall be classified as a Group R-2 occupancy and comply with all the requirements of Group R-2 occupancy in this code.

U202.4.1 Occupancy.

Notwithstanding Section 27-751 of the 1968 Building Code, Section 27-2087 of the Housing Maintenance Code, Section 1208.2, and any applicable laws in existence prior to December 6, 1968, a basement or cellar ADU in a one-family dwelling may be occupied in accordance with the provisions of this Appendix, or a basement or cellar ADU in a one- or two-family dwelling in the program area may be occupied in accordance with Article 507 of Chapter 5 of Title 28 of the Administrative Code.

U202.5 Minimum ceiling height.

Notwithstanding Section 1208.2, all habitable rooms in basements shall have a minimum clear ceiling height of 7 feet (2.1 meters). The minimum clear ceiling height of all habitable rooms in a cellar shall be 7 feet (2.1 meters).

U202.6 Window requirements.

Each habitable room shall have at least 1 window with 6 square feet (.55 m

2

) of openable area to provide natural ventilation as required pursuant to Section 1203.5.1.2.1. The total net glazed area of all windows shall be not less than 10 percent of the floor area of the room served, or 12 square feet (1.1 m

2

), whichever is greater. Such area may include glazed areas in doors providing light directly into such room.

U202.6.1 Portions of windows below grade.

Portions of windows below grade plane may be included in calculations of such minimum net glazed area required to provide natural light where all the following conditions are met:

1. The window head is located not more than 6 inches (152 millimeters) below the lowest permitted projection below ceiling height; and

2. Such portions are surrounded by a window well or similar open area that:

2.1. is at least 6 inches (152 millimeters) deeper than the bottom of the window;

2.2. is at least 3 times as wide, in the direction perpendicular to the window, as the depth below grade plane of such window portions, not to exceed 5 feet (1.5 meters), provided the top of such window is at least 2 feet (.6 meters) above the adjoining grade;

2.3. is at least twice as wide, in the direction parallel to the window, including 6 inches (152 millimeters) wider on each side, as the depth below grade plane of such window portions; and

2.4. is provided with a drain to prevent any ponding of storm water, in accordance with Chapter 11 of the New York City Plumbing Code;

3. No cantilever, permanent shading structure, or other obstruction, is less than 3 feet (.9 meters) above the window head or protrudes more than 1 foot (.3 meters) in the direction perpendicular to the window; and

4. No other encroachment or obstruction is within the window well, except as otherwise required by this code. Supplemental steps that provide access to the required yard, court, open space, or street may also be permitted. Where provided, such steps shall be dimensioned in accordance with Section 1011.5 and shall include a landing at the bottom of such window well in accordance with Section 1011.6.

U202.7 Fire separation.

An ADU in a basement or cellar shall be constructed with the following fire separations:

1.

Boilers and furnaces. Any boiler or furnace in such ADU must be enclosed and separated from all habitable spaces by a noncombustible fire barrier having at least a 1-hour fire-resistance rating in accordance with Section 707, provided that any opening in such fire barrier shall be protected with a self-closing door.

2.

Stairway enclosure. Any stairway connecting more than 1 dwelling unit shall be provided with an enclosure in accordance with Section 713. Where the stairway is fully contained within the ADU and such ADU is fully sprinklered in accordance with Section U103.6.1, such stairway shall be permitted to be unenclosed.

3.

Existing above grade unit. The ADU must be separated from all other dwelling units by noncombustible construction having at least a 1-hour fire-resistance rating meeting the requirements of Section 420.

U202.8 Means of egress.

An ADU in a basement or cellar shall be provided with means of egress in accordance with this section.

U202.8.1 Emergency escape and rescue openings.

All sleeping rooms shall be provided with at least 1 emergency escape and rescue opening in accordance with Section 1030.

U202.8.2 Means of egress from a basement ADU.

An ADU in a basement shall be provided with at least 1 means of egress exterior door opening directly to the outdoors in accordance with Chapter 10, including access to a public way. Such exterior door shall swing inward and be provided with landings on both the interior and exterior sides in accordance with Section 1010.1.6, excepted as provided in Section U202.8.4.

U202.8.3 Means of egress from a cellar ADU.

An ADU in a cellar shall be provided with at least two means of egress doors, remotely located from each other. In addition, the following shall be provided:

1. At least 1 means of egress door shall be an exterior door opening directly to the outdoors in accordance with Chapter 10, including access to the public way, even if compliance with such standards is not otherwise required by Chapter 10 or any other law. Such exterior door shall swing inward and be provided with landings on both the interior and exterior sides of the door in accordance with Section 1010.1.6, excepted as provided in Section U202.8.4.

2. Such cellar shall be considered as a story above a grade plane for the purpose of complying with Chapter 9 and Chapter 10.

U202.8.4 Landing exception.

An exterior landing shall not be required where the landing or floor on the exterior side is no more than 7.75 inches (197 millimeters) below the top of threshold of the exit door, and the door does not swing over the landing or floor.

U202.9 Radon levels.

No certificate of occupancy or temporary certificate of occupancy may be issued for an ADU located in a basement or cellar unless a certification is submitted to the commissioner that the level of radon in such ADU is tested in accordance with, and meets the standards set forth in rules promulgated by the department of health and mental hygiene, in consultation with the department, the fire department, and the office of emergency management.

U202.10 Vapor levels.

No certificate of occupancy or temporary certificate of occupancy shall be issued for an ADU located in a basement or cellar unless a certification is submitted to the commissioner that the vapor level in such ADU is tested in accordance with, and meets the standards set forth in rules promulgated by the department of health and mental hygiene, in consultation with the mayor’s office of environmental remediation, the department, the fire department, and the office of emergency management.

U202.11 Basic stormwater prevention requirements.

An ADU located in a basement or cellar shall comply with the following:

1.

Water sensor and alarm. Every habitable room shall be provided with at least 1 water sensor with backup battery power to warn the occupants in the event of a flood. The department may promulgate rules to supplement the requirement of such water sensors and alarms.

2.

Emergency preparedness information. The owner shall post all required signage in a manner prescribed by the Housing Maintenance Code and the rules of the department of housing preservation and development and shall notify any tenants about enrollment in an emergency alert system operated by the office of emergency management.

U202.12 Special requirements for certain basement or cellar ADUs.

The department may issue an authorization for temporary residence in accordance with Article 507 of Chapter 5 of Title 28 of the Administrative Code. An eligible basement or cellar residence in the program area shall comply with the provisions of such article and the rules of the department.

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